The influence of hedgerow networks in bocage landscapes on surface water pathways
In Brittany, the bocage is the typical landscape, a network of hedgerows planted on an earthen bank. It could play a hydrological role by modifying the water pathways. This was studied by analysing the modification of the drainage network at the catchment scale, for 5 densities of the hedgerow network. The drainage network, basically controlled by the topography, was modified taking into account the hedges, which cannot be crossed by the water pathway. The digital elevation model and a vector map of hedges were the data used. The impact of hedgerows on different parameters influencing surface runoff was tested. The main modification is that a part of the catchment, up to 40% of the total area, is disconnected from the river course due to the presence of hedges acting as sinks. A reduction of the surface runoff length and a decrease of the slope of the pixel-hedges in the drainage direction are also measured. But none of these factors is dependent of the hedgerow density, which appears as a poor descriptor of the hydrological buffer capacity of the bocage landscape. We draw attention to the need to take into account the hedgerow structure for hydrological purposes, in order to improve the new policy of re-building a bocage landscape that is currently being implemented.