bluuebunny/crossref_metadata_2025 huggingface dataset:
On numerical errors associated with the iterative alternating direction implicit (Iadi) finite difference solution of the two dimensional transient saturated‐unsaturated flow (Richards) equation
Authors: Parissopoulos G. A. , Wheater H. S.
Published: February 2007

Numerical models for simulation of multidimensional unsaturated flow are becoming increasingly available, but relatively little has been reported on the detailed analysis of numerical errors associated with such schemes. For unsaturated‐saturated flow, further complexity is introduced to the highly non‐linear unsaturated problem as the form of governing equation changes within the flow field. In this paper, two‐dimensional simulation of infiltration to a water table is considered. Numerical errors associated with selection of time step, grid geometry, convergence criteria, and the representation of internodal hydraulic conductivity are discussed with respect to moisture content profiles and mass balance error. Although solution sensitivity to numerical parameters is problem specific, the results presented indicate the nature and magnitude of numerical effects which should not be overlooked in model applications.
Interactions between groundwater seepage and sediment porewater sulphate concentration profiles in lake anna, Virginia
Authors: McIntire Pamela E. , Mills Aaron L. , Hornberger George M.
Published: February 2007

Most sulphur diagenesis models predict that SO42‐ concentrations decrease exponentially with increasing sediment depth and are lower than that of the overlying water throughout the sediments. Low SO42‐ concentrations (less than 0.2 mM) are common in the sediments of Lake Anna that receive acid mine drainage; however, sediment with as much as 20 mM SO42‐ at about 20cm below the sediment surface is also seen in this section of the lake. A decision tree was proposed to investigate the cause of the high SO42‐ concentrations at depth (HSD) in the sediment. The first possibility proposed was that an increase in the quantity of groundwater flowing through Lake Anna sediments may increase groundwater advection of SO42‐ or oxygen which would induce sulphide oxidation. This hypothesis was tested by measuring groundwater flow. HSD profiles were found in a discrete region of the lake; however, stations having these profiles did not have higher groundwater flow than other sites sampled. Alternate explanations for the HSD profiles were that the region in which they occurred had: (1) unusual sediment chemical compositions; (2) a different source of regional groundwater, or (3) a lateral intrusion of high SO42‐ groundwater. There were no differences in sulphide and organic matter concentrations between the two regions. The area which has HSD in the sediment covers a large area in the middle of the lake, so it is unlikely that it has a unique source of regional groundwater. The third alternative was supported by the fact that in all three sample years, HSD stations were located in the preimpoundment stream channel, which is a likely lateral flow path for groundwater containing high SO42‐ concentrations.
Modelling rainfall/watertable relations using linear response functions
Authors: Armstrong Adrian C.
Published: February 2007

Linear system theory can be used to model and predict watertable responses to precipitation inputs in an artificially drained field. The response function is mathematically equivalent to the Unit Hydrograph concept familiar to hydrologists. This paper shows that it is possible to derive such response functions, and comments on the problems encountered in their derivation. Response functions for two contrasted sites are presented, and the possibilities for their use discussed.
A comparison of instrumental dewatering methods for the separation and concentration of suspended sediment for subsequent trace element analysis
Authors: Horowitz A. J. , Elrick K. A. , Hooper R. C.
Published: February 2007

A comparison involving both field and laboratory trials was performed to evaluate the utility of two continuous‐flow centrifuges and a tangential‐flow filtration system for dewatering suspended sediments for subsequent trace element analysis. Although recovery efficiencies for the various devices differ, the analytical results from the separated suspended sediments indicate that any of the tested units can be used effectively and precisely for dewatering. Further, the three devices appear to concentrate and dewater suspended sediments in such a manner as to be equivalent to that which could be obtained by in‐line filtration. Only the tangential‐flow filtration system appears capable of providing both a dewatered sediment sample and a potentially usable effluent, which can be analysed for dissolved trace elements.

