| Popis: |
According to the US EPA, excess sediment is a significant cause of water quality impairment for rivers. The goal of this study was to compare different methods of determining two parameters used to estimate stream bank erosion, soil critical shear stress ( o c ) and soil erodibility (kd,) and to determine the impact of those differences on predictions of stream bank erosion. In situ erosion tests were conducted using a submerged jet test device at twenty-five field sites. Determination of kd and o c using the jet test device requires an initial estimation of oc; o c was estimated using the Shield’s diagram, the Blaisdell method, and by assuming it was zero. Soil erodibility was then determined using a least squares fit of the jet test data for three o c estimates. Additionally, using a single set of o c values, the kd measured by the jet test was compared to two empirical kd relationships. Using these two sets of parameter values, stream bank erosion rates were predicted for a local stream. Critical shear stresses produced by the Blaisdell method were an order of magnitude greater than those predicted by the Shield’s diagram and the zero o c assumption. However, the kd values and stream bank erosion predictions based on the jet test measurements were relatively insensitive to o c . The two empirical kd equations produced similar kd and erosion predictions that were generally an order of magnitude less than the values based on the jet test measurements. Field validation of these methods over a wide range of soil types is recommended to further develop methods of estimating kd and o c for stream bank soils. |
