ALBERT

Description: For sediment yield estimation, intermittent measurements of suspended sediment concentration (SSC) have to be interpolated to derive a continuous sedigraph. Traditionally, sediment rating curves (SRCs) based on univariate linear regression of discharge and SSC (or the logarithms thereof) are used but alternative approaches (e.g. fuzzy logic, artificial neural networks, etc.) exist. This paper presents a comparison of the applicability of traditional SRCs, generalized linear models (GLMs) and non-parametric regression using Random Forests (RF) and Quantile Regression Forests (QRF) applied to a dataset of SSC obtained for four subcatchments (0.08, 41, 145 and 445 km2) in the Central Spanish Pyrenees. The observed SSCs are highly variable and range over six orders of magnitude. For these data, traditional SRCs performed inadequately due to the over-simplification of relating SSC solely to discharge. Instead, the multitude of acting processes required more flexibility to model these nonlinear relationships. Thus, alternative advanced machine learning techniques that have been successfully applied in other disciplines were tested. GLMs provide the option of including other relevant process variables (e.g. rainfall intensities and temporal information) but require the selection of the most appropriate predictors. For the given datasets, the investigated variable selection methods produced inconsistent results. All proposed GLMs showed an inferior performance, whereas RF and QRF proved to be very robust and performed favourably for reproducing sediment dynamics. QRF additionally provides estimates on the accuracy of the predictions and thus allows the assessment of uncertainties in the estimated sediment yield that is not commonly found in other methods. The capabilities of RF and QRF concerning the interpretation of predictor effects are also outlined. Copyright © 2008 John Wiley & Sons, Ltd.

Description: A three-dimensional model for predicting redox controlled, multi-species reactive transport processes in groundwater systems is presented. The model equations were fully integrated within a MODFLOW-family reactive transport code, RT3D. The model can simulate organic compound biodegradation coupled to different terminal electron acceptor processes. A computational approach, which uses the spatial and temporal distribution of the rates of different redox reactions, is proposed to map redox zones. The method allows one to quantify and visualize the biological degradation reactions occurring in three distinct patterns involving fringe, pseudo-core and core processes. The capabilities of the numerical model are demonstrated using two hypothetical examples: a batch problem and a simplified two-dimensional reactive transport problem. The model is then applied to an unconfined aquifer underlying a leaking landfill located near the city of Turin, in Piedmont (Italy). At this site, high organic load from the landfill leachate activates different biogeochemical processes, including aerobic degradation, denitrification, manganese reduction, iron reduction, sulfate reduction and methanogenesis. The model was able to describe and quantify these complex biogeochemical processes. The proposed model offers a rational framework for simulating coupled reactive transport processes occurring beneath a landfill site. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Hedgerow is one of the most important rural landscapes in the world, especially in Europe. Knowledge about the hydrological role of hedgerows is useful in many fields of study, such as hydrological modelling and rural landscape management. The aim of this study was to investigate the impact of a hedgerow on rainfall distribution, soil-water potential gradient, lateral water transfer and water balance. A hillslope with a hedgerow perpendicular to the slope was monitored. To evaluate hedgerow rainfall interception, rainfall was measured (hourly, daily, and by rainfall event) both next to and up to 16 m upslope and 12 m downslope perpendicularly away from the hedgerow. The strongest correlation between rainfall next to the hedgerow and rainfall at more distant points was obtained using data measured per rainfall event. The average percentage of rainfall intercepted equalled 28% for the leafed period and 12% for the leafless period. The impact of the hedgerow on spatial rainfall distribution was related to distance from the hedgerow and rainfall amount. Annual distribution of soil-water potential showed that the hedgerow influenced it up to 9 m upslope and 6 m downslope, the area in which most of the hedgerow's roots were observed. The soil was driest at the end of summer, which delayed soil rewetting during autumn in areas surrounding the hedgerow. Annual groundwater dynamics exhibited three distinct periods due to temporal rainfall distribution and, especially at the end of summer, root-water uptake. In addition, the total potential gradient showed that unsaturated flow was directed towards the hedgerow in summer and autumn. These results indicate that at the local scale hedgerows influences (1) spatial rainfall distribution, (2) soil rewetting, and (3) groundwater recharge, often at distances well beyond the hedgerow's drip line. Consequently, the processes involved in soil-water dynamics around hedgerows should be integrated into relevant hydrological models, especially for catchments with a dense hedgerow network. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Water temperature is an important determinant of the growth and development of malaria mosquito immatures. To gain a better understanding of the daily temperature dynamics of malaria mosquito breeding sites and of the relationships between meteorological variables and water temperature, three clear water pools (diameter x depth: 0.16 × 0.04, 0.32 × 0.16 and 0.96 × 0.32 m) were created in Kenya. Continuous water temperature measurements at various depths were combined with weather data collections from a meteorological station. The water pools were homothermic, but the top water layer differed by up to about 2 °C in temperature, depending on weather conditions. Although the daily mean temperature of all water pools was similar (27.4-28.1 °C), the average recorded difference between the daily minimum and maximum temperature was 14.4 °C in the smallest versus 7.1 °C in the largest water pool. Average water temperature corresponded well with various meteorological variables. The temperature of each water pool was continuously higher than the air temperature. A model was developed that predicts the diurnal water temperature dynamics accurately, based on the estimated energy budget components of these water pools. The air-water interface appeared the most important boundary for energy exchange processes and on average 82-89% of the total energy was gained and lost at this boundary. Besides energy loss to longwave radiation, loss due to evaporation was high; the average estimated daily evaporation ranged from 4.2 mm in the smallest to 3.7 mm in the largest water pool. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Flow from artificial subsurface (tile) drainage systems may be contributing to increasing baseflow in Midwestern rivers and increased losses of nitrate-nitrogen. Standard hydrograph analysis techniques were applied to model simulation output and field monitoring from tile-drained landscapes to explore how flow from drainage tiles affects stream baseflow and streamflow recession characteristics. DRAINMOD was used to simulate hydrologic response from drained (24 m tile spacing) and undrained agricultural systems. Hydrograph analysis was conducted using programs PART and RECESS. Field monitoring data were obtained from several monitoring sites in Iowa typical of heavily drained and less-drained regions. Results indicate that flow from tile drainage primarily affects the baseflow portion of a hydrograph, increasing annual baseflow in streams with seasonal increases primarily occurring in the late spring and early summer months. Master recession curves from tile-drained watersheds appear to be more linear than less-tiled watersheds although comparative results of the recession index k were inconsistent. Considering the magnitude of non-point source pollutant loads coming from tile-drained landscapes, it is critical that more in-depth research and analysis be done to assess the effects of tile drainage on watershed hydrology if water quality solutions are to be properly evaluated. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Runoff hydrology has a large historical context concerned with the mechanisms and pathways of how water is transferred to the stream network. Despite this, there has been relatively little application of runoff generation theory to cold regions, particularly the expansive treeless environments where tundra vegetation, permafrost, and organic soils predominate. Here, the hydrological cycle is heavily influenced by 1) snow storage and release, 2) permafrost and frozen ground that restricts drainage, and 3) the water holding capacity of organic soils. While previous research has adapted temperate runoff generation concepts such as variable source area, transmissivity feedback, and fill-and-spill, there has been no runoff generation concept developed explicitly for tundra environments. Here, we propose an energy-based framework for delineating runoff contributing areas for tundra environments. Aerodynamic energy and roughness height control the end-of-winter snow water equivalent, which varies orders of magnitude across the landscape. Radiant energy in turn controls snowmelt and ground thaw rates. The combined spatial pattern of aerodynamic and radiant energy control flow pathways and the runoff contributing areas of the catchment, which are persistent on a year-to-year basis. While ground surface topography obviously plays an important role in the assessment of contributing areas, the close coupling of energy to the hydrological cycles in arctic and alpine tundra environments dictates a new paradigm. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The advance of technology has led to more competent countermeasures, but lives and properties still continue to suffer from water-induced disasters, such as floods, landslides, and debris flows. To increase the effectiveness of counter systems, improved methods of planning and designing such systems are prerequisite. This paper describes briefly a methodological approach for predicting debris flow characteristics, and proposes techniques for evaluating and improving the mitigative effectiveness of check dams against debris flows in steep mountain torrents. Additionally, a non-dimensional parameter, namely potential storage volume, is introduced to generalize the evaluation processes. As an example, the 1999 debris-flow event in the San Julian River, Venezuela, is chosen for discussion. The paper also proposes a method of evaluating the control function of a series of check dams as well as the criteria for the selection of their sizes, numbers and locations. It is hoped that this work will help to determine which combinations of check dams will fit best together for the optimal control of debris flows and available resources in any river basin. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The spectral method is based on the assumption of exponential forms of autocorrelation functions of the input and output time series. The results of practical applications of the spectral method on several karst springs in Croatia show that this assumption cannot always be reliably applied to the time series of rainfall and spring discharge, especially if short time periods are analysed. For this reason, the method is modified. The scale factor between the transfer function of total rainfall and the transfer function of groundwater recharge is considered as an additional model parameter which is determined in the optimization procedure. In addition to the theoretical background, this paper also presents the results of application of the modified spectral method on the springs Jadro and Žrnovnica located in the Dinaric karst area in Croatia. The parameters of groundwater recharge model are determined separately for both the springs and the obtained values are discussed and compared with the results of previous investigations. The values of the scale factors determined in the optimization procedure are compared to the values calculated using the theoretical equation. The comparison shows that the theoretical equation underestimates the optimal values of the scale factor. The underestimations are especially evident for periods of one year. Finally, the characteristics of rainfall-runoff relations of two springs are compared using the identified transfer functions and the results of simulations of the periodogram of observed discharge by the parametric periodogram. Copyright © 2008 John Wiley & Sons, Ltd.

Description: On the basis of the mean air temperature, precipitation, sunshine duration and pan evaporation at 23 meteorological stations in the headwater catchment of the Yellow River basin from 1960 to 2001, the long-term monotonic trend and abrupt changes for major climate variables have been investigated. The plausible monotonic trend of annual climatic time series are detected using a non-parametric method. The abrupt changes have been investigated in terms of a 5 year moving averaged annual series, using the moving t-test (MTT) method, Yamamoto method and Mann-Kendall method. The results showed that the annual air temperature has increased by 0.80 °C in the headwater catchment of the Yellow River basin during the past 42 years. One obvious cold period and one warm period were detected. The warmest centre was located in the northern part of the basin. The long-term trend for annual precipitation was not significant during the same period, but a dry tendency was detected. According to the Kendall slope values, the declining centre for annual precipitation was located in the eastern part and the centre of the study area. The long-term monotonic trend for annual sunshine duration and pan evaporation were negative. The average Kendall slopes are -29.96 h/10 yr and -39.63 mm/10 yr, respectively. The tests for abrupt changes using MTT and Yamamoto methods show similar results. Abrupt changes occurred in the mid 1980s for temperature, in the late 1980s for precipitation and in the early 1980s for sunshine duration and pan evaporation. It can be seen that the abrupt changes really happened in the 1980s for the climate variables. Different results are shown using the Mann-Kendall method. Both the abrupt changes of temperature and precipitation took place in the early 1990s, and that of pan evaporation occurred in the 1960s. The only abrupt change in sunshine duration happened during the similar period (in the 1980s) with the results detected by the MTT and Yamamoto methods. The abrupt changes which occurred in the 1990s and 1960s are not detectable using the MTT and Yamamoto methods because of the data limitation. However, the results tested by the MTT and Yamamoto methods exhibited great consistency. Some of the reasons may be due to the similar principles for these two methods. Different methods testing the abrupt climatic changes have their own merits and limitations and should be compared based on their own assumption and applicable conditions when they are used. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Changes in stream chemistry were studied for 4 years following large wildfires that burned in Glacier National Park during the summer of 2003. Burned and unburned drainages were monitored from December 2003 through August 2007 for streamflow, major constituents, nutrients, and suspended sediment following the fires. Stream-water nitrate concentrations showed the greatest response to fire, increasing up to tenfold above those in the unburned drainage just prior to the first post-fire snowmelt season. Concentrations in winter base flow remained elevated during the entire study period, whereas concentrations during the growing season returned to background levels after two snowmelt seasons. Annual export of total nitrogen from the burned drainage ranged from 1.53 to 3.23 kg ha-1 yr--1 compared with 1.01 to 1.39 kg ha-1 yr-1 from the unburned drainage and exceeded atmospheric inputs for the first two post-fire water years. Fire appeared to have minimal long-term effects on other nutrients, dissolved organic carbon, and major constituents with the exception of sulfate and chloride, which showed increased concentrations for 2 years following the fire. There was little evidence that fire affected suspended-sediment concentrations in the burned drainage. Sediment yields in subalpine streams may be less affected by fire than in lower elevation streams because of the slow release rate of water during spring snowmelt.