The continuous‐flow centrifuges can process whole water at an influent feed rate of 41 per minute; however, when suspended sediment concentrations are low (<30mg−1), when small volumes of whole water are to be processed (30 to 401), or when suspended sediment mean grain size is very fine (<10 μm), influent feed rates of 21 per minute may be more efficient. Tangential‐flow filtration can be used to process samples at the rate of 11 per minute.
A laboratory test of the soil chemical submodels of two models of catchment acidification
Authors: Grieve Ian C.
Published: February 2007

Parameters for ion exchange selectivity and aluminium hydroxide dissolution in the soil chemical submodels used in applications of the Birkenes model and of MAGIC are compared and several discrepancies identified for organic soils. A laboratory column simulation of the soil chemical submodels is proposed and applied to soils from the Loch Dee area in Galloway. Experimental results were well predicted by a simplified version of MAGIC, with ion exchange selectivity parameters similar to those used in a previous simulation of one subcatchment of Loch Dee. The aluminium hydroxide dissolution parameter used previously was found to be too low for the organic soil materials, where a value of 106 predicted the experimental results more closely. The model developed also included a simple silicate weathering reaction to release base cations into the system. It is concluded that such simple laboratory simulations are useful for independent calibration of the soil chemical submodel of catchment models.
Trials of an acoustic method of measuring piezometric levels in standpipes
Authors: Heath W. , S. Dedi
Published: February 2007

The role of the open standpipe Casagrande piezometer for determining soil pore pressures is still important because of its simplicity and reliability in comparison with transducer type instruments. Such factors are especially relevant when instrumentation is used on remote and inaccessible sites. The limitations of Casagrande type systems relate to poor response times, particularly in soils of low permeability, and the complexity of the normal gas bubbling equipment used to monitor and record data from this type of piezometer.

The response can be improved, providing the design of the installation is taken into consideration in terms of the piezometer collection area and standpipe sizes. A simple acoustic technique has been developed by Geotechnical Monitoring Ltd, to monitor and record piezometric levels. This is based on measuring the period for the return echo of a high frequency signal; a technique widely used to focus cameras that has been found to be reliable and accurate. However, trials on landslide sites in Indonesia highlighted problems which related more to a lack of development rather than any fundamental problems in the method of monitoring standpipes. This paper describes such problems and how they might be overcome.
Analysis of solute transport with a hyperbolic scale‐dependent dispersion model
Authors: Mishra S. , Parker J. C.
Published: February 2007

An empirical hyperbolic scale‐dependent dispersion model, which predicts a linear growth of dispersivity close to the origin and the attainment of an asymptotic dispersivity at large distances, is presented for deterministic modelling of field‐scale solute transport and the analysis of solute transport experiments. A simple relationship is derived between local dispersivity, which is used in numerical simulations of solute transport, and effective dispersivity, which is estimated from the analysis of tracer breakthrough curves. The scale‐dependent dispersion model is used to interpret a field tracer experiment by nonlinear least‐squares inversion of a numerical solution for unsaturated transport. Simultaneous inversion of concentration‐time data from several sampling locations indicates a linear growth of the dispersion process over the scale of the experiment. These findings are consistent with the results of an earlier analysis based on the use of a constant dispersion coefficient model at each of the sampling depths.
Mathematical modelling of sea water intrusion, Nauru Island
Authors: Ghassemi F. , Jakeman A. J. , Jacobson G.
Published: February 2007

A two‐dimensional finite element model for density dependent groundwater flow was calibrated to simulate sea water intrusion in Nauru Island in the Central Pacific Ocean. Nauru Island occupies an area of 22 km2 and supports a population of 8500. The island has been mined for its phosphate deposits and current reserves indicate that the mine has about eight years life remaining. The water supply of the island is about one third dependent on imported water which is also used as ballast on the phosphate ships. Imported water will not be available in the future, and a hydrogeological investigation shows that the island is underlain by a fresh water layer, less than 5 m thick. The freshwater layer overlies a thick transition zone of brackish water which in turn overlies sea water. Simulation of several management options shows that it is possible to substitute current importation of fresh water by careful extraction from the groundwater resources of the island.
Role of hypsometry and planform in basin hydrologic response
Authors: Howard Alan D.
Published: February 2007

The effects of variations of drainage basin morphometry and relief characteristics on flood peak magnitude and time‐to‐peak are investigated using simulated stream networks. The networks are produced by three models: headward growth, systematic capture, and minimum power relaxation. Translational and kinematic wave flood routing were used to generate synthetic hydrographs. Peak discharge and time‐to‐peak are predictable to a high degree by five different sets of morphometric‐relief parameters. In order of decreasing order of importance in predictive ability the parameters characterize basin size, relative relief, basin concavity, and basin shape. Both simulated and natural stream networks exhibit strong dependence of planimetric morphometry upon basin concavity. The effect of this dependency is to increase the effect of basin concavity upon flood hydrographs.
Applications of hydrologic information automatically extracted from digital elevation models
Authors: Jenson Susan K.
Published: February 2007

