Simulating the effects of spatial configurations of agricultural ditch drainage networks on surface runoff from agricultural catchments

networks on surface runoff from agricultural catchments Levavasseur F., Bailly J.S., Lagacherie P., Colin F., Rabotin M. a UMR 1221 LISAH F-34035, INRA, Montpellier, France. b UMR 1221 LISAH F-34035, AgroParisTech, Montpellier, France. c UMR TETIS F-34093, AgroParisTech, Montpellier, France. d UMR 1221 LISAH F-34035, Montpellier SupAgro, Montpellier, France. Abstract The study of runoff is a crucial issue because it is closely related to flooding, water quality and erosion. In cultivated catchments, agricultural ditch drainage networks are known to influence runoff. As anthropogenic elements, agricultural ditch drainage networks can therefore be altered to better manage surface runoff in cultivated catchments. However, the relationship between the spatial configuration, i.e., the density and the topology, of agricultural ditch drainage networks and surface runoff in cultivated catchments is not understood. We studied this relationship by using a random network simulator that was coupled to a distributed hydrological model. The simulations explored a large variety of spatial configurations corresponding to a thousand stochastic agricultural ditch drainage networks on a 6.4 km2 Mediterranean cultivated catchment. Next, several distributed hydrological functions were used to compute water flow-paths and runoff for each simulation. The results showed that (i) denser networks increased the drained volume and the peak discharge and decreased hillslopes runoff, (ii) greater network density did not affect the surface runoff any further above a given network density, (iii) the correlation between network density and runoff was weaker for small subcatchments (< 2 km2) where the variability in the drained area that resulted from changes in agricultural ditch drainage 1