AN ANALYSIS OF THE DYNAMIC COMPONENT OF THE GEOMORPHOLOGIC INSTANTANEOUS UNIT-HYDROGRAPH

A geomorphologic instantaneous unit hydrograph (IUH) consists of two c omponents, one relevant to the geomorphology and the other to the hydr aulic aspect describing the movement of a drop of water along a stream . Different formulations of the geomorphologic IUH are reviewed, and a contrast is drawn between the geomorphologic and hydraulic components of the geomorphologic IUH (GIUH) proposed by Rodriguez-Iturbe and Val des (Water Resour. Res., 15(6); 1409-1420, 1979) and those of a width function based IUH (WFIUH). In this paper a comparison has been carrie d out of the original GIUH and a WFIUH which allows the effects of dif ferent geomorphologic and hydraulic components to be identified. The c omparison, which is based on four sub-basins of the River Tyne, UK, cl early shows that the GIUH velocity parameter lacks physical interpreta tion, in contrast to the hydraulic parameters of the WFIUH, which are seen to be physically consistent. For practical application of the GIU H, an equation is then proposed to estimate the velocity parameter thr ough the basin concentration time, the Horton length ratio and the len gth of the stream of the highest order of the channel network.