The impact of vegetated landscape elements on runoff in a small agricultural watershed: A modelling study

•Modelling results confirm that landscape elements contribute to lowering flood risk.•Higher initial soil wetness levels result in more and faster discharge.•Runoff is controlled by the density of landscape elements and their upstream area. Flooding of settlements is a growing concern in Europe, also in agricultural areas. Restoration and installation of vegetated landscape elements (vLE) such as hedges, lines of trees and grass buffers, along the parcel boundaries is increasingly recognized as a way to mitigate downstream flood risk. However, there is a lack of scientific evidence to support their implementation. We used the Landlab modelling framework to gain knowledge about the importance of the presence and characteristics of vLEs for the hydrological response in a 26 ha undulating watershed representative for the Belgian loess belt for which a multitude of vLE scenarios were developed. Our model results demonstrated that the total runoff volume, the peak discharge rate and its lag time in such small watersheds are mainly controlled by the density of the vLE objects and their upstream area. First and foremost we demonstrated a negative correlation between the discharge volume and peak discharge rate and the density of the vLE objects and their upstream area. A positive correlation was observed between the lag time and density of the vLE objects for both dry and wet soils and between the lag tag time and upstream area for dry soils. Further, we found that the impact of the value of the saturated hydraulic conductivity of the soil covered by the vLE became increasingly important with increasing soil wetness, with the hydraulic conductivity being negatively correlated with the discharge volume and peak discharge rate. The impact of hydraulic conductivity on the lag time was limited. A negative correlation between hydraulic conductivity and lag time for intermediate wet soils was demonstrated. Our model results also showed that the roughness, expressed as the Manning n-coefficient, of the soil underneath a vLE and the spatial connectivity of the vLE objects have little impact on the hydrological response.