Effects of the spatial organization of agricultural management on the hydrological behaviour of a farmed catchment during flood events

Abstract

Abstract:Field limits, tillage practices and ditch networks constitute man-made hydrological discontinuities in farmed catchments, and are expected to influence hydrological response during flood events. The purpose of this study is to assess the role of human impact, especially the existence of tillage practices and ditch network, on flood events. The study area is the farmed catchment of Roujan (0Ð91 km 2 ) located in Southern France for which a spatially distributed hydrological model, MHYDAS, was developed and tested. The model considers the catchment as a series of interconnected field parts linked to the ditch network. Descriptions are provided for the main model procedures: computation of Hortonian excess rainfall on fields using the Green and Ampt approach, conversion of excess rainfall to surface runoff, interaction between ditch network and groundwater using a simple Darcian model and flood routing through the ditch network using the diffusive wave model. To analyse the role of both tillage practices and the ditch network, two sets of sensitivity analysis of the model were applied. The first set studied the role of tillage practices by comparing the actual spatial distribution of tillage practices on the catchment with three hypothetical scenarios. The second set studied the role of the ditch network by comparing the actual man-made ditch network with a hypothetical drainage network automatically extracted from a digital elevation model. Results show the importance of the role of tillage and the ditch network on the form of the hydrograph, the lag time, the runoff volume and the peak discharge. This technique could also be applied to study the impact of land use change on the hydrological behaviour of the catchment.

Managing ditches for agroecological engineering of landscape. A review

“…Note that a given process may have both positive and negative effects across the range of ecosystem services considered for ditches. The maximization of a given process may thereby contribute to the optimization of one service and the attenuation of another +positive effect of the given processes on ecosystem services, − negative effect of the given processes on ecosystem services Moussa et al 2002;Vaughan et al 2008). For example, Marofi (1999) measured saturated hydraulic conductivities ranging 20 to 600 mm h −1 in ditch beds in a catchment in southern France.…”

“…It is important to notice that the latter properties are often not well known and are therefore generally calibrated as an exchange coefficient in hydrological modeling approaches (Carluer and Marsily 2004;Moussa et al 2002;VanderKwaak 1999). The hydraulic conductivity gives an estimation of the potential intensity of infiltration fluxes.…”

“…As a consequence, they generally induce a higher peak discharge, a lower lag time, and a higher flow volume at the catchment outlets (Buchanan et al 2012;Carluer and de Marsily 2004;Moussa et al 2002), increasing the flood hazard intensity downstream. For example, by simulation, Moussa et al (2002) quantified an increase of 9 to 43 % of the peak flow due to the presence of a manmade ditch network. However, under particular conditions, ditch networks may also reduce flood hazards by reducing the peak discharge and increasing the lag time (Loumagne and Tallec 2013).…”

A spatial stochastic algorithm to reconstruct artificial drainage networks from incomplete network delineations

“…As has been done in most ADN hydrology studies (Lagacherie et al, 2010;Moussa et al, 2002;Varado, 2004), we considered that the d graph is also a directed tree (ditree) with a root r corresponding to the physical outlet.…”

“…Therefore, most environmental diagnoses and impact assessments at the catchment scale in agrarian areas now take these networks and their spatial variabilities into account through physical modelling (Lagacherie et al, 2010;Moussa et al, 2002;Varado, 2004). However, to date, these approaches have only been used for small areas where major investments were made in terrain surveys to map drainage networks (Lagacherie et al, 2006), which limits the 2 generalisation of these studies.…”