Determination of Spatially Distributed Velocity for Flow Routing

The physically-based distributed hydrological models play an important role in watershed hydrology. Physical simulation of flow routing depends largely on the field distribution of flow velocity.Terrain analysis studies have previously focused more on the delineation of geomorphologic structures rather than the description of hydraulic factors. As affected by multiple uncertain factors including topography, soil properties and water depth in channel, the determination of overland flow velocity is limited.This study proposed a statistical method to generate a field map of spatially distributed flow velocity from a grid structure. The upstream drainage area for each grid cell was involved to represent the hydraulic radius in Manning's equation. The weight of hydraulic factor was calibrated by adjusting the impact on flow velocity. Case study of flow routing was undertaken to validate the field distribution of flow velocity. The results indicate that the proposed method can reasonably estimate flow velocity field distribution,and the calibrated value of weighting coefficient of hydraulic factor can produce acceptable unit hydrograph for rainfall-runoff processes.