The geomorphic origin of recession curves
An important study domain in hydrology is dedicated to understand how the spatial organization of river networks is reflected in the hydrologic response to rainfall inputs (Biswal and Marani, 2010). Base flow (or recession flow) is the discharge rate in a river that results from the natural release of the water stored in the upstream river channels and adjoining riparian aquifers in the absence of precipitation, snowmelt or other inputs (Brutsaert W. , 2005). Biswal and Marani (2010) sustain that the recession flow is dominated by aquifer drainage and they find a link between recession flows and network morphology. Since geomorphologic characteristics can be readily obtained from maps and air photos, a relationship between the groundwater outflow rate and the geomorphologic parameters of the basin would permit to extract the characteristics of recession hydrographs solely from Digital Terrain Models (DTMs). The practical importance of base flow prediction stems mainly from the fact that it is the rate of flow that a given catchment can sustain in the absence of precipitation and in the absence of artificial storage works (Brutsaert & Nieber, 1977). In the first chapter is presented the theoretical background dedicated to the study of the processes controlling recession flows with a particular attention to the aquifer drainage process. A method to describe the behaviour of the base flow rate at the outlet of the basin is presented, introducing the concept of recession slope analysis. The same method is used to define aquifer hydraulic parameters using Boussinesq equations, which are shortly described. Finally the relationship with geomorphic parameters found by Biswal and Marani (2010) is presented. In the second chapter the data and methods used to analyse the recession flows of the Chamberonne river are explained. In the last part of the report the results of the analysis are showed, followed by some propositions for the future work.