ALBERT

Description: Streams draining the Barrier Range uplands in arid western N.S.W. are ephemeral and undergo rapid channel contraction away from the uplands as a consequence of transmission loss. These processes are documented on the basis of surveys of channel form and bed material at sequential sites located along the contracting lowland reaches of two representative streams. Channel width and depth display considerable fluctuation downstream, but cross‐sectional area and maximum bed surface grain size decline in a very regular manner. Flood discharge, estimated from the channel capacity and predicted critical and mean flow velocities, also declines regularly. the trends are well fitted by log‐linear models, and are reported in terms of a half‐distance, the channel length in km over which the value of a morphometric parameter declines by 50 per cent. Rates of channel contraction and transmission loss are inferred to be inversely proportional to the volume of flow delivered from the upland section of the drainage basin. Unusual channel characteristics, including extensive tree growth in the bed, make application of ordinary flow equations difficult, because friction factors cannot be estimated with confidence. Systematic changes in the nature of the bed surface in contracting streams such as those studied here also have implications for the application of critical velocity equations, and highlight a need for further study of desert channels. Copyright © 1992 John Wiley & Sons, Ltd

Description: A rainfall and run‐off model has been developed which is based on a rectangular grid cell network. the run‐off in each cell is estimated empirically and is routed through the network to the principal drainage lines. Information on the land cover in each 50 × 50 m cell is interpreted from remotely sensed data, gathered by an orbiting satellite. Values of topographic parameters for each cell are derived from a digital model of the terrain. Other more conventional data are acquired by digitizing maps. the large amounts of data required in this approach are handled by a geographical information system (GIS), which is a management system specially designed for data with spatial characteristics. a GIS has functions which allow the user to combine the many layers of data within the GIS arithmetically or logically to provide fresh information. At the current stage of development the GIS provides estimates of the United States Department of Agriculture Soil Conservation Service curve number for estimating the run‐off in each cell. an analysis of the digital terrain model defines the pathway taken by run‐off from each cell and the run‐off is routed from cell to cell as far as the principal drainage lines, where a conventional hydraulic analysis is used. the model benefits from a simple and robust approach to run‐off estimation distributed on a very fine grid. an important feature of the model is its ability to use historical satellite images to estimate changes in the catchment's response over a period of time. Future changes in land use May, also be easily incorporated into the GIS. the model is being tested on data from the Tywi catchment in West Wales, UK, which had undergone large changes in land cover due to forestation. Copyright © 1992 John Wiley & Sons, Ltd

Description: The relatively high cost of commercially available turbidity meters has inhibited detailed and intensive research on spatiotemporal patterns of suspended sediment transport. We describe here the electronic and physical design of an inexpensive turbidity sensor which is easy to construct, simple to interface with portable millivolt meters, dataloggers, computers, or chart recorders, consumes exceptionally small currents, and is robust and reliable. the very low individual cost allows a large number of sensors to be distributed throughout the water body of interest to facilitate turbidity mapping. Turbidity profilers to detect vertical or lateral turbidity changes in rivers, lakes, estuaries, or near‐shore zones are also shown to be feasible. Test data are presented from a highly turbid glacial river in southern Iceland. Copyright © 1992 John Wiley & Sons, Ltd

Description: This paper is the second in a series of three papers, dealing with the hydrology of a forested lowland catchment, within the context of soil acidification research. the hydrological behaviour of the unsaturated soil zone is described with the numerical simulation model SWIF. the first paper presents a site specific model calibration and discusses the implications of the hydrological behaviour for soil acidification (Bouten et al., 1992). the present paper deals with the extension of the model results from one specific site to a larger research area. a third paper gives a model description and discusses its numerical behaviour (Tiktak and Bouten, 1992). In order to evaluate the effects of the field variability of soil horizon thicknesses, the model SWIF is validated by using measured groundwater table dynamics of three sites, each having different soil horizon thicknesses. Subsequently, a sensitivity analysis is carried out in order to select the location‐dependent model parameters that cause the main variation in hydrological behaviour. Finally, the spatial patterns of model results and of the location‐dependent model parameters are compared. The drainage depth and the depth of the boundary between the sandy top soil and the underlying boulder clay appear to be the key parameters that cause large differences in transpiration and in the vertical distribution of root water uptake and soil water fluxes. Spatial patterns of model results, therefore, also show resemblance with the spatial patterns of these location‐dependent model parameters. Simulation results for a reference location with averaged soil horizon thicknesses turn out to be beyond the 90 per cent confidence interval of the areal mean model results. This emphasizes the necessity to simulate first and then average. Copyright © 1992 John Wiley & Sons, Ltd

Description: Time sequences of tracer release from an alpine snowpack were investigated at Mammoth Mountain, California in 1989. Lysimeter discharge and conductivity were recorded at 30 minute intervals. Three separate applications of chemical tracers were added to the snow surface to provide an ionic signal with known origins in the snowpack. Grab samples of meltwater and snow from snow pits were analysed for chemical composition. There were three distinct discharge periods, each characterized by diurnal fluctuations in discharge and conductivity. An inverse relation between discharge and conductivity was interpreted as the combination of a concentrated signal from regions in the pack less subject to leaching and a relatively dilute signal from near the snow surface where the snow was actively melting Conductivity peaks were highest and diurnal changes greatest immediately following periods of freezing. Grab samples showed little correlation with either 30 minute or daily average conductivity. Relative concentrations of individual ions in meltwater were similar between samples. Non‐systematic grab sampling of snowpack meltwater is shown to be potentially misleading because of multiple ionic pulses over the ablation season and strong diurnal fluctuations in chemical concentrations. Continuous measurements of discharge conductivity are a good indicator of diurnal and seasonal changes in the rate of ion release from the snowpack, and should be used to guide sampling. Composite, or time‐integrated samples rather than grab samples may be required to estimate daily and weekly rates of ion release in melting snow. Copyright © 1993 John Wiley & Sons, Ltd

Description: Environmental magnetism can be used for sediment source tracing in situations such as stream junctions where two catchments deliver magnetically distinguishable, well combined average source mixes to a trunk stream. Consistent mineral magnetic parameter relationships show that spatially and temporally constant magnetic mineral assemblages occur along reaches of natural streams. For most of the confluence mixing situations examined it is possible to distinguish between tributaries using magnetic parameter relationships. Using these relationships, relative tributary contributions to the resultant downstream mix can be quantified. The method can be used for tracing suspended and bedload sediments so that the principal source catchments can be determined by a sequence of measurements at stream junctions along a drainage network. There is considerable potential for using this new and easily applied method for studies of sediment delivery processes and sediment movement in fluvial environments. Copyright © 1993 John Wiley & Sons, Ltd

Description: Basin lag time varies not only between basins but also within a basin. To explain this variation, the basin lag time was hypothesized as a function of the ratio of the channel length from the centroid to the outlet of the basin, divided by the velocity of flow at the gauging site at the time of passage of peak discharge. The records of six basins were used to test this hypothesis. The results are not incompatible with this hypothesis. Copyright © 1993 John Wiley & Sons, Ltd

