Hortonian and Variable Source Area Modeling in Urbanizing Basins

The conventional hydrological model QualHYMO, which uses infiltration excess overland flow as the primary mechanism for runoff generation, is compared with a variable source area model that was modified for use on urbanizing watersheds. The modified variable source area model is known as TOPURBAN, as it uses TOPMODEL concepts to generate saturation excess overland flow. TOPURBAN proved to provide better modeling efficiency than QualHYMO in four continuous modeling tests, and slightly better efficiency in two continuous modeling tests. QualHYMO was found to produce large overpredictions due to its representation of urban areas, and the assumption of the entire rural area contributing to flow when rural losses were exceeded. TOPURBAN slightly underpredicted peak flows, but other hydrograph characteristics were modeled well. TOPURBAN outperformed QualHYMO in applications to two single events with similar antecedent moisture conditions. TOPURBAN is considered by the writers to be a good predictor of flow rates for certain urbanizing catchments.