Sediment Deposition and Entrapment in Vegetated Streambeds

One aspect of the riparian-stream ecosystem, which is imperative for the restoration or reestablishment of a streambank and streambed that has been disrupted, is the ability of the stream system to entrap and retain sediment. Sediment deposition in a degraded stream system is essential to the natural rebuilding of channel morphology. Although it is recognized that herbaceous vegetation enhances sediment deposition, a quantitative measure of entrapment has not been developed. Furthermore, once sediment has been deposited or entrapped, a measure of sediment retention during flushing has not been identified. A meandering stream was physically simulated in the laboratory. A series of 29 tests was conducted to evaluate the sediment deposition and entrapment potential of Kentucky bluegrass when placed in the streambed. Sediment was injected into the stream for 6 h and then subjected to sediment-free flushing flows. The maximum amount of sediment deposition and the amount of sediment retained after flushing was documented. The results indicate that the presence of vegetation significantly enhances not only the deposition, but also the entrainment/entrapment of sediment on the vegetative bases. The amount of sediment entrapped is a function of the flow and vegetation blade length. It was determined that the vegetation could retain from 30-70% of the deposited sediments.