Description: Causes of recent salinization of numerous plots in the Yizre'el Valley of Israel were examined through a detailed field study of two severely affected sites. in particular, the theory of artesian influence on salt build‐up in the upper cultivated soil layer was investigated. Two piezometer nests and 12 wells were installed to study the subsurface hydraulic regime. Water samples and soil extracts were taken to characterize the chemical composition down to 10m. No significant head differences were measured at the lower site, while at the upper site 96 per cent of the head that existed at the deep (7.5 m) artesian layer was dissipated within the overlying thick clay layer. Slight head differences were noted in the shallow layers. the deep‐lying, coarse‐textured aquifer differs markedly from the upper confining layers and constitutes an independent water body that has little relevance to surface processes. Chemical and hydrological analyses indicate that applied low‐quality irrigation waters May, be the primary cause of downward‐moving salinity and alkalinity which, in turn, affect soil permeability and site productivity. Copyright © 1992 John Wiley & Sons, Ltd

Description: Despite considerable research performed on forested catchments in the Ouachita Mountains of Oklahoma and Arkansas, little information on hydrological processes in operation is available. Based on catchment physical characteristics, subsurface flow was thought to be an important hydrological process in the region. Therefore, this study was undertaken to determine the occurrence, rates, timing and volumes of subsurface flow, and to estimate the importance of subsurface flow as a streamflow generating process. Subsurface flow was collected from three hillslope sites on a 7.7 ha forested catchment. Hillslope sites drained through natural seepage faces located near stream channels. Subsurface flow was collected from three depths at each hillslope site, below the litter layer, below the a horizon, and within the B horizon (Bt21). Subsurface flow occurred and was measured during 11 of 31 rainfall events. Subsurface flow responded rapidly to the initiation of and to changes in intensity of rainfall at all depths. the rapid response was indicative of flow through soil macropores. B horizon subsurface flow commenced within 10 to 180 min of the initiation of rainfall. Multiple linear regression showed that the volume of subsurface flow generated during a given storm was directly related to rainfall depth and a 7‐day antecedent precipitation index used to represent antecedent water content. About 67 per cent of the total subsurface flow collected during the study was produced in one large storm under wet antecedent conditions. the storm was equal to the 2‐year, 24‐hour storm for the region. Measured subsurface flow volumes were extended to the watershed scale to provide estimates of catchment‐wide contributions to streamflow. It was estimated that subsurface flow contributed from 1 to 48 per cent of total quickflow measured at the catchment outlet. Based on the timing of subsurface flow, it was estimated that subsurface flow May, contribute up to 70 per cent of quickflow before and soon after peak flow. Copyright © 1992 John Wiley & Sons, Ltd

Description: Environmental tritium was measured in 33 natural water samples representative of precipitation, stream runoff, and groundwater (derived principally from production wells) within the Georgia Piedmont Province. Major ion analyses were used to assist in the interpretation of the tritium results. Tritium concentrations were significantly greater within shallow groundwater derived from the regolith (28–34 TU) and stream runoff (25–30 TU) than within recent rainfall (4–17 TU). Based upon the decay‐corrected tritium input function, this probably indicates that at least some of the shallow water is stored within the regolith for a period of approximately 25 years. A ‘post‐bomb’ component of recharge was present in all groundwater derived from production wells in the study area. Groundwater sampled from the bedrock aquifers was commonly less tritiated than either stream runoff or shallow water stored in the regolith. the lower tritium concentrations May, have resulted from the mixing of ‘pre‐bomb’ water stored within the fractures or the transitional zone directly above the bedrock and modern water stored in the shallow regolith. the preponderance of modern water provides evidence that groundwater flow paths are areally restricted within this setting, probably confined to local surface water drainage basins. the residence time of groundwater in the Piedmont is limited by the lack of deep, gravity‐driven regional flow and the localized vertical flow induced by pumping. the results of this study indicate that relatively small tritium concentration variations (10‐20 TU) May, have regional hydrological significance in the southeastern Piedmont Province and similar settings. Copyright © 1992 John Wiley & Sons, Ltd

Description: The different depth penetration characteristics of 137Cs, 7Be and 210Pb excess in undisturbed soils can be used to identify erosion processes by analysis of sediments derived from surface erosion. Caesium‐137 concentrations (half‐life 30 years) typically decrease to half the surface value at between 30 and 50 mm. Beryllium‐7 (half‐life 53 days) has half‐penetration depths of between 0.7 and 10 mm, whereas 210Pb excess (half‐life 20.2 years) has half‐penetration depths between 10 and 30 mm. Experiments designed to determine the applicability of these depth penetration characteristics to soil erosion studies are reported. Surface runoff was artificially generated at two locations in a grazed paddock using a rainfall simulator. Suspended sediment was extracted from runoff and analysed for natural and artificial gamma emitting radio‐nuclides. Suspended sediment derived from sheet flow contained initially high values of 137Cs, 7Be and 210Pb excess. As the experiment continued 137Cs concentrations remained high, but 7Be and 210Pb excess value decreased with time. This is interpreted as indicating a change from sheet dominated erosion to rill dominated erosion. During a second experiment artificial rain was allowed to fall onto an eroded gully wall. The derived suspended sediment contained no detectable 137Cs, 7Be or 210Pb excess. Overland flow from above the gully wall was then allowed to run down the gully face and mix with the water falling directly onto the gully wall. There was no detectable change in the radionuclide signature, showing that the gully wall was the predominant source of sediment. This was tested independently by mass balance and 226Ra to 232Th ratios. The good correlation between 210Pb excess and 7Be at this site suggests that the differential technique described here may be applicable over time‐scales longer than are possible with 7Be. It may therefore be practical to examine catchment erosion history through analysis of 210Pb excess and 137Cs in sediment cores. Copyright © 1993 John Wiley & Sons, Ltd

Description: Samples of snowpack leachate were collected over a 60 day period of the spring melt season in 1988 and 1989 at a 10 km2 upland catchment in the Cairngorm mountains of Scotland. These were analysed for major ions to assess snowpack chemistry dynamics through the spring and to assess the melt water influence on stream water chemistry. The data clearly show preferential elution of sulphate and nitrate over chloride and hydrogen over the other cations during the early melt of 1988. Following the addition of ions to the snow surface, either as snow or later in the season as rain, the elution sequence is reproduced. Comparison of leachate chemistry with stream chemistry samples taken at the basin outlet indicate that snow pack melt water contributes directly to stream water. The stream water chemistry signal is, however, noisy and the stream concentrations are considerably damped relative to the snowpack leachate. This is thought to be a consequence of differential melting within the catchment as the snowpack at lower altitudes is at a more advanced stage of melt and so holds fewer solutes and mixing with groundwater contributions. Temperature observations at different altitudes within the catchment support this interpretation. Copyright © 1993 John Wiley & Sons, Ltd

Description: Remote sensing technology has matured significantly over the past decade. Operational satellites provide reliable, periodic coverage for all areas of the Earth. Data from these satellites are in a digital format that provides enhanced flexibility in hydrological modelling. Considerable advances in acquiring hydrological data from airborne and in situ sensors have also been achieved. Additionally, data from non‐traditional remote sources such as weather radar from which spatial and temporal rainfall rates may be estimated are widely available. These new data acquisition capabilities have been paralleled by equal advancements in digital array processing and geographic information systems, which allow the effective extraction of both temporal and spatial information. This paper examines the use of object‐oriented programming techniques to create dynamic hydrological models, and explores their potential to receive real and near real‐time data from remote sensors as input to improve hydrological forecasting. In particular, the COE SSARR model is used to illustrate how an established hydrological model may be adapted to create a dynamic object model. Copyright © 1993 John Wiley & Sons, Ltd

