Improved unit hydrograph identification for seven Welsh rivers: implications for estimating continuous streamflow at ungauged sites

Hydrological Sciences Journal-journal Des Sciences Hydrologiques - HYDROLOG SCI J 01/2003; 48(5):743-762. DOI: 10.1623/hysj.48.5.743.51454

ABSTRACT A unit hydrograph-based continuous rainfall—streamflow model is applied at daily time step to several catchments in Wales. Two calibration methods are compared for seven catchments. Five of the catchments are among 60 basins in England and Wales for which models were derived by other investigators using the first calibration method, in order to devise a regionalization scheme allowing model parameters to be estimated from catchment properties. The paper shows that in several cases the first calibration method tends to overestimate low flows and give a positively biased estimate for one of the unit hydrograph parameters. It also shows that the second parameter calibration method can often overcome this problem, yielding model parameters more suitable for regionalization with respect to physical catchment properties. Implications of the work are discussed in the context of improving regionalization schemes where the estimation of streamflow in ungauged basins is the major objective.

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    ABSTRACT: Employing 1-, 2-, 4-, 6-, 12- and 24-hourly data sets for two catchments (10.6 and 298 km) in Wales, the calibrated parameters of a unit hydrograph-based model are shown to change substantially over that range of data time steps. For the smaller basin, each model parameter reaches, or approaches, a stable value as the data time step decreases, providing a straightforward method of estimating time-step independent model parameter values. For the larger basin, the model parameters also reach, or approach, stable values using hourly data, but, for reasons given in the paper, interpretation of the results is more difficult. Model parameter sensitivity analyses are presented that give insights into the relative precision on the parameters for both catchments. The paper discusses the importance of accounting for model parameter data time-step dependency in pursuit of a reduction in the uncertainty associated with estimates of flow in ungauged basins, and suggests that further work along these lines be undertaken using different catchments and models.
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