ALBERT

Description: In humid, forested mountain belts, bedrock landslides can harvest organic carbon from above ground biomass and soil (OC modern ) while acting to refresh the landscape surface and turnover forest ecosystems. Here we assess the impact of landslides on organic carbon cycling in 13 river catchments spanning the length of the western Southern Alps, New Zealand, over four decades. We combine spatial and temporal landslide maps with the observed distribution and measured variability of hillslope OC modern stocks. On average, we estimate that landslides mobilised 7.6 ± 2.9 tC km -2  yr -1 of OC modern , ~30% of which was delivered to river channels. Comparison with published estimates of OC modern export in river suspended load suggests additional erosion of OC modern by small, shallow landslides or overland flow in catchments. The exported OC modern may contribute to geological carbon sequestration if buried in sedimentary deposits. Landslides may have also contributed to carbon sequestration over shorter timescales (〈100 years). 5.4 ± 3.0 tC km -2  yr -1 of the eroded OC modern was retained on hillslopes, representing a net-carbon sink following re-vegetation of scar surfaces. In addition, we find that landslides caused rapid turnover of the landscape, with rates of 0.3 % of the surface area per decade. We measured high rates of net ecosystem productivity in this forest of 94 ± 11 tC km -2  yr -1 , which is consistent with rapid landscape turnover suppressing ecosystem retrogression. Landslide-OC modern yields and rates of turnover vary between river catchments and appear to be controlled by gradients in climate (precipitation) and geomorphology (rock exhumation rate, topographic slope). Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Compared to surface soil erosion by water, subsurface erosion (piping) is generally less studied and harder to quantify. However, wherever piping occurs, it is often a significant or even the main sediment source. In this study, the significance of soil loss due to piping is demonstrated through an estimation of soil volume lost from pipes and pipe collapses (n = 560) in 137 parcels under pasture on loess-derived soils in a temperate humid climate (Belgium). Assuming a period of 5 to 10 years for pipe collapse to occur, mean soil loss rates of 2.3 and 4.6 t ha −1  yr −1 are obtained, which are at least one order of magnitude higher than surface erosion rates (0.01-0.29 t ha −1 yr −1 ) by sheet and rill erosion under a similar land use. The obtained results for the study area in the Flemish Ardennes (Belgium) correspond well to other measurements in temperate environments, they are however considerably smaller compared to soil loss rates due to subsurface erosion in semi-arid environments. Although local slope gradient and drainage area largely control the location of collapsed pipes in the study area, these topographic parameters do not explain differences in eroded volumes by piping. Hence, incorporation of subsurface erosion in erosion models is not straightforward. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Many numerical landform evolution models assume that soil erosion by flowing water is either purely detachment-limited (i.e. erosion rate is related to the shear stress, power, or velocity of the flow) or purely transport-limited (i.e. erosion/deposition rate is related to the divergence of shear stress, power, or velocity). This paper reviews available data on the relative importance of detachment-limited versus transport-limited erosion by flowing water on soil-mantled hillslopes and low-order valleys. Field measurements indicate that fluvial and slope-wash modification of soil-mantled landscapes is best represented by a combination of transport-limited and detachment-limited conditions with the relative importance of each approximately equal to the ratio of sand and rock fragments to silt and clay in the eroding soil. Available data also indicate that detachment/entrainment thresholds are highly variable in space and time in many landscapes, with local threshold values dependent on vegetation cover, rock-fragment armoring, surface roughness, soil texture and cohesion. This heterogeneity is significant for determining the form of the fluvial/slope-wash erosion or transport law because spatial and/or temporal variations in detachment/entrainment thresholds can effectively increase the nonlinearity of the relationship between sediment transport and stream power. Results from landform evolution modeling also suggest that, aside from the presence of distributary channel networks and autogenic cut-and-fill cycles in non-steady-state transport-limited landscapes, it is difficult to infer the relative importance of transport-limited versus detachment-limited conditions using topography alone. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The ASTER Global Digital Elevation Model (GDEM) has made elevation data at 30 m spatial resolution freely available, enabling reinvestigation of morphometric relationships derived from limited field data using much larger sample sizes. We use these data to analyse a range of morphometric relationships derived for dunefields (between dune height, spacing, and equivalent sand thickness) in the Namib Sand Sea, which was chosen because there are a number of extant studies we could use for comparison with our results. We test the relative accuracy of GDEM for capturing dune height and shape against multiple individual ASTER DEM scenes and against field surveys, highlighting the smoothing of the dune crest and resultant underestimation of dune height, and the omission of the smallest dunes, due to the 30 m sampling of ASTER DEM products. We demonstrate that morphometric relationships derived from GDEM data are broadly comparable with relationships derived by previous methods, across a range of different dune types. The data confirm patterns of dune height, spacing and equivalent sand thickness mapped previously in the Namib Sand Sea, but add new detail to these patterns. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Gullies are conceptualized in the literature as essentially fluvial forms with dimensional boundaries arbitrarily defined between rills and river channels. This notion is incompatible with the existing variability as to form and process, as mass movements frequently exert a fundamental control on gully initiation and expansion, to the point of features outgrowing their original contributing area. The inability of a conceptual framework to incorporate existing observations inevitably constrains methodologies and research results. In this commentary, several examples of published results are contrasted to the prevailing assumption of an essentially fluvial nature with the purpose of encouraging discussion on the need for a revised conceptual framework in gully erosion research. Copyright © 2011 John Wiley & Sons, Ltd.

Description: We quantify erosion rates in the higher sectors of the Huasco Valley, in the Main Cordillera of the semi-arid Andes of Chile, using elevation differences between three successive geomorphic markers (pediments and paleo-valleys) and the present day valley. Available Ar-Ar ages of Neogene pediments are used to estimate mean erosion rates for the three periods (16 to 13 My, 13 to 8 My, and following 8 My). The landscape of the Huasco Valley is in a transient state, as indicated by well-preserved pediment surfaces in interfluves, valleys deeply incised by fluvial and glacial erosion and scarped head-valleys that represent the current knickzones. Higher erosion rates (45-75 m/My) are calculated for the more recent period (〈8 My) during which deep incision developed compared to previous periods (6-31 m/My). Quantitative data indicate that glaciers had a much higher erosional capability than fluvial activity in the higher sectors of the Main Cordillera. Comparison with erosion rates calculated in other drainage basins of the Chilean Andes suggests that the variability of erosion rates depends on the landscape's transient erosive state. The landscape's geomorphologic response to the uplift of the Main Cordillera results in the retreat of a knickzone, for which retreat velocity depends on precipitation rate pattern and glacial erosion intensity. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In this study, the artificial opening of a new tidal inlet in an existing multiple inlet system is shown to significantly modify the adjacent nearshore and backbarrier morphology, as well as both updrift and downdrift shorelines. The study focuses on the dominant Faro-Olhão and Armona inlets in the Ria Formosa barrier island system of southern Portugal. The equilibrium state and future evolution of the system are inferred using a range of morphological and hydrodynamic indicators, including the evolution of the inlet cross-section, changes in tidal prism, and changes in the dimensions (length and area) of barrier islands. The results reveal how the morphology of an inter-connected two-inlet bay system and the adjacent coastlines has evolved following the artificial opening and stabilisation of Faro-Olhão inlet since 1929. A clear relationship between barrier island size, inlet cross-section/width, and tidal prism is demonstrated. Decadal time-scale changes in the tidal prism of the two inter-connected inlets are shown to be the main mechanism responsible for morphological change, and have resulted in the remobilisation of ebb-tidal delta sediments deposited during previous hydraulic configurations. These changes, in turn, have contributed to a narrowing of Armona inlet and an increase in the size of Culatra Island. The work highlights the importance of ebb-tidal deltas both as sand reservoirs and as conduits through which sand exchange between estuaries or lagoons and the open coast is regulated. It also shows the pivotal role of ebb-tidal deltas in trapping longshore-transported sediment and releasing it again during periods of increased wave activity. The findings have implications regarding the accurate assessment of the stability of multiple inlet systems. Copyright © 2011 John Wiley & Sons, Ltd.

Description: There is growing acknowledgement of the interaction between animals and the river bed on which they live and the implications of biological activity for geomorphic processes. It has been observed that signal crayfish ( Pacifastacus leniusculus ) disturb gravel substrates, potentially promoting sediment transport and impacting ecological communities. However, the mechanisms involved and the extent of their impact remain poorly understood, especially in relation to other processes that affect grain mobility in gravel-bed rivers. A series of flume experiments, using loose and water-worked gravel beds of narrowly-graded grain sizes that were exposed to six hours of crayfish activity under low-velocity flows, showed a substantial increase in the number of grains entrained by subsequent higher-velocity flows when compared with control runs in which crayfish were never introduced. Crayfish alter the topography of their substrate by constructing pits and mounds, which affect grain protrusion. When walking and foraging, they also alter gravel fabric by reorienting and changing the friction angle of surface grains. In water-worked surfaces, this fabric rearrangement is shown to lead to a statistically significant, partial reversal of the structuring that had been achieved by antecedent flow. For these previously water-worked surfaces, the increase in entrainment arising from disturbance by crayfish was statistically significant, with grain transport nearly twice as great. This suggests that signal crayfish, an increasingly widespread invasive species in temperate latitudes beyond their native NW North America, have the potential to enhance coarse-grained bedload flux by altering the surface structure of gravel river beds and reducing the stability of surface grains. This study illustrates further the importance of acknowledging the impact of mobile organisms in conditioning the river bed when assessing sediment entrainment mechanics in the context of predicting bedload flux. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Riffle-pool sequences are a common feature of gravel-bed rivers. However, mechanisms of their generation and maintenance are still not fully understood. In this study a monitoring approach similar to the one of Andrews (1979 and 1982) is employed. It focuses on analysing cross-sectional and longitudinal channel geometry of a large floodplain river (Vereinigte Mulde, Sachsen-Anhalt, Germany) with a high temporal and spatial resolution, in order to conclude from stage-dependant morphometric changes to riffle and pool maintaining processes. In accordance with Richards (1976a), Andrews (1979 and 1982) among others, pool cross sections of the Mulde River are narrow and riffle cross sections are wide suggesting that they should rather be addressed as two general types of channel cross-sections than solely as bedforms. At high flows, riffles and pools in the study reaches changed in length and height but not in position. Pools were scoured and riffles aggraded, a development which was reversed during receding flows below the threshold of 0.4·Q bf (40% bankfull discharge). An index for the longitudinal amplitude of riffle-pool sequences, the bed undulation intensity or bedform amplitude, is introduced and proved to be highly significant as a form parameter, its first derivative as a process parameter. The process of pool scour and riffle fill is addressed as bedform maintenance or bedform accentuation. It is indicated by increasing longitudinal bed amplitudes. According to the observed dynamics of bed amplitudes, maintenance of riffle-pool sequences lags behind discharge peaks. Maximum bed amplitudes may be reached with a delay of several days after peak discharges. Increasing bed undulation intensity is interpreted to indicate bed mobility. Post-flood decrease of the bed undulation intensity indicates a retrograde phase when transport from pools to riffles has ceased and bed mobility is restricted to riffle tails and heads of pools. This type of transport behaviour is referred to as disconnected mobility. The comparison of two river reaches, one with undisturbed sediment supply, the other with sediment deficit, suggests that high bed undulation intensity values at low flows indicate sediment deficit and potentially channel degrading conditions. It is more generally hypothesised that channel bed undulations constitute a major component of form roughness and that increased bed amplitudes are an important feature of channel bed adjustment to sediment deficit be it temporally during late floods or permanently due to a supply limitation of bedload. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Impact forces associated with major debris flows (Jiangjia Ravine, China, August 25, 2004) were recorded in real time by a system consisting of three strain sensors installed at different flow depths. This provides the first real time and long duration record impact forces associated with debris flows. A comprehensive approach including low-pass filtering and moving average methods were used to preprocess the recorded signals. The upper limit of impact frequency in the debris flows was estimated at 188.66 Hz under the assumption that only coarse grains cause effective impact loadings. Thus, a low-pass filter with a 200 Hz cut-off frequency was needed to denoise the original data in order to extract the impact force. Then the moving average method was applied to separate long-term and random components of the filtered data. These were interpreted as, respectively, the fluid pressure and grain impact loading. It was found that the peak grain impacts at different depths were nonsynchronous within the debris flows. The impact loadings were far greater than, and not proportional to the fluid pressures. Analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density, i.e., the product of debris-flow density and mean velocity square, which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems. Copyright © 2011 John Wiley & Sons, Ltd.

Description: A series of laboratory flume experiments under conditions of sediment starvation (zero sediment feeding) and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers. The experiments were carried out in a 8 m long flume using a bimodal grain-size mixture ( D 50  = 6.2 mm) and a range of shear stresses ranging from 4.0 to 8.6 N m  − 2 . The results confirm that a static armour layer is coarser than a mobile one, and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength. An analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer. Under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges. The topography of mobile armour layers created by rising discharges differed. They exhibited a greater roughness length scales and were less organized, despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation. Also, the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges. These differences were mainly due to the transport of the coarser fraction of bed sediments, which diminished to zero over the static armour because of being hidden within the bed, whereas in the mobile armour the coarser particles protruded into the flow and were actively transported, increasing the vertical roughness length scale. Overall, the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness. Detailed elevation models of exposed surfaces of gravel-bed rivers are required to provide critical insight on the sediment availability and sedimentation processes. Copyright © 2011 John Wiley & Sons, Ltd.