Description: Current and projected UK activities with the Système Hydrologique Européen (SHE) hydrological modelling system are examined. Development of the SHE arose from the need for a new modelling approach for use in assessing the environmental impacts of river basin development and the system is particularly suited to predicting the impacts of land use and climatic changes and to applications to basins with sparse data sets. the basic hydrology model is now being developed into a powerful contaminant and sediment transport modelling system called SHETRAN‐UK and components are also being proposed to account for landslide and gully erosion. Applications of the SHE have been made at spatial scales ranging from 30 m2 to 5000 km2 and in a variety of environments. These have demonstrated an ability to achieve calibration on the basis of short time series records and field evaluation of parameters, to provide multiple outputs on a spatially and temporally distributed basis, and to explore basin response mechanisms. They have also indicated the importance of integrating field measurements within the calibration process. the effect of the scale of model grids on parameter evaluation and on simulation results still needs to be investigated and there is a need for field process studies in areas where there is a poor understanding, to improve certain of the process representations within the SHE. However, new ideas are being explored to account for subgrid spatial variability in parameter values and to develop a validation methodology for testing the predictive capability of the SHE. Future developments will include the use of geographical information systems and data processing packages to aid data handling, expert systems to improve the efficiency of calibration, and parallel processing and other new computational techniques. an expanding range of applications will see physically based hydrological modelling systems at the core of decision support systems and integrated at the continental scale with general circulation modelling systems. Copyright © 1992 John Wiley & Sons, Ltd

Description: Sediment redistribution within near‐level agricultural fields in the Gray Wooded soil zone of Saskatchewan was studied using the artificial environmental tracer caesium‐137 (137Cs). the objective of this study was to estimate erosion rates caused by wind erosion, and land clearing techniques (i.e. bulldozing). Net rates of erosion and deposition were quantified over the past 30 years on three fields. Wind erosion was estimated to be approximately 1.0 t ha−1 y−1 on a near‐level field, with 50 per cent of the sampling sites having erosion rates in excess of soil formation. Bulldozing produced median net sediment flux values of between 40 and 90 t ha−1 y−1. in addition, between 65 and 85 per cent of the sampling sites had erosion rates in excess of the maximum tolerable limit (i.e. 11.0 t ha−1 y−1). These results indicate significant accelerated erosion results from land clearing techniques used in central Saskatchewan. Bulldozing of the fields removed the LFH‐horizon and exposed the underlying mineral horizon. Bulk densitites of the 0 to 15 cm layer in the cleared fields were 27 to 55 per cent greater than the comparable depth increment within the undisturbed forest site. Organic carbon concentrations within the 1930s, 1979, and 1987 fields were decreased by 47, 42, and 37 per cent, respectively following cultivation and bulldozing. Decreases in total nitrogen for the cultivated fields ranged from 33 to 38 per cent. Copyright © 1992 John Wiley & Sons, Ltd

Description: Snow cover patterns in a 9.4 km2 basin in the Austrian Alps are examined during spring and summer 1989. Digital mono‐plotting from oblique aerophotographs is used for mapping. on the basis of a square grid with 25 m spacing, snow cover as mapped during nine surveys is analysed as a function of elevation and slope. During winter conditions the snow cover is found to be much better related to these terrain features than during the late ablation period. Copyright © 1992 John Wiley & Sons, Ltd

Description: A combination of hydrometric data and observations of natural isotope (oxygen‐18) variations in saturation overland flow and stream discharge were used to investigate the sources of storm run‐off in a headwater swamp located in a permanent groundwater discharge zone near Toronto, Canada. The results of a two‐component hydrograph separation indicated that pre‐event water formed 80–90% of the stream hydrograph volume for six of the seven storms analyzed in June–November 1990. However, the instantaneous event water contribution showed considerable variability, ranging from maximum values of 20–25% for four moderate intensity storms to 63% for a high intensity thunderstorm with a return period of two years. The relative contribution of event and pre‐event water to storm run‐off from saturated areas and small streamlets within the swamp was similar to the main outlet stream. The dominance of pre‐event water during storms could be accounted for by the mixing of a small volume of event water with a large pool of pre‐event water on the surface of permanently saturated areas within the swamp. Occasional storms of high intensity or long duration produced a greater shift towards an event water signature in the saturated areas and a larger event water contribution to the outlet stream hydrograph. Copyright © 1993 John Wiley & Sons, Ltd

Description: Soil moisture is one of the few directly observable hydrological variables that has an important role in water and energy budgets necessary for climate studies. At the present time there is no practical approach to measuring and monitoring soil moisture at the frequency and scale necessary for these large scale analyses. Current and developing satellite systems have not addressed this important question. A solution utilizing passive microwave remote sensing is presented here and an optimum system, soil moisture estimation algorithms and a microwave simulation model are described. Copyright © 1993 John Wiley & Sons, Ltd

Description: Under controlled laboratory conditions, artificial rain leaches solute from snow columns, and gives rise to leachate with a composition similar to snowmelt, in addition to the solute initially present in the artificial rain. the initial concentration of ions in the leachate, normalized to the concentration of ions found in the original snow and corrected for the solute present in the artificial rain, is similar to those reported in other laboratory and field studies of snowmelt composition, but there is some evidence that the concentration of leached ions declines more rapidly than during snowmelt. Similarly, as in snowmelt studies, not all ions are leached with the same efficiency. Bearing in mind the confounding influences of snow crystal morphology and snow column hydrology, it seems likely that rain will leach solute from snowpack during rain‐on‐snow events, in a manner similar to leaching by snowmelt, and that the precise composition of the leachate will depend on the hydrological routing of rain‐meltwater mixtures through the snowpack. Copyright © 1992 John Wiley & Sons, Ltd

Description: Erosion of soil from pre‐afforestation plough furrows has been measured on four soil types in Scotland for 12 to 18 month periods between 1987 and 1990. Rainfall‐run‐off was also measured at one site. Run‐off is directly proportional to furrow length and rainfall intensity, and for a wide range of intensities (typically 〉 6 mm hr−1) small amount of soil is flushed out of the furrows. However, for furrow spacings of 3.8 m, a critical downslope run‐off increment associated with significant soil loss is of the order of 25 cm3 s−1 m−1, which is in accord with a storm of five years return period and a maximum intensity of 25 mm hr−1. The total run‐off volume for any hydrograph is commensurate with the total rainfall in the rainstorm — typically 40–80% by the hydrograph peak and approaching 100% by the end of the hydrograph; i.e. long term storage is negligible. A positive relationship was recorded between furrow length, slope angle and sediment yield, with deposition predominating in furrows less than 30 m in length on slopes less than a few degrees. Soil loss is proportional to the excess streampower expended by the run‐off with an exponent in the range 1–1.5. For the soils examined, significant differences in soil loss when comparing sites for low power expenditure become undifferentiated at high power expenditures. For the rainfall regimes monitored, maximum soil losses were in the region of 40 kg per meter run‐length of furrow, when soil peds were ripped from the bed. Laboratory data concerning the critical erosion threshold power and shear stress to erode soil peds are in general accord with the threshold furrow run‐lengths defined using the field data for a five year storm and the soil losses observed. Copyright © 1993 John Wiley & Sons, Ltd

