| Issue
The creation of a reservoir changes the hydraulic and sediment transport characteristics of the river, with implications for sediment and erosion processes at the reservoir, in the downstream river system, and in cases in the estuarine/deltaic zone. The natural sediment load in a river is usually trapped within the storage and this material is deprived to the downstream river system. Sediment accumulation is a sustainability issue for some reservoirs and in cases can reduce the long-term viability of developments. Erosion issues in the reservoir itself can occur depending on the lake level operating regime, the retention of stabilizing vegetation, the control of recreational activities on the lake, and other factors such as wind-induced wave action or rapid drawn-downs.
Impacts of a reduced sediment load to the river downstream of a power station may arise depending on the pre-existing sedimentation and erosion patterns, the nature of the regulated flow release and the altered flooding regimes, and the riparian vegetation condition. Where diversions out of river systems have occurred, and sediment inputs continue from the downstream catchment, channels can accumulate sediments, vegetative species may encroach on the river channel, and this can exacerbate the impacts of floods. Downstream of power stations, reduced sediment loads and in cases, higher than natural base flows, may lead to erosion of the existing channel sediments and destabilization of riparian vegetation through a range of mechanisms, e.g. rapidly fluctuating discharges, rapid water level draw-downs, or continuous discharges at a single flow. |
