Impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion in Belgium and northern France

• Hydrological rainfall for high intensity rainfall events was modelled and mapped.
• It was linked to the magnitude of rill erosion on conical mine spoil heaps.
• Rill volumes on windward slopes are three times higher than on leeward slopes.

The impact of slope aspect on hydrological rainfall and on the magnitude of rill erosion has rarely been studied. The dominant wind direction in Belgium and northern France is the southwest, which brings large amounts of rain with it. We investigated whether this leads to greater rates of rill erosion on the southwestern slopes, due to the greater amount of hydrological precipitation on these slopes. The study was executed on six barren conical spoil heaps, which are excellent study objects to bring the slope aspect in relation with rill erosion. Three indicators for rill erosion (volume of rills, drainage density and mean distance of the head cut of the five uppermost rills till the top of the spoil heap) were associated with four explanatory factors (slope gradient, vegetation density, rock fragment cover and slope aspect). The amount of hydrological rainfall is the greatest on the western and southwestern slopes. As a result, the largest volume of rills was measured on the slopes facing the southwest (96%), which indicates that there is a connection between the slope aspect and the magnitude of rill erosion. On the northeastern (32%) and eastern (36%) slopes the volume of rills is lower due to the effect of rain shadow. The other explanatory factors showed little influence on the magnitude of rill erosion, as the spoil heaps were selected to be similar in as many parameters as possible.