Abstract:
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.