Description: Using current meters to estimate flows in fast mountain streams is difficult and inaccurate. The salt dilution method offers an easier and more accurate alternative. The method has been used for many years but is time consuming and messy because of the need to mix chemical solutions and measure chemical concentrations in the field. A computer program has been developed which uses a laptop computer to calculate the mixing length and the mass of salt needed. The program controls the conductivity measurements and calculates the streamflow directly in the field. The development of this program is described and examples are presented of the application of the method in the Rocky Mountains of Alberta and British Columbia. Copyright © 1993 John Wiley & Sons, Ltd

Description: The uncertainty in a transducer/tensiometer system was assessed with temperature and pressure calibrations. A reference transducer/tensiometer pair was used to factor out temperature related deviations from two monitoring pairs. The reference pair removed most of the deviations, resulting in a high estimate of precision. In contrast to earlier reports of high accuracy, these estimates of accuracy were considerably reduced by a time correlated residual pattern. The calibrations suggested that the electronic components may be responsible for these residual errors and illustrated the need for experimentation which isolates the error among groups of components. The complexity of transducer/tensiometer networks, and the differing response of each component to thermal loading, demonstrated the necessity of using a reference system, which when properly designed can yield reliable pressure readings for soil water. Copyright © 1993 John Wiley & Sons, Ltd

Description: In the last 20 years remote sensing research has led to significant progress in monitoring and measuring certain snow hydrology processes. Snow distribution in a drainage basin can be adequately assessed by visible sensors. Although there are still some interpretation problems, the NOAA‐AVHRR sensor can provide frequent views of the areal snow cover in a basin, and snow cover maps are produced operationally by the National Weather Service on about 3000 drainage basins in North America. Measurement of snow accumulation or snow water equivalent with microwave remote sensing has great potential because of the capabilities for depth penetration, all‐weather observation and night‐time viewing. Several critical areas of research remain, namely, the acquisition of snow grain size information for input to microwave models and improvement in passive microwave resolution from space. Methods that combine both airborne gamma ray and visible satellite remote sensing of the snowpack with field measurements also hold promise for determining areal snow water equivalent. Some remote sensing techniques can also be used to detect different stages of snow metamorphism. Various aspects of snowpack ripening can be detected using microwave and thermal infra‐red capabilities. The capabilities for measurement of snow albedo and surface temperature have direct application in both snow metamorphism and snowpack energy balance studies. The potentially most profitable research area here is the study of the bidirectional reflectance distribution function to improve snow albedo measurements. Most of the remote sensing capabilities in snow hydrology have been developed for improving snowmelt‐run‐off forecasting. Most applications have used the input of snow cover extent to deterministic models, both of the degree day and energy balance types. Snowmelt‐run‐off forecasts using satellite derived snow cover depletion curves and the models have been successfully made. As the extraction of additional snow cover characteristics becomes possible, remote sensing will have an even greater impact on snow hydrology. Important remote sensing capabilities will become available in the next 20 years through space platform observing systems that will improve our capability to observe the snowpack on an operational basis. Copyright © 1993 John Wiley & Sons, Ltd

Description: Solute leaching in unsaturated soil is influenced by the variability in hydraulic functions (water retention and conductivity) that govern the flow process. Variability in measured soil hydraulic functions of a coarse‐, medium‐ and fine‐textured soil group was quantified with the scaling theory of similar media. Solute leaching in these soils was calculated with Monte Carlo simulation assuming, successively, hydraulic conductivity, K, volumetric water content, 0, and pressure head, h, to be constant. In addition to variability in hydraulic functions, variability in the solute retardation factor was also taken into account. To examine this effect five solutes were considered: a conservative solute (chloride), a non‐retarded solute subject to decay (nitrate), a retarded solute that does not decay (cadmium) and two organic solutes which are retarded but have different sorption and decay parameters (the pesticide atrazine and a chlorinated hydrocarbon). The numerical results obtained with Monte Carlo simulation were in a number of instances verified with analytical solutions. The three soil groups distinguished showed considerable differences in vulnerability for leaching of the five solutes, emphasizing the importance of the effect of variability in soil hydraulic functions when studying solute leaching. Numerical and analytical results showed good agreement. Therefore, in relatively simple situations analytical solutions are attractive. However, in complicated situations, analytical solutions are cumbersome and numerical solutions are the only realistic alternative. Copyright © 1993 John Wiley & Sons, Ltd

Description: Bypass flow in structured soils is dominated by soil hydrological processes, such as rain intensity, initial pressure head of the soil, surface storage of rain, horizontal contact area and absorption rate, and hydraulic conductivity of the soil matrix. This study was conducted to determine the relative impact of these processes in different soil types. A quasi 3‐dimensional simulation model was used to calculate the effects of these soil hydrological input parameters on surface infiltration, macropore flow (with related horizontal absorption) and drainage. For light textured soils, surface infiltration was the most important term in the water balance. Heavy textured soils, in contrast, had drainage as the main term. In the latter soils bypass flow, when occurring, was almost equal to the amount of rain applied, indicating that absorption processes were strongly reduced. Lateral absorption on macropore walls was a minor fraction in the total mass balances, due to limited contact area and relatively weak diffusivity forces. Surface infiltration is a crucial parameter in bypass flow and is mainly dependent on rain intensity, initial pressure head and conductivity of the soil matrix. This requires measurement methods for hydraulic conductivity that specifically consider the effect of macropores. Copyright © 1993 John Wiley & Sons, Ltd

Description: The portable surface capacitance insertion probe was used to measure the in situ water content of near surface soil layers. The probe readings were calibrated against gravimetric samples collected over a wide range of water contents, and were found to be very closely correlated. The capacitance probe was used repeatedly in time and space at a field site where ridges and furrows ensured a regular pattern of soil water variations. The observed spatial variations of the water content were related to topography and land mangement. The degree of variability was dependent on the average water content. Copyright © 1993 John Wiley & Sons, Ltd

Description: The composition and amount of colloidal and suspended participate matter transported during a small flood event in Magela Creek in tropical northern Australia was investigated. The flood studied constituted approximately 3 % of the total annual flow, most (90%) of which occurred between mid‐January and mid‐February of the study year. Three fractions were separated from water samples using a sequential method involving a continuous flow centrifuge to separate suspended particulate matter (SPM; nominally 〉 1 μm) followed by hollow fibre filtration, first using a 0.1 μm filter to separate course colloidal matter (CCM; nominal size 1–0.1 μm) and then a 0–015 μm filter to separate fine colloidal matter (FCM; nominal size 0.1–0.015 μm). The SPM was predominantly inorganic (organic matter 21 %), whereas the colloidal fractions were dominantly organic matter (CCM 60%; FCM 83%). Analysis of individual particles using electron microprobe and automated image analysis indicated that the mineral fractions in both the SPM and CCM were dominated by iron‐enriched aluminosilicates (including kaolinite) (72–82%) and quartz (9–10%), indicative of a highly weathered and extensively laterized catchment. Surprisingly there was very little difference in the composition of the SPM or CCM fractions during the flood event studied, which may indicate either that sediment availability was restricted following the major run‐off events in January and February, or that all the sediment sources within the catchment are geochemically similar. Approximately the same amounts of particulate (20 tonne), colloidal (21 tonne) and dissolved material (17 tonne) were transported during the 25 hour period of the main flood peak; over 90% of the colloidal matter was 0.1–1.0 μm in size. These data suggest that previous estimates of the amounts of particulate (and colloidal) matter transported by Magela Creek, which were based on suspended solids measurements, may have underestimated the particulate matter load by as much as 50%. It is possible that the relatively high proportion of colloidal matter is unique to Magela Creek because coagulation and aggregation of colloidal matter to particulate matter is slow due to the very low concentations of calcium and magnesium in these waters. However, if the result is more widespread, there are important implications for the global estimates of fluvially transported particulate and dissolved materials as many of the previous studies may have underestimated the particulate load and overestimated the dissolved load. Copyright © 1993 John Wiley & Sons, Ltd

