bluuebunny/crossref_metadata_2025_split huggingface dataset:
DISTRIBUTED MODELS 7: A CIS APPROACH
Authors: Drayton R. S. , Wilde B. M. , Harris J. H. K. 
Published: February 2007

AbstractA 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.
Modelling soil water dynamics in a forested ecosystem. I: A site specific evaluation
Authors: Bouten W. , Schaap M. G. , Bakker D. J. , Verstraten J. M. 
Published: February 2007

AbstractSoil 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).
Modelling soil water dynamics in a forested ecosystem. III: Model description and evaluation of discretization
Authors: Tiktak A. , Bouten W. 
Published: February 2007

AbstractThe 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.
Temporal and spatial variations of runoff and rainwash erosion on an agricultural field
Authors: Mathier L. , Roy A. G. 
Published: February 2007

AbstractThis 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.
Longer‐term water temperature behaviour in an upland stream
Authors: Webb B. W. , Walling D. E. 
Published: February 2007

AbstractWater temperature behaviour in a small upland Exmoor catchment (the Black Ball Stream) has been studied over a 14‐year period since January 1976. Results from continuous records revealed annual mean stream temperatures to have a coefficient of variation of less than 5 per cent, and values of 5,10 and 15°C to be equalled or exceeded 90,41.8 and 4 per cent of the time respectively. The annual regime of water temperature was relatively predictable but diel cycles of varying magnitude were superimposed on the seasonal march. A clear seasonal hysteresis was evident whereby diel range in spring exceeded that in autumn by typically more than 2°C. Trend analysis of monthly temperature time series highlighted the stability of the thermal regime in recent years, although investigation of air‐water temperature relationships indicated that an increase in mean surface air temperature projected for southwest England by the Year 2050 would result in a rise of mean winter and summer stream temperatures by 1.6 and 1.3°C respectively. Analysis of streamflow effects on water temperature suggested that future indirect impacts of climatic change on thermal regime via changes in stream discharge are likely to be minor.
Sensitivity analysis on processes affecting bypass flow
Authors: Booltink H. W. G. , Bouma J. 
Published: February 2007

AbstractBypass 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.
A gis‐based distributed parameter hydrologic model for urban areas
Authors: Smith Michael B. 
Published: February 2007

AbstractA hydrologic model for urban areas has been developed which incorporates distributed parameter modelling concepts and functions in the context of a geographic information system. In the proposed model, the watershed is represented as a cascade of grid cells, whose size can be specified by the user. Preliminary processing includes the determination of overland flow directions for each cell. An automated procedure is used to establish the cell‐to‐cell connectivity scheme, which is used to order the computations within each time step. Infiltration is computed using the Green‐Ampt equation, while runoff rates are computed using a coupling of the continuity equation and Manning's equation for turbulent flow. Storm sewer flows are routed using time‐shift routing. The model is capable of simulating flow through streets and offers the possibility of predicting the downstream movement of sewer system overflows. In preliminary testing on a small residential watershed, the model was able to reproduce measured hydrographs.
Obtaining basic simulation data for a heterogeneous field with stratified marine soils
Authors: Finke P. A. , Bosma W. J. P. 
Published: February 2007

AbstractThinly 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.
II. Snow hydrology processes and remote sensing
Authors: Rango Albert 
Published: February 2007

AbstractIn 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.
Sensitivity of bocage landscapes to surfaces run‐off: Application of the kirkby index
Authors: Merot Ph. , Bruneau P. 
Published: February 2007

AbstractThe 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.
Melt water chemistry and its impact on stream water quality
Authors: Jenkins Alan , Ferrier Robert , Waters David 
Published: February 2007

AbstractSamples 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.
The calibration and use of pressure transducers in tensiometer systems
Authors: Hoelscher James R. , Nuttle William K. , Harvey Judson W. 
Published: February 2007

AbstractThe 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.
Analysis of storm run‐off sources using oxygen‐18 in a headwater swamp
Authors: Hill A. R. , Waddington J. M. 
Published: February 2007

AbstractA 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.
Design of stable drainage networks in upland forestry plantations
Authors: Flintham T. P. , Carling P. A. 
Published: February 2007

AbstractErosion of man‐made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil.
Spatial and temporal predictions of soil moisture dynamics, runoff, variable source areas and evapotranspiration for plynlimon, mid‐wales
Authors: Quinn P. F. , Beven K. J. 
Published: February 2007

AbstractFor 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.