On the hydrological modeling of dry-stone walls

Terraces are among the most evident human signatures on the landscape, and they cover large areas of the Earth. The importance of dry-stone terrace walls has always played a key role in the management of the agricultural areas in hilly and mountain environments. They are generally built to allow machinery and ploughs to work in better conditions, to make human work in the slopes easy and comfortable, and to promote irrigation. Few studies in literature are available about rainfall-runoff transformation in terraces areas and its role in flood risk mitigation. Research results in this field are still missing. In fact, bench terraces reduce the terrain slope and the length of the overland flow, quantitatively controlling the runoff flow velocity, facilitating the drainage and thus leading to a reduction of soil erosion. From the point of view of hydrological response, a terraced slope should result in a reduction in the peak runoff at the toe of hillslope and in a delay in the passage of the peak flow. This occurs mainly due to the change of the original topography. The goal of the work is highlighting the benefits in terms of runoff reduction, which is provided by sequence of dry-stone walls under different space arrangements along the hillslope. In particular, the FLO-2D model was applied recursively to a schematic hillslope simulating both the local variation of the hydrological soil characteristics and the morphological stepped profile. The simulations were carried out by varying the basic parameters underlying the design of the terrace system (the spacing, the height and the number of terraces). The results have clearly identified the relationships between the peak discharge reduction of the overland flow and the area managed using series of dry-stone walls. The modeling outcomes well support design criteria and the performances to expect from this consolidation system.