Description: There has been little work to date into the controls on slope-to-channel fine sediment connectivity in alpine environments largely ice-free for most of the Holocene. Characterization of these controls can be expected to result in better understanding of how landscapes ‘relax’ from such perturbations as climate shock. We monitored fine sediment mobilisation on a slope segment hydrologically connected to a stream in the largely ice-free 8.3 km 2 Hoophorn Valley, New Zealand. Gerlach traps were installed in ephemeral slope channels to trap surficial material mobilized during rainfall events. Channel sediment flux was measured using turbidimeters above and below the connected slope, and hysteresis patterns in discharge-suspended sediment concentrations were used to determine sediment sources. Over the 96 day measurement period, sediment mobilization from the slope segment was limited to rainfall events, with increasingly larger particles trapped as event magnitude increased. Less than 1% of the mass of particles collected during these events was fine sediment. During this period, 714 t of suspended sediment was transported through the lower gauging station, 60% of it during rainfall events. Channel sediment transfer patterns during these events were dominated by clockwise hysteresis, interpreted as remobilisation of nearby in-channel sources, further suggesting limited input of fine sediment from slopes in the lower valley. Strong counter-clockwise hysteresis, representing input of fine sediment from slope segments, was restricted to the largest storm event (JD2, 2009) when surfaces in the upper basin were activated. The results indicate that the slopes of the lower Hoophorn catchment are no longer functioning as sources of fine sediment, but rather as sources of coarse material, with flux rates controlled by the intensity and duration of rainfall events. Although speculative, these findings suggest a shift to a coarse sediment dominated slope-to-channel transfer system as the influence of pre-Holocene glacial erosion declines. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Megagrooves are kilometre-scale linear topographic lows carved in bedrock, separated by ridges, typically in areas of largely devoid of till. They have been reported from several areas covered by Pleistocene glaciations, such as Canadian NW Territories, Michigan and NW Scotland. Here we report two previously undocumented megagroove fields from Ungava, Canada, and northern England, and present new analyses of the megagrooves from NW Scotland. This paper seeks to determine the nature of the lithological and structural controls on the occurrence and formation of megagrooves. Analysis of both geomorphological and bedrock properties shows that megagrooves are generally: confined to well stratified or layered bedrock, such as (meta)sedimentary rocks with closely spaced joints, and tend not to occur on massive rocks such as gneiss or granite, or thick-bedded sedimentary rocks; subparallel to palaeo-ice flow and the strike of the strata; and tend not to occur where palaeo-ice flow is at high angles to the strike of strata; produced by significant glacial erosion by sustained unidirectional ice flow. Detailed analysis of megagrooves in NW Scotland shows that neither glacio-fluvial erosion, nor differential abrasion was the dominant mechanism of formation. A mechanism, here termed ‘lateral plucking’, is suggested that involves block plucking on rock steps parallel to ice flow. Removal of joint-bounded blocks from such rock steps involves a component of rotation along a vertical axis. Block removal may be enhanced by a direct component of shear stress onto the vertical stoss sides. The lateral plucking mechanism results in horizontal erosion at right angles to the ice flow, and enhances the groove/ridge topography. Megagrooves are potentially useful as palaeo-ice flow indicators in areas devoid of till, and can thus complement the palaeo-ice stream datasets which are presently largely based on soft-sediment landform studies. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT This research builds on the concept of hydraulic geometry and presents a methodology for estimating bankfull discharge and the hydraulic geometry coefficients and exponents for a station using limited data; only stage-discharge and Landsat imagery. The approach is implemented using 82 streamflow gauging locations in the Amazon Basin. Using the estimated values for the hydraulic geometry relations, bankfull discharge, discharge data above bankfull and upstream drainage area at each site, relationships for estimating channel and floodplain characteristics as a function of drainage area are developed. Specifically, this research provides relationships for estimating bankfull discharge, bankfull depth, bankfull width, and floodplain width as a function of upstream drainage area in the Amazon Basin intended for providing reasonable cross-section estimates for large scale hydraulic routing models. The derived relationships are also combined with a high resolution drainage network to develop relationships for estimating cumulative upstream channel lengths and surface areas as a function of the specified minimum channel width ranging from 2 m to 1 km (i.e. threshold drainage areas ranging from 1 to 431,000 km 2 ). At the finest resolution (i.e. all channels greater than 2 m or a threshold area of 1 km 2 ), the Amazon Basin contains approximately 4.4 million kilometers of channels with a combined surface area of 59,700 km 2 . The intended use of these relationships is for partitioning total floodable area (channels versus lakes and floodplain lakes) obtained from remote sensing for biogeochemical applications (e.g. quantifying CO 2 evasion in the Amazon Basin). Copyright © 2011 John Wiley & Sons, Ltd.

Description: Westaway and Bridgland (2010) discuss the causes, the consequences and the chronology of large-magnitude palaeoflows in Pleistocene river systems of northwest Europe. Based on their calculations, these authors suggest that the combined effects of meltwater from Alpine glaciers, rainfall, snowmelt and melting of permafrost during Heinrich Events (HE) explain the large-magnitude discharges of the Fleuve Manche palaeoriver which punctuated the last glacial period. This comment identifies some approximations and inconsistencies regarding ( i ) the timing of the last massive Fleuve Manche palaeoriver discharge and its relation to the deglacial pattern of the British-Irish Ice Sheet (Point 1); ( ii ) the palaeoclimatic conditions prevailing on land and the antagonistic forcing mechanism proposed by the authors to explain the large-magnitude palaeoflows (Point 2); ( iii ) Westaway and Bridgland's (2010) revised interpretation of the deep-sea records from the Bay of Biscay (Point 3); and ( iv ) the relationship between the offshore sedimentation since the Middle Pleistocene and the formation of the Dover Strait (Point 4). Each of these points is detailed below. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Occurrence and development of channel bars are major components of the morphodynamics of rivers and their relation to river meandering has been much explored through theory and experimentation. However, field and documentary data of characteristics and evolution over timescales from years to several decades are lacking. Four sets of aerial photographs in the period 1984–2007 were used to map and quantify bar numbers and areas in GIS on an active meandering reach. Bar types were classified. Additional temporal resolution was provided by annual ground photography and mapping for 1981–2010. Analysis was extended backward by use of large scale Ordnance Survey maps from 1873 onwards. As expected, point bars are the most common type but ‘free’ bars of several types are major components of bar deposition. Point bars and attached bars are significantly larger in size than mid-channel and side bars. Spatial distribution of bars varies down the reach and over time but is related to channel sinuosity, gradient and mobility and to bend evolution. Different types of bar occur in distinctive channel locations, with point and concave-bend bars in zones of high curvature. Bar activity shows relation to discharge events and phases and possibly to changing riparian conditions, but superimposed on this is a common sequence of bar evolution from incipient gravel mid-channel bars to full floodplain integration. This lifecycle is identified as 7–9 years on average. No evidence for mobility of free bars within the course is found. The results are compared with bar and bend theory; the bars are forced and conform in general to bend theory but detailed variation relates to geomorphic factors and to autogenic sequences of bends and bars. Mid-channel bars are width induced. Variability of bar occurrence needs to be taken into account in river management and ecological evaluation, including for the EU WFD. Copyright © 2011 John Wiley & Sons, Ltd.

Description: We evaluate the validity of the beaver-meadow complex hypothesis, used to explain the deposition of extensive fine sediment in broad, low-gradient valleys. Previous work establishes that beaver damming forms wet meadows with multi-thread channels and enhanced sediment storage, but the long-term geomorphic effects of beaver are unclear. We focus on two low-gradient broad valleys, Beaver Meadows and Moraine Park, in Rocky Mountain National Park (Colorado, USA). Both valleys experienced a dramatic decrease in beaver population in the past century and provide an ideal setting for determining whether contemporary geomorphic conditions and sedimentation are within the historical range of variability of valley bottom processes. We examine the geomorphic significance of beaver-pond sediment by determining the rates and types of sedimentation since the middle Holocene and the role of beaver in driving floodplain evolution through increased channel complexity and fine sediment deposition. Sediment analyses from cores and cutbanks indicate that 33–50% of the alluvial sediment in Beaver Meadows is ponded and 28–40% was deposited in-channel; in Moraine Park 32–41% is ponded sediment and 40–52% was deposited in-channel. Radiocarbon ages spanning 4,300 years indicate long-term aggradation rates of ~0.05 cm yr −1 . The observed highly variable short-term rates indicate temporal heterogeneity in aggradation, which in turn reflects spatial heterogeneity in processes at any point in time. Channel complexity increases directly downstream of beaver dams. The increased complexity forms a positive feedback for beaver-induced sedimentation; the multi-thread channel increases potential channel length for further damming, which increases the potential area occupied by beaver ponds and the volume of fine sediment trapped. Channel complexity decreased significantly as surveyed beaver population decreased. Beaver Meadows and Moraine Park represent settings where beaver substantially influence post-glacial floodplain aggradation. These findings underscore the importance of understanding the historical range of variability of valley bottom processes, and implications for environmental restoration. Copyright © 2011 John Wiley & Sons, Ltd.

Description: A progression of induration, erosion, and redeposition of transverse and networked transverse aeolian ridges (TARs) has been documented in the Medusae Fossae Formation (MFF), Mars. Cratered and eroded aeolian bedforms are rarely observed Mars, indicating that those found in the Medusae Fossae Formation have been inactive for much longer than those found elsewhere. Indurated TARs are observed to grade into faceted MFF terrain, indicating a genetic relationship between the two. We propose that TAR deposition, induration and erosion have played a larger role in the surface morphology and evolution of the MFF than previously recognized. The deposition, induration, and erosion of TARs indicate that the MFF has undergone multiple cycles of reworking, and that much of its current surface morphology does not reflect the circumstances of its primary emplacement. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In the first decades of the 20th century, the Ebro River was the Iberian channel with the most active fluvial dynamics and the most remarkable spatial-temporal evolution. Its meandering typology, the dimensions of its floodplain, and the singularities of its flow regime produced an especially interesting set of river functions. The largest dynamics of the Ebro River are concentrated along the meandering profile of the central sector. During the 20th century, this sector experienced a large alteration of its geomorphological structure. We present here an analysis of this evolution through the cartographic study of a long segment of the river (~250 km) in 1927, 1956 and 2003. The results show a large reduction in bank sinuosity, a progressive loss of fluvial territory, and a large decrease in channel width. These changes are especially clear in the areas previously most ecologically connected with the active channel. The fluvial territory of the river in 2003 was approximately half that found during the first decades of the 20th century. Forest plantations, which were non-existent in 1927, occupied more than 1,500 ha of the study area in the last decade. This intense geomorphological transformation becomes ecologically visible in (i) a 35% reduction of the area occupied by riparian vegetation; (ii) a loss of the heterogeneity of riparian forest spots, which were formerly structured in an irregular mosaic far from the river thalweg; and (iii) a modification of the riparian forest structure, which is currently linear, uniform, thin and very close to the river axis. The ecomorphological alteration was intensified by the remarkable reduction in bank length (13%) and the reduced dynamism of the present river system, indicated by an increase in the percentage of fluvial territory occupied by riparian forests and a reduction in the area occupied by the active channel. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Data are reported demonstrating the potential role of microscale morphologies, induced by endolithic lichen communities, specifically Verrucaria baldensis , in the initiation and development of mesoscale solution basin formation on limestone in the Burren, Co. Clare. A biophysical model is proposed outlining the different microscale stages leading to solution basin initiation with a progression from initial lichen colonisation and growth, associated perithecial biopitting followed by biopit coalescence to form biotroughs, their subsequent enlargement and eventual incipient solution basin formation. This model provides one explanation for solution basin development as this end state may also be achieved through simple solutional means without biological input. The complexity of interactions at the rock / lichen interface are identified with emphasis on the spatial and temporal variability of these underlining the point that, as with macrotopographies at the landscape scale, rock surface microtopographies also reflect historical weathering legacies. Copyright © 2011 John Wiley & Sons, Ltd.