Description: This study suggested a numerical model using the Tabu search algorithm along with the Adjoint State method to identify the hydrogeological characteristics of an anisotropic groundwater aquifer. The Tabu search algorithm was applied to identify the anisotropic transmissivity components to avoid a local optimum. Then, the Adjoint State method was used to calculate the sensitivity of the parameters in order to increase the efficiency of the optimization. For an anisotropic and homogeneous aquifer, results showed that the optimal procedure presented combining the Tabu search algorithm and the Adjoint State method might successfully identify the values of the transmissivity components. If the duration of the pumping test was long enough (12-h pumping test), the value of the transmissivity components could be optimized with type-curve, straight-line, and Tabu search methods, along with the Adjoint State methods. If the duration of the pumping test was short (0.5-h pumping test), the Tabu search method, along with the Adjoint State method proposed herein, might successfully optimize the transmissivity components. For an anisotropic but heterogeneous aquifer, results showed that the suggested optimal procedure still successfully identified the values of the transmissivity components. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This paper evaluates the feasibility of using an artificial neural network (ANN) methodology for estimating the groundwater levels in some piezometers placed in an aquifer in north-western Iran. This aquifer is multilayer and has a high groundwater level in urban areas. Spatiotemporal groundwater level simulation in a multilayer aquifer is regarded as difficult in hydrogeology due to the complexity of the different aquifer materials. In the present research the performance of different neural networks for groundwater level forecasting is examined in order to identify an optimal ANN architecture that can simulate the piezometers water levels. Six different types of network architectures and training algorithms are investigated and compared in terms of model prediction efficiency and accuracy. The results of different experiments show that accurate predictions can be achieved with a standard feedforward neural network trained usung the Levenberg-Marquardt algorithm. The structure and spatial regressions of the ANN parameters (weights and biases) are then used for spatiotemporal model presentation. The efficiency of the spatio-temporal ANN (STANN) model is compared with two hybrid neural-geostatistics (NG) and multivariate time series-geostatistics (TSG) models. It is found in this study that the ANNs provide the most accurate predictions in comparison with the other models. Based on the nonlinear intrinsic ANN approach, the developed STANN model gives acceptable results for the Tabriz multilayer aquifer. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one-dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front-tracking model that innovatively combines a soil-moisture-based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non-iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Equilibrium detention storage is an important parameter as it has a proportional effect on flood attenuation. In this paper, based on the kinematic wave theory, a working formula for the equilibrium detention storage of an overland plane with upstream inflow has been derived. Since the flow regime over a concrete plane can vary throughout the entire range laminar to turbulent, this case has been selected to examine the effect of flow regime on the equilibrium detention storage. In the examination, the derived formula has been applied to four flow regimes: (a) laminar, (b) transitional, (c) near turbulent, and (d) turbulent. The examination shows that for planes with a small discharge, laminar flow gives the maximum detention storage. For planes with a medium discharge, transitional flow gives the maximum detention storage, and for planes with a large discharge, near turbulent flow gives the maximum detention storage. The flow regime can cause more than two-fold increase in detention storage. All these results can be attributed to the respective flow resistance, and have been endorsed with analyses of the water surface profile and the rising limb of the hydrograph. Finally, relating the results to real-life situations, it shows that the flow regime that gives the maximum detention storage is also the dominating flow regime in nature. Hence, extraordinarily, the flow regimes that exist in nature in fact provide maximum flood attenuation. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The modified Soil Conservation Service curve number (CN) method is widely used in long-term continuous models to predict daily surface runoff. However, it has been shown that this method gives poor results in reproducing peak flows in high rainfall periods. This is because there is an inaccuracy stemming from the model algorithm as it adjusts the daily runoff curve number as a function of soil moisture content at the end of the previous day. This paper proposes an alternative daily based curve number technique that can provide better prediction of daily runoff during the high flow season. The proposed method uses the temporally weighted average curve number (TWA-CN) to estimate daily surface runoff, while considering the effect of rainfall during a given day as well as the antecedent soil moisture condition. To test the applicability of the TWA-CN method, it was incorporated with the long-term, continuous simulation watershed models SWAT and SWAT-G. Simulations were conducted for the Miho River watershed located in the middle of South Korea. The graphical displays and statistics of the determination coefficient (R2) and the Nash-Sutcliffe model efficiency (NSE) of the observed and simulated daily runoff indicated that the modified SWAT with the TWA-CN method may provide better runoff prediction (R2 = 0.837, NSE = 0.833) than the original SWAT (R2 = 0.815, NSE = 0.824). Likewise, the determination coefficient (R2 = 0.816) and the Nash-Sutcliffe efficiency (NSE = 0.834) for the modified SWAT-G are also higher than the original version (R2 = 0.782, NSE = 0.825). It is expected that the improved capability in predicting surface runoff using the suggested CN estimate method will provide a sound contribution to the accurate simulations of water yield. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Extensive land use changes have occurred in many areas of SE Spain as a result of reforestation and the abandonment of agricultural activities. Parallel to this the Spanish Administration spends large funds on hydrological control works to reduce erosion and sediment transport. However, it remains untested how these large land use changes affect the erosion processes at the catchment scale and if the hydrological control works efficiently reduce sediment export. A combination of field work, mapping and modelling was used to test the influence of land use scenarios with and without sediment control structures (check-dams) on sediment yield at the catchment scale. The study catchment is located in SE Spain and suffered important land use changes, increasing the forest cover 3-fold and decreasing the agricultural land 2-5-fold from 1956 to 1997. In addition 58 check-dams were constructed in the catchment in the 1970s accompanying reforestation works. The erosion model WATEM-SEDEM was applied using six land use scenarios: land use in 1956, 1981 and 1997, each with and without check-dams. Calibration of the model provided a model efficiency of 0.84 for absolute sediment yield. Model application showed that in a scenario without check dams, the land use changes between 1956 and 1997 caused a progressive decrease in sediment yield of 54%. In a scenario without land use changes but with check-dams, about 77% of the sediment yield was retained behind the dams. Check-dams can be efficient sediment control measures, but with a short-lived effect. They have important side-effects, such as inducing channel erosion downstream. While also having side-effects, land use changes can have important long-term effects on sediment yield. The application of either land use changes (i.e. reforestation) or check-dams to control sediment yield depends on the objective of the management and the specific environmental conditions of each area. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Large floods are often attributed to the melting of snow during a rain event. This study tested how climate variability, snowpack presence, and basin physiography were related to storm hydrograph shape in three small (〈1 km2) basins with old-growth forest in western Oregon. Relationships between hydrograph characteristics and precipitation were tested for approximately 800 storms over a nearly 30-year period. Analyses controlled for (1) snowpack presence/absence, (2) antecedent soil moisture, and (3) hillslope length and gradient. For small storms (〈150 mm precipitation), controlling for precipitation, the presence of a snowpack on near-saturated soil increased the threshold of precipitation before hydrograph rise, extended the start lag, centroid lag, and duration of storm hydrographs, and increased the peak discharge. The presence of a snowpack on near-saturated soil sped up and steepened storm hydrographs in a basin with short steep slopes, but delayed storm hydrographs in basins with longer or more gentle slopes. Hydrographs of the largest events, which were extreme regional rain and rain-on-snow floods, were not sensitive to landform characteristics or snowpack presence/absence. Although the presence of a snowpack did not increase peak discharge in small, forested basins during large storms, it had contrasting effects on storm timing in small basins, potentially synchronizing small basin contributions to the larger basin hydrograph during large rain-on-snow events. By altering the relative timing of hydrographs, snowpack melting could produce extreme floods from precipitation events whose size is not extreme. Further work is needed to examine effects of canopy openings, snowpack, and climate warming on extreme rain-on-snow floods at the large basin scale. Copyright © 2008 John Wiley & Sons, Ltd.

