SEDIMENT DEPOSITION AND ENTRAPMENT IN VEGETATED STREAMBEDS

One aspect of the riparian-stream ecosystem, which is imperative for t he restoration or reestablishment of a streambank and streambed that h as been disrupted, is the ability of the stream system to entrap and r etain sediment. Sediment deposition in a degraded stream system is ess ential 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. Furthermo re, once sediment has been deposited or entrapped, a measure of sedime nt retention during flushing has not been identified. A meandering str eam was physically simulated in the laboratory. A series of 29 tests w as conducted to evaluate the sediment deposition and entrapment potent ial of Kentucky bluegrass when placed in the streambed. Sediment was i njected into the stream for 6 h and then subjected to sediment-free fl ushing flows. The maximum amount of sediment deposition and the amount of sediment retained after flushing was documented. The results indic ate that the presence of vegetation significantly enhances not only th e deposition, but also the entrainment/entrapment of sediment on the v egetative bases. The amount of sediment entrapped is a function of the flow and vegetation blade length. It was determined that the vegetati on could retain from 30-70% of the deposited sediments.