Description: There has been limited success in determining critical thresholds of ground cover or soil characteristics that relate to significant changes in runoff or sediment production at the microscale (〈1 m 2 ), particularly in semi-arid systems where management of ground cover is critical. Despite this lack of quantified thresholds, there is an increasing research focus on the two-phase mosaic of vegetation patches and inter-patches in semi-arid systems. In order to quantify ground cover and soil related thresholds for runoff and sediment production, we used a data mining technique known as conditional inference tree analysis to determine statistically significant values of a range of measured variables that predicted average runoff, peak runoff, sediment concentration and sediment production at the microscale. On Chromic Luvisols across a range of vegetation states in semi-arid south-eastern Australia, large changes in runoff and sediment production were related to a hierarchy of different variables and thresholds, but the percentage of bare soil played a primary role in predicting runoff and sediment production in most instances. The identified thresholds match well with previous thresholds found in semi-arid and temperate regions (including the approximate values of 30%, 50% and 70% total ground cover). The analysis presented here identified the critical role of soil surface roughness, particularly where total ground cover is sparse. The analysis also provided evidence that a two-phase mosaic of patches and inter-patches identified via rapid visual assessment could be further delineated into distinct groups of hydrological response, or a multi-phase rather than a two-phase system. The approach used here may aid in assessing scale-dependent responses and address data non-linearity in studies of semi-arid hydrology. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Channel fills are common elements of Holocene river systems and older fluvial sequences, but surprisingly little is known about formation and their sedimentary build-up. Abandoned channels result from channel shifting processes at various scales, including meander cutoff and channel-belt avulsion. Channel-fill sequences are of importance as containers of palaeoenvironmental proxy-records, can be used to reconstruct palaeochannel dynamics and derive palaeoflood records, and contain materials that allow dating the abandonment. Integrated knowledge on the dynamic nature (geometrical and physical insights) of channel abandonment and resultant sedimentary recording is a necessity for comparing and collating records from series of abandoned channel fills. This paper intends to make channel-fill sedimentological sequences more useful recorders of channel abandonment processes and palaeofloods, for which improved understanding is needed of the internal build-up of channel fills. We review oxbow lake infilling along meandering rivers, and supplement this with highly detailed descriptions of two selected field examples of channel fills from the apex-region of the Netherlands’ Rhine delta. From these examples it becomes clear that regional setting and type of abandonment result in different channel-fill end-members; oxbow cutoffs generally produce thick laminated clayey fills as the channel entrance is plugged rapidly, avulsion-abandoned channels are filled with coarse (proximal) deposits as a result of a maintained open river connection. Field examples of channel fills are integrated with knowledge on channel abandonment dynamics in meander cutoff and bifurcating river situations, including insights from recent numerical modeling. We propose a sedimentary-architecture descriptive scheme that distinguishes elements from two stages of channel-fill development; (i) the abandonment stage with initial proximal fill, and (ii) the subsequent fully abandoned palaeochannel that collects distal fill. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Quaternary period palaeoenvironmental and palaeoclimatic reconstructions are based on a wide and diverse array of proxy data sets, some of which are geomorphological in nature. In drylands, where organic proxies may be limited, the use of landforms is particularly important, but challenging. The capacity to establish the age of depositional forms, particularly through the use of luminescence dating, has advanced the use of landforms in dryland palaeo-research, though interpretation of these ‘geoproxy’ records can be complex, especially at the nexus of palaeoclimate and palaeonvironmental interpretations of past conditions. In this paper the use of aeolian and lacustrine forms in Quaternary research is considered, focusing on the relationships between dynamics, form and climate, and on the essential linkage between process research and palaeoenvironmental research. It is concluded that landform analysis is a critical part of dryland palaeoenvironmental/climate reconstruction, contributing a different set of data compared to other data sources, in terms of the elements of past conditions that are revealed. Five principles are identified to improve the use of geoproxy records in Quaternary research: 1) greater use of geomorphic process studies by Quaternary scientists, to better inform palaeolandform interpretation; 2) further development of the use of chronometric data, especially in terms of interpreting large data; 3) interpret landform records in location-specific contexts, not in general terms; 4) capitalise of the complexity of spatially-extensive landform records, which may offer better representations of real Quaternary environmental complexity than ‘at a point’ proxies; 5) establish ways of integrating spatially-extensive geoproxy records with other palaeoenvironmental records. These challenges are major, but not insurmountable, and should represent goals for geomorphologists, chronologists and quaternary scientists alike. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Fluvial sediment transport in the high mountain Partnach River (Reintal Valley, Bavarian Alps) was investigated during a 10-year observation period (2001–2010). During this period, the downstream reach of the Partnach River was decoupled from upstream sediment throughput by a rockslide deposit until 2005. In August 2005, the dam was partially breached during a flood event resulting in renewed sediment coupling between the upstream and downstream reaches. A comparison of pre- and post-dambreak river sediment load data showed that the dissolved load dominated sediment transport prior to August 2005 with a switch to the dominance of bed load transport, post-dambreak. The higher post-dambreak bed load rates were particularly evident during the first years after the dam failure due to significant coarse material coupling between active sediment sources (undercut banks/talus cones) and the Partnach River. In the last years of the observation period (2009 and 2010) the dominance of dissolved load transport was reestablished. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Predicting gully initiation in the catchment scale was done previously by integrating a geographical information system (GIS) with physically-based models, statistical procedures or with knowledge-based expert systems. However, the reliability and validity of applying these procedures are still questionable. In this paper, a data mining (DM) procedure based on decision trees was applied to identify areas of gully initiation risk. Performance was compared with the analytic hierarchy process (AHP) expert system and with the commonly used topographic threshold (TT) technique. A spatial database was used to test the models, composed of a target variable (presence or absence of initial points) and ten independent environmental, climatic and human-induced variables. The following findings emerged: using the same input layers, DM provided better predictive ability of gully initiation points than the application of both AHP and TT. The main difference between the DM and TT was the very high overestimation inherent in TT. In addition, the minimal slope observed for soil detachment was 2°, whereas in other studies it is 3°. This could be explained by soil resistance, which is substantially lower in agricultural fields, while most studies test unploughed soil. Finally, rainfall intensity events of 〉 62.2 mmh -1 (in a period of 30 minutes) were found to have a significant effect on gully initiation. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Dark aeolian deposits on Mars are thought to consist of volcanic materials due to their mineral assemblages, which are common to basalts. However, the sediment source is still debated. Basaltic dunes on Earth are promising analogues for providing further insights into the assumed basaltic sand dunes on Mars. In our study we characterize basaltic dunes from the Ka'u Desert in Hawaii using optical microscopes, electron microprobe, and spectral analyses. We compare the spectra of terrestrial and Martian dune sands to determine possible origins of the Martian dark sediments. Our results show that the terrestrial sands consist primarily of medium to coarse sand-sized volcanic glass and rock fragments as well as olivine, pyroxene, and plagioclase minerals. Grain shapes range from angular to subrounded. The sample composition indicates that the material was derived from phreatomagmatic eruptions partially with additional proportions of rock fragments from local lava flows. Grain shape and size indicate the materials were transported by aeolian processes rather than by fluvial processes. Spectral analyses reveal an initial hydration of all terrestrial samples. A spectral mineralogical correlation between the terrestrial and Martian aeolian sands shows a similarity consistent with an origin from volcanic ash and lava. We suggest that the Martian deposits may contain similar abundances of volcanic glass, which has not yet been distinguished in Martian spectral data. Copyright © 2011 John Wiley & Sons, Ltd.

Description: This study analyzes beach morphological change during six consecutive storms acting on the mesotidal Faro Beach (S. Portugal) between 15 December 2009 and 7 January 2010. Morphological change of the sub-aerial beach profile was monitored through frequent topographic surveys across 11 transects. Measurements of the surf/swash zone dimensions, nearshore bar dynamics, and wave run-up were extracted from time averaged and timestack coastal images, and wave and tidal data were obtained from offshore stations. All the information combined suggests that during consecutive storm events, the antecedent morphological state can initially be the dominant controlling factor of beach response; while the hydrodynamic forcing, and especially the tide and surge levels, become more important during the later stages of a storm period. The dataset also reveals the dynamic nature of steep-sloping beaches, since sub-aerial beach volume reductions up to 30 m 3 /m were followed by intertidal area recovery (−2 〈 z 〈 3 m) with rates reaching ~10 m 3 /m. However, the observed cumulative dune erosion and profile pivoting imply that storms, even of regular intensity, can have a dramatic impact when they occur in groups. Nearshore bars seemed to respond to temporal scales more related to storm sequences than to individual events. The formation of a prominent crescentic offshore bar at ~200 m from the shoreline appeared to reverse the previous offshore migration trend of the inner bar, which was gradually shifted close to the seaward swash zone boundary. The partially understood nearshore bar processes appeared to be critical for storm wave attenuation in the surf zone; and were considered mainly responsible for the poor interpretation of the observed beach behaviour on the grounds of standard, non-dimensional, morphological parameters. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Historical, human-induced channel adjustments in lowland gravel bed rivers have been documented in several geographical contexts worldwide. In particular, it is now widely accepted that the vast majority of European rivers are far from any natural, reference state prior to anthropic disturbances, and a “complete” restoration is hardly achievable. However, few investigations have addressed changes occurred in mountain rivers of the Alps, and these channels are commonly reckoned quite “natural” by society. The paper intends to describe how human pressure on Italian Alpine basins has been quite relevant for several centuries – in terms of land use variations, in-channel structures, timber transport (splash damming) and riparian vegetation management – such that nowadays “reference conditions” cannot be found even in small mountain creeks. In addition, recent natural climatic variations (e.g. the Little Ice Age) are superimposed on human disturbances, thus defying the definition of any “equilibrium” morphological conditions even under “human-free” states. A summary of published as well as unpublished works on historical channel adjustments in rivers of the Italian Alps is presented in order to document the impacts deriving from human pressure at different basin scales and for different river morphologies, from steep confined streams to large unconfined rivers. General options for river management and restoration actions aiming to combine geomorphological functionality and flood hazard mitigation are discussed, in the light of the current European legislative context. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT In 1820, the lower Canadian River meandered through a densely forested floodplain. By 1898, most of the floodplain had been cleared for agriculture and changes in channel geometry and specific stream power followed, particularly channel widening and straightening with a lower potential specific stream power. In 1964, a large upstream hydropower dam was constructed, which changed the flow regime in the lower Canadian River and consequently the channel geometry. Without destructive overbank floods, the channel narrowed rapidly and considerably due to encroachment by floodplain vegetation. The lower Canadian River, which was once a highly dynamic floodplain-river system, has now been transformed into a relatively static river channel. These changes over the past 200 years have not been linear or independent. In this article, we use a variety of data sources to assess these historical changes along the lower Canadian River floodplain and identify feedbacks among floodplain cultivation, dam construction, specific stream power, and channel width, slope, and sinuosity. Finally, we combine the results of our study with others in the region to present a biogeomorphic response model for large Great Plains rivers that characterizes channel width changes in response to climate variability and anthropogenic disturbances. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The general nature of bulk flow within bedrock single-channel reaches has been considered by several studies recently. However, the flow structure of a bedrock-constrained, large river with a multiple channel network has not been investigated previously. The multiple channel network of the Siphandone wetlands in Laos, a section of the Mekong River, was modelled using a steady one-dimensional hydraulic model. The river network is characterised by a spatially-varying channel-form leading to significant changes in the bulk flow properties between and along the channels. The challenge to model the bulk flow in such a remote region was the lack of ideal boundary conditions. The flow models considered both low flow, high inbank and overbank flows and were calibrated using SPOT satellite sensor imagery and limited field data concerning water levels. The application of the model highlighted flow characteristics of a large multi-channel network and also further indicated the field data that would be required to properly characterise the flow field empirically. Important results included the observation that adjacent channels within the network had different water surface slopes for the same moments in time; thus calibration data for modelling similar systems needs to account for these significant local differences. Further, the in-channel hydraulic roughness coefficient strongly varied from one cross-section to the next (Manning's ‘n’ range: 0.01 to 0.10). These differences were amplified during low flow but persisted in muted form during high discharges. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT This paper reports a RFID tracing experiment implemented in a high-sediment-load mountain stream typical of alpine gravel-bed torrents. The study site is the Bouinenc Torrent, a tributary to the Bléone River in SE France that drains a 38·9-km² degraded catchment. In spring 2008, we deployed 451 tracers with b -axes ranging from 23 to 520 mm. Tracers were seeded along eight cross-sections located in the upstream part of the lowest 2·3 km of the stream. Three tracer inventories were implemented in July 2008, 2009 and 2010. Recovery rates calculated for mobile tracers declined from 78% in 2008 to 45% in 2009 and 25% in 2010. Observations of tracer displacement revealed very high sediment dispersion, with frontrunners having travelled more than 2 km only 3 months after their deployment. The declining recovery rate over time was interpreted as resulting from rapid dispersion rather than deep burial. We evaluated that 64% of the tracers deployed in the active channel were exported from the 2·3-km study reach 3 years after the onset of the tracing experiment. Travel distances were characterized by right-skewed and heavy-tailed distributions, correctly fitted by a power-law function. This supports the idea that in gravel-bed rivers with abundant sediment supply relative to transport capacity, bedload transport can be viewed as a superdiffusive sediment dispersion process. It is also shown that tracers initially deployed in the low-flow channel were characterized by a 15- to 30-fold increase of mobility compared to tracers deployed in gravel bars. Copyright © 2011 John Wiley & Sons, Ltd.

Description: This study developed and evaluated a hybrid approach to remote measurement of river morphology that combines LiDAR topography with spectrally-based bathymetry. Comparison of filtered LiDAR point clouds with surveyed cross-sections indicated that subtle features on low-relief flood plains were accurately resolved by LiDAR but that submerged areas could not be detected due to strong absorption of near-infrared laser pulses by water. The reduced number of returns made the active channel evident in a LiDAR point density map. A second data set suggested that pulse intensity also could be used to discriminate land from water via a threshold-based masking procedure. Fusion of LiDAR and optical data required accurate co-registration of images to the LiDAR, and we developed an object-oriented procedure for achieving this alignment. Information on flow depths was derived by correlating pixel values with field measurements of depth. Highly turbid conditions dictated a positive relation between green band radiance and flow depth and contributed to under prediction of pool depths. Water surface elevations extracted from the LiDAR along the water's edge were used to produce a continuous water surface that preserved along-channel variations in slope. Subtracting local flow depths from this surface yielded estimates of the bed elevation that were then combined with LiDAR topography for exposed areas to create a composite representation of the riverine terrain. The accuracy of this terrain model was assessed via comparison with detailed field surveys. A map of elevation residuals showed that the greatest errors were associated with underestimation of pool depths and failure to capture cross-stream differences in water surface elevation. Nevertheless, fusion of LiDAR and passive optical image data provided an efficient means of characterizing river morphology that would not have been possible if either data set had been used in isolation. Copyright © 2002 John Wiley & Sons, Ltd.

Description: The mineral magnetic properties of deposited dusts collected along a broadly north-to-south transect across Niger have been investigated on both a bulk and particle size-specific basis. Dusts display a general north-to-south gradient in fine-grained ferrimagnetic mineral (magnetite/maghemite) concentrations, with samples south of the Sahara/Sahel transition (south of ~15.5 o N) generally containing greater concentrations than dusts from further north where the climate is much drier. This distinction is seen especially clearly in the clay (〈2 µm) fraction, which harbours the products of weathering and pedogenesis. This gradient in ferrimagnetic mineral concentrations broadly parallels that previously reported for surface soils/sands across a similar latitudinal range. We suggest that the regional distinction in both dust and surface soil/sand magnetic properties can be related to differences in weathering regime between the arid Saharan parts of the transect and the Sahel sites where higher rainfall has permitted stronger weathering and pedogenesis. Given that the weathering-related magnetic signatures in the clays dominate the magnetic properties of the 〈16 µm fractions in these samples, and that this particle size component is most likely to be involved in long-range transport, magnetic measurements hold out the potential of discriminating Sahara and Sahel dusts deposited in remote areas. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Comparative assessment of stone weathering intensities and bioclimatic conditions was conducted at four temples located in cleared and forested sites of the Angkor park, based on similar protocols. 4000 sculpted lotus petals carved in the same grey sandstone were categorized by using two customised scales of weathering intensity, and climate monitoring was conducted from December 2008 to November 2009. Whereas 70% of the sandstone lotus petals are almost completely destroyed by sandstone weathering in cleared areas, 74% of petals located in forested environments appear to be totally free of mechanical weathering and are only affected by superficial biochemical weathering. Ambient conditions are also contrasting, with the magnitude of the diurnal surface temperature and relative humidity ranges being three times higher at cleared sites than in wooded areas. As wetting-drying cycles are the driving force of sandstone decay at Angkor, causal links are suggested between weathering and climate regimes. In wooded areas, the microclimate is buffered by the forest and the associated lithobionts, which maintain constant humidity levels, reduce thermal stresses at the stone surface and induce a slow biochemical weathering regime. In cleared areas, direct exposure to sunshine and monsoon rains induces pronounced wetting-drying cycles conducive to swelling-shrinking movements and other potential processes, provoking the rapid mechanical decay of the sandstone. Even if local damage can be caused by tree roots, the forest cover and the associated lithobionts obviously play an overall protective role. Additionally, microtopographical factors related to architectural designs and post-building events probably explain intra-site and between site minor differences in the amount of sandstone decay, by influencing key factors such as the water residence time at the stone surface. Last, the contrasting weathering regimes in forested and cleared sites are but a trend, for besides overwhelming mechanical weathering, chemical weathering is also operative at cleared sites, as indicated by salt efflorescences and ferric oxidation. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Prevailing ideas and calculations of coastal response to sea level rise (SLR) are often based on the Bruun model (Bruun, 1962) that predicts upward and landward transfer of an equilibrium profile during SLR through offshore sediment transport on the shoreface. The model is based on a number of assumptions of questionable validity as well as outdated concepts on how sediment is transported across the shoreface. This contribution takes a numerical modelling approach that is based on first-order processes contributing to the movement of sediment across the shoreface. Using a wave transformation model that predicts hydrodynamic processes driving cross-shore sediment transport and an energetics-based model for the coupling between hydrodynamics and sediment transport, we show that cross-shore sediment transport is mainly onshore directed at the boundary between the lower and the upper shoreface, in agreement with the model proposed by Davidson-Arnott (2005). The transition from onshore to offshore directed transport is located well within the surf zone and with a rising sea level this transition point becomes displaced landward and upward. Tests also show that substrate slope is of fundamental importance to the manner in which beaches react to rising sea level. Copyright © 2011 John Wiley & Sons, Ltd.

