Evaluation of overland flow models using laboratory catchment data II. Parameter identification of physically based (kinematic wave) models

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Abstract
Using the Imperial College laboratory catchment facility data from 96 experiments on a slightly-roughened varnished strip catchment (1 m x 9.925 m) are used to investigate the performance of numerical models of overland flow based on the kinematic wave approximation. A simple four-parameter model incorporates the Darcy-Weisbach laminar flow and Manning turbulent flow friction relationships, with different values of the friction parameter permitted under “rain” and “no-rain” flow states. The optimization strategy combines grid-search and gradient-search algorithms. Model fits are good by conventional standards and the effect of raindrop impact on effective roughness is clearly identified. However, the Manning relationship is not valid in the zone of transition to rough turbulent flow and some physical inconsistencies in optimal parameter values are apparent. Incorporation of a Colebrook-White friction relationship gives similar goodness of fit, but identified parameters conform more closely to expectation from hydraulic theory.