Description: In this study, short-term river flood forecasting models based on wavelet and cross-wavelet constituent components were developed and evaluated for forecasting daily stream flows with lead times equal to 1, 3, and 7 days. These wavelet and crosswavelet models were compared with artificial neural network models and simple perseverance models. This was done using data from the Skrwa Prawa River watershed in Poland. Numerical analysis was performed on daily maximum stream flow data from the Parzen station and on meteorological data from the Plock weather station in Poland. Data from 1951 to 1979 was used to train the models while data from 1980 to 1983 was used to test the models. The study showed that forecasting models based on wavelet and cross-wavelet constituent components can be used with great accuracy as a stand-alone forecasting method for 1 and 3 days lead time river flood forecasting, assuming that there are no significant trends in the amplitude for the same Julian day year-to-year, and that there is a relatively stable phase shift between the flow and meteorological time series. It was also shown that forecasting models based on wavelet and cross-wavelet constituent components for forecasting river floods are not accurate for longer lead time forecasting such as 7 days, with the artificial neural network models providing more accurate results. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The isotope hydrology of a set of nested sub-catchments in the north-east of Scotland has been studied to examine the mixing processes and residence times of water in the catchments. The measured δ 18O in stream waters was found to be exceptionally uniform both temporally and spatially. Hydrochemical mixing analyses showed that groundwater contributes between 62 and 90% of the stream flow in all sub-catchments. Model analysis indicated that the δ 18O in stream water is indicative of a highly mixed system in which near surface runoff appears to be mixed with groundwater, within the soil profile, before being released from the catchment. Small fluctuations in the stream water δ18O response are generated by a small proportion (〈10%) of less-well mixed water in infiltration excess runoff during storm events. A comparative application of the model to a nearby catchment, which has a lower proportion of groundwater runoff, demonstrated contrasting behaviour, with significantly less mixing of waters occurring and a more distinct difference in the age of runoff generated by different flow paths. This highlighted that standard methods for characterization of mixing mechanisms are often insufficient and may not discriminate between systems that have retained quite distinct flow paths throughout catchment transit, and those which have been mixed at some stage. Model sensitivity analysis also indicated that the simulated mean residence time of water varies most strongly in response to different parameters compared with the δ18O response. This has implications for estimating water residence times from isotope data. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This paper presents a vertically averaged model for studying water and solute exchanges between a large river and its adjacent alluvial aquifer. The hydraulic model couples horizontal 2D Saint Venant equations for river flow and a 2D Dupuit equation for aquifer flow. The dynamic coupling between river and aquifer is provided by continuity of fluxes and water level elevation between the two domains. Equations are solved simultaneously by linking the two hydrological system matrices in a single global matrix in order to ensure the continuity conditions between river and aquifer and to accurately model two-way coupling between these two domains. The model is applied to a large reach (about 36 km2) of the Garonne River (south-western France) and its floodplain, including an instrumented site in a meander. Simulated hydraulic heads are compared with experimental measurements on the Garonne River and aquifer in the floodplain. Model verification includes comparisons for one point sampling date (27 piezometers, 30 March 2000) and for hydraulic heads variations measured continuously over 5 months (5 piezometers, 1 January to 1 June 2000). The model accurately reproduces the strong hydraulic connections between the Garonne River and its aquifer, which are confirmed by the simultaneous variation of the water level in the river and in piezometers located near the river bank. The simulations also confirmed that the model is able to reproduce groundwater flow dynamics during flood events. Given these results, the hydraulic model was coupled with a solute-transport component, based on advection-dispersion equations, to investigate the theoretical dynamics of a conservative tracer over 5 years throughout the 36 km2 reach studied. Meanders were shown to favour exchanges between river and aquifer, and although the tracer was diluted in the river, the contamination moved downstream from the injection plots and affected both river banks. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Some relatively straightforward modifications to the Distributed Hydrology-Soil-Vegetation Model (DHSVM) are described that allow it to represent urban hydrological processes. In the modified model, precipitation that falls on impervious surfaces becomes surface runoff, and a spatially varying (depending on land cover) fraction of surface runoff is connected directly to the stream channel, with the remainder stored and slowly released to represent the effects of stormwater detention. The model was evaluated through application to Springbrook Creek watershed in a partially urbanized area of King County, Washington. With calibration, the modified DHSVM simulates hourly streamflow from these urbanized catchments quite well. It is also shown how the revised model can be used to study the effects of continuing urbanization in the much larger Puget Sound basin. Model simulations confirm many previous studies in showing that urbanization increases peak flows and their frequency, and decreases peak flow lag times. The results show that the urbanization parameterizations for DHSVM facilitate use of the model for prediction and/or reconstruction of a range of historic and future changes in land cover that will accompany urbanization as well as other forms of vegetation change. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This work develops a top-down modelling approach for storm-event rainfall-runoff model calibration at unmeasured sites in Taiwan. Twenty-six storm events occurring in seven sub-catchments in the Kao-Ping River provided the analytical data set. Regional formulas for three important features of a streamflow hydrograph, i.e. time to peak, peak flow, and total runoff volume, were developed via the characteristics of storm event and catchment using multivariate regression analysis. Validation of the regional formulas demonstrates that they reasonably predict the three features of a streamflow hydrograph at ungauged sites. All of the sub-catchments in the study area were then adopted as ungauged areas, and the three streamflow hydrograph features were calculated by the regional formulas and substituted into the fuzzy multi-objective function for rainfall-runoff model calibration. Calibration results show that the proposed approach can effectively simulate the streamflow hydrographs at the ungauged sites. The simulated hydrographs more closely resemble observed hydrographs than hydrographs synthesized using the Soil Conservation Service (SCS) dimensionless unit hydrograph method, a conventional method for hydrograph estimation at ungauged sites in Taiwan. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Concerns related to climate change have resulted in an increasing interest in the importance of hydrological events such as droughts in affecting biogeochemical responses of watersheds. The effects of an unusually dry summer in 2002 had a marked impact on the biogeochemistry of three watersheds in the north-eastern USA. Chemical, isotopic and hydrological responses with particular emphasis on S dynamics were evaluated for Archer Creek (New York), Sleepers River (Vermont) and Cone Pond (New Hampshire) watersheds. From 1 August to 14 September 2002, all three watersheds had very low precipitation (48 to 69 mm) resulting in either very low or no discharge (mean 0.015, 0.15 and 0.000 mm day-1 for Archer Creek, Sleepers River and Cone Pond, respectively). From 15 September to 31 October 2002, there was a substantial increase in precipitation totals (212, 246 and 198 mm, respectively) with increased discharge. Archer Creek was characterized by a large range of SO42- concentrations (152 to 389 μeq L-1, mean = 273 μeq L-1) and also exhibited the greatest range in δ34S values of SO42- (-1.4 to 8.8 ‰). Sleepers River's SO42- concentrations ranged from 136 to 243 μeq L-1 (mean = 167 μeq L-1) and δ 34S values of SO42- ranged from 4.0 to 9.0 ‰. Cone Pond's SO42- concentrations (126-187 μeq L-1, mean = 154 μeq L-1) and δ34S values (2.4 to 4.3 ‰) had the smallest ranges of the three watersheds. The range and mean of δ18O-SO42- values for Archer Creek and Cone Pond were similar (3.0 to 8.9 ‰, mean = 4.5 ‰; 3.9 to 6.3 ‰, mean = 4.9 ‰; respectively) while δ18O-SO42- values for Sleepers River covered a larger range with a lower mean (1.2 to 10.0 ‰, mean = 2.5). The difference in Sleepers River chemical and isotopic responses was attributed to weathering reactions contributing SO42-. For Archer Creek wetland areas containing previously reduced S compounds that were reoxidized to SO4 2- probably provided a substantial source of S. Cone Pond had limited internal S sources and less chemical or isotopic response to storms. Differences among the three watersheds in S biogeochemical responses during these storm events were attributed to differences in S mineral weathering contributions, hydrological pathways and landscape features. Further evaluations of differences and similarities in biogeochemical and hydrological responses among watersheds are needed to predict the impacts of climate change. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This paper proposes the application of a neuro-wavelet technique for modelling monthly stream flows. The neuro-wavelet model is improved by combining two methods, discrete wavelet transform and multi-layer perceptron, for one-month-ahead stream flow forecasting and results are compared with those of the single multi-layer perceptron (MLP), multi-linear regression (MLR) and auto-regressive (AR) models. Monthly flow data from two stations, Gerdelli Station on Canakdere River and Isakoy Station on Goksudere River, in the Eastern Black Sea region of Turkey are used in the study. The comparison results revealed that the suggested model could increase the forecast accuracy and perform better than the MLP, MLR and AR models. Copyright © 2008 John Wiley & Sons, Ltd.

Description: In boreal forested wetlands, the observed increase in the water table level after clearcutting (watering-up) is often a threat to sustained ecosystem productivity. Hydrologic recovery refers to the processes by which a water table progressively drops back to its initial level after the cut. In eastern Canada, drainage is used operationally after clearcutting wet sites in order to lower the water table level and accelerate hydrologic recovery. The objective of this study was to evaluate the duration of the watering-up caused by timber harvesting and the extent to which drainage affected the water table recovery on five peatlands and three hydromorphic mineral sites located in the St. Lawrence Lowlands of Québec (Canada). The mixed wood stands studied are dominated by balsam fir (Abies balsamea (L.) Mill.), eastern white cedar (Thuja occidentalis L.), and red maple (Acer rubrum L). Results indicate that, 10 years after clearcutting, water table levels in undrained plots are still 5 to 7 cm higher than the pre-cut levels. The slight recovery in water table level plateaued after the third year. Rainfall interception by vegetation was also monitored, and after 10 years had reached nearly 50% of the pre-cut rate. The immediate water table drawdown following drainage mitigated watering-up within 40 m of a ditch. The persistent watering-up observed in this study should encourage using sylvicultural systems adapted to boreal forested wetlands in order to prevent productivity loss and stand conversion. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Modelling of physical processes such as ablation or runoff at continental or global scales provides a key challenge: a high degree of abstraction is required in order to minimize computational demands, while spatial and temporal variability of key processes, often at the sub-scale level, need to be adequately captured and reproduced within a lower resolution model. For some approaches, such as temperature index models, downscaling to lower resolutions is straightforward. However a key issue when using these downscaled models is to assess the impact of scaling on model behaviour and results, including the associated uncertainties. We assess the impact of scaling on both a simple and an enhanced temperature index melt model from 100 m to 1, 5 and 10 km resolutions. Different sub-grid parameterization approaches are applied to both models across all resolutions and tested for their suitability against high-resolution reference data, with the aim of developing a robust, scalable and computationally undemanding parameterization. Results show patterns of over- and underestimation of potential melt rates for both models, with clear dependencies on scale, terrain roughness and variations of temperature thresholds, among other quantities. The sub-grid parameterizations tested in this article are found to effectively compensate these effects at little additional computational cost. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Little Kickapoo Creek (LKC), a low-gradient stream, mobilizes its streambed-fundamentally altering its near-surface hyporheic zone-more frequently than do higher-gradient mountain and karst streams. LKC streambed mobility was assessed through streambed surveys, sediment sampling, and theoretical calculations comparing basal shear stress (τb) with critical shear stress (τc). Baseflow τb is capable of entraining a d50 particle; bankfull flow could entrain a 51.2 mm particle. No particle that large occurs in the top 30 cm of the substrate, suggesting that the top 30 cm of the substrate is mobilized and redistributed during bankfull events. Bankfull events occur on average every 7.6 months; flows capable of entraining d50 and d85 particles occur on average every 0.85 and 2.1 months, respectively. Streambed surveys verify streambed mobility at conditions below bankfull. While higher gradient streams have higher potential energy than LKC, they achieve streambed-mobilization thresholds less frequently. Heterogeneous sediment redistribution creates an environment where substrate hydraulic conductivity (K) varies over four orders of magnitude. The frequency and magnitude of the substrate entrainment has implications on hyporheic zone function in fluid, solute and thermal transport models, interpretations of hyporheic zone stability, and understanding of LKC's aquatic ecosystem. Copyright © 2008 John Wiley & Sons, Ltd.