Description: To quantify landscape change resulting from processes of erosion and deposition and to establish spatially distributed sediment budgets, ‘models of change’ can be established from a time series of digital elevation models (DEMs). However, resolution effects and measurement errors in DEMs may propagate to these models. This study aimed to evaluate and to modify remotely-sensed DEMs for an improved quantification of initial sediment mass changes in an artificially-created catchment. DEMs were constructed from photogrammetry-based, airborne (ALS) and ground-based laser scanning (TLS) data. Regions of differing morphological characteristics and vegetation cover were delineated. Three-dimensional (3D) models of volume change were established and mass change was derived from these models. DEMs were modified region-by-region for rill, interrill and alluvial areas, based on logical and hydro-geomorphological principles. Additional DEMs were constructed by combining multi-source, modified data. Models were evaluated by comparison with d-GPS reference data and by considering sediment budget plausibility. Comprehensive evaluation showed that DEM usability depends on a relation between the technique used to obtain elevation data, surface morphology and vegetation cover characteristics. Photogrammetry-based DEMs were suited for quantification of change in interrill areas but strongly underestimated surface lowering in erosion rills. TLS DEMs were best suited in rill areas, while ALS DEMs performed best in vegetation-covered alluvial areas. Agreement with reference data and budget plausibility were improved by modifications to photogrammetry- and TLS-based DEMs. Results suggest that artefacts in DEMs can be reduced and hydro-geomorphic surface structures can be better represented by applying region-specific modifications. Photogrammetry-based DEMs can be improved by combining higher and lower resolution data in defined structural units and applying modifications based on principles given by characteristic hydro-geomorphic evolution. Results of the critical comparative evaluation of remotely-sensed elevation data can help to better interpret DEM-based quantifications of earth-surface processes. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Soil redistribution on arable land significantly affects lateral and vertical soil carbon (C) fluxes (caused by C formation and mineralisation) and soil organic carbon (SOC) stocks. Whether this serves as a (C) sink or source to the atmosphere is a controversial issue. In this study, the SPEROS-C model was modified to analyse erosion induced lateral and vertical soil C fluxes and their effects upon SOC stocks in a small agricultural catchment (4.2 ha). The model was applied for the period between 1950 and 2007 covering 30 years of conventional tillage (1950–1979) followed by 28 years of conservation tillage (1980–2007). In general, modelled and measured SOC stocks are in good agreement for three observed soil layers. The overall balance (1950–2007) of erosion induced lateral and vertical C fluxes results in a C loss of −4.4 g C m -2 a -1 at our test site. Land management has a significant impact on the erosion induced C fluxes, leading to a predominance of lateral C export under conventional and of vertical C exchange between soil and atmosphere under conservation agriculture. Overall, the application of the soil conservation practices, with enhanced C inputs by cover crops and decreased erosion, significantly reduced the modelled erosion induced C loss of the test site. Increasing C inputs alone, without a reduction of erosion rates, did not result in a reduction of erosion induced C losses. Moreover, our results show that the potential erosion induced C loss is very sensitive to the representation of erosion rates (long-term steady state vs. event driven). A first estimate suggests that C losses are very sensitive to magnitude and frequency of erosion events. If long-term averages are dominated by large magnitude events modelled erosion induced C losses in the catchment were significantly reduced. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The development of cavernous weathering features such as tafoni remains poorly understood. In particular, the roles played by internal moisture and case hardening remain unclear. In this study, Electric Resistivity Tomography (ERT) has been used to map moisture distribution within inner walls of tafoni developed in sandstone, and an Equotip device used to measure rock surface hardness as a proxy measure of the degree of weathering and case hardening. Seven large tafoni in the Golden Gate Highlands National Park (South Africa), varying in size and degree of development have been monitored. A dynamic relationship between surface hardness, degree of weathering and internal moisture regimes has been found. We propose a new conceptual model which illustrates the complex interaction between case hardening and internal moisture and suggests a new direction for cavernous weathering research. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Field investigations that help clarify local sedimentary processes involved in the migration of alternate bars as a consequence of flood events are lacking. A simple approach combining scour chains, stratigraphy and frequent bathymetric surveys is proposed to connect the dynamics of free migrating alternate bars present in disconnected channels of large sandy-gravelly rivers with their sedimentary products and vice versa. The results show that the spatial distribution of bars before a flood partly governs the scour and fill processes and that the sediment transport rates vary significantly on a single cross section. This can be due to preferential axes of the migration of the bars determined by their location on the cross section, the bank direction and the discharge. The approach allows the reconstruction of local sedimentary processes involved in alternate bar migration by combining maximum scour depths reached during a flood with frequent channel bed topography surveys and post-flood stratigraphy. It is also possible to distinguish deposited and preserved sediments compared with sediments by-passed during the flood. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Rain splash erosion is an important soil transport mechanism on steep hillslopes. The rain splash process is highly stochastic; here we seek to constrain the probability distribution of splash transport distances on natural hillslopes as a function of hillslope gradient and total precipitation depth. Field experiments were conducted under natural precipitation events to observe splash travel on varying slope gradients. The downslope fraction of splash transport on 15°, 25° and 33° gradients were 85%, 96% and 96% respectively. Maximum splash transport ( L max ) was related to the rain splash detachment of soil particles and slope gradient. An empirical relationship of L max to the precipitation depth and gradient was obtained; it is linearly proportional to hillslope gradient and logarithmically related to precipitation depth. Measured splash distances were calibrated to the fully two dimensional model of splash transport of Furbish et al. (2007) that is based on the assumption that radial splash distances are exponentially distributed; calibrated values of mean splash transport distances are an order of magnitude greater than those previously determined in a controlled laboratory setting. We also compared measured data with several one dimensional probability distributions to asses if splash transport distances could be better explained by a heavy-tailed probability distribution rather than an exponential probability distribution. We find that for hillslopes of 15° and 25°, although a log-normal probability distribution best describes the data, we find its likelihood is nearly indistinguishable from an exponential distribution based on computing maximum likelihood estimators for all 1-D distributions (exponential, log-normal and Weibull). At 33°, however, we find stronger evidence that measured travel distances are heavy-tailed. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Concentrated flow is often the dominant source of water erosion following disturbance on rangelands. Because of the lack of studies that explain the hydraulics of concentrated flow on rangelands, cropland-based equations have typically been used for rangeland hydrology and erosion modeling, leading to less accurate predictions due to different soil and vegetation cover characteristics. This study investigates the hydraulics of concentrated flow using unconfined field experimental data over diverse rangeland landscapes within the Great Basin Region, United States. The results imply that the overall hydraulics of concentrated flow on rangelands differ significantly from those of cropland rills. Concentrated flow hydraulics on rangelands are largely controlled by the amount of cover or bare ground and hillslope angle. New predictive equations for concentrated flow velocity (R 2  = 0.47), hydraulic friction (R 2  = 0.52), and width (R 2  = 0.4) representing a diverse set of rangeland environments were developed. The resulting equations are applicable across a wide span of ecological sites, soils, slopes, and vegetation and ground cover conditions and can be used by physically-based rangeland hydrology and erosion models to estimate rangeland concentrated flow hydraulic parameters. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Our understanding of the effect of scale on runoff and sediment transfers within catchments is currently limited by a lack of available data. We present a multi-scale dataset of seventeen rainfall events collected simultaneously at four spatial scales within a small agricultural catchment in 2005–2006. Analysis using exploratory techniques and a two-step, Zero-Inflated LogNormal mixed-effects regression model, has demonstrated that event responses, and event response characteristics representing runoff and sediment peaks and area normalised yields, are scale dependent, and hence cannot be transferred directly between scales. Runoff and sediment yields increase as scale increases, and we propose this effect, which differs from that observed in the few other studies of scale effects undertaken, is due to increasing connectivity within the catchment, and the dominance of preferential flow pathways including through macropores and field drains. The processes contributing to scale dependence in the data, and the possibility that certain processes dominate at particular scales, are discussed. The data presented here help to improve our spatial understanding of runoff and sediment transport in small agricultural catchments, and provide examples of the type of spatial dataset and the type of analysis that are essential if we are to develop models which are able to predict runoff and soil erosion accurately, and allow us to manage runoff and sediment transport effectively across scales. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Despite significant advances over the past decades, our understanding of drumlin formation and associated ice-bed processes is still incomplete. In this paper, we present the integrated use of geomorphological, sedimentological and geophysical techniques as a powerful means to force a breakthrough towards solving the drumlin enigma. We report on investigations of the anatomy of the Pigeon Point drumlin, Clew Bay, Ireland. We found that the bulk of the landform, which displays a classical drumlin shape, consists of silty-clayey diamicton showing evidence of deformation, hydrofracturing and comminution. The unit is interpreted as a subglacial traction till/comminution till. The thin unit overlying this basal till consists of silty-sandy diamicton, and is interpreted as a paraglacially modified melt-out till. The partly cemented third unit consists of stratified, massive to graded sands and gravels. Its contact with the subglacial traction till consists of a series of concave shapes, which suggests that it was deposited in meltwater channels that flowed in subglacial cavities and that cut laterally into the drumlin. We propose that highs in the undulating rockhead relief, as shown in the seismic profile, have provided nuclei which initiated drumlin formation. This idea is supported by the observation of local detached bedrock slabs that grade upwards into a comminution till. In the long profile, very high normalised IP values form a wedge-shape, which is interpreted as a set of conjugate thrusts, or a ‘pop-up’ structure. The structure is positioned directly above one of the undulations in the bedrock, suggesting a direct relationship. The high values are thought to reflect the presence of pre-existing clays, which were sheared into the till, thus forming linings in the thrust features. It is concluded that glacitectonic processes, notably differential bedrock weathering and thrusting, have played a key role in the formation of this drumlin. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Detection of surface change is a fundamental task in geomorphology. Terrestrial laser scanners are increasingly used for monitoring surface change resulting from a variety of geomorphic processes, as they allow the rapid generation of high resolution digital elevation models. Irrespective of instrument specifics, survey design or data processing, such data are subject to a finite level of ambiguity in position measurement, a consideration of which must be taken into account when deriving change. The propagation of errors is crucial in change detection because even very small uncertainties in elevation can produce large uncertainties in volume when extrapolated over an area of interest. In this study we propose a methodology to detect surface change and to quantify the resultant volumetric errors in areas of complex topography such as channels, where data from multiple scan stations must be combined. We find that a commonly proposed source of error, laser point elongation at low incidence angles, has a negligible effect on the quality of the final registered point cloud. Instead, ambiguities in elevation inherent to registered data sets have a strong effect on our ability to detect and measure surface change. Similarly we find that changes in surface roughness between surveys also reduce our ability to detect change. Explicit consideration of these ambiguities, when propagated through to volume calculations, allows us to detect volume change of 87 ± 5 m 3 , over an area of ≈4900 m 2 , due to passage of a debris flow down a 300 m reach of the Illgraben channel in Switzerland. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Infragravity wave (IGW) transformation was quantified from field measurements on two shore platforms on New Zealand's east coast, making this the first study to describe the presence, characteristics and behaviour of infragravity waves (IGWs) on rock platform coasts. Data was collected using a cross-shore array of pressure transducers during a 22 hour experiment on Oraka shore platform and a 36 hour experiment at Rothesay Bay shore platform. A low pass Fourier filter was used to remove gravity wave frequency oscillations, allowing separate analysis of IGWs and the full wave spectrum. Offshore IGW heights were measured to be 7 cm (Oraka) and 9 cm (Rothesay Bay), which were 21% (Oraka) and 7.5% (Rothesay Bay) the height of incident wave height. At the cliff toe, significant IGW height averaged 15 cm at Oraka and 13 cm at Rothesay Bay. This increase in IGW height over the platform during both experiments is attributed to shoaling of 40–55% over the last 50–60 m before the cliff toe respectively. Shoaling across the platform was quantified as the change in IGW height form the platform edge to cliff toe, resulting in a maximum increase of 1.88 and 2.63 on Rothesay Bay and Oraka platforms. IGW height at the cliff toe showed a strong correlation with incident H s . The proportional increase in IGW height shows a strong correlation to water level on each platform. The rate of shoaling of long period waves on the shallow, horizontal platforms increased at higher water levels resulting in a super elevation in water level at the cliff toe during high tide. Greater IGW shoaling was also observed on the wider (Oraka) shore platform. Results from this study show the first measurements of IGWs on shore platforms and identify long wave motion a significant process in a morphodynamic understanding of rock coast. Copyright © 2011 John Wiley & Sons, Ltd.