Digital elevation models (DEMs) can be used to derive a wealth of information about the morphology of a land surface. Traditional raster analysis methods can be used to derive slope, aspect, and shaded relief information; recently‐developed computer programs can be used to delineate depressions, overland flow paths, and watershed boundaries. These methods were used to delineate watershed boundaries for a geochemical stream sediment survey, to compare the results of extracting slope and flow paths from DEMs of varying resolutions, and to examine the geomorphology of a Martian DEM.
Geographic information systems and non‐point source water quality and quantity modelling
Authors: Vieux B. E.
Published: February 2007

Hydrologic processes are affected by the spatial variability of soils, topography, land use and cover, climate, and human‐induced changes and management. Because contaminants are transported by runoff to surface waters and by infiltration and deep percolation to groundwater, hydrologic processes are often at the core of water quality and quantity concerns. Water quality and quantity affected by non‐point sources of contaiminants is dependent on spatially distributed attributes of a catchment or watershed.

The integration or linkage of the spatial data handling capabilities of a GIS with a distributed process, hydrologic model offers the advantages associated with utilizing the full information content of the spatially distributed data to analyse the hydrologic processes. Distributed process models use computational elements smaller than the scale of the process or the system being modelled. The information content of the model output is greater than a lumped model though obtained at greater cost. A GIS is capable of manipulating both the input and output parameters required by distributed process models.

This paper presents a review of water quality and quantity modelling and GIS applications in water resources. An application of the GIS, ARC/INFO and the finite element solution to the kinematic wave equations is presented. In this application, ARC/INFO is used to process the spatially variable terrain in a small watershed using a Triangular Irregular Network on TIN. The TIN facets are used to provide land surface slope in a finite element solution of overland flow which is a fundamental subprocess affecting non‐point source, water quality and quantity.
An evaluation of an automated hollow‐fibre ultrafiltration apparatus for the isolation of colloidal materials in natural waters
Authors: Marley N. A. , Gaffney J. S. , Orlandini K. A. , Dugue C. P.
Published: February 2007

Colloidal materials and macromolecules that are less than 0.45 mircons in diameter can act to transport both hydrophobic and hydrophilic contaminations in subsurface waters. An automated hollow‐fibre ultrafiltration apparatus is described and evaluated regarding its ability to physically size and isolate colloidal materials from natural waters. Sufficient size‐fractionated colloidal samples can be obtained from 60 litre samples to perform inorganic, organic, and radionuclide characterizations, as well as allow the binding capacities of humic and fulvic materials to be evaluated. Samples processed in the field with the automated system were compared with laboratory analyses using single cartridge hollow‐fibre ultrafilters and found to agree well with each other. Typical sample reproducibilities were with 15 per cent. The results indicate that field collection of colloidal materials is feasible with minimal sample perturbation using the automated sampler.
Infiltration measurements—a review
Authors: Youngs E. G.
Published: February 2007

Infiltration theory developed from Richards' equation for the movement of water in unsaturated soil is outlined and used as a basis for considering measurements made with ring infiltrometers, rainfall simulators and tension infiltrometers. In particular, the three‐dimensional soil‐water flow occurring with many of these measurement techniques is considered. Complicating factors of soil heterogeneity, soil swelling and shrinking, and soil aggregation, that limit the interpretation of field measurements using classical theory, are discussed.
Soil pipe contribution to steady subsurface stormflow
Authors: Nieber John L. , Warner Glenn S.
Published: February 2007

Flow through a saturated idealized hillslope with a single soil pipe was simulated using a finite difference solution to the equation for three‐dimensional Darcian flow in saturated heterogeneous media. The proportions of hillslope discharge originating from flow through the soil matrix and from flow through a soil pipe were determined, considering such factors as the radius, depth and length of the pipe, pipe spacing, and the length and slope of the hillslope. Results demonstrate that soil pipes can contribute a significant amount, and in many instances, the majority of total subsurface stormflow.
Dynamics of seasonal recharge beneath a semiarid vegetation on the gnangara mound, Western Australia
Authors: Sharma M. L. , Bari M. , Byrne J.
Published: February 2007

To estimate seasonal changes in recharge to the underlying sandy aquifer, the soil water dynamics of the unsaturated zone was monitored down to a depth of 20 m over a period of three years (1985 to 1987). The measurements were made by a neutron probe at eight locations beneath a native vegetation in a semiarid region, Western Australia, receiving precipitation of 775 mm yr−1. A relatively simple method, based on the analyses of sequentially measured soil water profiles involving utilization of zero flux plane in the unsaturated zone, is presented and used to compute seasonal recharge rates.