Description: In this experimental study, measurements were conducted to explore the impacts of different forms of individual natural vegetative elements within the flow domain on velocity and turbulence characteristics. All the experiments were performed in a flume measuring 26 m in length, 0.98 m in width and 0.85 m in depth, and real tree saplings were utilized to represent the vegetation element. In order to analyse this commonly observed nature phenomenon in floodplains, trees with wide trunks were classified into three groups on the basis of their volume versus height relation. Throughout the velocity measurements three acoustic Doppler velocimeters were employed. Time-averaged velocity, streamwise and vertical turbulence intensities and turbulent kinetic energy parameters were examined. Additionally, a formulation that gives the velocity profile at a certain distance downstream of vegetation was introduced and the validity of the proposed formulation was checked with experimental data. It is seen that despite their porous structures, the presence of vegetation considerably disturbs the flow field and dissipates a remarkable amount of energy by turbulence. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Isotopic fractionation of 10B/11B provides a sound tool for identifying hydrogeochemical processes in complex areas, owing to its ability to discriminate between various scenarios. In addition, the occurrence of boron as a minor element in areas of active volcanism allows its use in comparison with concentrations of other conservative or non-conservative ions. This allows the detection of water mixtures of diverse origin and temperature, deep or shallow, including fresh water, seawater and even brines. This tool was applied in studies of the volcanic islands of Ischia and São Miguel, across widely differing geographical and climatic contexts. Five groups of waters have been identified in Ischia Island: marine, transition, hot carbonated, cold carbonated and fresh waters. For São Miguel Island the identified groups are cold carbonic, hot carbonic, boiling and acidic boiling waters. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Excessive application of poultry litter to pastures in the Sand Mountain region of north Alabama has resulted in phosphorus (P) contamination of surface water bodies and buildup of P in soils of this region. Since surface runoff is recognized as the primary mechanism of P transport, understanding surface runoff generation mechanisms are crucial for alleviating water quality problems in this region. Identification of surface runoff generation mechanisms is also important for delineation of hydrologically active areas (HAAs). Therefore, the specific objective of this study was to identify surface runoff generation mechanisms (infiltration excess versus saturation excess) using distributed surface and subsurface sensors and rain gauge. Results from three rainfall events (2.13-3.43 cm) of differing characteristics, and sensor data at four locations with differing soil hydraulic properties along the hillslope showed that the main surface runoff generation mechanism in this region is infiltration excess. Because of this, rainfall intensity and soil hydraulic conductivity were found to play dominant roles in surface runoff generation in this region. Further, only short periods of a few rainfall events during which the rainfall intensity is high produce surface runoff. This study indicates that perhaps subsurface flows and transport of P in subsurface flows need to be quantified to reduce P contamination of surface water bodies in this region. Current studies at this location are identifying spatial and temporal distribution of HAAs, quantifying rainfall characteristics that generate runoff, and estimating runoff volume that results from connected HAAs. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The identification of runoff contributing areas would provide the ideal focal points for water quality monitoring and Best Management Practice (BMP) implementation. The objective of this study was to use a field-scale approach to delineate critical runoff source areas and to determine the runoff mechanisms in a pasture hillslope of the Ozark Highlands in the USA. Three adjacent hillslope plots located at the Savoy Experimental Watershed, north-west Arkansas, were bermed to isolate runoff. Each plot was equipped with paired subsurface saturation and surface runoff sensors, shallow groundwater wells, H-flumes and rain gauges to quantify runoff mechanisms and rainfall characteristics at continuous 5-minute intervals. The spatial extent of runoff source areas was determined by incorporating sensor data into a geographic information-based system and performing geostatistical computations (inverse distance weighting method). Results indicate that both infiltration excess runoff and saturation excess runoff mechanisms occur to varying extents (0-58% for infiltration excess and 0-26% for saturation excess) across the plots. Rainfall events that occurred 1-5 January 2005 are used to illustrate the spatial and temporal dynamics of the critical runoff source areas. The methodology presented can serve as a framework upon which critical runoff source areas can be identified and managed for water quality protection in other watersheds. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Prescribed burning is a forest management tool to reduce forest fire hazards. It is largely applied in the USA and is gaining importance worldwide, particularly in Europe. However, its effects on soils still have to be better understood. This study analyses the effects of two types of prescribed burnings (i.e. low and high burn severities of up to 200 °C and at or above 400 °C) on soil hydrophobicity, infiltration, and water storage capacity of top soils. Prescribed burnings were performed on four different plots in southern and western Catalonia, Spain. Soil samples were collected before and after burning to assess water repellency with the water drop penetration time (WDPT). Three rainfall simulations before burning and three after burning were executed on areas of 1 m2, and soil water contents at four to five depths were measured every 4 min during and after rainfall simulations using time domain reflectometry equipment (TDR). Following burning at both severities, water storage capacity of the top soil decreased between 1.7 and 5.4%vol on all four plots. No significant changes in volume flux density and velocity of the wetting fronts were discernible. Water drop penetration times increased moderately at the soil surface of the plots that were exposed to the high burn severity, and decreased slightly when burn severity was low. On two of the four plots the presence of partially moist organic litter prevented the underlying soil from excessive heating. Changes in hydrophobicity and water storage capacity of the top soil did not affect infiltration. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Evaporation from the forest floor (Ef) of a secondary broad-leaved forest was monitored for 1 year at 30 min intervals using a closed chamber system. The diurnal and seasonal variation of Ef and forest structure were analysed for days undisturbed by rainfall. The diurnal change in Ef reached a maximum at about 14:00 and gradually decreased towards midnight along with the vapour pressure deficit (D). Although Ef comprised about 20% of evapotranspiration from the dry canopy (Et), it had only a small influence on diurnal evaporation efficiency (β) characteristics above the canopy because its diurnal range was much smaller than that of Et. Although leaf emergence and leaf fall clearly affected available energy (Ae) beneath the canopy, the influence was not clear with Ef. In contrast, seasonal variation in Ef was strongly correlated with D and Ae above the canopy, and the determination coefficient (R 2 ) changed with the Bowen ratio (B). At night, Et was almost equal to Ef when the friction velocity (u*) ranged between 0.2 and 0.4 m s -1 . The ratio of Ef to Et was exponentially correlated with leaf area index (LAI) when the soil was not dry. The ratio of Ef to Et was mainly influenced by LAI and soil moisture, but the existence of understory vegetation did not have a strong influence. Copyright © 2008 John Wiley & Sons, Ltd.

Description: In this study, three artificial neural network methods, i.e. feed forward back propagation, the radial basis function neural network, and the generalized regression neural network are employed to compute the longitudinal dispersion coefficient in order to evaluate its behaviour in predicting dispersion characteristics in natural streams. These methods, which use hydraulic and geometrical data to predict dispersion coefficients, can easily be applied to natural streams and are proven to be superior in explaining their dispersion characteristics more precisely than existing equations. This method of predicting the longitudinal dispersion coefficient in river flows was tested on 65 data sets, obtained by researchers from 30 rivers in the USA. Results using the models are compared with results obtained in many other studies, and are shown to be more accurate than the other methods considered. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Using the annual runoff series for the last 40 years from the Tarim River Basin, their periodic properties were analysed and their future trends predicted. Runoff data were collected at five hydrological gauging stations in the three main branches of the Tarim River. An extrapolation method and variance analysis were used to identify periods in annual runoff, and a trend superposition model to predict future changes. Results show that, there is a common period of 17 years in annual runoff changes for all three branches, with Hotan River showing an additional period of 10 years. Based on this trend, it is suggested that the annual runoff of the Tarim River should decrease in the period of 2006-2008, but increase in year 2009, and the flow may possibly begin to decrease significantly in year 2010. The long term trend of runoff in Tarim Basin has followed the global prediction of GCMs, i.e. began to increase in accordance with global increase of air temperature and precipitation in 1990. However, it has shown a local feature of uneven changes among the head streams in the same basin, which needs to be further investigated. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Performance of process-based hydrological models is usually assessed through comparison between simulated and measured streamflow. Although necessary, this analysis is not sufficient to estimate the quality and realism of the modelling since streamflow integrates all processes of the water cycle, including intermediate production or redistribution processes such as snowmelt or groundwater flow. Assessing the performance of hydrological models in simulating accurately intermediate processes is often difficult and requires heavy experimental investments. In this study, conceptual hydrological modelling (using SWAT) of a semi-arid mountainous watershed in the High Atlas in Morocco is attempted. Our objective is to analyse whether good intermediate processes simulation is reached when global-satisfying streamflow simulation is possible. First, parameters presenting intercorrelation issues are identified: from the soil, the groundwater and, to a lesser extent, from the snow. Second, methodologies are developed to retrieve information from accessible intermediate hydrological processes. A geochemical method is used to quantify the contribution of a superficial and a deep reservoir to streamflow. It is shown that, for this specific process, the model formalism is not adapted to our study area and thus leads to poor simulation results. A remote-sensing methodology is proposed to retrieve the snow surfaces. Comparison with the simulation shows that this process can be satisfyingly simulated by the model. The multidisciplinary approach adopted in this study, although supported by the hydrological community, is still uncommon. Copyright © 2007 John Wiley & Sons, Ltd.

Description: We want to develop a dialogue between geophysicists and hydrologists interested in synergistically advancing process based watershed research. We identify recent advances in geophysical instrumentation, and provide a vision for the use of electrical and magnetic geophysical instrumentation in watershed scale hydrology. The focus of the paper is to identify instrumentation that could significantly advance this vision for geophysics and hydrology during the next 3-5 years. We acknowledge that this is one of a number of possible ways forward and seek only to offer a relatively narrow and achievable vision. The vision focuses on the measurement of geological structure and identification of flow paths using electrical and magnetic methods. The paper identifies instruments, provides examples of their use, and describes how synergy between measurement and modelling could be achieved. Of specific interest are the airborne systems that can cover large areas and are appropriate for watershed studies. Although airborne geophysics has been around for some time, only in the last few years have systems designed exclusively for hydrological applications begun to emerge. These systems, such as airborne electromagnetic (EM) and transient electromagnetic (TEM), could revolutionize hydrogeological interpretations. Our vision centers on developing nested and cross scale electrical and magnetic measurements that can be used to construct a three-dimensional (3D) electrical or magnetic model of the subsurface in watersheds. The methodological framework assumes a 'top down' approach using airborne methods to identify the large scale, dominant architecture of the subsurface. We recognize that the integration of geophysical measurement methods, and data, into watershed process characterization and modelling can only be achieved through dialogue. Especially, through the development of partnerships between geophysicists and hydrologists, partnerships that explore how the application of geophysics can answer critical hydrological science questions, and conversely provide an understanding of the limitations of geophysical measurements and interpretation. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Spatial and temporal patterns of spring break-up flooding in the Slave River. Delta (SRD), Northwest Territories, are characterized during three years (2003-2005) using water isotope tracers and total inorganic suspended sediment (TSS) concentrations measured from lakewater samples collected shortly after the spring melt. Strongly contrasting spring melt periods led to a moderate flood in 2003, no flooding in 2004 and widespread flooding in 2005. Flooded lakes have isotopically-depleted δ18O (δ2H) signatures, ranging between - 19.2‰ (-146‰) and - 17.‰ (-146‰) and most have high TSS concentrations (〉 10 mg L-1), while non-flooded lakes have more isotopically-enriched δ18O (δ2H) signatures, ranging between - 18.2‰ (-149‰) and -10.6‰ (-118‰) and low TSS concentrations (〈10 mg L-1). These results, in conjunction with the isotopic signatures of Slave River water and snowmelt, are used to estimate the proportion of river- or snowmelt-induced dilution in delta lakes during the spring of each study year. Calculations indicate river flooding caused dilution of ∼70-100% in delta lakes, while snowmelt dilution in the absence of river flooding ranged from ∼0-56%. A positive relationship exists between the spatial extent of spring flooding in the SRD and level and discharge on the Slave River and upstream tributaries, suggesting that upstream flow generation plays a key role in determining the magnitude of spring flooding in the SRD, Parallel variations in the 46-year instrumental Slave River discharge record and flood stratigraphy in the active delta indicate that there is potential for extending the flood history of the SRD, a development that will contribute to a more robust understanding of the drivers of historic, contemporary and future flood frequency in the delta. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Field experiments at Tiramoana station 30 km north of Christchurch, New Zealand using an erosion plot 16.5 m long, 0.6 m wide, and with a slope of 14-14.5° on rendzina soil aimed to measure the variability of flow velocity and of soil aggregates transport rate in shallow overland flow. Discharge/cross-section area ratio was used to estimate mean velocity, and high-speed digital video camera and image analysis provided information about flow and sediment transport variability. Six flow runs with 0.5-3.0 L s-1 discharges were supercritical with Froude numbers close to or more than 1. Mean flow velocity followed Poiseuille law, float numbers were more than 1.5 and hydraulic resistance was an inverse proportional function of the Reynolds number, which is typical for laminar flows. Hence actual velocity varied through time significantly and the power spectrum was of 'red-noise', which is typical for turbulent flow. Sediment transport rates had even higher variability, and soil aggregates transport was a compound Poisson process. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Using a dataset of gauged river discharges taken from sites in England and Wales, linear multilevel models (also known as mixed effects models) were applied to quantify the variability in discharge and the discharge-hydraulic geometry relationships across three nested spatial scales. A jackknifing procedure was used to test the ability of the multilevel models to predict hydraulic geometry, and therefore width, mean depth and mean velocity, at ungauged stations. These models provide a framework for making predictions of hydraulic geometry parameters, with associated levels of uncertainty, using different levels of data availability. Results indicate that as one travels downstream along a river there is greater variability in hydraulic geometry than is the case between rivers of similar sizes. This indicates that hydraulic geometry (and therefore hydrology) is driven by catchment area, to a greater extent than by natural geomorphological variations in the streamwise direction at the mesoscale, but these geomorphological variations can still have a major impact on channel structure. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Seasonal waves accompanying annual changes in the sliding velocity of ice travel down glacier at speeds much faster than the ice itself. A simple explanation for these waves in terms of the passage of a pressure wave through the subglacial drainage system is given. Drainage by both distributed and localized systems is explored, with the sliding velocity governed by a dependence on the effective pressure. Waves are caused by drainage through a slow distributed system, but may be damped if this is well connected to an efficient channelized system. A possible connection between these waves and high velocity spring events is discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Description: To supplement conventional geophysical log data, this study presents temporal variations in electrical conductivity (EC) and temperature with depth in a multilayered coastal aquifer, on the eastern part of Jeju Island, Korea. One-month time-series data obtained at eight points from a multi-depth monitoring system showed that semidiurnal and semimonthly tidal variations induced dynamic fluctuations in EC and temperature. At some depths, EC ranged from 1483 to 26822 μS cm-1, while some points showed no significant variations. The results of EC log and time-series data revealed that a sharp fresh-saltwater interface occurred at low fide, but the diffusion zone broadened to 20 m at high tide. EC, temperature, and tide level data were used for the cross-correlation analysis. The response time of EC and temperature to tide appears to range from less than 30 min to 11 h. Using end-member mixing analysis (EMMA), the fraction of variations of chloride concentration in the multilayered aquifer was explained, and a conceptual model was developed which subdivided the coastal aquifer into four vertical zones. The percentage of water derived from seawater varied from 2 to 48 at specific depth, owing to tidal fluctuations. Continuous observations of EC and temperature at multiple depths are powerful tools for quantifying the transport of saline water by tidal variations in multilayered coastal aquifers. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Sublimation from thin snow cover at the edge of the Eurasian cryosphere in Mongolia was calculated using the aerodynamic profile method and verified by eddy covariance observations using multiple-level meteorological data from three sites representing a variety of geographic and vegetative conditions in Mongolia. Data were collected in the winter and analysed from three sites. Intense sublimation events, defined by daily sublimation levels of more than 0.4 mm, were predominant in their effect on the temporal variability of sublimation. The dominant meteorological elements affecting sublimation were wind speed and air temperature, with the latter affecting sublimation indirectly through the vapour deficit. Seasonal and interannual variations in sublimation were investigated using long-interval estimations for 19 years at a mountainous-area meteorological station and for 24 years at a flat-plain meteorological station. The general seasonal pattern indicated higher rates of sublimation in both the beginning and ending of the snow-covered period, when the wind speed and vapour deficit were higher. Annual sublimation averaged 11.7 mm at the flat-plain meteorological station, or 20.3% of the annual snowfall, and 15.7 mm at the site in the mountains, or 21.6% of snowfall. The sum of snow sublimation and snowmelt evaporation represented 17 to 20% of annual evapotranspiration in a couple observation years. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The hydrologic properties of the geomorphologic instantaneous unit hydrograph (GIUH) are analysed as a function of the topological properties of the channel network and hillslopes, the hydraulic characteristics of flows (such as celerity and diffusivity), and the spatial distribution of effective rainfall. Applications were conducted on seven basins located in southern France. First, we study the effects of the spatial discretization of the catchment as a function of morphometric properties, such as the number of source points N, the total length of the channel network T and the mainstream length function M of the drained area S. Relationships are established between N(S), T(S) and M(S) and new descriptors are proposed and correlated with the hydrological properties of the GIUH. Results show that a subdivision of the basin into subcatchments determined by only two main nodes of the channel network is sufficient to identify the GIUH. Second, the sensitivity analysis shows that the GIUH is more sensitive to the channel topology and to the spatial distribution of rainfall when correlated with altitude than it is to the hydraulic properties of flow on hillslopes and in the channel. Numerical simulations enable one to compare the travel time on hillslopes and the travel time through the channel network as a function of the parameters of the GIUH, and to define constraints for basin segmentation in spatially distributed hydrological modelling. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Catchment scale hydrological process studies in southern Chile are of special interest as little research at this scale has been carried out in this region. In particular, the young volcanic ash soils, which are typical for this area, are not well understood in their hydrological behaviour. In addition, extensive land use changes require detailed knowledge of hydrological processes in disturbed as well as undisturbed catchments in order to estimate resulting risks of erosion, eutrophication, floods and droughts. This study focuses on data collection and experimental determination of relevant processes in an undisturbed forested catchment in the Andes of southern Chile. The here gained understanding of runoff generation can serve as a reference for comparison with sites subject to human intervention, improving estimation of the effects of land use change. Owing to the lack of long-term data for this catchment it was necessary to replace long time series by a multitude of experimental methods covering as many aspects of the runoff generation process as possible. The methods used in this investigation include: measurements of streamflow, rainfall, throughfall, water chemistry, soil water dynamics, groundwater dynamics, soil physics, soil mineralogy, geo-electrical sounding, and tracer techniques. Methods and equipment used during field campaigns are described and evaluated for usefulness versus expenditure (labour and financial costs). Selected results and the hypotheses developed from these findings are presented. The results suggest the importance of fast processes for rainfall runoff response on the one hand as well as considerable dampening effects of a large subsurface storage on the other hand. Copyright © 2008 John Wiley & Sons, Ltd.

