Soil Surface Roughness and Turbidity Measurements in Erosion Testing

Surface soil erosion is a world-wide engineering and environmental problem. Accurate measurements of the erodibility coefficient and critical shear stress are needed for soil erosion models. Unfortunately, soil erosion testing to obtain these parameters is often highly variable. The surface roughness following an erosion test is used for calculating shear stress on the sample and the erosion rate is used to determine the erodibility coefficient. The objectives of this study were to apply a photogrammetric technique to measure the roughness of soil samples and to use turbidity sensors to measure the volume of soil eroded in the erosion tests. Laboratory Kaolin clay samples were prepared using a clay mixer and tested for erodibility using an erosion function apparatus. Two turbidity sensors were installed in the upstream and downstream of the flume to measure the amount of suspended soil particles during the erosion tests. After each test, two photos of each sample were taken using a digital camera and processed in a custom computational program. The results of this study showed that the stereophotogrammetry computational program was able to measure the surface roughness of the soil samples accurately. Additionally, the results from turbidity measurements provide a secondary measurement of erosion and can determine the volume of soil eroded during testing.