Description: Soil water dynamics in a forested lowland catchment are studied in order to support a research on biogeochemical processes and soil acidification in particular. The numerical simulation model SWIF, describing soil water dynamics in forests, is calibrated and validated for a specific site by using three years of daily measurements of pressure head profiles. on the basis of model results, the hydrological behaviour of the forest system is discussed, with special attention to transpiration and to the vertical and temporal dynamics of soil water contents, root water uptake and soil water fluxes. as water uptake by oaks and beeches is restricted to the unsaturated soil zone, high groundwater tables in the rather poorly drained duplex soil appear to have a large impact on the soil water dynamics. Suggestions are made on the implications of the hydrology for soil acidification. This discussion shows that a thorough knowledge of the hydrological behaviour of the system can greatly contribute to the understanding of biogeochemical processes and soil acidification. This paper is the first in a series of three papers. the second discusses the possibilities of extrapolating model results from the calibration site to other locations within the research area, which have varying soil horizon thicknesses (Bouten and Witter, 1992). the third paper gives a full description of the model SWIF with some technical details. It also discusses its numerical behaviour (Tiktak and Bouten, 1992). Copyright © 1992 John Wiley & Sons, Ltd

Description: A sediment budget was developed for the 1.7 km2 Maluna Creek drainage basin located in the Hunter Valley, New South Wales, Australia, for the period 1971‐86. the impact of viticulture, which commenced at Maluna in 1971, was studied using erosion plots, with caesium‐137 as an indicator of both soil erosion and sedimentation. Two methods were used to estimate vineyard soil losses from caesium‐137 measurements. Sediment output from the catchment was measured for three years, and extrapolated from readings taken at a nearby long‐term stream flow gauging station for the remaining 13 years. Relative amounts of soil loss from forest (60 per cent basin area), grazing land (30 per cent) and vineyards (10 per cent) were calculated. Soil losses by rain splash detachment were ten times greater from bare/cultivated sufaces than from the forest. Erosion plots of area 2 m2 showed no significant differences in soil loss between forest and grassland but, under bare soil, losses were 100 times greater. the 137Cs method was employed to calculate net soil loss from all vineyard blocks using both a previously established calibration curve and a proportional model. the latter method gave estimates of soil loss which were 3‐9 times greater than by the calibration curve, and indicated that average soil losses from the vineyard were equivalent to 62 t ha−1 y−1 (1971‐86). It was estimated that the forest contributed 1‐8 per cent, the grazing land 1.6 per cent, and the vineyard 96.6 per cent of the total soil loss during that period. Sediment storages within the fluvial system adjacent to the vineyard ws 9460 t for the period, whereas sediment output was equivalent to 215 t km−1 y−1. Independent measurements of soil erosion, storage, and output showed that 56 per cent of the eroded sediment remained in the catchment, and 34 per cent was transported out by Maluna Creek. the budget was able to be balanced to within 10 per cent. Copyright © 1992 John Wiley & Sons, Ltd

Description: A physically‐based semidistributed model, TOPMODEL, is applied to a 340 hectare spruce forested catchment in mid‐Wales. the model is calibrated to runoff and the subsurface flow is divided into components of flow identified by depth of origin. in addition, chemical mixing techniques are used to provide a hydrograph separation between acidic soil waters and well buffered deep waters. the short‐term variations in the components of flow identified by these two approaches compare well. Copyright © 1992 John Wiley & Sons, Ltd

Description: During the summer of 1989 surface sediment samples were collected in Lake Coeur d'Alene, the Coeur d'Alene River and the St Joe River, Idaho, at a density of approximately one sample per square kilometre. Additional samples were collected from the banks of the South Fork of the Coeur d'Alene and the Coeur d'Alene Rivers in 1991. All the samples were collected to determine trace element concentrations, partitioning and distribution patterns, and to relate them to mining, mining related and discharge operations that have occurred in the Coeur d'Alene district since the 1880s, some of which are ongoing. Most of the surface sediments in Lake Coeur d'Alene north of Conkling Point and Carey Bay are substantially enriched in Ag, As, Cu, Cd, Hg, Pb, Sb and Zn relative to unaffected sediments in the southern portion of the lake near the St Joe River. All the trace element enriched sediments are extremely fine grained (mean grain sizes « 63 μm). Most of the enriched trace elements, based on both the chemical analyses of separated heavy and light mineral fractions and a two step sequential extraction procedure, are associated with an operationally defined Fe oxide phase; much smaller percentages are associated either with operationally defined organics/sulphides or refractory phases. The presence, concentration and distribution of the Fe oxides and heavy minerals indicates that a substantial portion of the enriched trace elements are probably coming from the Coeur d'Alene River, which is serving as a point source. Within the lake, this relatively simple point source pattern is complicated by a combination of (1) the formation of trace element rich authigenic Fe oxides that appear to have reprecipitated from material solubilized from anoxic bed sediments and (2) physical remobilization by currents and wind driven waves. The processes that have caused the trace element enrichment in the surface sediments of Lake Coeur d'Alene are likely to continue for the foreseeable future. Copyright © 1993 John Wiley & Sons, Ltd

Description: A joint strategy for parameter estimation which can systematically identify the important model parameters is presented. the strategy includes a regionalized sensitivity analysis (RSA) and an automatic parameter calibration technique (APCT). the RSA is based on a large number of Monte‐Carlo simulations to identify the sensitive parameters and to establish a range of appropriate values for each sensitive parameter. the APCT adjusts the values of the sensitive parameters based on changes in the residual variances between the predicted and observed values. the strategy is applied to the watershed acidification model—ILWAS. the strategy succeeds in identifying the sensitive parameter and increases the likelihood of obtaining a global optimal parameter set. Improvements in the model prediction of the streamflow and chemistry are obtained. Copyright © 1992 John Wiley & Sons, Ltd