Description: There is a strong possibility that environmental change (whether climate or land use) will be manifest as changes in the size-frequency distribution of landslides. Here we present evidence for this from western Kyrgyzstan, Central Asia. Remote sensing and spatial analysis have been applied to map mass movements in the central part of the Maily-Say Valley and to detect recent landslide activations. The evolution of the landslide activity over the past 50 years has been analysed on the basis of pre-existing landslide maps and new analyses of aerial photographs as well as Quickbird images. Finally, five inventories were produced for the years 1962 (based on the existing map of 1962 and aerial photographs of 1962), 1984 (based on the existing map of 1977 and aerial photographs of 1984), 1996 (based on aerial photographs of 1996), 2002 (based on the existing map of 2003 and Quickbird imagery of 2002) and 2007 (based on Quickbird imagery of 2007). The geomorphologic features contained in the catalogues represent the landslide bodies observed from remote imagery of the corresponding year. Mapped landslides are mostly considered as the result of a series of slope failure events. Size-frequency analyses applied to the five landslide inventories show that both the number and size of unstable slopes increased from 1962 (162 objects) to 2007 (208 objects) and the power-law exponent decreased over time. This changing power-law exponent may indicate that landslide-related hazards are increasing. This tendency is documented in more detail for two active landslide zones, one in the main valley and one located to the west of it. Landslide detection methods were used to assist the evolution of slope instabilities. Choosing appropriate thresholds, the image subtraction method based on Normalized Difference Vegetaion Index (NDVI) allowed accurate detection of new sliding activation in these two zones. This confirmed the results of the more extensive survey that there is a systematic shift in power law exponents and size-frequency distributions for Central Asian landslides. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides, particularly as a consequence of altered precipitation and temperature regimes. Whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated. We test this notion with simple Monte Carlo and bootstrap simulations of statistical models commonly used to characterise empirical landslide size distributions. Our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters, critically depending on, among others, the size of the largest of landslides recorded. Conversely, comparable model parameter values may obscure significant, i.e. more than twofold, changes to landslide occurrence, and thus inferred rates of hillslope denudation and sediment delivery to drainage networks. A time series of some of Earth's largest mass movements reveals clustering near and partly before the last glacial-interglacial transition and a distinct step-over from white noise to temporal clustering around this period. However, elucidating whether this is a distinct signal of first-order climate-change impact on slope stability or simply coincides with a transition from short-term statistical noise to long-term steady-state conditions remains an important research challenge. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Evaluation of historic range of variability (HRV) is an effective tool for determining baseline conditions and providing context to researchers and land managers seeking to understand and enhance ecological function. Incorporating HRV into restoration planning acknowledges the dynamic quality of landscapes by allowing variability and disturbance at reasonable levels and permitting riverine landscapes to adapt to the physical processes of their watersheds. HRV analysis therefore represents a practical (though under-utilized) method for quantifying process-based restoration goals. We investigated HRV of aggradational processes in the subalpine Lulu City wetland in Rocky Mountain National Park to understand the impacts of two centuries of altered land use and to guide restoration planning following a human-caused debris flow in 2003 that deposited up to 1 m of sand and gravel in the wetland. Historic aerial photograph interpretation, ground penetrating radar surveys, and trenching, coring, and radiocarbon dating of valley-bottom sediments were used to map sediment deposits, quantify aggradation rates, and identify processes (in-channel and overbank fluvial deposition, direct hillslope input, beaver pond filling, peat accumulation) creating alluvial fill within the wetland. Results indicate i) the Lulu City wetland has been aggrading for several millennia, ii) the aggradation rate of the past one to two centuries is approximately six times higher than long-term pre-settlement averages, iii), during geomorphically active periods, short-term aggradation rates during the pre-settlement period were likely much higher than the long-term average rate, and iv) the processes of aggradation during the last two centuries are the same as historic processes of aggradation. Understanding the HRV of aggradation rates and processes can constrain management and restoration scenarios by quantifying the range of disturbance from which a landscape can recover without active restoration. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Low-elevation areas within a sandy barrier island are subject to flooding via saturation overland flow following moderate storm surges and rainfall events. Using a high resolution topographic survey and simple hydrology models, we estimate the discharge and velocities from storm surge return flow and saturation overland flow. Results show that return flow velocities are of the same magnitude as the critical velocity necessary to mobilize sand when a hydraulic connection between the watershed and back-barrier bay is present. Storms of moderate strength and rainfall intensity may be sufficient to keep the return channels open within the back-barrier, thus providing natural conduits for water exchange from overwash events during extreme storm surges triggered by hurricanes. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Acquiring high resolution topographic data of natural gravel surfaces is technically demanding in locations where the bed is not exposed at low water stages. Often the most geomorphologically active surfaces are permanently submerged. Gravel beds are spatially variable and measurement of their detailed structure and particle-sizes is essential for understanding the interaction of bed roughness with near-bed flow hydraulics, sediment entrainment, transport and deposition processes, as well as providing insights into the ecological responses to these processes. This paper presents patch-scale laboratory and field experiments to demonstrate that through-water terrestrial laser scanning (TLS) has the potential to provide high resolution digital elevation models of submerged gravel beds, providing enough detail to depict individual grains and small scale forms. The resulting point cloud data requires correction for refraction before registration. Preliminary validation shows that patch-scale TLS through 200 mm of water introduces a mean error of less than 5 mm under ideal conditions. Point precision is not adversely affected by the water column. The resulting DEMs can be embedded seamlessly within larger sub-aerial reach-scale surveys and can be acquired alongside flow measurements to examine the effects of three-dimensional surface geometry on turbulent flow fields and their interaction with instream ecology dynamics. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In the year 2007, enhanced rockfall activity was observed within the scarp of a 500 a BP rockslide in the Reintal catchment (Northern Calcareous Alps, Germany); the largest of a series of events took place in August, when almost 50000 m³ of rock were detached from the subvertical rock face and deposited on a talus cone. In this case study, we focus on three aspects of rockfall research: First, we compile detailed geomorphological and geotechnical findings to explain the causes of the recent events. The results of laboratory tests and stability estimations suggest that rockfall activity will persist in the future as the old rockslide scarp still contains unstable rock masses. Second, we use digital elevation data from a pre-event airborne LiDAR survey (ALS) and post-event terrestrial laserscanning (TLS) to quantify landform changes and the mass balance of the rockfall event(s). The widespread availability of ALS elevation data provides a good opportunity to quantify fresh events using a comparatively inexpensive TLS survey; this approach is complicated by uncertainties resulting from the difficult coregistration of ALS and TLS data and the specific geometric problems in steep (ALS) and flat (TLS) terrain; it is therefore limited to at least medium-sized events. Third, the event(s) is simulated using the results of the LiDAR surveys and a modified GIS-based rockfall model in order to test its capability of predicting the extent and the spatial distribution of deposition on the talus cone. Results show that the model generally reproduces the process domain and the spatial distribution of topographic changes but frequently under- and overestimates deposition heights. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Studies on pool morphologies include reports of over 80% or 90% of pools being associated with structural controls and large obstructions that include boulders, bedrock outcrops and Large woody debris (LWD). A Monte Carlo simulation approach and developmental computer model was created to predict pool formation, spacing and the percent length covered by pools, riffles, scour holes and runs based on input data that include channel slope, width, the number of small and large boulders, and the number of 10–30 cm, 30–60 cm and 〉60 cm pieces of wood. The statistical-empirical model is founded on the idea that boulders, bedrock outcrops and large woody debris provide a physical framework that then controls local water-surface slopes, velocity patterns and the locations of pools and riffles. The spacing values of individual types and sizes of obstructions are modeled as log-normal distributions with separate distributions for each obstruction type. Pools are assigned different probabilities of development depending on the obstruction type. Pool and riffle lengths used to create the subsequent morphology follow their own slope-dependent, log-normal trends. A minimum distance develops between successive pools because of the backwater and turbulent conditions needed for pool formation. The total number and spacing of pools, riffles and scour holes thus reflects the number and locations of obstructions and characteristics of the pool-riffle couplet. The simulation model accurately captures the number of pools in the modeled data range at 65% of all the verification field sites, and 86% of the verification field sites with a more limited range of width and slope characteristics. Lower levels of prediction capabilities are associated with modeled numbers of scour holes and log jams. The model accurately mimics some statistical attributes of pool spacing, and future versions of the model could be developed to improve overall predictive capabilities. Copyright © 2011 John Wiley & Sons, Ltd.

Description: A key problem in computational fluid dynamics (CFD) modelling of gravel-bed rivers is the representation of multi-scale roughness which spans the range from grain size, through bedforms, to channel topography. These different elements of roughness do not clearly map onto a model mesh and use of simple grain-scale roughness parameters may create numerical problems. This paper presents CFD simulations for three cases: a plane bed of fine gravel, a plane bed of fine gravel including large, widely-spaced pebble clusters, and a plane gravel bed with smaller, more frequent, protruding elements. The plane bed of fine gravel is modelled using the conventional wall function approach. The plane bed of fine gravel including large, widely-spaced pebble clusters is modelled using the wall function coupled with an explicit high-resolution topographic representation of the pebble clusters. In these cases, the three-dimensional Reynolds-averaged continuity and Navier-Stokes equations are solved using the standard k  −  ε turbulence model, and model performance is assessed by comparing predicted results with experimental data. For gravel bed rivers in the field, it is generally impractical to map the bed topography in sufficient detail to enable the use of an explicit high-resolution topography. Accordingly, an alternative model based on double-averaging is developed. Here, the flow calculations are performed by solving the three-dimensional double-averaged continuity and Navier-Stokes equations with the spatially-averaged 〈 k  −  ε 〉 turbulence model. For the plane bed of fine gravel including large, widely-spaced pebble clusters, the model performance is assessed by comparing the spatially-averaged velocity with the experimental data. The case of a plane gravel bed with smaller, more frequent, protruding elements is represented by a series of idealised hypothetical cases. Here, the spatially-averaged velocity and eddy viscosity are used to investigate the applicability of the model, compared to using the explicit high-resolution topography. The results show the ability of the model to capture the spatially-averaged flow field and, thus, illustrate its potential for representing flow processes in natural gravel-bed rivers. Finally, practical data requirements for implementing such a model for a field example are given. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT The effect of changes in catchment processes and conditions can be studied by using connectivity as a framework for understanding the feedbacks and interactions occurring within the system. The sediment record preserved in reservoirs can be a useful archive of catchment changes, but needs to be considered in conjunction with the different elements that compose and act on the system to take into account its complexity. Changing patterns of connectivity have been studied in the Ingbirchworth Catchment (Yorkshire, UK), using a multiple methodology approach combining the analysis of reservoir-sediment records with knowledge of recent land-use history, high resolution rainfall records, catchment characteristics and management aspects. Sedimentation rates inferred from reservoir-sediment cores from two reservoirs in the Ingbirchworth catchment show sedimentation peaks which coincide with periods of significant changes in the catchment, such as the introduction of arable crops, the establishment of land drainage and the widespread intensification and mechanization of agriculture. Rainfall patterns, including combinations of events such as droughts and increased precipitation, contribute to increased sediment transfer under catchment conditions in which more sediment and/or new pathways are made available due to catchment changes. Sediment fingerprinting supports the notion that changes in sedimentation rates are not just related to increased/reduced erosion and transport in the same areas, but also to the establishment of different pathways increasing sediment connectivity. The results demonstrate that typical calculations of catchment-area yields are not sufficient as sediment-contributing areas vary as a consequence of changing conditions. The study provides insights into the complex interactions influencing connectivity, such as the relation between catchment changes and climatic inputs, and the subsequent effect on catchment conditions and transfer networks. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Progress in some areas of process-based aeolian sediment transport research is hampered by limited opportunities for data comparison, synthesis, and integration. This is partially due to a lack of reliable comparison methods. Many comparison methods are forms of calibration that are either restrictive (e.g., time-averages only) or non-existent (e.g., for field-based sediment transport thresholds or vertical mass flux profiles). It is believed that the adoption of standard methods for common measurements may improve inter-study comparison, add value and longevity to data, and advance integrative modeling efforts. Examples of approaches in allied disciplines where standards are used routinely are reviewed and we discuss how the mutual benefits of standardized data could outweigh perceived disadvantages. Overall, the goal of this commentary is to encourage discussion, self-assessment, and forethought with regard to measurement methods used in process-based aeolian geomorphology. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT A 177 river km georeferenced aerial survey of in-channel large wood (LW) on the lower Roanoke River, NC was conducted to determine LW dynamics and distributions on an eastern USA low-gradient large river. Results indicate a system with approximately 75% of the LW available for transport either as detached individual LW or as LW in log jams. There were approximately 55 individual LW per river km and another 59 pieces in log jams per river km. Individual LW is a product of bank erosion (73% is produced through erosion) and is isolated on the mid and upper banks at low flow. This LW does not appear to be important for either aquatic habitat or as a human risk. Log jams rest near or at water level making them a factor in bank complexity in an otherwise homogenous fine-grained channel. A segmentation test was performed using LW frequency by river km to detect breaks in longitudinal distribution and to define homogeneous reaches of LW frequency. Homogeneous reaches were then analyzed to determine their relationship to bank height, channel width/depth, sinuosity, and gradient. Results show that log jams are a product of LW transport and occur more frequently in areas with high snag concentrations, low to intermediate bank heights, high sinuosity, high local LW recruitment rates, and narrow channel widths. The largest concentration of log jams (21.5 log jams/km) occurs in an actively eroding reach. Log jam concentrations downstream of this reach are lower due to a loss of river competency as the channel reaches sea level and the concurrent development of unvegetated mudflats separating the active channel from the floodplain forest. Substantial LW transport occurs on this low-gradient, dam-regulated large river; this study, paired with future research on transport mechanisms should provide resource managers and policymakers with options to better manage aquatic habitat while mitigating possible negative impacts to human interests. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Vertical sediment exchange is a fundamental component of bedload transport in gravel-bed channels. This paper describes the characteristic depth of exchange achieved over a long flood series. Analysis is based on 11 recoveries of magnetically tagged gravels deployed in Carnation Creek, Canada, completed between 1990 and 2008. Vertical grain exchange mixes gravels throughout the streambed relatively rapidly. Within one to eight floods the mean burial depth approaches two times the surface layer thickness, quantified by the 90th percentile of the size distribution. Finer gravels are mixed more rapidly into the bed than coarser gravels. Both active and passive grain exchanges throughout most of the bed produce the overall vertical distribution of marked grains. Gravel exchanges exhibit fairly consistent patterns once tracers are well mixed by large floods. Results highlight the role of flood sequence in determining exchange depths, support the notion of an upper limit to exchange, and underscore the importance of passive grain exchange. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Riparian vegetation and hydrogeomorphic processes are intimately connected parts of upland catchment and fan environments. Trees, shrubs and grasses and hydrogeomorphic processes interact and depend on each other in complex ways on the hillslopes, channels and cone-shaped fans of torrential watersheds. While the presence and density of vegetation have a profound influence on hydrogeomorphic processes, the occurrence of the latter will also exert control on the presence, vitality, species, and age distribution of vegetation. This contribution aims at providing a review of foundational and more recent work on the dependencies and interactions between hydrogeomorphic processes and vegetation. In particular, we address the role of vegetation in the initiation of hydrogeomorphic processes and its impact on stream morphology as well as immediate and long-term effects of hydrogeomorphic disturbance on vegetation. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Field-measured patterns of mean velocity and turbulent airflow are reported for isolated barchan dunes. Turbulence was sampled using a high frequency sonic anemometer, deriving near-surface Reynolds shear and normal stresses. Measurements upwind of and over a crest-brink separated barchan indicated that shear stress was sustained despite a velocity reduction at the dune toe. The mapped streamline angles and enhanced turbulent intensities suggest the effects of positive streamline curvature are responsible for this maintenance of shear stress. This field evidence supports an existing model for dune morphodynamics based on wind tunnel turbulence measurements. Downwind, the effect of different dune profiles on flow reattachment and recovery was apparent. With transverse incident flow, a reattachment length between 2.3 and 5.0  h ( h is dune brink height) existed for a crest-brink separated dune and 6.5 to 8.6  h for a crest-brink coincident dune. The leeside shear layer produced elevated turbulent stresses immediately downwind of both dunes, and a decrease in turbulence with distance characterised flow recovery. Recovery of mean velocity for the crest-brink separated dune occurred over a distance 6.5  h shorter than the crest-brink coincident form. As the application of sonic anemometers in aeolian geomorphology is relatively new, there is debate concerning the suitability of processing their data in relation to dune surface and streamline angle. This paper demonstrates the effect on Reynolds stresses of mathematically correcting data to the local streamline over varying dune slope. Where the streamline angle was closely related to the surface (windward slope), time-averaged shear stress agreed best with previous wind tunnel findings when data were rotated along streamlines. In the close lee, however, the angle of downwardly projected (separated) flow was not aligned with the flat ground surface. Here, shear stress appeared to be underestimated by streamline correction, and corrected shear stress values were less than half of those uncorrected. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The management of reclaimed slopes derived from industrial and civil activities (e.g. surface mining and road construction) requires the development of practical stability analysis approaches that integrate the processes and mechanisms that rule the dynamics of these ubiquitous emerging ecosystems. This work describes a new modelling approach focused on stability analysis of water-limited reclaimed slopes, where interactive relationships between rill erosion and vegetation regulate ecosystem stability. Our framework reproduces two main groups of possible trends along the temporal evolution of reclaimed slopes: successful trends, characterised by widespread vegetation development and the effective control of rill erosion processes; and gullying trends, characterised by the progressive loss of vegetation and a sharp logistic increase in erosion rates. Furthermore, this analytical approach allows the determination of threshold values for the state variables (i.e. vegetation cover and rill erosion) that drive the system's stability, facilitating the identification of critical situations that require specific human intervention (e.g. revegetation or, in very problematic cases, revegetation combined with rill network destruction) to ensure the long-term sustainability of the restored ecosystem. The application of our threshold analysis framework in Mediterranean-dry reclaimed slopes derived form surface coal mining (the Teruel coalfield in central-east Spain) showed a good field-based performance. Therefore, we believe that this model is a valuable contribution for the management of water-limited reclaimed systems, including those associated with rill erosion, as it provides a tool for the evaluation of restoration success and can play an important role in decision-making during ecosystem restoration in severely disturbed landscapes. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In protection of karstic aquifers, the role played by dolines is under focus as these shallow structures can be preferential infiltration pathways for groundwater recharge. In this paper, three depressions in South France (Orniac, Lot) were identified and characterized using combined geophysical methods. Apparent conductivity mapping allows precise definition of dolines corresponding to topographic depressions. It also reveals other dolines that are hidden by soil cover. Electrical resistivity and seismic refraction tomography provide detailed cross-sections. Even though the studied dolines are close one to another, they exhibit high variability in shape and content. Moreover, time-lapse data show that the most saturated regions are on the edges of the first doline. Such information helps to better evaluate human impacts and forecast potential groundwater contamination. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Although flow turbulence in rivers is of critical importance to earth scientists, ecologists and engineers, its relations with larger flow scales are not well understood, thus leaving a fundamental gap in our knowledge. From an analysis of a long time series of the streamwise and vertical flow velocity fluctuations measured in a gravel-bed river, we show that the signature of the fundamental turbulent flow structures (e.g. ejections and sweeps) is embedded within increasingly larger flow scales in a self-similar manner. The imbrication of turbulent structures into large flow pulsations of flow acceleration and deceleration covers more than two-orders of magnitude from a few seconds to nearly 10 minutes. This property is explained by the clustering of turbulent events creating an emergent pattern at larger scales. The size of the larger flow pulsations scales with the spacing of the pools and riffles in the river. This implies a mutual adjustment between turbulence generation mechanisms and long pulsations of flow acceleration and deceleration controlled by the bed morphology. These results bridge a gap in our understanding of flows in rivers and offer a new perspective on the interactions between the turbulent flow with larger scales of flow motion that are critical for sediment transport, habitat selection and fish behaviour. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT The retreat of cliffs may constitute the dominant erosional response to base-level fall in arid settings underlain by horizontally-bedded sedimentary rock. These vertical cliffs typically loom above a relatively straight bedrock slope (‘plinth’) that is mantled with a thin layer of sediment and perched near the angle of repose. In detail, a plinth consists of a system of quasi-parallel ridges and channels. We ask how the sediment supplied from a retreating cliff influences the erosion of the plinth hillslopes and channels, and how this affects the rate of cliff retreat. Motivated by field observations and high-resolution topographic data from two sites in western Colorado, we develop a two-dimensional (2D), rules-based numerical model to simulate the erosion of channels draining a plinth and diffusive erosion of the intervening interfluves. In this model, retreat of a cliffband occurs when the height of the vertical cliff exceeds a threshold due to incision by channels on the plinth below. Debris derived from cliff retreat is distributed over the model plinth according to the local topography and distance from the source. This debris then weathers in place, and importantly can act to reduce local bedrock erosion rates, protecting both the plinth and ultimately the cliff from erosion. In this paper, we focus on two sets of numerical model experiments. In one suite, we regulate the rate of rockfall to limit the cliff retreat rate; in most cases, this results in complete loss of the plinth by erosion. In a second suite, we do not impose a limit on the cliff retreat rate, but instead vary the weathering rate of the rockfall debris. These runs result in temporally steady cliff-plinth forms and retreat rates; both depend on the weathering rate of the debris. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The contribution of bioturbation to downslope soil transport is significant in many situations, particularly in the context of soil formation, erosion and creep. Our study explored the direct flux of soil caused by Aphaenogaster ant mounding, vertebrate scraping and tree-throw on a wildfire-affected hillslope in southeast Australia. This included the development of methods previously applied to Californian gopher bioturbation, and an evaluation of methods for estimating the volume of soil displaced by tree-throw events. All three bioturbation types resulted in a net downslope flux, but any influence of hillslope angle on flux rates appeared to be overshadowed by environmental controls over the spatial extent of bioturbation. As a result, the highest flux rates occurred on the footslope and lower slope. The overall contribution of vertebrate scraping (57.0 ± 89.4 g m −1 yr −1 ) exceeded that of ant mounding (36.4 ± 66.0 g m −1 yr −1 ), although mean rates were subject to considerable uncertainty. Tree-throw events, which individually cause major disturbance, were limited in their importance by their scarcity relative to faunalturbation. However, tree-throw might be the dominant mechanism of biotic soil flux on the mid-slope provided that it occurs at a frequency of at least 2–3 events ha −1 yr −1 . Although direct biotic soil flux appears to be geomorphologically significant on this hillslope, such transport processes are probably subordinate to other impacts of bioturbation at this site such as the enhancement of infiltration following wildfire. Copyright © 2011 John Wiley & Sons, Ltd.

