Design and initial evaluation of a portable in situ runoff and sediment monitoring device

Abstract

Summary An inexpensive portable runoff and sediment monitoring device (RSMD) requiring no external electric power was developed for measuring water runoff and associated sediment loss from field plots ranging from 0.005 to 0.1 ha. The device consists of runoff gauge, sediment mixing and sectional subsampling assemblies. The runoff hydrograph is determined using a calibrated tipping bucket. The sediment mixing assembly minimizes fluid splash while mixing the runoff water/sediment mixture prior to subsampling this material. Automatic flow-proportional sampling utilizes mechanical power supplied by the tipping bucket action, with power transmitted to the sample collection assembly via the tipping bucket pivot bar. Runoff is well-mixed and subdivided twice before subsamples are collected for analysis. The resolution of this device for a 100 m 2 plot is 0.025 mm of runoff; the device is able to capture maximum flow rates up to 82 mm h −1 in a plot of the same dimension. Calibration results indicated the maximum error is 2.1% for estimating flow rate and less than 10% for sediment concentration in most of the flow range. The RSMD was assessed by measuring field runoff and soil loss from different tillage and slope treatments for a single natural rainfall event. Results were in close agreement with those in published literature, giving additional evidence that this device is performing acceptably well. The RSMD is uniquely adapted for a wide range of field sites, especially for those without electric power, making it a useful tool for studying soil management strategies.