Impact Assessment of Flushing Flow from a Dam to Invasive Aquatic Plant Egeria densa in a Gravel-bed River

The implications of artificial water release, flushing flow, on the invasive aquatic plant Egeria densa in a gravel bed river, downstream of a dam, were investigated from the viewpoint of ecological characteristics, biomass change, open-channel hydraulics, and river engineering. To understand seasonal changes associated with Egeria densa, as well as the native species Hydrilla verticillata found within a reach, a series of surveys was conducted. A new method for assessing biomass flux during flushing flows is proposed. Our data indicated that Egeria densa biomass within the surveyed reach was reduced by approximately half following flushing flows conducted every March. Biomass flux was also evaluated using the proposed method. Our results imply that flushing flow supports native Hydrilla verticillata inhabitation within the downstream reach of a dam.