Description: For decades, stochastic modellers have used computerized random number generators to produce random numeric sequences fitting a specified statistical distribution. Unfortunately, none of the random number generators we tested satisfactorily produced the target distribution. The result is generated distributions whose mean even diverges from the mean used to generate them, regardless of the length of run. Non-uniform distributions from short sequences of random numbers are a major problem in stochastic climate generation, because truly uniform distributions are required to produce the intended climate parameter distributions. In order to ensure generation of a representative climate with the stochastic weather generator CLIGEN within a 30-year run, we tested the climate output resulting from various random number generators. The resulting distributions of climate parameters showed significant departures from the target distributions in all cases. We traced this failure back to the uniform random number generators themselves. This paper proposes a quality control approach to select only those numbers that conform to the expected distribution being retained for subsequent use. The approach is based on goodness-of-fit analysis applied to the random numbers generated. Normally distributed deviates are further tested with confidence interval tests on their means and standard deviations. The positive effect of the new approach on the climate characteristics generated and the subsequent deterministic process-based hydrology and soil erosion modelling are illustrated for four climatologically diverse sites. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Knowledge of rainfall characteristics is very important for the accurate estimation of rainfall kinetic energy and prediction of soil erosion. In this study, a reliable and efficient data collection and analysis system was developed to analyse the natural raindrop data collected in subtropical Taiwan. Both raindrop size distributions by number and volume were carefully analysed. The seasonal variations of the rainfall erosivity factor R, which is an index of the erosive potential of rainfall and a function of rainfall kinetic energy, was also discussed. An isoerodent map of Taiwan was also developed based on the rainfall data recorded by 158 automated rainfall-measuring stations within 26 years. Copyright © 2007 John Wiley & Sons, Ltd.

Description: A procedure to simulate karstic aquifers is presented. It is based on a simulation of spring discharge using precipitation and, where necessary, temperature as input data. The karstic aquifer system is considered to be divided into three zones: the surface zone, the unsaturated zone (UZ) and the saturated zone (SZ). Each of these is described by a transfer function that determines the water supplied from the overlying zone. Water loss through evapotranspiration is calculated empirically and subtracted from the total precipitation in order to obtain the effective infiltration into the UZ. The transfer function characterizing the UZ can be expressed as a convolution function. The UZ acts as a buffer, delaying effective infiltration into the SZ. Water discharge from the SZ is described by the recession function of the spring, and this becomes the transfer function that characterizes the emergence of water from the SZ. The model permits the simulation of the influence of pumped abstractions from the system by a simple modification of the transfer functions involved. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Evaporation dominates the water balance in arid and semi-arid areas. The estimation of evaporation by land-cover type is important for proper management of scarce water resources. Here, we present a method to assess spatial and temporal patterns of actual evaporation by relating water balance evaporation estimates to satellite-derived radiometric surface temperature. The method is applied to a heterogeneous landscape in the Krishna River basin in south India using 10-day composites of NOAA advanced very high-resolution radiometer satellite imagery. The surface temperature predicts the difference between reference evaporation and modelled actual evaporation well in the four catchments (r 2 = 0.85 to r 2 = 0-88). Spatial and temporal variations in evaporation are linked to vegetation type and irrigation. During the monsoon season (June-September), evaporation occurs quite uniformly over the case-study area (1.7-2.1 mm day -1 ), since precipitation is in excess of soil moisture holding capacity, but it is higher in irrigated areas (2.2-2.7 mm day -1 ). In the post-monsoon season (December-March) evaporation is highest in irrigated areas (2.4 mm day -1 ). A seemingly reasonable estimate of temporal and spatial patterns of evaporation can be made without the use of more complex and data-intensive methods; the method also constrains satellite estimates of evaporation by the annual water balance, thereby assuring accuracy at the seasonal and annual time-scales. Copyright © 2007 John Wiley & Sons, Ltd.

Description: To analyse the long-term water balance of the Yellow River basin, a new hydrological model was developed and applied to the source area of the basin. The analysis involved 41 years (1960-2000) of daily observation data from 16 meteorological stations. The model is composed of the following three sub-models: a heat balance model, a runoff formation model and a river-routing network model. To understand the heat and water balances more precisely, the original model was modified as follows. First, the land surface was classified into five types (bare, grassland, forest, irrigation area and water surface) using a high-resolution land-use map. Potential evaporation was then calculated using land-surface temperatures estimated by the heat balance model. The maximum evapotranspiration of each land surface was calculated from potential evaporation using functions of the leaf area index (LAI). Finally, actual evapotranspiration was estimated by regulating the maximum evapotranspiration using functions of soil moisture content. The river discharge estimated by the model agreed well with the observed data in most years. However, relatively large errors, which may have been caused by the overestimation of surface flow, appeared in some summer periods. The rapid decrease of river discharge in recent years in the source area of the Yellow River basin depended primarily on the decrease in precipitation. Furthermore, the results suggested that the long-term water balance in the source area of the Yellow River basin is influenced by land-use changes. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Hydrology, particularly the water table position below the surface (relative water level, RWL), is an important control on biogeochemical and ecological processes in peatlands. The surface elevation (SE) in a peatland oscillates in response to changes in effective stress on the peat matrix mainly caused by water level fluctuations. This phenomenon is called peatland surface oscillation (PSO). To investigate the spatiotemporal variability of PSO, surface elevation and the water level above sea level (AWL) were measured monthly (23 sites) over one year in a warm-temperate restiad peatland, New Zealand. At one site peat surface elevation was measured indirectly by monitoring AWL and RWL continuously with pressure transducers. Annual PSO (the difference between maximum and minimum surface elevation) ranged from 3.2 to 28 cm (mean = 14.9 cm). Surface elevation changes were caused by AWL fluctuations. Spatially homogenous AWL fluctuations (mean 40 cm among sites) translated into RWL fluctuations reduced 27-56% by PSO except for three sites with shallow and dense peat at the peatland margin (7-17%). The SE-AWL relationship was linear for t5 sites. However, eight sites showed significantly higher rates of surface elevation changes during the wet season and thus a non-linear behaviour. We suggest flotation of upper peat layers during the wet season causing this non-linear behaviour. Surprisingly, PSO was subjected to hysteresis: the positive SE-AWL relationship reversed after rainfall when the surface slowly rose despite rapidly receding AWL. Hysteresis was more prominent during the dry season than during the wet season. Total peat thickness and bulk density together could only explain 50% of the spatial variability of PSO based on manual measurements. However, we found three broad types of SE-AWL relationships differing in shape and slope of SE-AWL curves. These oscillation types reflected patterns in vegetation and flooding. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Topography is a dominant factor in hillslope hydrology. TOPMODEL, which uses a topographical index derived from a simplified steady state assumption of mass balance and empirical equations of motion over a hillslope, has many advantages in this respect. Its use has been demonstrated in many small basins (catchment areas of the order of 2-500 km2) but not in large basins (catchment areas of the order of 10 000-100 000 km2). The objective of this paper is to introduce the Block-wise TOPMODEL (BTOP) as an extension of the TOPMODEL concept in a grid based framework for distributed hydrological simulation of large river basins. This extension was made by redefining the topographical index by using an effective contributing area af(a) (0 ≤ f(a) ≤ 1) per unit grid cell area instead of the upstream catchment area per unit contour length and introducing a concept of mean groundwater travel distance. Further the transmissivity parameter T0 was replaced by a groundwater dischargeability D which can provide a link between hill slope hydrology and macro hydrology. The BTOP model uses all the original TOPMODEL equations in their basic form. The BTOP model has been used as the core hydrological module of an integrated distributed hydrological model YHyM with advanced modules of precipitation, evapotranspiration, flow routing etc. Although the model has been successfully applied to many catchments around the world since 1999, there has not been a comprehensive theoretical basis presented in such applications. In this paper, an attempt is made to address this issue highlighted with an example application using the Mekong basin. Copyright © 2007 John Wiley & Sons, Ltd.

