Estimation of the time scale of the geomorphologic instantaneous unit hydrograph from effective streamflow velocity

The greatest difficulty in applying the geomorphologic instantaneous unit hydrograph is the estimation of the time scale of the hydrologic response of a basin. We derive the time scale from the effective streamflow velocity of the highest‐order stream and the spatial distribution of velocity throughout the stream network. The latter is described by a dimensionless geomorphologic function with a single‐shape parameter. The proposed method is applied to some Italian basins.