Drainage fluxes (recharge rates) below two specified depths were estimated. These were: R1 (water flux at a depth of 10 m, just below the maximum rooting depth) and R2 (water flux at a depth of 18 m, just above the water table). These two estimates were significantly different both on a seasonal and annual basis, but their cumulative values for the three year period were very similar. While the annual precipitation varied from 525 to 850 mm yr−1, the corresponding spatially averaged R1 varied from 34 to 149 mm yr−1, and R2 varied from 65 to 80 mm yr−1. A significant difference in recharge between the upslope and downslope positions on a hillslope was ascribed to differences in vegetation density of the understorey and differences in hydraulic properties of subsoils.

For the three year period, the average R1 and R2 were 13 per cent and 10 per cent of the precipitation respectively. These values compare favourably with a long‐term estimate based on an environmental tracer technique.
Transmission losses to alluvium and associated moisture dynamics in a semiarid ephemeral channel system in Southern Africa
Authors: Hughes D. A. , Sami K.
Published: February 2007

Transmission losses through the bed of ephemeral rivers in arid and semiarid regions can account for a large proportion of the total amount of runoff generated upstream. Losses have typically been estimated by measuring discharge at two points in the channel system. This paper presents some results from a semiarid catchment in South Africa based on moisture observations of the alluvial material using neutron probe access tubes. Channel flow in this catchment is a very infrequent occurrence and consequently presents few opportunities to observe the processes of transmission loss. Only two events have occurred since the beginning of observations in this area (3 October, and 14 November, 1989). the available information is far from complete but suggests that some 75 per cent of the upstream flow in the first event and 22 per cent in the second event was lost to the alluvial material.
Factors controlling the major ion chemistry of streams in the blue ridge and valley and ridge physiographic provinces of Virginia and Maryland
Authors: Puckett Larry J. , Bricker Owen P.
Published: February 2007

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 SO2−4 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 SO2−4 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 SO2−4. 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.
Estimating the effects of spatial variability of infiltration on the output of a distributed runoff and soil erosion model using Monte Carlo methods
Authors: De Roo A. P. J. , Hazelhoff L. , Heuvelink G. B. M.
Published: February 2007

Monte Carlo procedures were used to evaluate the effects of spatial variations in the values of the infiltration parameter on the results of the ANSWERS distributed runoff and erosion model. Simulation results obtained were compared with measured values. Field infiltration measurements indicated spatial correlation at much smaller distances than the size of an element. Therefore, at first only the error of the mean had to be taken into consideration for block infiltration rates. Consequently, not only single hydrographs were produced, but also error bands. Secondly, nine other hypothetical spatial correlation structures were also evaluated using Monte Carlo methods. in particular at low nugget variances, increasing spatial correlation of infiltration resulted in increasing coefficients of variation in model outputs.

In general, rainstorms with low rainfall intensities were more difficult to simulate accurately than extreme events with high rainfall intensities. This is explained by the greater influence of the infiltration uncertainties at low rainfall intensities.
Developing a sediment budget for a small drainage basin in Australia
Authors: Loughran R. J. , Campbell B. L. , Shelly D. J. , Elliott G. L.
Published: February 2007

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.
Flow frequency responses to hardwood‐to‐grass conversion and subsequent succession
Authors: Burt T. P. , Swank W. T.
Published: February 2007

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.
Particle size characteristics of suspended and bed sediments in the rhône river
Authors: Santiago S. , Thomas R. L. , McCarthy L. , Loizeau J. L. , Larbaigt G. , Corvi C. , Rossel D. , Tarradellas J. , Vernet J. P.
Published: February 2007

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).
Subsurface flow simulation of a small plot at loch chon, Scotland
Authors: Koide S. , Wheater H. S.
Published: February 2007

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.
Three‐dimensional modelling of hillslope hydrology
Authors: Binley Andrew , Beven Keith
Published: February 2007

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.
Modelling soil water dynamics in a forest ecosystem. II: Evaluation of spatial variation of soil profiles
Authors: Bouten W. , Witter J. V.
Published: February 2007

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.
Effects of lithology and land use on storm run‐off in east luxembourg
Authors: Hendriks Martin R.
Published: February 2007

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.
Spatial and temporal mapping of water in soil by magnetic resonance imaging
Authors: Amin M. H. G. , Chorley R. J. , Richards K. S. , Bache B. W. , Hall L. D. , Carpenter T. A.
Published: February 2007

