The Sediment Erosion Rate Flume (SERF): A New Testing Device for Measuring Soil Erosion Rate and Shear Stress

A new apparatus that measures soil erosion in a flume is described. It is designed to measure a bed material’s erosion rate and approximate its corresponding applied shear stress (erosion function). The apparatus, or Sediment Erosion Rate Flume (SERF), is unlike similar devices, in that during an erosion test, sample advancement is computer-controlled through a feedback loop via a series of lasers, ultrasonic depth sensors, and a Servo-stepper motor. Because of this computerized control mechanism, the SERF can be used to measure near-instantaneous erosion rate as opposed to average erosion rate over an elapsed time domain. Also, included with the SERF is a device that can measure shear stress directly for a sample with a certain uniform roughness. Using the SERF, erosion versus time curves were used to estimate erosion rate for both synthetic and natural samples. For synthetic samples, a roughness approximation was conducted to estimate shear stress. Tests with the shear stress sensor appear to indicate that smooth-wall approximations used in previous flume-style erosion rate testing apparatuses under-predict shear stress. However, further analysis of erosion results indicates that the smooth-wall approximation is conservative; and until a direct method for measuring shear stress is discovered, it may be appropriate for devices like this. Using this rationale, erosion functions were estimated for natural samples.