Description: Particulate matter suspended in the River Severn (Shropshire, UK) consists chiefly of clay‐sized mineral particles, together with living and dead micro‐organisms (algae and bacteria). Its concentration depends strongly on discharge, but the particle size distribution shows no systematic variability. For most samples, the particle volume is log‐normally distributed with respect to diameter, the mean diameter being ca. 9 μm. The particles are mainly aggregates, including some with linear dimensions of the order of tens or hundreds of micrometres. Particle density depends appreciably on size, decreasing from ca. 2.5 × 106 g m−3 at a diameter of 2.5 μm to ca. 1.3 × 106 g m −3 at 20 μm. The collision efficiency factor for particle aggregation is estimated to be 0.01–0.03. At low discharge, the ‘dead zone’ in the River Severn at Leighton is a well defined region of stagnant water behind a gravel bar. The rate of deposition of fine particles on its bed is of the order of tens of grams per square metre per day. Resuspension requires a critical bed shear velocity of 0.03–0.04 m s−1, which occurs at main river discharges greater than about 150 m3 s−1. Under such conditions the gravel bar is underwater and the dead zone is a region of highly turbulent return flow. A simple mechanistic model of particle dynamics in the dead zone accounts reasonably well for particle accumulation rates when run with parameter values based on measured particle and hydraulic properties. Calculations with the model suggest that most of the sedimentation flux to the dead zone bed is due to particles with equivalent sphere diameters in the range 30–240 μm. Simulations indicate that deposition proceeded continuously during spring and summer, whereas repeated deposition and resuspension occurred in autumn and winter. Copyright © 1993 John Wiley & Sons, Ltd

Description: The factors controlling the chemistry of 69 low‐order streams in the Blue Ridge and Valley and Ridge physiographic provinces of Virginia and Maryland were studied over a 13‐month period. Principal component analysis was used to examine regional patterns in stream chemistry and to examine the degree to which the chemistry of low‐order streams is controlled by the bedrock upon which they flow. Streams clustered into regionally isolated groups, strongly related to bedrock type, with SO 2− 4 and HCO − 3 the chemical variables of most importance. Sulphate concentrations appear to be strongly controlled by climate and hydrology, and sorption in the soils within the watershed. Much of the atmospherically derived SO 2− 4 accumulates in watersheds during the growing season and is later flushed out. Weathering reactions were found to be particularly important in the production of HCO − 3 , accounting for 91 per cent on an annual basis, and export of divalent cations from these watersheds, accounting for 48–50 per cent on an annual basis. About half of non‐anthropogenic Na + was derived from weathering of silicates, whereas nearly all K + was identified with leaching by SO 2− 4 . Water chemistry was strongly related to the rock type in the watershed and the weatherability of the component minerals. Rock type is not a randomly distributed function; instead, it is controlled by geologic factors that result in clusters of similar rock types in a given region. When planning large synoptic studies, it is extremely important to consider that a sampling scheme based on random sampling of a non‐randomly distributed function May, not provide the most accurate representation of the variables of interest. Instead, a hierarchical sampling scheme May, be indicated. Our results also suggest that, although one sample in time May, be sufficient to characterize the primary geochemical factors controlling stream chemistry throughout the year, it May, not be sufficient to detect subtle, flow‐related alterations in chemistry. Copyright © 1992 John Wiley & Sons, Ltd

Description: This paper presents an introductory overview of recently developed stochastic theories for tackling spatial variability problems in predicting groundwater flow and solute transport. Advantages and limitations of the theories are discussed. Lastly, strategies based on the stochastic approaches to predict solute transport in aquifers are recommended. Copyright © 1992 John Wiley & Sons, Ltd

Description: The Breton bocage is a landscape of fields enclosed by a network of hedgerow banks and ditches. Organization of this bocage varies considerably in different areas of Brittany. However, one constant feature of the different bocage landscapes is the presence of banks enclosing bottom lands, which enclose elongated plots in the thalweg bottoms. The banks enclosing the bottom lands influence the sensitivity of the basin to surface run‐off and also the presence of excess surface water zones. To analyse the part played by banks enclosing bottom lands, the topography of a typical first order basin was modelled and the existence of such a bank within the catchment was simulated. The effect of the bank on the Kirkby index, a topographical parameter defining the sensitivity of soils to surface run‐off was analysed. Modification of its spatial distribution is considerable for mean values of the index. The saturation zone, the storm run‐off source area, is reduced to that area of bottom land enclosed by the bank; it thus varies very little so that run‐off conditions are almost constant whatever the climatic conditions. From the methodological point of view, the interest of analysing the spatial distribution of morphometric parameters of a catchment may be noted; in the example studied, the heterogeneity of the Kirkby index distribution is an important factor in the analysis. Copyright © 1993 John Wiley & Sons, Ltd

Description: Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified. Copyright © 1992 John Wiley & Sons, Ltd

Description: Discharge of groundwater from a limestone aquifer through floodplain sediments is associated with a large decrease in the nitrate concentration of the water. Results are presented to show that only a small amount of this reduction is caused by dilution of groundwater by water already present within the floodplain sediments; most of the effect is an active reduction process, most probably biological denitrification. The nitrate reduction process appears to operate independently of surface vegetation type and tends to be focused in specific regions of the floodplain where sediments are anaerobic and carbon‐rich. The results suggest that active denitrification can operate throughout the winter, when nitrate concentrations in groundwater are at their highest and that the process remains effective even during periods of maximum run‐off. The results show that undrained floodplains can be used as buffer zones to protect surface waters from groundwater polluted with agriculturally derived nitrate. Copyright © 1993 John Wiley & Sons, Ltd

Description: For many years hydrologists have tried to build physically realistic models which are still simple enough to be fitted to a range of observations made in the field. This is an ongoing process which will become even more difficult as the quality and variety of field and remotely sensed data improves. Hence models must be able to predict soil moisture patterns in time and in space as well as the outflow hydrograph. The model presented here (TOPMODEL) aims to predict the nature of variable source areas in a way that reflects their dynamics over space and time. All component processes are described and shown in operation. As TOPMODEL and similar models have a growing popularity, this paper can be seen as a demonstration of the model's predictive capabilities. The model is applied to the catchments of Plynlimon, mid‐Wales for 1984, 1985 and 1986 data sets. The model has been thoroughly tested and cross‐validated against independent data sets for different time periods, for a separate catchment, for internal gauges and for wet and dry periods. The resulting predicted soil moisture patterns show a small, semi‐permanent variable source area that has the ability during large storms to expand dynamically over short time periods. Spatial predictions of evapotranspiration are also shown which reflect the influence of soil moisture patterns on this process. The weakest component of the model is the representation of root zone evaporation and how this pre‐sets the antecedent condition of the catchment during long dry periods. Copyright © 1993 John Wiley & Sons, Ltd

Description: This paper investigates the spatial and temporal variations of runoff, erosion and rate of sediment transport on an agricultural field submitted to natural rainfalls. The site, located in the Eastern Townships (Québec, Canada), is a corn field (10000 m2) where sheetwash erosion is active. Water (Q) and sediment (Qs) discharges were measured from June to October at eight locations on the field and for ten rainfall events. Analysis of the data was carried out on an aggregate data set and on the distributed measurements in time and space. The results showed that changes in vegetation, soil compaction and crusting are critical in determining temporal variations of runoff and erosion. Until August, the increase in soil compaction reduced infiltration capacity and depression storage and generated greater runoff for a given rainfall intensity (I). Sediment transport decreased as particle detachment is less likely to occur when vegetation breaks the drop impact and the soil surface is sealed. Later in the season, we observed an increase in sediment concentration associated with the presence of burrowing insects and harvest activity, providing loose sediments to the broken down surface. Intercepts and slopes of the relationship between Q and Qs also vary during the period of measurement. High sediment availability over the soil surface in June and October gives high intercept values. The slope of the relationship is more stable but difficult to estimate for extreme events (high values of I or low Q values) where the number of sampled points are small. During a rainfall, the response of the field is dominated by the topography and drainage area. The largest amount of runoff and erosion occurred on straight and steep slopes with small drainage areas, and on converging gentle slopes with large drainage areas. Although aggregate runoff and erosion values are decreasing with drainage area, parameters of the Qs‐Q relationship for different locations on the field are not statistically different. These results bear important consequences for models of sheetwash erosion on agricultural fields. Copyright © 1993 John Wiley & Sons, Ltd

