We investigate the role of cross-section geometry in flow routing by developing an analytical framework based on the instantaneous response function (IRF) and relationships of river basin geomorphology. The cross-section geometry is included explicitly within the framework by assuming a power law cross section that is, in turn, used to derive expressions for the at-a-site hydraulic geometry. The analysis performed using the Illinois River basin indicates that the cross-section geometry takes on different roles depending on whether flows are in the channel or floodplain. The cross-section geometry where width dominates over depth (width dominant), i.e., the at-a-site width-depth ratio increases with increasing depth, tends to produce a larger network celerity and dispersion for the channel, and the trend reverses for the high floodplain flows. We found that the cross-section geometry can influence the relative contribution of hydrodynamic and kinematic dispersion. For the channel, the depth-dominant cross section produces a lower hydrodynamic dispersion than the width-dominant cross section and vice versa for the floodplain. We found that the nonlinear dependence of the IRF on effective rainfall, expressed in the IRF time to peak and peak flow, may vary depending on the cross-section geometry, with the nonlinearity decreasing for the width-dominant cross sections. Additionally, the effect of cross-section geometry on the basin response can alter the relative contribution of the stream network and hillslopes to the basin dispersion. The derived framework has potential as an a priori tool for incorporating channel and floodplain geometry into distributed rainfall-runoff models.
All Science Journal Classification (ASJC) codes
- Water Science and Technology