Description: We develop numerical solutions of a theoretical model which has been proposed to explain the formation of subglacial bedforms. The model has been shown to have the capability of producing bedforms in two dimensions, when they may be interpreted as ribbed moraine. However, these investigations have left unanswered the question of whether the theory is capable of producing fully three-dimensional bedforms such as drumlins. We show that, while the three-dimensional calculations show realistic quasi-three-dimensional features such as dislocations in the ribbing pattern, they do not produce genuine three-dimensional drumlins. We suggest that this inadequacy is due to the treatment of subglacial drainage in the theory as a passive variable, and thus that the three-dimensional forms may be associated with conditions of sufficient subglacial water flux. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Historic- and prehistoric-tsunami sand deposits are used to independently establish runup records for tsunami hazard mitigation and modeled runup verification in Crescent City, California, located in the southern Cascadia Subduction Zone. Inundation from historic (1964) farfield tsunami (~5–6 m runup height) left sand sheet deposits (100–200 m width) in wetlands located behind a low beach ridge [3–4 m elevation of the National Geodetic Vertical Datum of 1988 (NAVD88)]. The most landward flooding lines (4·5–5 m elevation) in high-gradient alluvial wetlands exceed the 1964 sand sheet records of inundation by 1–2 m in elevation. The most landward flooding in low-gradient alluvial wetlands exceed the corresponding sand sheet record of inundation distance by 1000 m. Nevertheless, the sand sheet record is an important proxy for high-velocity inundation. Sand sheet deposition from the 1964 historic tsunami closely corresponds to the landward extent of large debris transport and structural damage in the Crescent City waterfront. The sand sheet deposits provide a proxy for maximum hazard or ‘kill zone’ in the study area. Six paleotsunami sand sheets (0·3–3 ka) are recorded in the back-ridge marshes in Crescent City, yielding a ~450 year mean recurrence interval for nearfield Cascadia tsunami. Two paleotsunami sand deposit records, likely correlated to Cascadia ruptures between 1·0 and 1·5 ka, are traced to 1·2 km distance and 9–10 m elevation, as adjusted for paleo-sea level. The paleotsunami sand deposits demonstrate at least twice the runup height, and four times the inundation distance of the farfield 1964 tsunami sand sheet in the same marsh system. The preserved paleotsunami deposits in Crescent City are compared to the most landward flooding, as modeled by other investigators from a predicted Cascadia (~ Mw 9) rupture. The short geologic record (~1·5 ka) yields slightly lower runup records than those predicted for the modeled Mw 9 rupture scenario in the same marsh, but it generally verifies predicted maximum tsunami runup for use in the planning of emergency response and rapid evacuation. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Black marls form very extensive outcrops in the Alps and constitute some of the most eroded terrains, thus causing major problems of sedimentation in artificial storage systems (e.g. reservoirs) and river systems. In the experimental catchments near Draix (France), soil erosion rates have been measured in the past at the plot scale through a detailed monitoring of surface elevation changes and at the catchment scale through continuous monitoring of sediment yield in traps at basin outlets. More recently, erosion rates have been determined by means of dendrogeomorphic techniques in three monitored catchments of the Draix basin. A total of 48 exposed roots of Scots pine have been sampled and anatomical variations in annual growth rings resulting from denudation analysed. At the plot scale, average medium-term soil erosion rates derived from exposed roots vary between 1.8 and 13.8 mm yr –1 (average: 5.9 mm yr –1 ) and values are significantly correlated with slope angle. The dendrogeomorphic record of point-scale soil erosion rates matches very well with soil erosion rates measured in the Draix basins. Based on the point-scale measurements and dendrogeomorphic results obtained at the point scale, a linear regression model involving slope angle was derived and coupled to high-resolution slope maps obtained from a LiDAR-generated Digital Elevation Model so as to generate high-resolution soil erosion maps. The resulting regression model is statistically significant and average soil erosion rates obtained from the areal erosion map (5.8, 5.2 and 6.2 mm yr –1 for the Roubine, Moulin and Laval catchments) prove to be well in concert with average annual erosion rates measured in traps at the outlet of these catchments since 1985 (6.3, 4.1 and 6.4 mm yr –1 ). This contribution demonstrates that dendrogeomorphic analyses of roots clearly have significant potential and that they are a powerful tool for the quantification and mapping of soil erosion rates in areas where measurements of past erosion is lacking.

Description: Wind erosion is an important soil erosion and hence soil degradation problem in the Sahelian zone of West Africa. Potentially, the characteristic dryland vegetation with scattered trees and shrubs can provide for soil erosion protection from wind erosion, but so far adequate quantification of vegetation impacts is lacking. The aim of this study was to develop a model of wind-blown soil erosion and sediment transport around a single shrub-type vegetation element. Starting with the selection of a suitable transport equation from four possible sediment transport equations, the effects of a single vegetation element on wind speed were parameterised. The modified wind speed was then applied to a sediment transport equation to model the change in sediment mass flux around a shrub. The model was tested with field data on wind speed and soil erosion and sediment transport measured around isolated shrubs in a farmer's field in the north of Burkina Faso. The simple empirical equation of Radok (1977) performed best in modelling soil erosion and sediment transport, both for the entire event duration and for each minute within an event. Universal values for the empirical constants in the sediment transport equation could not be obtained because of the large variability in soil and roughness characteristics. The pattern of wind speed, soil erosion and sediment transport behind a shrub and on either side of it was modelled. The wind speed changed in the lee of the vegetation element depending on its porosity, height and downwind position. Wind speed was recovered to the upstream speed at a downwind distance of 7.5 times the height of the shrub. The variability in wind direction created a “rotating” area of influence around the shrub. Compared to field measurements the model predicted a 8 % larger reduction in sediment transport in the lee of the vegetation element, and a 22 % larger increase beside the vegetation element. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Dynamics and rates of rockfalls have been repeatedly studied in mountain environments with archival records as well as lichenometric, radiocarbon or dendrogeomorphic approaches. In this study, we test the potential of conifers growing at a low-latitude, high-elevation site as a dendrogeomorphologic tool to reconstruct to calendar dates associated rockfall activity. Analysis is based on tree-ring records of Mexican mountain pine ( Pinus hartwegii Lindl.) growing at timberline (~4,000 m a.s.l.) and at the runout fringe of a NNE-facing slope of the dormant Iztaccíhuatl volcano (Mexico), which is subject to frequent rockfalls. The potential and limitations of tree-ring data are demonstrated based on 67 rockfall impacts dated in the increment-ring series of 24 trees since AD 1836. While findings of this paper are site-specific, the study clearly shows the potential of dendrogeomorphic approaches in extra-Alpine, low-latitude environments and for the understanding of rockfall processes in space and time. Copyright © 2011 John Wiley & Sons, Ltd.