Description: It is now 2 years since I responded to a discussion about uncertainty estimation at EGU2006 with the commentary 'On Undermining the Science' (OUTS) and the suggestion that Hydrological Processes should become the first hydrological journal to insist that all the papers submitted should include an uncertainty analysis of both measurements and modelling results (Beven, 2006a). That commentary provoked a number of varied responses (Hall et al., 2007; Andréassian et al., 2007; Montanari, 2007; Todini and Mantovan, 2007; Sivakumar, 2008) and the discussion should hopefully continue so that the hydrological community can reflect on the issues raised (though there has been a notable silence all round about imposing a requirement on submitted papers!). Jim Buttle has now asked me to provide a commentary on the commentaries of the OUTS commentary to further this reflection. Copyright © 2008 John Wiley & Sons, Ltd.

Description: A methodology is developed to examine the susceptibility of a transport system to rainfall-induced landslides and is demonstrated for part of the UK rail network with regard to the potential changes that might occur with climate change. A mathematical model is given for the system failure and a statistical model is formulated for the joint distribution of rainfall at different points along the railway line. These are used to investigate the response of earth embankments along the railway line to current and future climate scenarios, including the effects of rainfall and evapotranspiration on slope hydrology and stability. It is shown that, for the system of clay embankments in question, the moisture profile through the embankment at the end of the summer months has a critical effect on system stability, both in terms of expected failure timing and probability of failure. Further, it is seen that, with changing climate, the system stability is likely to increase unless the degradation of embankment material properties, another potential effect of changed climate, is taken into account. The spatial distribution of failures is also likely to change. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The PC versions of the Illinois Urban Drainage Area Simulator ILLUDAS (ILUDRAIN) and the Penn State Runoff Quality Model (PSRM-QUAL) are used to predict hydrographs from four relatively small urban sites (5.97 to 23.57 ha), each having a distinct land use designation (commercial, high density residential, low density residential, and highway), and all located in south Florida. The description of the sites and observed rainfall and runoff data were available from the US Geological Survey (USGS), and have been used in the past to validate their model (DR3M). The two models were calibrated and verified using measured rainfall-runoff data (72 storm events for calibration and 26 different events for verification) and measured hydrological characteristics of the four sites. The methodology and input parameters are presented. Predicted hydrographs from the two models are plotted against observed ones and show good agreement. Model performance is evaluated using the mean normalized error computation and scattergrams of predicted versus observed data. A comparison is also made with the results, using the same data and drainage areas, of the following three methods/models tested in previous studies: the runoff curve number (SCS) method combined with the Santa Barbara urban hydrograph method (SCS-SBUH); the Environmental Protection Agency (EPA) stormwater management model (SWMM); the USGS Distributed Routing Rainfall-Runoff Model (DR3M). The predictions from all models tested in this study showed good agreement with the observed data, with better predictions generally obtained for the more impervious sites. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Streamflow forecasting is very important for the management of water resources: high accuracy in flow prediction can lead to more effective use of water resources. Hydrological data can be classified as non-steady and nonlinear, thus this study applied nonlinear time series models to model the changing characteristics of streamflows. Two-stage genetic algorithms were used to construct nonlinear time series models of 10-day streamflows of the Wu-Shi River in Taiwan. Analysis verified that nonlinear time series are superior to traditional linear time series. It is hoped that these results will be useful for further applications. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Forecasting of hydrologic time series, with the quantification of uncertainty, is an important tool for adaptive water resources management. Nonstationarity, caused by climate forcing and other factors, such as change in physical properties of catchment (urbanization, vegetation change, etc.), makes the forecasting task too difficult to model by traditional Box-Jenkins approaches. In this paper, the potential of the Bayesian dynamic modelling approach is investigated through an application to forecast a nonstationary hydroclimatic time series using relevant climate index information. The target is the time series of the volume of Devil's Lake, located in North Dakota, USA, for which it was proved difficult to forecast and quantify the associated uncertainty by traditional methods. Two different Bayesian dynamic modelling approaches are discussed, namely, a constant model and a dynamic regression model (DRM). The constant model uses the information of past observed values of the same time series, whereas the DRM utilizes the information from a causal time series as an exogenous input. Noting that the North Atlantic Oscillation (NAO) index appears to co-vary with the time series of Devil's Lake annual volume, its use as an exogenous predictor is explored in the case study. The results of both the Bayesian dynamic models are compared with those from the traditional Box-Jenkins time series modelling approach. Although, in this particular case study, it is observed that the DRM performs marginally better than traditional models, the major strength of Bayesian dynamic models lies in the quantification of prediction uncertainty, which is of great value in hydrology, particularly under the recent climate change scenario. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This paper studies the links between scaling properties of river flow time series by comparing the results of three techniques applied to an extended data set of 34 French discharge gauging stations. The three approaches used are based on different mathematical tools and hypotheses: (1) shape analysis of flood hydrographs; (2) a multifractal framework through spectral and moment analyses, and (3) flood frequency analysis through the fitting of flood duration frequency curves (QdF). The general aim is to test the hypothesis of scaling invariance of river flow and the shape invariance of the hydrographs, in order to investigate the link between scaling properties and flow dynamics. In particular, the coherence between different approaches widely used in the literature to describe these characteristics is evaluated through the estimation of parameters defining the range of time-scales on which the scaling properties are valid. The results show that most of these timescale parameters are linked to the flow dynamics and suggest that the approaches applied are interrelated. Copyright © 2008 John Wiley & Sons, Ltd.

Description: An understanding of groundwater flow and chemistry is important to operate underground storage caverns. Groundwater flow is mainly affected by cavern operating conditions. Groundwater chemistry is modified by disinfection activities for removing possible biological clogging and by mixing with cement pore water. It is important to discern these two effects, because wells affected by the disinfection activities may have hydrological connections with water curtains used to inject the disinfectant. However, it is difficult to separate these two effects using graphical methods because of their similar chemical characteristics. Instead, multivariate statistical analysis, such as principal component analysis (PCA) and factor analysis (FA), can be used. Groundwater samples for chemical analysis were obtained from four surveys in 1999-2000. Based on the results from PCA and FA, it appears that there were temporal variations of seepage water into the propane area when the cavern operation fluctuated, but we could not observe such variation in the butane area. These changes may occur mainly at depth, where water flow is slow and water renewal in the cavern surrounding is limited. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Performance of a feed-forward back-propagation artificial neural network on forecasting the daily occurrence and annual depth of rainfall at a single meteorological station is presented. Both short-term and long-term forecasting was attempted, with ground level data collected by the meteorological station in Colombo, Sri Lanka (79°52′E, 6°54′N) during two time periods, 1994-2003 and 1869-2003. Two neural network models were developed; a one-day-ahead model for predicting the rainfall occurrence of the next day, which was able to make predictions with a 74.3% accuracy, and one-year-ahead model for yearly rainfall depth predictions with an 80-0% accuracy within a ±5% error bound. Each of these models was extended to make predictions several time steps into the future, where accuracies were found to decrease rapidly with the number of time steps. The success rates and rainfall variability within the north-east and south-west monsoon seasons are also discussed. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Cryoturbated Upper Chalk is a dichotomous porous medium wherein the intra-fragment porosity provides water storage and the inter-fragment porosity provides potential pathways for relatively rapid flow near saturation. Chloride tracer movement through 43 cm long and 45 cm diameter undisturbed chalk columns was studied at water application rates of 0.3, 1.0, and 1.5 cm h-1. Microscale heterogeneity in effluent was recorded using a grid collection system consisting of 98 funnel-shaped cells each 3.5 cm in diameter. The total porosity of the columns was 0.47 ± 0.02 m3 m-3, approximately 13% of pores were ≥15 μm diameter, and the saturated hydraulic conductivity was 12.66 ± 1.31 m day-1. Although the column remained unsaturated during the leaching even at all application rates, proportionate flow through macropores increased as the application rate decreased. The number of dry cells (with 0 ml of effluent) increased as application rate decreased. Half of the leachate was collected from 15, 19 and 22 cells at 0.3, 1.0, 1.5 cm h-1 application rates respectively. Similar breakthrough curves (BTCs) were obtained at all three application rates when plotted as a function of cumulative drainage, but they were distinctly different when plotted as a function of time. The BTCs indicate that the columns have similar drainage requirement irrespective of application rates, as the rise to the maxima (C/C0) is almost similar. However, the time required to achieve that leaching requirement varies with application rates, and residence time was less in the case of a higher application rate. A two-region convection-dispersion model was used to describe the BTCs and fitted well (r2 = 0.97-0.99). There was a linear relationship between dispersion coefficient and pore water velocity (correlation coefficient r = 0.95). The results demonstrate the microscale heterogeneity of hydrodynamic properties in the Upper Chalk. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Changes in climate and land use can significantly influence the hydrological cycle and hence affect water resources. Understanding the impacts of climate and land-use changes on streamflow can facilitate development of sustainable water resources strategies. This study investigates the flow variation of the Zamu River, an inland river in the arid area of northwest China, using the Soil and Water Assessment Tool distributed hydrological model. Three different land-use and climate-change scenarios were considered on the basis of measured climate data and land-use cover, and then these data were input into the hydrological model. Based on the sensitivity analysis, model calibration and verification, the hydrological response to different land-use and climate-change scenarios was simulated. The results indicate that the runoff varied with different land-use type, and the runoff of the mountain reaches of the catchment increased when grassland area increased and forestland decreased. The simulated runoff increased with increased precipitation, but the mean temperature increase decreased the runoff under the same precipitation condition. Application of grey correlation analysis showed that precipitation and temperature play a critical role in the runoff of the Zamu River basin. Sensitivity analysis of runoff to precipitation and temperature by considering the 1990s land use and climate conditions was also undertaken. Copyright © 2007 John Wiley & Sons, Ltd.

