Proposal of a new methodology to assess the effectiveness of check-dams

Abstract

Check dams are transverse structures that are built in some streams to mitigate erosion, and frequently used in forest-hydrology restoration projects in Spain. Their main functions are: controlling and retaining solid particles transported by flow discharge; slope and bed stream stabilization; reducing flow water velocities and their erosivity. Nevertheless, the erosion control effectiveness of check dams is a matter under discussion during the last years. Because of this, we want to verify how the check dams work controlling sediment yields, and so on how they reduce soil losses in gullies. We propose a method based in estimating the sediment volume retained through an accurate topographical survey. Our results have been compared with two other methods, most frequently used because of their geometric simplicity. A significant variation appears between the three methods. Therefore, to probe the effectiveness of the check dams a better estimation of their sediment retained surface justifies the full topographical survey. We have worked in Tórtoles (Ávila, Spain), in a deep gully from the Corneja river headwaters. There is a forest-hydrological restoration that was projected in 1964 and executed one year later. The topographical survey results show that check dams in the gully have retained 237.95 m³ of sediments. This is a 30.3% and a 7.9% bigger than the calculated by the other two methods. The unit volumes of the check dams range between ± 5% y ± 50% respect the obtained with our method. Our results show important differences compared with the other methodologies, but a better land surveying justifies the use of the topographic method to estimate the check dams effectiveness.