Description: River networks have been shown to obey power scaling laws and to follow self-organization principles. Their self-similar (fractal) properties open a path to relate small scale and large scale hydrological processes, such as erosion, deposition or geological movements. However, the existence of a self-similar dimension has only been checked using either the whole channel network or, on the contrary, a single channel link. No study explicitly addressed, to our knowledge, the possible spatial variation of the self-similar properties between these two extreme geomorphologic objects. Here, we propose a new method based on Self-Similarity Maps (SSM) to spatially explore the stream-length self-similar dimension D l within a river network. The mapping principle consists in computing local self-similar dimensions deduced from a fit of stream-lengths estimations using increasing divider sizes. A local uncertainty related to the fit quality is also computed and localized on every stream. To assess the efficiency of our approach, we simulate contrasted river networks using Optimal Channel Networks (OCN), where each network is characterized by an exponent γ conditioning its overall topology. By building SSM of these networks, we show that deviations from uniform self-similarity across space occur. Depending on the type of network (γ parameter), these deviations are or are not related to Strahler's order structure. Finally, we numerically find that the structural averaged stream-length self-similar dimension D l is closely related to the more functional γ parameter. Our results cast a bridge between the studies on river sinuosity (single channel) and growth of channel networks (watershed). As for every method providing spatial information where they were lacking before, the SSM may soon help to accurately interpret natural networks as well as to help to simulate more realistic channel networks. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In this paper we compare three landscape evolution models with respect to their ability to correctly simulate measured 2500 year landscape evolution in two small catchments in the Belgian Loess Belt. WATEM LT and LAPSUS both model tillage and water erosion and deposition and have detachment-limited descriptions for water erosion and deposition. Equations in LAPSUS are more mechanistic than those in WATEM LT. WATEM LTT resembles WATEM LT, but is a transport-limited model. All three models are DEM-based. Calibration and validation simulations were performed forward in time on (1D) transects for four spatial resolutions, and backward in time for (2D) catchments at 20 m resolution. For transects, model outputs were compared to discretized observations of transect shape. For catchments, outputs were compared to point observations of palaeo-altitude, averaged over landscape element classes. For transects, the three models performed well, resulting in Model Efficiency Factors of 0.92 to 0.99 for calibration and 0.62 to 0.96 for validation. However, for catchments, simulations showed that the transport-limited WATEM LTT model could not realistically simulate long-term landscape evolution. Performance of WATEM LT and LAPSUS at catchment scale was similar to that on transects, although LAPSUS has problems with backward calculation. Our tests demonstrate that a transport-limited approach cannot be used to model long-term landscape evolution in the Belgian loess Belt, which is in agreement with our theoretical and empirical understanding of soil erosion processes in this environment. The difference in performance between transport-limited and detachment-limited models is only clear when the models are evaluated in a 2D catchment. The lack of such distinction when models were applied in a 1D transect highlights the importance of evaluating landscape evolution models in a 2D setting so that effects of flow convergence/divergence can be accounted for. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The erosion of sediment by wind and the resulting mass-flux density profile is thought to be described by a mathematical function that bears information on the mechanisms responsible for the movement of individual particles by the wind, and such functions have been studied extensively. In this paper, we evaluate several functions that have been proposed to describe the variation in mass-flux density with height of wind-blown sediment, with the flux containing a mixture of particles in suspension and saltation, based on detailed field data at four land types in the Minqin area of northwestern China, where severe wind erosion occurs. High-resolution mass-flux density measurements at 50 heights, collected at 20-mm intervals to a height of 1 m above the surface, were obtained using vertically segmented samplers. Three kinds of functions fit the measured flux density profiles reasonably well, but a three-parameter modified exponential function is preferred because it contains fewer coefficients to be defined and provides reasonably good fit to the measured mass-flux density profiles. This and previous conclusions suggest that the decay with height of mass-flux density of sediments dominated by saltation particles as in the present study tends to follow a modified exponential function law, but a modified power function law will replace the modified exponential function law when the height extends to a level high enough to be dominated by suspension particles. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post-orogenic landscape remain enigmatic. The non-glaciated Cullasaja River basin of southwestern North Carolina, with uniform lithology, frequent debris flows, and the availability of high-resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post-orogenic landscape through the lens of hillslope-channel coupling. We limit our investigation to channels with upslope contributing areas 〉2.7 km2, a conservative estimate of the transition from fluvial to debris-flow dominated channel processes. We utilize values of normalized hypsometry, hypsometric integral, and mean slope vs. elevation for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Our results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. We capture the transient effect of knickpoint-driven channel incision on basin hillslopes by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results to the distance from major knickpoints along the Cullasaja River. We present a conceptual model of area-elevation and slope distributions that may be representative of post-orogenic landscape evolution in analogous geologic settings. Importantly, our model explains how knickpoint migration and channel-hillslope coupling is an important factor in tectonically-inactive (i.e. post-orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering-limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.

Description: In this paper, a method to predict the equilibrium bed slope in natural streams based on the incipient motion criterion is proposed. The method is based on the criterion suggested by Gessler to simulate the grain size distribution of the armour coat using the concept of critical shear stress of a sediment mixture. In particular, a different expression of the probability for a single particle size to be part of the armour coat is firstly proposed; then, a simple two-steps criterion is suggested to estimate the safety factor required by the proposed approach. The method is applied in three different Italian regions (Calabria, Basilicata, and Tuscany) and required several field campaigns involving the survey of 251 stream reaches upstream of grade-control structures. The area including five Calabrian streams is firstly used to test the suitability of the two-steps approach. In this area, considering the detailed information about the particle size of bed material, the effect of using a simplified grain size distribution for each torrent is also checked. The method is then applied within the two additional areas (Basilicata and Tuscany) in order to check the geographic influence on the prediction of the stable longitudinal profile. A comparison between measured and estimated values of the equilibrium bed slope showed a good agreement for the Calabrian streams, where the number of the investigated stream reaches is greater, and satisfactory results for the torrents located in Basilicata and Tuscany where the field data set is more limited. The overall results encourage the extension of the proposed method to additional field data and suggest the use of this approach by hydraulic designers in order to stabilize the longitudinal profile of natural streams. Copyright © 2011 John Wiley & Sons, Ltd.

Description: The behaviour of offshore-directed winds over coastal dune and beach morphology was examined using a combination of modelling (3-D Computational Fluid Dynamics (CFD)) and field measurement. Both model simulations and field measurements showed reversal of offshore flows at the back beach and creation of an onshore sediment transport potential. The influence of flow reversals on the beach-dune transport system and foredune growth patterns has previously received little attention. Detailed wind flow measurements were made using an extensive array of mast-mounted, 3-D ultrasonic anemometers (50 Hz), arranged parallel to the dominant incident wind direction. Large Eddy Simulation (LES) of the offshore wind flow over the dune was conducted using the open-source CFD tool openFOAM. The computational domain included a terrain model obtained by airborne LiDAR and detailed ground DGPS measurements. The computational grid (~22 million cells) included localised mesh refinement near the complex foredune terrain to capture finer details of the dune morphology that might affect wind flows on the adjacent beach. Measured and simulated wind flow are presented and discussed. The CFD simulations offer new insights into the flow mechanics associated with offshore winds and how the terrain steering of wind flow impacts on the geomorphological behaviour of the dune system. Simulation of 3-D wind flows over complex terrain such as dune systems, presents a valuable new tool for geomorphological research, as it enables new insights into the relationship between the wind field and the underlying topography. The results show that offshore and obliquely offshore winds result in flow reversal and onshore directed winds at distances of up to 20 m from the embryo dune toe. The potential geomorphological significance of the findings are discussed and simple calculations show that incoming offshore and obliquely offshore winds with mean velocities over 13 m s -1 and 7 m s -1 , respectively have the potential to create onshore-directed winds at the back beach with mean velocities above 3.3 m s -1 . These are above the threshold of movement for dry sand and support previous conclusions about the significance of offshore winds in dune and beach budget calculations. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Channelisation of the lowermost part of Vedder River in 1922 initiated a natural experiment relevant to the unresolved question of how abrupt gravel-sand transitions develop along rivers. The new channel (Vedder Canal) had a fine bed and a much lower slope than the gravel-bed river immediately upstream. Changes in morphology and sedimentology as gravel advanced into and along the Canal are documented using air photos, historical surveys, and fieldwork. The channel aggraded and steepened until stabilised by occasional gravel extraction in recent decades. The deposited material fines progressively along the Canal but the gravel front has retained an abrupt appearance because it has advanced by the sequential development of discrete gravel tops on initially sandy alternate bars. Near the gravel front the bed is highly bimodal and there is a sharper drop in the extent of gravel-framework surface facies than in bulk gravel content. Ahead of the front, gravel is restricted to thin ribbons which often become buried by migrating sand. Calculations show that even though the gravel bed at the head of the Canal is almost unimodal, size-selective transport during floods can account for the strong bimodality farther downstream.

Description: Geostatistical topographic analysis is widely recognized as a useful tool for the statistical reconstruction of planar geomorphic markers from relict surfaces. This works is aimed at improving the geostatistical approach used in previous works and at developing a method for evaluating the incision rates of rivers in their lower catchments during the Late Quaternary. We chose the major valleys of the Adriatic foothills (central Italy), affected since Late Miocene by a differential tectonic uplift which is still active. In particular, i) we applied the geostatistical analysis to reconstruct the original top surfaces of fluvial to coastal terrace bodies at the Metauro and Cesano Rivers mouths; ii) we performed correlations between the height distribution of the alluvial terrace sequences and the Quaternary climatic curve to estimate the average long term fluvial incision rates in the lowermost reaches of the Metauro, Cesano, Misa and Esino Rivers. The obtained averaged incision rates have been interpreted also in the light of Stream Length Gradient Index (SL Index), Steepness Index (K s ), and Concavity Index (θ) as proxies of the stream power per unit length. Results confirm that geostatistical and terrain analysis of topographic and geometric arrangements of fluvial and coastal terraces is an effective tool in detecting geomorphic and tectonic factors inducing perturbations on planar geomorphic markers. In particular, we better delineated the surface geometry and boundaries of well developed coastal fans at the mouths of the Metauro and Cesano Rivers, already recognized in previous works through sedimentological, morphostratigraphic, and chronological data. Moreover, we found evidence for cut and fill phases that took place during and immediately after the river aggradation of the late Quaternary glacial periods. Despite the Slope Area analysis evidenced a widespread influence of the regional differential uplift on single river basin configuration, we observed some space and time variability of averaged incision rates for adjacent valleys, mainly explained by physiographic configuration and dynamics of drainage network. Copyright © 2011 John Wiley & Sons, Ltd.

Description: To date, most studies of the effectiveness of geotextiles on soil erosion rates and processes have been conducted in laboratory experiments for less than 1 h. Hence, at Hilton (52°33′ N, 2°19′ W), UK, the effectiveness of employing palm-mat geotextiles for soil erosion control under field conditions on arable loamy sands was investigated. Geotextile-mats constructed from Borassus aethiopum (Borassus palm of West Africa) and Mauritia flexuosa (Buriti palm of South America) leaves are termed Borassus mats and Buriti mats, respectively. Duplicate runoff plots (10 m × 1 m on a 15° slope) had five treatments (bare, permanent grass, Borassus total plot cover, Borassus buffer strip and Buriti buffer strip). Borassus covered plots had about 72% ground cover and to differentiate between this treatment and Borassus buffer strips, the former treatment is termed Borassus completely-covered. Runoff and eroded soil were collected from each bounded plot in a concrete gutter, leading to a receptacle. Results from 08/01/2007–23/01/2009 (total precipitation = 1776·5 mm; n = 53 time intervals) show that using Borassus buffer strips (area coverage ∼10%) on bare soil decreased runoff volume by about 71% ( P 〉 0·05) and soil erosion by 92% ( P 〈 0·001). Bare plots had nearly 29·1 L m −2 runoff and 2·36 kg m −2 soil erosion during that period. Borassus buffer strip, Buriti buffer strip and Borassus completely-covered plots had similar effects in decreasing runoff volume and soil erosion. Runoff volumes largely explain the variability in soil erosion rates. Although buffer strips of Borassus mats were as effective as whole plot cover of the same mats, the longevity of Borassus mats was nearly twice that of Buriti mats. Thus, use of Borassus mats as buffer strips on bare plots is highly effective for soil erosion control. The mechanisms explaining the effectiveness of buffer strips require further studies under varied pedo-climatic conditions. Copyright © 2011 John Wiley & Sons, Ltd.

