VALIDATION OF A NUMERICAL METHOD TO QUANTIFY DEPRESSION STORAGE BY DIRECT MEASUREMENTS ON MOULDED SURFACES

Abstract

Surface depression storage influences runoff, but is difficult to measure, because water infiltrates into the soil. Therefore, it is usually estimated using a numerical method. This consists of taking height measurements over a surface, constructing a digital elevation model (DEM), filling it virtually with water and subtracting the original DEM from the filled one. The aim of this study was to verify this numerical method, by comparing it to a direct measurement of water stored on a surface.To allow us to measure the amount of water on a surface directly, we needed an impermeable soil surface. We managed to create an impermeable reproduction of a soil surface in polyester, using a silicone mould. In this way we reproduced two surfaces, representing seedbeds. To obtain a DEM, we used a laser roughness meter with an original optical principle. To calculate storage, we used an existing filling algorithm.Measured depression storage values ranged from 0.36 to 51.8 mm, whereas estimated values ranged from 0.26 to 48.0 mm. Comparing these results, we conclude that the numerical method is acceptable, unless the soil surface is cloddy and contains cavities that cannot be detected by the roughness meter. Fortunately, in field situations, a cloddy soil surface usually coincides with high infiltration capacity and these situations are generally not subject to runoff, no matter what the value of surface storage.