Impacts of Channel Network Type on the Unit Hydrograph

Unit hydrographs (UHs) remain widely used in hydrologic modeling to predict the stormflow that is produced at a basin outlet in response to runoff generated throughout the basin. Numerous studies have demonstrated that a basin’s UH depends on its geomorphic properties, and several methods estimate synthetic UHs using such properties. However, previous studies have not examined whether the channel network type (such as dendritic, parallel, pinnate, rectangular, and trellis) impacts the UH shape. The objectives of this study were to determine: (1) whether those five network types exhibit distinct UHs, and (2) whether knowledge of the network type is sufficient to replace the actual flow path structure in UH estimation. To achieve these objectives, a UH framework is developed based on kinematic wave theory. The framework allows the impacts of the network structure on the UH to be isolated into two random variables, which facilitates comparisons between network types. The framework is applied to 10 basins of each type. The results show that the five network types exhibit distinct instantaneous UHs, but the type allows accurate UH determination only for pinnate basins.