Browsing by Author "Marechal, David"
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Item Open Access Development and application of a soil classification-based conceptual catchment- scale hydrological model(Elsevier Science B.V., Amsterdam., 2005-10-01T00:00:00Z) Marechal, David; Holman, Ian P.A conceptual, continuous, daily, semi distributed catchment-scale rainfall- runoff model that has the potential to be ultimately used in ungauged catchments is described. The Catchment Resources and Soil Hydrology (CRASH) model is developed from the basis that the transformation of rainfall into simulated river discharge can be parameterised using pre-existing national datasets of soil, land use and weather; and that the spatial variability in soil properties and land use are important to the hydrological response of a catchment and should be incorporated into the catchment representation. Both infiltration- excess and saturation-excess runoff mechanisms are simulated, with water movement through each soil layer simulated using a capacitance approach limited according to layer physical properties. The hydrological linkage between the response unit and catchment is parameterised using the existing national Hydrology of Soil Types (HOST) classification. The HOST classification groups all UK soil types into one of 29 hydrological classes for which nationally calibrated values of Base Flow Index and Standard Percentage Runoff are provided. CRASH has been calibrated and validated for three catchments in England with contrasting soil characteristics and meteorological conditions. The model was successful at simulating time series and flow duration curves in all catchments during the calibration and validation periods. The next development stage will be to test CRASH for a large number of catchments covering a wider range of soils, land uses and meteorological conditions, in order to derive a set of regionalised model parameters based upon the HOST classification. The successful cross-scale linkage between water movement through the response unit and the catchment-scale hydrological response using the HOST classification, which incorporates the scale effects between plot and catchment, suggests that such national soil hydrological classifications may provide a sound and consistent framework for hydrological modelling in both gauged and ungauged catchments which should be extended to other regions.Item Open Access A soil-based approach to rainfall-runoff modelling in ungauged catchments for England and Wales(Cranfield University, 2004) Marechal, David; Holman, Ian P.Hydrological models are powerful tools for the investigation of many hydrological issues. The historical approach for the development of rainfall-runoff models, with regard to the choice of model structure and the calibration of the free parameters, has been to focus on gauged catchments where sufficient data, in particular stream flow data, are available. Applications of models were then extended to the case of ungauged catchments. In recent years, it has become apparent that this approach did not lead to satisfying results in ungauged catchments, and that the main focus should instead be on ungauged catchments for the implementation of new modelling strategies. This thesis demonstrates the potential of a new conceptual, catchment-scale, semi-distributed, integrated rainfall-runoff model as a modelling tool in both ungauged and gauged catchments for the assessment of water resources management, land use change or climate changes at the catchment scale. The review of existing model structures and regionalisation methods has lead to the development of the Catchment Resources and Soil Hydrology (CRASH) model following the top-down modelling strategy. The free parameters of the model are directly related to controlling factors of the hydrological processes in the United Kingdom, i.e. soil and land use. The classification of the soils according to their hydrological behaviour is based on the Hydrology Of Soil Types (HOST) system. CRASH also incorporates a novel rainfall disaggregation scheme for the derivation of infiltration excess surface runoff. A regional set of model parameters has been derived from the calibration of CRASH in 32 catchments throughout England and Wales covering contrasting climatic, soil, geological, and land use conditions. The single-site and regional CRASH models performed satisfactorily according to reviewed performance criteria for gauged catchments and to a scoring system proposed for ungauged catchments. However the quality of stream flow data in the UK which was used for the calculation of the regional parameter set, in particular the widespread unavailability of naturalised flow data, tends to limit the performance of the regional CRASH model for low flows.