Description: The model SWIF (Soil Water in Forested ecosystems) is presented. SWIF is a model for the simulation of water flow in the unsaturated soil zone, including water extraction by roots and lateral saturated drainage. the model gives a halfimplicit finite difference solution to the flow equation. for minimizing computing time, the model chooses its integration time steps based on the rate of change of soil water conditions. the model is not a conceptually new model. However, it meets the requirements of an entirely modular programme in which new theories can easily be implemented. the hydrology of the canopy and the forest floor is described in independent modules. Simulation results are evaluated in relation to temporal and vertical discretization, using a simulation of soil water dynamics in a forest over a period of two growing seasons. Both the site description and the simulation results are given in an accompanying paper (Bouten et al., 1992). in another paper a sensitivity analysis of the model is given (Bouten and Witter, 1992). In order to evaluate the effects of temporal discretization of boundary condition's, the length of the interval of constant averaged boundary conditions was varied from one hour to one month. the simulated annual transpiration is found to be dependent on this interval for a wet year, but not for a dry year. When the boundary conditions are taken constant for intervals shorter than one day, simulated soil water contents show a highly dynamic behaviour during and directly after heavy rainfall. Then small integration time steps are required and computing time increases strongly. For the evaluation of the effects of vertical discretization, the number of soil layers was varied from 5 to 40. the yearly transpiration appears to be almost independent of the layer thickness as long as the horizon boundaries are not altered, but the temporal distribution of transpiration and water contents are affected. the required computing time for the simulation of the water balance of a full growing season increases from 2.5 minutes for a simulation of five layers to 18 minutes for a simulation of 40 layers. When model results are evaluated on a yearly basis, they appear to be not very sensitive to the temporal and vertical discretization. Only if research aims require more detailed model results on a shorter timescale, higher computing times are to be accepted. Copyright © 1992 John Wiley & Sons, Ltd

Description: Subsurface flow through a small forested hillslope plot in central Scotland has been studied by simulating the flow dynamics using a two‐dimensional saturated‐unsaturated subsurface flow finite element model. Parameter calibration based on the extensive hydrological data available at plot scale, has been performed using various search strategies and alternative objective functions. Good soil water potential simulations were obtained for mainly saturated events, although the simulated throughflows were significantly overestimated. the simulation of unsaturated events was less satisfactory. Throughflow overestimation May, reflect measurement uncertainty, but is also consistent with the effects of macroporosity. Copyright © 1992 John Wiley & Sons, Ltd

Description: A kinematic flood routing procedure has been devised for a small dendritic headwater gully network on the Western slope of Colorado. the program is spatially‐distributed, incorporating lateral inflows from 103 field sites on the network for which channel geometry variables are known. This model, in which a lateral inflow algorithm for the sideslopes between each channel site is convoluted into a Freeze‐type (1978) numerical scheme, is fully developed in this paper. Although the field basis of the lateral inflow algorithm has been tested elsewhere (Faulkner, 1990), sensitivity tests were needed for the roughness and hillslope velocity estimates used in the routing procedure. After these successful tests, a suitably precalibrated run of the model was compared with a field‐monitored runoff event on the watershed, and results again were encouraging. However, peak attentuation downstream was more pronounced in reality than on the simulation, so the model was also modified by inclusion of allowances for transmission loss. the tendency that the model had displayed for peak size attenuation downstream was considerably enhanced. Using the model, the geomorphic role of the flashfloods which affect the watershed in the summer months is briefly considered by applying the model to existing records of local summer storm rainfall events as a basis for event simulation. These simulations show that downstream attenuation of the flood wave on concave networks in steep semiarid terrain was likely to be a common occurrence, possibly resulting in down‐net deposition and differences in geomorphic behaviour between upstream and downstream sites. the discussion is finally broadened to consider the relative importance of ‘common’ as compared to ‘freak’ watershed events in maintaining these differences. Copyright © 1992 John Wiley & Sons, Ltd

Description: Physically‐based models of catchment hydrology are computationally demanding. the cost of even small scale simulations of multidimensional subsurface flow problems is often considered too high and yet May, be important if one is to appreciate the complex flow pathways in heterogeneous catchments. This is likely to be the case for problems concerned with transport of chemical substances in soils, in particular those with some localized origin. Recent advances in computer hardware technology and numerical algorithms are beginning to make detailed simulations more feasible. We discuss here issues relating to using these new tools in modelling hillslope flow processes and document an example three‐dimensional simulation of a heterogeneous Darcian headwater. Copyright © 1992 John Wiley & Sons, Ltd

Description: A 8.9 ha (22 acre) catchment at the Coweeta Hydrologic Laboratory in western North Carolina was cleared of hardwood forest in 1958 and 1959 and seeded to Kentucky 31 fescue grass in 1959 and 1960. Grass production was high in years when fertilizer was applied and water yield was very similar to that expected from the original forest cover. as grass production declined, so water yields rose, with important increases in the magnitude of both low frequency flows and, particularly, in baseflow. in 1967 and 1968, when all vegetation was deadened in the catchment, the discharge levels in all flow frequency classes were higher. Natural revegetation was then allowed and water yields gradually declined towards the expected level, although there remained a tendency for winter flows to remain higher, and for summer flows to be lower than expected. This paper updates the earlier work of Hibbert (1969) and uses flow duration curves to extend his results. Copyright © 1992 John Wiley & Sons, Ltd

Description: Ten large volume water samples were taken from the Rhône River (Switzerland‐France) in November, 1989 for recovery of total suspended sediment by continuous flow centrifugation. the samples were freeze‐dried and analysed for particle size, organic carbon, total nitrogen, and carbonate. for comparative purposes, four bed sediments collected in July, 1989 are also described. the Rhône can be subdivided into three sections on the basis of the origins of the water. the first section is the Upper Rhône River draining into Lake Geneva. Waters are derived from glaciers, with low temperature and conductivity and high turbidity. Suspended sediment is coarse, has a bimodal distribution, and is low in both organic matter and carbonate. the second reach is from Lake Geneva to the confluence with the Saône at Lyon and has warmer water with higher conductivity and very low turbidity. Suspended sediment is higher in organic matter, with high carbonate originating from the lake. the final section is from Lyon to Arles, with warmer water and higher conductivity and turbidity due to modification by the Saône. Sediment is rich in organic matter, which May, account for an observed decline in oxygen in the river waters downstream from Lyon. Carbonate in these sediments also decreases due to increased turbidity from the Saône. Suspended sediments other than from the Upper Rhône show a remarkable consistency in grain size, predominantly in the fine silts (mode 9‐11 μm). This consistency indicates a high degree of suitability for geochemical analysis. Bed sediments were bimodal throughout, with a dominant coarse population in two out of the four samples. Grain size statistical parameters could be easily explained by application of the theory of mixing of two major populations in the sand size (bed traction load) and the fine silt/clay size (suspended sediment load). Copyright © 1992 John Wiley & Sons, Ltd