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.
Soil erosion and conservation on land cultivated and drained for afforestation
Authors: Carling P. A. , Glaister M. S. , Flintham T. P.
Published: February 2007

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.
Sediment source tracing using environmental magnetism: A new approach with examples from Australia
Authors: Caitcheon G. G.
Published: February 2007

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.
Effect of mining and related activities on the sediment trace element geochemistry of lake coeur D'Alene, idaho, USA. Part I: Surface sediments
Authors: Horowitz Arthur J. , Elrick Kent A. , Cook Robert B.
Published: February 2007

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.
Aquatic weed growth and flow resistance: Influence on the relationship between discharge and stage over a 25 year river gauging station record
Authors: Gurnell Angela M. , Midgley Peter
Published: February 2007

In developing a method for establishing reliable flow estimates from monthly current metered discharge measurements and continuous stage records at a site subject to seasonal aquatic weed growth, a 25 year series of estimates of the resistance of the channel to flow was generated. Analysis of this data set produced estimated relationships between flow resistance, discharge and stage which support the models developed from shorter term research investigations. In addition, the annual cycle in flow resistance at the section studied was found to range from a minimum resistance in January to a maximum in August and September.
Differences in oxygen‐18 content of throughfall and rainfall in hardwood and coniferous forests
Authors: Dewalle David R. , Swistock Bryan R.
Published: February 2007

The differences between δ18O in throughfall and open rainfall were studied for 16 selected spring and summer storms in deciduous, pine and spruce forests in central Pennsylvania, USA. Throughfall δ18O averaged 0.17, 0.32 and 0.24%o greater than δ18O of open rainfall for all storms at the deciduous, pine and spruce sites, respectively. Throughfall 18O enrichment was greater in low intensity spring rainfall events than higher intensity growing season storms and greater in the coniferous stands than the deciduous hardwood stand. Maximum throughfall 18O enrichment of l.61%o occurred in the spruce forest during one spring event. The differences between rainfall and throughfall 18O observed in this study for individual storm events may have important implications for isotope flow separation studies.
Water balance modelling in lateritic terrain
Authors: Langsholt Elin
Published: February 2007

An analytical approximate model for unsaturated flow in a spatially variable field, coupled with infiltration and evapotranspiration at the upper boundary and a fluctuating water‐table at the lower boundary, has been developed. The unsaturated flow equations depend on parameterizations of θ(Φ) and K(Φ). They are based on the notion of a moving, discontinuous front. The field heterogeneity refers to saturated hydraulic conductivity only. Horizontal variability is considered, and the flow medium is approximated as a set of uncorrelated, vertically homogeneous columns. Expectations and variances obtained with this approach have been compared with observations of the field hydrological processes. Three important aspects of the hydrology in this lateritic terrain are rapid water‐table response, Hortonian surface runoff generation and soil suction variability. The stochastic conceptualization used explains to a high degree these characteristics, although some limitations are demonstrated.
In‐channel surficial fine‐grained sediment laminae. Part I: Physical characteristics and formational processes
Authors: Droppo I. G. , Stone M.
Published: February 2007

An in‐channel surficial depositional feature (surficial fine‐grained laminae) composed of loosely bound fine sediment deposited during low flow conditions has often been observed in river systems in south‐western Ontario. The physical characteristics of this feature have been determined by a direct observation image analysis system. This sediment consists primarily of flocculated fine‐grained material. The size distributions of surficial fine‐grained laminae and suspended sediment were not significantly different. Each distribution is bimodal in nature and shows a characteristic grain size deficiency in the 4‐5 μm size range. This observation suggests that flocculation and not low discharge or low competence is the dominant mechanism for the formation of surficial fine‐grained laminae under conditions of low flow in fluvial systems of south‐western Ontario. A quantitative assessment of this feature shows its potential importance as a source of fine‐grained sediment and associated contaminants for downstream transport.
A case study in catchment hydrochemistry: Conflicting interpretations from hydrological and chemical observations
Authors: Jenkins Alan , Ferrier Robert C. , Harriman Ron , Ogunkoya Yinka O.
Published: February 2007