Description: To evaluate the effects of hillslope topography on storm runoff in a weathered granite mountain, discharge rate, soil pore water pressures, and water chemistry were observed on two types of hillslope: a valley-head (a concave hillslope) and a side slope (a planar hillslope). Hydrological responses on the valley-head and side slope reflected their respective topographic characteristics and varied with the rainfall magnitude. During small rainfall events (〈35 mm), runoff from the side slope occurred rapidly relative to the valley-head. The valley-head showed little response in storm runoff. As rainfall amounts increased (35-60 mm), the valley-head yielded a higher flow relative to the side slope. For large rainfall events (〉60 mm), runoff from both hillslopes increased with rainfall, although that from the valley-head was larger than that from the side slope. The differences in the runoff responses were caused by differences in the roles of lower-slope soils and the convergence of the hillslope. During small rainfall events, the side slope could store little water; in contrast, all rainwater could be stored in the soils at the valley-head hollow. As the amount of rainfall increased, the subsurface saturated area of the valley-head extended from the bottom to the upper portion of the slope, with the contributions of transient groundwater via lateral preferential flowpaths due to the high concentration of subsurface water. Conversely, saturated subsurface flow did not contribute to runoff responses, and the subsurface saturated area at the side slope did not extend to the upper slope for the same storm size. During large rainfall events, expansion of the subsurface saturated area was observed in both hillslopes. Thus, differences in the concentration of subsurface water, reflecting hillslope topography, may create differences in the extension of the subsurface saturated area, as well as variability in runoff responses. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Precipitation is the most fundamental input of water for terrestrial ecosystems. Most precipitation inputs are vertical, via rain, but can be horizontal, via wind-driven rain and snow, or, in some ecosystems such as tropical montane cloud forests (TMCFs), via fog interception. Fog interception can be particularly important in ecosystems where fog is frequently present and there are seasonal periods of lower rainfall. Epiphytes in trees are a major ecological component of TMCFs and are particularly dependent on fog interception during periods of lower rainfall because they lack access to soil water. But assessing fog interception by epiphytes remains problematic because: (i) a variety of field or laboratory methods have been used, yet comparisons of interception by epiphytes versus interception by various types of fog gauge are lacking; (ii) previous studies have not accounted for potential interactions between meteorological factors. We compared fog interception by epiphytes with two kinds of commonly used fog gauges and developed relations between fog interception and meteorological variables by conducting laboratory experiments that manipulated key fog characteristics and from field measurements of fog interception by epiphytes. Fog interception measured on epiphytes was correlated with that measured from fog gauges but was more than an order of magnitude smaller than the actual measurements from fog gauges, highlighting a key measurement issue. Our laboratory measurements spanned a broad range of liquid water content (LWC) values for fog and indicate how fog interception is sensitive to an interaction between wind speed and LWC. Based on our results, considered in concert with those from other studies, we hypothesize that fog interception is constrained when LWC is low or high, and that fog interception increases with wind speed for intermediate values of LWC - a net result of deposition, impaction, and evaporation processes - until interception begins to decrease with further increases in wind speed. Copyright © 2007 John Wiley & Sons, Ltd.

Description: The stable isotopic composition of dissolved inorganic carbon (δ13C-DIC) was investigated as a potential tracer of streamflow generation processes at the Sleepers River Research Watershed, Vermont, USA. Downstream sampling showed δ 13C-DIC increased between 3-5‰ from the stream source to the outlet weir approximately 0·5 km downstream, concomitant with increasing pH and decreasing PCO2. An increase in δ13C-DIC of 2.4 ± 0·1‰ per log unit decrease of excess PCO2 (stream PCO2 normalized to atmospheric PCO2) was observed from downstream transect data collected during snowmelt. Isotopic fractionation of DIC due to CO2 outgassing rather than exchange with atmospheric CO2 may be the primary cause of increased δ 13C-DIC values downstream when PCO2 of surface freshwater exceeds twice the atmospheric CO2 concentration. Although CO2 outgassing caused a general increase in stream δ13C-DIC values, points of localized groundwater seepage into the stream were identified by decreases in δ13C-DIC and increases in DIC concentration of the stream water superimposed upon the general downstream trend. In addition, comparison between snowmelt, early spring and summer seasons showed that DIC is flushed from shallow groundwater flowpaths during snowmelt and is replaced by a greater proportion of DIC derived from soil CO2 during the early spring growing season. Thus, in spite of effects from CO2 outgassing, δ13C of DIC can be a useful indicator of groundwater additions to headwater streams and a tracer of carbon dynamics in catchments. Copyright © 2007 John Wiley & Sons, Ltd.

Description: This study considers the impact of managed rotational burning of vegetation and sheep grazing upon the composition of soil waters within an upland peat soil. The study has considered soil water compositions from a complete factorial design of treatment plots where three different burning treatments were considered in replication with grazing and no grazing. All plots were sampled across a complete year with three dipwells in each plot. The study included aluminium (Al), iron, calcium, sodium (Na), magnesium (Mg), potassium, sulphate, chloride (Cl-), bromide, fluoride, phosphate (PO4 3-) and nitrate; and in order to clarify the nature of the results, the pH, conductivity and dissolved organic carbon were also considered, but the major results for these are reported elsewhere. The study finds: (1) Ca, Na, Mg and PO43- concentrations are significantly lower on all burnt plots, with only Al concentration being significantly higher on burnt plots. (2) Only Cl- showed any significant changes (a decrease) with the presence of sheep grazing, and then only when plots were also burnt. (3) A principal component analysis shows that the composition of most soil waters can be described by rainwater and soil water components, but in unburnt plots a base-rich, high ionic strength water is sometimes present. The study suggests that burning, but not grazing, caused significant changes in soil water composition leading to increased interaction between incoming rainwaters and the peat soil but led to loss of interaction with deeper waters. However, no evidence was found for structural change in the soils even after long term (50 years) grazing and burning management. Copyright © 2007 John Wiley & Sons, Ltd.

Description: The spatial and temporal variations of precipitation and runoff for 139 basins in South Korea were investigated for 34 years (1968-2001). The Precipitation-Runoff Modelling System (PRMS) was selected for the assessment of basin hydrologic response to varying climates and physiology. A non-parametric Mann-Kendall's test and regression analysis are used to detect trends in annual, seasonal, and monthly precipitation and runoff, while Moran's I is adapted to determine the degree of spatial dependence in runoff trend among the basins. The results indicated that the long-term trends in annual precipitation and runoff were increased in northern regions and decreased in south-western regions of the study area during the study period. The non-parametric Mann-Kendall test showed that spring streamflow was decreasing, while summer streamflow was increasing. April precipitation decreased between 15% and 74% for basins located in south-western part of the Korean peninsula. June precipitation increased between 18% and 180% for the majority of the basins. Trends in seasonal and monthly streamflow show similar patterns compared to trends in precipitation. Decreases in spring runoff are associated with decreases in spring precipitation which, accompanied by rising temperatures, are responsible for reducing soil moisture. The regional patterns of precipitation and runoff changes show a strong to moderate positive spafial autocorrelation, suggesting that there is a high potential for severe spring drought and summer flooding in some parts of Korea if these trends continue in the future. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Owing to the scarcity of hydro-climatic data in high latitudes, most hydrological models are validated using only discharge data from the basin outlets. In view of the important contribution of snowmelt to northern river flows, there is a need to evaluate model performance in terms of the ability to simulate the seasonal pattern of change in the basin snow cover. The paucity of ground observations renders satellite information a suitable alternative. The moderate resolution imaging spectroradiometer (MODIS) global snow-cover product provided by the National Snow and Ice Data Center (NSIDC) offers one such tool to validate simulated snow coverage in rugged sub-arctic and boreal terrain. This study examines the usefulness of applying MODIS data to validate the hydrological simulation for two test basins: the Liard (275 000 km2) and the Athabasca (133 000 km2) Basins in Canada. Changing extent of snow cover simulated by the Semi-distributed Land Use-based Runoff Processes (SLURP) macro-hydrologic model was compared with MODIS imagery at four bi-weekly intervals in 2000 and 2001. The simulated patterns of seasonal snow-cover change are consistent with the remotely sensed information, with melt beginning from the lower elevations in the east where less snow was accumulated, to the higher elevations in the west bearing more snow. The overall results show the need and the usefulness of MODIS as a tool for validating snow distribution simulated by the hydrological model in large northern basins. Copyright © 2008 John Wiley & Sons, Ltd.

Description: This paper describes the impacts of new river geomorphic and flow parameterizations on the simulated surface waters dynamics of the Amazon River basin. Three major improvements to a hydrologic model are presented: (1) the river flow velocity equation is expanded to be dependent on river sinuosity and friction in addition to gradient forces; (2) equations defining the morphological characteristics of the river, such as river height, width and bankfull volume, are derived from 31 622 measurements of river morphology and applied within the model; (3) 1 km resolution topographic data from the Shuttle Radar Topography Mission (SRTM) are used to provide physically based fractional flooding of grid cells from a statistical representation of sub-grid-scale floodplain morphology. The discharge and floodplain inundation of the Amazon River is simulated for the period 1968-1998, validated against observations, and compared with results from a previous version of the model. These modifications result in considerable improvement in the simulations of the hydrological features of the Amazon River system. The major impact is that the average wet-season flooded area on the Amazon mainstem for the period 1983-1988 is now within 5% of satellite-derived estimates of flooded area, whereas the previous model overestimates the flooded area by about 80%. The improvements are a consequence of the new empirical river geomorphologic functions and the SRTM topography. The new formulation of the flow velocity equation results in increased river velocity on the mainstem and major tributaries and a better correlation between the mean monthly simulated and observed discharge. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Future catchment planning requires a good understanding of the impacts of land use and management, especially with regard to nutrient pollution. A range of readily usable tools, including models, can play a critical role in underpinning robust decision-making. Modelling tools must articulate our process understanding, make links to a range of catchment characteristics and scales and have the capability to reflect future land-use management changes. Hence, the model application can play an important part in giving confidence to policy makers that positive outcomes will arise from any proposed land-use changes. Here, a minimum information requirement (MIR) modelling approach is presented that creates simple, parsimonious models based on more complex physically based models, which makes the model more appropriate to catchment-scale applications. This paper shows three separate MIR models that represent flow, nitrate losses and phosphorus losses. These models are integrated into a single catchment model (TOPCAT-NP), which has the advantage that certain model components (such as soil type and flow paths) are shared by all three MIR models. The integrated model can simulate a number of land-use activities that relate to typical land-use management practices. The modelling process also gives insight into the seasonal and event nature of nutrient losses exhibited at a range of catchment scales. Three case studies are presented to reflect the range of applicability of the model. The three studies show how different runoff and nutrient loss regimes in different soil/geological and global locations can be simulated using the same model. The first case study models intense agricultural land uses in Denmark (Gjern, 114 km2), the second is an intense agricultural area dominated by high superphosphate applications in Australia (Ellen Brook, 66 km2) and the third is a small research-scale catchment in the UK (Bollington Hall, 2 km2). Copyright © 2007 John Wiley & Sons, Ltd.

Description: The potential impact of climate change on fluvial flooding is receiving considerable scientific and political interest thanks to evidence from climate model projections and a widely held belief that flood risk may be increasing at European levels. This review compares published work on historical trends in UK rainfall and river flow records with high-resolution regional climate change projections, and attempts to reconcile apparent differences between the two. Attention is focused on the techniques used for climate change detection and attribution, as well as the potential confounding effects of land-use change. International and domestic efforts to build adaptive capacity rest on improved quantification of uncertainty in flood risk at very local, catchment and regional scales. This will involve further research to better integrate climate and land-management interactions, to understand changes in the dependence between different flood generating mechanisms, and to improve the characterization and communication of uncertainty at all stages of analysis. Resources are also needed to ensure that latest, but still uncertain, science is presented in an appropriate form to underpin policy development and is translated into sensible guidance for practitioners. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Infiltration devices are traditionally evaluated as standalone entities that do not interact with each other. A model is outlined that will allow interactions between proposed infiltration devices to be predicted prior to a development commencing. The model allows prediction of seepage into downslope devices and the assessment of the locations where the combined ground-water mound will reach the surface and result in overland flow. The volume of overland flow discharged by the seepage zone may exceed the overland and piped flow received by the infiltration devices. Copyright © 2007 John Wiley & Sons, Ltd.

