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: 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: 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: 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: 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: 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: 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: 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: 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