Effects of Dams and Diversions

Dams alter the flow and sediment load of rivers downstream, and thereby may induce changes in channel form in alluvial rivers. By reducing the magnitude of frequent, moderate floods, dams may lead to channel narrowing as riparian vegetation invades the active channel that was formerly scoured of vegetation by frequent floods. By trapping sand and gravel in reservoirs, dams deprive downstream reaches of their normal sediment load and release sediment-starved, or hungry water, which tends to erode its bed and banks unless the dam has reduced flood magnitude so much that sediment accumulate on the bed instead. On some rivers, such as the Trinity River in California, reduced flows resulted in accumulation of tributary-derived sediment, degrading aquatic habitat, and leading to a program of artificial high flow releases known as flushing flows (discussed on webpage Flow Releases from Dams and Diversions).

SELECTED RELEVANT PUBLICATIONS

Batalla, R.J., C.M. Gomez, and G.M. Kondolf. 2004. River impoundment and changes in flow regime, Ebro River basin, northeastern Spain. Journal of Hydrology 290, 117-136.

Kondolf, G.M. 1997. Hungry water: Effects of dams and gravel mining on river channels. Environmental Management 21(4):533-551.

Wilcock, P.R., G.M. Kondolf, W.V. Matthews, and A.F. Barta. 1996. Specification of sediment maintenance flows for a large gravel-bed river. Water Resources Research 32(9):2911-2921.

Kondolf, G.M. 1995. Managing bedload sediments in regulated rivers: Examples from California, USA. Geophysical Monograph 89:165-176.

Kondolf, G.M., and W.V.G. Matthews. 1990. Assessment of potential impacts of Monterey Peninsula Water Supply Project Alternatives on downstream channel geometry of the Carmel River. Report to the Monterey Peninsula Water Management District.

View upstream to Stony Gorge Dam, Stony Creek, California