Geomorphic Signatures on Brutsaert Base Flow Recession Analysis: case study of 27 Swiss catchments

Recession flow analysis are crucial in many areas of water resource management and useful to forecast base flow in gauged rivers. Moving from a classical recession curve analysis method, a large set of recession curves has been analyzed from Swiss streamflow data of 27 watersheds. For these catchments, digital elevation models have been precisely analyzed and a method aimed at the geomorphic origins of recession curves has been applied to the Swiss dataset. The method links river network morphology, epitomized by time-varying distribution of contributing channel sites, with the classic parametrization of recession events. This is done by assimilating two scaling exponents,  and bG, with |dQ/dt|Q where Q is at-a-station gauged flow rate and N(l)  G(l)bG where l is the downstream distance from the channel heads receding in time at constant speed c, N(l) is the number of draining channel reaches located at distance l from their heads, and G(l) is the total drainage network length at a distance greater or equal to l. We find that the method provides good results in catchments where drainage density can be regarded as spatially constant. We propose several corrections to the method accounting for arbitrary local drainage densities affecting the local drainage inflow per unit channel length. In particular, we relax the assumption of uniform constant speed c. Such corrections properly vanish when the local drainage density become spatially constant. Overall, definite geomorphic signatures are recognizable for recession curves. In general, we suggest that this conceptual model might be useful to estimate the low flow regime of natural ungauged basins by predicting its features solely from information remotely acquired and objectively manipulated through DEM data.