Soil water, stream water, groundwater and rain water were sampled through a storm event in a moorland catchment. Samples were analysed for major ions and deuterium. Chloride and deuterium are used as tracers to enable separation of the stream runoff hydrograph into three components: rain, soil and groundwater. The results indicate that rain water arrives in the stream quickly during the event and contributes a significant volume to the runoff peak. The chemical signal in the rain water is, however, significantly damped, apparently due to mixing with soil water held in the catchment before the event. This is further modified before reaching the stream, apparently through mixing with a deeper groundwater component. Interpretation of tracer, chemistry and hydrological data to present an integrated picture of catchment hydrochemical response is difficult due to problems in the chemical and conceptual definition of the flow components.
Isotopic study of alluvial groundwaters, south‐west lockyer valley, queensland, australia
Authors: Dixon William , Chiswell Barry
Published: February 2007

The isotopic chemistry of alluvial groundwaters from two adjacent valleys are described and hydrological processes within related aquifers are identified as evidenced by oxygen‐18, deuterium, tritium and chloride data. A plot of δ18O against δD values reveals isotopic enrichment of the groundwater by the recycling of spray irrigation water. A plot of tritium versus chloride concentrations displays separate linear correlations for alluvial groundwaters within the two valleys. The salinity has a common source, therefore the separate correlations are interpreted as the past transfer of low salinity groundwater from the alluvial aquifers in one valley to the underlying sandstone aquifers.
Numerical versus field studies of delayed yield in response to a moving water‐table
Authors: Gutub S. A. , Awadalla S. A.
Published: February 2007

As pumping proceeds in an unconfined aquifer the water‐table is lowered and slowly drains out of the initially saturated material giving a delayed yield from storage. Although considerable work has been carried out on delayed yield, a definitive solution is still lacking. The unsaturated zone was treated here as a significant factor in delayed yield analysis. The one‐dimensional unsaturated flow equation was solved numerically to simulate the flow in the zone located between successive water levels in the unconfined aquifer for the case with zero flux at the upper boundary. The moisture content distribution curve was integrated numerically to determine the amount of water drained with time. The study shows that the numerical results are in close agreement with the monitored field data, which implies the important role of the unsaturated zone and the reliability of the numerical simulation in describing this physical phenomenon. The results show that the relationship between the flux and time is sensibly in exponential form, which agrees with the general applicability of Boulton's assumption.
Automated system for measuring snow surface energy balance components in mountainous terrain
Authors: Sauter Keith A. , McDonnell Jeffrey J.
Published: February 2007

The ability to continually monitor several meteorological parameters is needed to estimate snow surface energy balance components in mountainous terrain. In remote mountainous locations, limited accessibility and extreme weather conditions limit the use of delicate meteorological instrumentation. Robust instrumentation and radio telemetry are often needed to measure snow surface energy exchanges. This study examined the practicality and effectiveness of robust instrumentation in estimating radiative and turbulent exchanges in the forested Bear River Mountains of northern Utah. Measurement of reflected shortwave radiation was problematic due to possible selective absorption in the infra‐red range. This resulted in overestimates of reflected shortwave radiation and decreased estimates of now surface albedo. During high snowfall, the pyranometer and net radiometer were occasionally covered with snow, resulting in inaccurate radiation measurements. Snow typically melted from instrument surfaces in less than one day under full sun. A relative humidity measurement accuracy of ± 4% may have resulted in a possible error of 20% in the calculation of vapour pressure. Snow depth measurement with an acoustical sensor was affected by new or blowing snow, which resulted in inaccurate snow depth measurement 16.2% of the time. The longest period without a valid snow depth measurement was 19.5 hours. A new snow temperature thermocouple ladder was designed and constructed and provided accurate within‐pack temperature measurements throughout the pre‐melt and melt season.
The link between glacier velocity and the drainage of ice‐dammed lakes: Comment on a paper by knight and tweed
Authors: Lawler D. M.
Published: February 2007

The interesting suggestion by Knight and Tweed (1991) that a link exists between glacier velocity changes and the filling and draining of a marginal ice‐dammed lake at Sólheimajökull, southern Iceland, is examined. The main problem lies not with plausibility, but with a lack of field data to substantiate the argument. Some pertinent hydrological, glaciological and meteorological data from the area are presented here, many of which do not entirely support certain inferences and observations made in their paper. It is shown that this very small lake is likely to have limited quantitative significance in the operation of the glacio‐hydrological or solute and sediment transfer systems in this basin. Further, specific, difficulties include the absence of crucial observations on glacier velocity variations and the precise timing and pattern of lake drainage in relation to such velocity changes, the lack of evidence for a significant relationship between precipitation receipt and ice velocity here [a component of the Knight and Tweed (1991) proposition], and the occurrence of the lake drainage event in a rain‐free period (contrary to the authors' suggestion). The opportunity is also taken to correct some incidental errors.