Description: The decommissioning of roads is occurring in many forest environments with the aim of reducing the negative impacts of road runoff on water quality and aquatic habitat. Works associated with decommissioning are expensive so prior assessment of the outcomes of various options is merited. This paper presents a method of quantifying the degree to which a road is hydrologically connected to the stream network and thus the likely impacts of constructing a road of different configurations upon water quality. The method permits comparisons between different road network management options and is useful for assessing the likely result of decommissioning works. Emphasis is placed on quantifying the uncertainty of key performance measures. The procedures developed here are an extension of the probabilistic 'volume to breakthrough' model recently formulated by Australian water quality researchers and allow the quantification of road/stream connectivity without the need for extensive parameterization. To demonstrate its utility, the model was applied to an actual road decommissioning and replacement project in southeast Australia. Road areas and drainage outlets were surveyed in the field and flow paths to streams derived from a 1 metre resolution LiDAR based digital elevation model. The results demonstrate that the actual road decommissioning examined in this case was unlikely to reduce runoff to the stream network and that the overall impact of the works in conditions of design storms are likely to result in a net reduction in stream water quality. Copyright © 2007 John Wiley & Sons, Ltd.

Description: A multifractal analysis was carried out in order to validate the simulation of hourly rainfall records of a local climate model for the Iberian Peninsula. Observed and simulated hourly rainfall data from four locations in Andalusia (southern Spain) were used to carry out the study. In order to detect the influence of the length of the data series on the results, two different sizes were used for the real data: 4 years, and 20 years. The results show that algebraic tails are required to fit the probability distribution of extreme rain event sizes, and rain and dry event durations for both kinds of rainfall data. Similar results are found for the extreme rain event sizes and dry event durations fits when the real and synthetic data are considered. Nevertheless, some differences appear in the cases of rain event durations. The detection of the presence of a first-order multifractal phase transition associated with a critical moment in the empirical moment scaling exponent function and the results of the extreme rain event sizes fits, reveal that real rainfall is a self-organized criticality (SOC) process. That behaviour is less evident in the simulated rainfall series. The same 'synoptic maximum' value was found for each place with both types of rainfall data. A time clustering analysis was carried out applying the count-based periodogram and the Fano factor methods. Some periodicities have been detected in the periodograms, especially for the longest real rainfall data series. Copyright © 2007 John Wiley & Sons, Ltd.

Description: In 1969, Nelson County, Virginia received up to 71 cm of rain within 12 h starting at 7 p.m. on August 19. The total rainfall from the storm exceeded the 1000-year return period in the region. Several thousands of landslides were induced by rainfall associated with Hurricane Camille causing fatalities and destroying infrastructure. We apply a distributed transient response model for regional slope stability analysis to shallow landslides. Initiation points of over 3000 debris flows and effects of flooding from this storm are applied to the model. Geotechnical data used in the calculations are published data from samples of colluvium. Results from these calculations are compared with field observations such as landslide trigger location and timing of debris flows to assess how well the model predicts the spatial and temporal distribution. of landslide initiation locations. The model predicts many of the initiation locations in areas where debris flows are observed. Copyright © 2007 John Wiley & Sons, Ltd.

Description: The objective of this study was to quantify components of the water balance related to root-water uptake in the soil below a hedgerow. At this local scale, a two-dimensional (2D) flow domain in the x-z plane 6 m long and 1.55 m deep was considered. An attempt was made to estimate transpiration using a simulation model. The SWMS-2D model was modified and used to simulate temporally and spatially heterogeneous boundary conditions. A function with a variable spatial distribution of root-water uptake was considered, and model calibration was performed by adjusting this root-water uptake distribution. Observed data from a previous field study were compared against model predictions. During the validation step, satisfactory agreement was obtained, as the difference between observed and modelled pressure head values was less than 50 cm for 80% of the study data. Hedge transpiration capacity is a significant component of soil-water balance in the summer, when predicted transpiration reaches about 5.6 mm day-1. One of the most important findings is that hedge transpiration is nearly twice that of a forest canopy. In addition, soil-water content is significantly different whether downslope or upslope depending on the root-water uptake. The high transpiration rate was mainly due to the presence of a shallow water table below the hedgerow trees. Soil-water content was not a limiting factor for transpiration in this context, as it could be in one with a much deeper water table. Hedgerow tree transpiration exerts a strong impact not only on water content within the vadose zone but also on the water-table profile along the transect. Results obtained at the local scale reveal that the global impact of hedges at the catchment scale has been underestimated in the past. Transpiration rate exerts a major influence on water balance at both the seasonal and annual scales for watersheds with a dense network of hedgerows. Copyright © 2007 John Wiley & Sons, Ltd.

Description: This paper describes a coupled, distributed, hydrological-geotechnical model, GEOtop-FS, which simulates the probability of occurence of shallow landslides and debris flows. We use a hydrological distributed model, GEOtop, which, models latent and sensible heat fluxes and surface runoff, and computes soil moisture in 3-D by solving Richards'equation numerically, together with an infinite-slope geotechnical model, GEOtop-FS. The combined model allows both the hydraulic and geotechnical properties of soil to be considered and realistically modelled. In particular, the model has been conceived to make direct use of field surveys, geotechnical characteristics and soil moisture measurements. In the model the depth of available sediments is also used to characterize the hydraulic properties of the area examined. To account for the uncertainty related to the natural variability in the factors influencing the stability of natural slopes, the safety factor is computed with a probabilistic approach. In order to determine the likelihood of slope failures, soil parameters are assigned distributions instead of single deterministic values. The analysis presented was carried out for an alpine watershed, located in the Friuli region, Italy, for which some geological and geotechnical data were available. In the past, this watershed experienced landslides and debris flows during intense storms following long and moderate intensity rainfall events. The distributed coupled GEOtop-FS model was calibrated by reproducing some of these events and validated in order to map future failure probabilities. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Evaluating performances of four commonly used evaporation estimate methods, namely; Bowen ratio energy balance (BREB), mass transfer (MT), Priestley-Taylor (PT) and pan evaporation (PE), based on 4 years experimental data, the most effective and the reliable evaporation estimates model for the semi-arid region of India has been derived. The various goodness-of-fit measures, such as; coefficient of determination (R2), index of agreement (D), root mean square error (RMSE), and relative bias (RB) have been chosen for the performance evaluation. Of these models, the PT model has been found most promising when the Bowen ratio, β is known a priori, and based on its limited data requirement. The responses of the BREB, the PT, and the PE models were found comparable to each other, while the response of the MT model differed to match with the responses of the other three models. The coefficients, β of the BREB, μ of the MT, α of the PT and Kp of the PE model were estimated as 0.07, 2.35, 1.31 and 0.65, respectively. The PT model can successfully be extended for free water surface evaporation estimates in semi-arid India. A linear regression model depicting relationship between daily air and water temperature has been developed using the observed water temperatures and the corresponding air temperatures. The model helped to generate unrecorded water temperatures for the corresponding ambient air temperatures. Copyright © 2007 John Wiley & Sons, Ltd.

Description: The goal of this article is to describe the integrated water balance and water temperature model LARSIM-WT (large area runoff simulation model-water-temperature). The integrated model is an extension of the water balance model LARSIM, which simulates all major aspects of the terrestrial water cycle. The newly added water temperature module allows simulation and forecasting of river water temperatures (RWTs) throughout the complete river network using a deterministic approach, accounting for heat exchange processes along the flow path as well as local sources such as thermal discharges. In addition, it is also possible to calculate RWTs with regression models for specific locations in the river network. Applying LARSIM-WT to the 14 000 km2 watershed of the Neckar River showed that the model is well-suited to simulate RWTs along with discharges. Forecast tests proved the adequacy of the model for operational RWT forecasting for up to seven days ahead. The model has been continuously used for automated daily river temperature and discharge forecasting for the Neckar River since 2004. Moreover, it has also been successfully applied to predict the impact of climate change on water temperatures in the Neckar River. Copyright © 2008 John Wiley & Sons, Ltd.

Description: The hyporheic zone influences the thermal regime of rivers, buffering temperature by storing and releasing heat over a range of timescales. We examined the relationship between hyporheic exchange and temperature along a 24-krn reach of the lower Clackamas River, a large gravel-bed river in northwestern Oregon (median discharge = 75-7 m3/s; minimum mean monthly discharge = 22.7 in m3/s in August 2006). With a simple mixing model, we estimated how much hyporheic exchange cools the river during hot summer months. Hyporheic exchange was primarily identified by temperature anomalies, which are patches of water that demonstrate at least a 1°C temperature difference from the main channel. Forty hyporheic temperature anomalies were identified through field investigations and thermal-infrared-radiometry (TIR) in summer 2006. The location of anomalies was associated with specific geomorphic features, primarily bar channels and bar heads that act as preferential pathways for hyporheic flow. Detailed field characterization and groundwater modelling on three Clackamas gravel bars indicate residence times of hyporheic water can vary from hours to weeks and months. This was largely determined by hydraulic conductivity, which is affected by how recently the gravel bar formed or was reworked. Upscaling of modelled discharges and hydrologic parameters from these bars to other anomalies on the Clackamas network shows that hyporheic discharge from anomalies comprises a small fraction (≪1%) of mainstem discharge, resulting in small river-cooling effects (0-012°C). However, the presence of cooler patches of water within rivers can act as thermal refugia for fish and other aquatic organisms making the creation or enhancement of hyporheic exchange an attractive method in restoring the thermal regime of rivers. Copyright © 2008 John Wiley & Sons, Ltd.

Description: Key processes in stream ecosystems are linked to hydraulic retention, which is the departure of stream flow from ideal 'plug flow', and reflects fluid movement through surface and hyporheic storage zones. Most existing information about hyporheic exchange is based on flume studies or field measurements in relatively steep streams with beds coarser than sand. Stream tracer studies may be used to quantify overall hydraulic retention, but disaggregation of surface and hyporheic retention remains difficult. A stream tracer approach was used to compute the rates at which stream water is exchanged with water in storage zones (total storage) in short reaches of two small, sand-bed streams under free and obstructed flow conditions. Tracer curves were fit to the one-dimensional transport with inflow storage model OTIS-P. Networks of piezometers were used to measure specific discharge between the stream and the groundwater. In the sand-bed streams studied, parameters describing total retention were in the upper 50% of data compiled from the literature, most of which represented streams with beds coarser than sand. However, hyporheic storage was an insignificant component of total hydraulic retention, representing only 0.01-0-49% of total exchange, and this fraction did not increase after installation of flow obstructions. Total retention did not vary systematically with bed material size, but increased 50-100% following flow obstruction. Removal of roughness elements, such as large wood and debris dams, is detrimental to processes dependent upon transient storage in small, sand-bed streams. Copyright © 2007 John Wiley & Sons, Ltd.

Description: Stream-gauge data indicate that the flow of the Yellow River has declined during the past several decades. Zero flow in sections of the river channel, i.e. the Yellow River drying-up phenomenon, has occurred since the 1970s. In this paper we present an analysis of changes in the spatial patterns of climatic and vegetation condition data in the Yellow River basin based on data from meteorological stations and satellites. The climatic data are from 1960 to 2000 and the vegetation condition data are from 1982 to 2000. The angular-distance-weighted interpolation method is used to get climatic data coverage from station observations. The spatial distribution of tendency is detected with Student's t-test. The spatial patterns of climatic and vegetation condition change was analysed together with the statistical data on human activities. The analysis indicates that the precipitation decreases and temperature increases in most parts of the Yellow River basin, the evaporative demand of the atmosphere decreases in the upper reaches and increases in the lower reaches, and human activities have improved the vegetation condition in the irrigation districts. The Loess Plateau, the Tibetan Plateau, and the irrigation districts are respectively suggested as precipitation, temperature, and human activity hot spots of the Yellow River drying-up phenomenon. Copyright © 2007 John Wiley & Sons, Ltd.