Description: The state of the art of modelling hydrological systems using distributed modelling techniques is discussed and the theoretical problems caused by the heterogeneities always present in field soil systems are emphasized. It is argued that such heterogeneities need to be considered to develop physically based large‐scale models applicable at the scale of the numerical discretization blocks. Stochastic approaches seem to provide a rational framework for treating the difficult to characterize spatial variability and for establishing a link between parameter uncertainty and prediction uncertainty. It is emphasized that more research in theory development and testing is required before complete large‐scale models are obtained and this had to be carried out jointly with field tests. More research is also required in field measurement techniques to accurately supply the deterministic and statistical parameters required in distributed models. Copyright © 1992 John Wiley & Sons, Ltd

Description: In spite of the important relationship between sediment particle size and the transport/deposition of adsorbed pollutants in fluvial systems, little information regarding the size characteristics of suspended sediment transported by southern Ontario Great Lakes tributaries is currently available. This paper examines long‐term sediment and hydrometric data collected by the Water Resources Branch of Environment Canada in order to provide information on (1) typical particle size distributions of suspended sediment, (2) relationships between source material and particle size characteristics of suspended sediment, and (3) temporal variation in the particle size characteristics of suspended sediment from six southern Ontario rivers. Results illustrate the complex behaviour and variability of sediment particle size transport in these rivers and demonstrate the need for a better understanding of seasonal effects on sediment availability and conveyance processes in fluvial systems. Copyright © 1992 John Wiley & Sons, Ltd

Description: The water balance of a 600 m2 field site on a lateritic hillslope in Kerala, southwest India, has been studied during two southwest monsoon seasons. Surface runoff was of minor importance while infiltration and evapotranspiration were the major components amounting to approximately 2/3 and 1/3 of the rainfall, respectively. Groundwater response was rapid, involving fluctuations of several metres. Recharge mechanisms hypothesized are water movement via preferred pathways from the ground surface to the capillary fringe where rapid rise in groundwater level is brought about by a transmitted pressure pulse. Groundwater recharge was found normally to take place during the southwest monsoon season only. the field study demonstrates that seasonal shallow groundwater recharge representing the major portion of the rainfall May, be observed in this lateritic terrain in the humid tropics. It indicates a good potential for further groundwater development. Moreover, conditions are conducive to a considerable contribution to possible recharge to deeper aquifers. the observed groundwater recharge is the result of a complex process on which further research will throw more light. Copyright © 1992 John Wiley & Sons, Ltd

Description: An integrated programme of hydrological monitoring at the 10 km2 Allt a' Mharcaidh catchment in north‐east Scotland has been based on observations at plot, hillslope and catchment scale. The resonse of the principal soil types has been characterized from a combination of throughflow and three‐dimensional tensiometer data at plot scale, and plot sequences have been used to investigate hillslope scale effects. Seep emergence is associated with downslope drainage and local topographic convergence; in parallel preferential pathways generate a highly dynamic throughflow response. Catchment and subcatchment hydrographs mirror the twin dynamic observed at hillslope scale, and a unified hypothesis of response is presented which is consistent with all scales of observations. Copyright © 1993 John Wiley & Sons, Ltd

Description: Experiments on model and real soil blocks designed to assess the feasibility of using magnetic resonance imaging for three‐dimensional mapping of the time‐varying spatial distribution of water in structured soils are reported. The results show that, notwithstanding inherent problems in imaging natural soils with a significant iron content, experimental parameters can be identified which allow satisfactory images to be obtained. Magnetic resonance imaging may therefore provide important information on soil structure and water movement in dual porosity soils, with attendant benefits for the calibration of models of non‐Darcian flow in such soils. Copyright © 1993 John Wiley & Sons, Ltd

Description: For a large part of the year, the forested catchments in the Keuper formation of east Luxembourg produce more direct run‐off on a storm basis than paired cultivated catchments. The occurrence of shrinkage cracks, their pronounced opening and closing, and the occurrence of natural pipes in the forested environment play a major role in explaining this phenomenon. The effect of land use on storm run‐off is studied in relation to that found for lithology in the same area. Copyright © 1993 John Wiley & Sons, Ltd

Description: Large infiltration ponds (10–15 m2) were used, in conjunction with a ring infiltrometer and a well permeameter, to determine the infiltration characteristics of a complex lateritic soil profile in the jarrah (Eucalyptus marginata) forest of Western Australia. Simultaneous measurements of soil water content and soil water potential allowed a description of the infiltration and redistribution in the soil profile. The infiltration ponds effectively measured the conductivity of a subsurface lateritic duricrust which was found to have a relatively high saturated hydraulic conductivity (Ks) of 2.7 m d−1, despite its apparently massive and extensive nature. Removal of the topsoil identified large (≈1 m2) infilled holes penetrating the duricrust over about 6% by area. Measurements indicated that these large ‘holes’ had a high Ks value (≈ 10 m d−1), whereas the remaining duricrust had a lower Ks value (≈ 2m d−1). These results have implications for probable maximum flood design calculations and assessing the hydrological impact of extensive open‐cut bauxite mining. Copyright © 1993 John Wiley & Sons, Ltd

Description: Although littoral regions in northern lakes may sustain fish spawning grounds, little is known of the temporal or spatial aspects of their thermal and chemical regimes. This shortcoming is due in part to the difficulty in properly sampling these regions throughout the year with adequate spatial resolution. This problem is especially critical in lakes affected by episodic acidification during the spring snowmelt, a period of substantial importance to fisheries recruitment. A device was constructed to alleviate the problems associated with conventional water quality sampling of littoral regions. Constructed of thick walled polyvinyl chloride and permanently installed in the nearshore regions of an Adirondack lake, the episodic event sampler (EES) provided finely resolved (0.25 m) temperature and water chemistry data during the spring snowmelt period (February to May) of 1989. Although the construction and installation of the sampler represented a significant investment in labour and materials, this was offset by the high quality of the data collected. As the samplers were relatively undamaged by freeze‐thaw activity, it is expected that they will continue to provide excellent information for several years. Copyright © 1993 John Wiley & Sons, Ltd

Description: Thinly stratified sedimentary deposits in a heterogeneous field were investigated to obtain basic physical data for the simulation of water flow. A procedure is described which translates a thinly stratified soil profile into a number of functional layers using functional hydrological properties. A functional layer is defined as a combination of one or more soil horizons and should (i) be recognizable during a soil survey using an auger and (ii) show significantly different functional hydrological properties when compared with another functional layer. This procedure gave three easily recognizable functional layers. Sets of hydrological characteristics of these three functional layers were obtained by physical measurements of the soil and by estimation, using textural data for classification into a standard Dutch series. The performance of several combinations of these sets was tested by comparing simulated and measured soil matric potentials for seven plots during one year. The best simulation results were obtained if measured soil hydraulic characteristics were used for relatively homogeneous functional layers and if the soil hydraulic characteristics were estimated at each location for the most heterogeneous layer. Copyright © 1993 John Wiley & Sons, Ltd