Description: This study uses a combination of evidence from ground penetrating radar, borehole, video, and wireless probe data to assess temporal changes in englacial water content associated with Briksdalsbreen, a rapidly retreating Norwegian glacier. Over a 13 day period in 2006, ice radar-wave velocity varied between 0.135 m/ns (+/−0.009) and 0.159 m/ns (+/−0.003), and water content from 7.8% (+2.6, -2.8) to 2.5% (+0.9, -1.1) (derived from the Looyenga (1965) formula). It is suggested that during warm precipitation free days, void spaces within the glacier become filled with water, resulting in low radar-wave velocity. This stored water then drained during cold, high precipitation days, allowing the radar-wave velocity to rise. These changes in englacial storage were caused by the enhanced crevassing generated by the newly floating ice margin, and were associated with accelerated glacier retreat. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Optically stimulated luminescence (OSL) dating studies of linear (longitudinal) dunes have been extensively used to elucidate late Quaternary environments and climates in arid or formerly arid regions, yet understanding of the development of such dunes is incomplete. In particular, conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally, the degree to which they rework their own sediment during accumulation and whether they form primarily by extension, as opposed to lateral sand movement from adjacent interdunes. This study focuses on this last point, although the importance of the other controversies is discussed in context. A simple linear dune in the southwestern Kalahari which has a prominent termination on a pan (playa) surface provides an opportunity to directly test hypotheses of dune extension. A chronostratigraphy along a ~600 m transect along the crest of the dune, constrained by 42 OSL ages, reveals that the dune grew by extension on occasions in the late Pleistocene and early Holocene, but has also been subject to reworking along its length which has continued until recent times. Dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation, whereas reworking is largely independent of conditions throughout the last ~18 ka, and may represent seasonal fluctuations in the position of the dune crest. The relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT An excess of fine sediment (grain size 〈2 mm) supply to rivers leads to reservoir siltation, water contamination and operational problems for hydroelectric power plants in many catchments of the world, such as in the French Alps. These problems are exacerbated in mountainous environments characterized by large sediment exports during very short periods. This study combined river flow records, sediment geochemistry and associated radionuclide concentrations as input properties to a Monte Carlo mixing model to quantify the contribution of different geologic sources to river sediment. Overall, between 2007 and 2009, erosion rates reached 249 ± 75 t km −2 yr −1 at the outlet of the Bléone catchment, but this mean value masked important spatial variations of erosion intensity within the catchment (85–5000 t km −2 yr −1 ). Quantifying the contribution of different potential sources to river sediment required the application of sediment fingerprinting using a Monte Carlo mixing model. This model allowed the specific contributions of different geological sub-types (i.e. black marls, marly limestones, conglomerates and Quaternary deposits) to be determined. Even though they generate locally very high erosion rates, black marls supplied only a minor fraction (5–20%) of the fine sediment collected on the riverbed in the vicinity of the 907 km 2 catchment outlet. The bulk of sediment was provided by Quaternary deposits (21–66%), conglomerates (3–44%) and limestones (9–27%). Even though bioengineering works conducted currently to stabilize gullies in black marl terrains are undoubtedly useful to limit sediment supply to the Bléone river, erosion generated by other substrate sources dominated between 2007 and 2009 in this catchment. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT This special issue describes research arising from the megadelta project of the Asia-Pacific-Networks (APN), undertaken between 2004 and 2009 ( www.megadelta.ecnu.edu.cn ). Numerous delta-coast scientists from more than 20 countries were involved in the project concerned with developing our knowledge of land–estuarine–coastal interactions in megadeltas, and with fusing this knowledge with societal development and management. Project workshops were held in Bangkok (2004), Ho Chi Minh City (2005), Dhaka (2007) and Shanghai (2008) with over 500 participants. The main objectives of the project were: (1) development of regional databases; (2) understanding of delta formation and associated fluxes between land and sea; (3) knowledge transfer and building research capacity; and (4) understanding how better social management might follow. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Laboratory observations and computational results for the response of bedform fields to rapid variations in discharge are compared and discussed. The simple case considered here begins with a relatively low discharge over a flat bed on which bedforms are initiated, followed by a short high-flow period with double the original discharge during which the morphology of the bedforms adjusts, followed in turn by a relatively long period of the original low discharge. For the grain size and hydraulic conditions selected, the Froude number remains subcritical during the experiment, and sediment moves predominantly as bedload. Observations show rapid development of quasi-two-dimensional bedforms during the initial period of low flow with increasing wavelength and height over the initial low-flow period. When the flow increases, the bedforms rapidly increase in wavelength and height, as expected from other empirical results. When the flow decreases back to the original discharge, the height of the bedforms quickly decreases in response, but the wavelength decreases much more slowly. Computational results using an unsteady two-dimensional flow model coupled to a disequilibrium bedload transport model for the same conditions simulate the formation and initial growth of the bedforms fairly accurately and also predict an increase in dimensions during the high-flow period. However, the computational model predicts a much slower rate of wavelength increase, and also performs less accurately during the final low-flow period, where the wavelength remains essentially constant, rather than decreasing. In addition, the numerical results show less variability in bedform wavelength and height than the measured values; the bedform shape is also somewhat different. Based on observations, these discrepancies may result from the simplified model for sediment particle step lengths used in the computational approach. Experiments show that the particle step length varies spatially and temporally over the bedforms during the evolution process. Assuming a constant value for the step length neglects the role of flow alterations in the bedload sediment-transport process, which appears to result in predicted bedform wavelength changes smaller than those observed. However, observations also suggest that three-dimensional effects play at least some role in the decrease of bedform wavelength, so incorporating better models for particle hop lengths alone may not be sufficient to improve model predictions. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Alluvial fans and debris cones link two zones of the fluvial system (eg hillslope gully systems to stream channels; mountain catchment sediment source areas to main river systems or to sedimentary basins) and therefore have important coupling or buffering roles. These roles may be both functional and preservational. The functional role includes debris-cone coupling, which controls sediment supply from hillslope gully systems to stream channels, influencing channel morphology. Coupling through larger alluvial fans, expressed by fanhead trenching, causes a distal shift in sedimentation zones, or when expressed by through-fan trenching, causes complete sediment by-pass. The preservational role stems from the fact that fans and cones are temporary sediment storage zones, and may preserve a record of source-area environmental change more sensitively than would sediments preserved further downsystem. Fan coupling mechanisms include distally-induced coupling (basal scour, “toe cutting”, marginal incision) and proximally-induced coupling (fanhead and midfan trenching). These mechanisms lead initially to partial coupling, either extending the immediate sediment source area to the stream system or shifting the focus of sedimentation distally. Complete coupling involves transmission of sediment from the feeder catchment through the fan environment into the downstream drainage or a sedimentary basin. The implications of coupling relate to downstream channel response, fan morphology, sedimentation patterns and vertical sedimentary sequences. Temporal and spatial scales of coupling are related, and with increasing scales the dominant controls shift from storm events to land cover to climatic and base-level change and ultimately to the relationships between tectonics and accommodation space. Finally, future research challenges are identified. Modern dating techniques and sophisticated analysis of remotely sensed data can greatly improve our understanding of fan dynamics, and should lead to a better cross-scale integration between short-term process-based approaches and long-term sedimentological applications, while maintaining high quality field-based observations. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT On the Chinese Loess Plateau, serious slope and gully erosion have caused a decrease in soil water capacity and fertility, which has resulted in vegetation degradation and a reduction in agricultural productivity. Great efforts have been made to restore vegetation to control soil erosion, but the efficiency of artificial revegetation is not satisfactory. Natural revegetation is an alternative. However, while soil seed banks are an essential source for natural revegetation, their composition and distribution on eroded slopes remains unknown. In addition, whether or not seed loss during soil erosion limits vegetation colonisation is also unknown. In this work, soil seed bank composition and distribution were studied in three situations; specifically, three main microsites were selected as sampling plots: fish-scale pits, as artificial deposited micro-topography; under tussocks, as trap microsites; and open areas, as eroded areas. Soil samples were collected at depths of 0–2 cm, 2–5 cm and 5–10 cm. The soil seed bank was identified using germination experiments, and a total of 34 species were identified. The dominant species in the soil seed bank were annual/biennial herbs with an average proportion more than 90% and density reaching up to 19,000 seeds m -2 . The pioneer species Artemisia scoparia was especially abundant. The dominant later successional species, such as Lespedeza davurica , Artemisia giraldii , Artemisia gmelinii , Stipa bungeana and Bothriochloa ischcemum , were present in the soil at a density that ranged from 38 to 1,355 seeds m -2 . Compared with the eroded open areas, the fish-scale pits retained a higher density of seeds, and the tussocks retained a larger number of species. However, there was no serious reduction of the soil seed bank in the erosion areas. The present study indicates that, on these eroded slopes, the soil seed bank is not the key factor limiting the colonisation of natural vegetation. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Rockfall is an important process in the final sculpturing of the escarpments and scree slopes that originate in bedrock landslides in the Flysch Carpathians. The spatio-temporal characteristics of rockfall activity were studied at four localities representative of old landslides in the highest part of the Czech Flysch Carpathians (Moravskoslezské Beskydy Mountains). Historical activity, chronology, and spatial context of rockfall activity were reconstructed using dendrogeomorphic techniques and rockfall rate index (RR). A total of 1132 increment cores from 283 trees growing in the rockfall transport and accumulation zones enabled the dating of 989 rockfall events. Reconstruction of a 78-year-long RR chronology suggests similar rockfall histories and trends at all study sites, indicating the existence of major common factors driving rockfall dynamics in the region. Temporal analysis and correlation of the RR series obtained with monthly mean temperatures, numbers of days with temperature transitions through 0 °C and monthly precipitation totals show that meteorological characteristics have evident but variable influence on rockfall activity. The most important factor is the effect of freeze-thaw cycles throughout the year, supplemented by low temperatures, especially during autumn. The influence of precipitation totals is of lesser importance. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Investigations on the northern Seward Peninsula in Alaska identified zones of recent (〈50 years) permafrost collapse that led to the formation of floating vegetation mats along thermokarst lake margins. The occurrence of floating vegetation mat features indicates rapid degradation of near-surface permafrost and lake expansion. We report on the recent expansion of these collapse features and determine their geometry using geophysical and remote sensing measurements. The vegetation mats were observed to have an average thickness of 0.57 m and petrophysical modeling indicated that gas content of 1.5 - 5% enabled floatation above the lake surface. Furthermore, the geophysical investigation provides evidence that the mats form by thaw and subsidence of the underlying permafrost rather than terrestrialization. The temperature of the water below a vegetation mat was observed to remain above freezing late in the winter. Analysis of satellite and aerial imagery indicates that these features have expanded at maximum rates of 1 – 2 m yr -1 over a 56-year period. Including the spatial coverage of floating “thermokarst mats” increases estimates of lake area by as much as 4% in some lakes. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT The recent loss of mountain glaciers in response to climate warming has been reported across a range of latitudes globally, but the processes involved are not always straightforward. In southern Pacific mid-latitudes, twentieth-century glacier fluctuations are thought to reflect the strength of westerly atmospheric circulation, which brings increased precipitation, leading to mass gains. We present a study of the response of Mangaehuehu Glacier, a cirque glacier on Mt Ruapehu, to climate over the last two decades. Glacier surface area fluctuated in size over this period, corresponding closely with mean end-of-summer snowlines in the Southern Alps. The key control on glacier extent appears to be ablation season temperature, itself controlled by regional atmospheric circulation, including El Niño-Southern Oscillation, Interdecadal Pacific Oscillation (IPO), and to a lesser extent, Southern Annular Mode (SAM). Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT Digital elevation models (DEMs) were compared to characterize how well airborne lidar (light detection and ranging) data depict the microtopography of a salt marsh. 72,000 GPS points and 700,000 lidar points from a 1 km 2 salt marsh island were linearly interpolated using identical DEM configurations. Overall, 78% of lidar elevations were within ±0.15 m of the high precision GPS elevations. Spatial arrangement of difference values reveal that lidar performed best on the marsh platform, and poorly along tidal creeks and creek heads. Also, the overall shape of the salt marsh was poorly defined, even where lidar data were within the reported range of accuracy. These observations indicate that lidar appears to be a robust tool for mapping intertidal landscapes. However, lidar DEMs may not adequately resolve the microtopographic variations of a salt marsh, and for research questions that require accurate depiction of small scale tidal creek networks and subtle terrain features lidar data should be augmented with other information. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT In this paper a modelling approach is presented to predict local scour under time varying flow conditions. The approach is validated using experimental data of unsteady scour at bed sills. The model is based on a number of hypotheses, concerning the characteristics of the flow hydrograph, the temporal evolution of the scour and the geometry of the scour hole. A key assumption is that, at any time, the scour depth evolves at the same rate as in an equivalent steady flow. The assumption is supported by existing evidence of geometrical affinity and similarity of scour holes formed under different steady hydraulic conditions. Experimental data are presented that show the scour hole development downstream of bed sills due to flood hydrographs follow a predictable pattern. Numerical simulations are performed with the same input parameters used in the experimental tests but with no post-simulation calibration. Comparison between the experimental and model results indicate a good correspondence, especially in the rising limb of the flow hydrograph. This suggests that the underlying assumptions used in the modelling approach are appropriate. In principle, the approach is general and can be applied to a wide range of environments (e.g. bed sills, step-pool systems) in which scouring at rapid bed elevation changes caused by time varying flows occurs, provided appropriate scaling information is available, and the scour response to steady flow conditions can be estimated. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Although the importance of ENSO on hydrological anomalies has been recognised, variations in sediment fluxes caused by these extreme events are poorly documented. The effect of ENSO is not limited to changes in sediment mobilization. Since ENSO events can affect terrestrial ecosystems, they may have important effects on sediment production and transport in river basins over time spans that are longer than the duration of the event itself. The Catamayo-Chira basin is an interesting casestudy for investigating these geomorphic implications. The objectives were: (i) to study the effect of ENSO on stream flow and sediment yields in the basin, (ii) to investigate if ENSO events affect sediment yields in the post-ENSO period and (iii) to understand which factors control the ENSO and post-ENSO basin response. During strong negative ENSO periods, mean annual stream flow discharge at the inlet of the Poechos reservoir in the lower basin was 5.4 times higher than normal annual discharges, while average sediment fluxes exceeded those of normal years by a factor of about 11. In two heavily affected periods, 45.9% of the total sediment yield in the 29 years observation period was generated. Sediment fluxes in the post-ENSO period are lower than expected, which proves post-ENSO event dynamics are significantly different from pre-event dynamics. Our analysis indicates the increase of vegetation growth in the lower basin is not the main reason explaining considerable sediment flux decrease in post-ENSO periods. During strong ENSO events, sediment in alluvial stores in the lower part of the basin is removed due to enlarging and deepening of channels. In post-ENSO periods, normal discharges and persisting sediment supplies from the middle/upper basin lead to river aggradation and storage of large amounts of sediment in alluvial plains. The decrease in sediment export will last for several years until the equilibrium is re-established. Copyright © 2011 John Wiley & Sons, Ltd.

Description: ABSTRACT & INTRODUCTION Westaway and Bridgland (2010) (W&B2010) present a palaeoflow estimation for the Channel River, partly based on calculations using input from the Busschers et al . (2007) Rhine-Meuse dataset. There are flaws in these calculations. W&B2010 calculate high-magnitude ‘bankfull’ palaeoflows (Q bf ) for presumed critical periods within Marine Isotope Stage (MIS) 2 and MIS 6. To do so, geometric parameters were inferred from cored geological cross-sections, under the assumption that the source geometries represent former mega-scale channels, formed within critically brief periods. W&B2010 equate these assumed critically brief periods within MIS 2 to Heinrich Events 1 and 2 (HE1, HE2) and use individual OSL ages from our larger data-set to support this age correlation. This comment addresses: Severe overestimations in the W&B2010 method of discharge calculations due to erroneous use of our channel-belt geometry as if it represented the wetted-channel perimeter, Incomplete use of the Rhine-Meuse set of OSL dates in the process of correlating nested architectural elements to HE1 and HE2. Our comment points out that neither the architectural, nor the chronometric evidence from the Rhine-Meuse deposits supports the principal conclusion that during particular phases discharge reached values of several hundred thousand cubic meters per second. Instead, Rhine peak discharges were an order of magnitude smaller. This critically falsifies the inference that erosive records in downstream areas principally are the product of very high paleoflows generated by periglacial fluvial systems. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Vegetation and processes of erosion and deposition are interactive. An objective of this paper is to review selected studies that emphasize the interdependencies. The reviews suggest new directions for research uniting ecology and geomorphology – the sub-discipline of biogeomorphology. The research, which recently has become vigorous, includes the sources, movement, and fates of fluvial loads of sediment, organic carbon, nutrients, contaminants, and woody debris to low-energy storage sites; the function of biota in causing soil evolution, stability, and sequestration of carbon; the development of new methods to characterize watersheds based on edaphic conditions; and the refinement of current empirical and conceptual models and dendrochronological techniques to measure landscape change. These well acknowledged topics and others less well anticipated ensure that biogeomorphology will remain vibrant. Copyright © 2011 John Wiley & Sons, Ltd.