SS3.21 Deconstructing Rivers: The Ecological, Geomorphic, and Social Consequences of Dam Removal
Date: Thursday, June 13, 2002
Time: 11:15:00 AM
Location: Colwood
LisleTE, USFS, Arcata, CA, USA,
A primary concern in removing dams is what to do with all of the sediment The channel forming in the drained reservoir can only evolve as a restored lotic ecosystem, but the channel downstream of the dam is subject to a wave of released sediment. Recent research of sediment waves provides encouragement to proponents of dam removal. Sediment waves in gravel-bed channels evolve predominantly by dispersion rather than translation. This predicts that sediment released from a dam, however it is eroded from the reservoir, will spread downstream and mix with ambient sediment rather than move en masse. Sediment impacts will therefore be of low magnitude and long duration. However, a virtual translating wave can be created as a wave spreads into low-gradient, depositional zones in a gravel-bed river, and sediment waves are inherently translational in low-gradient, sand-bed channels. Even in these cases, dispersion can be expected to rapidly dampen the magnitude of sediment impacts downstream. One-dimensional, numerical models have accurately predicted the evolution of a variety of sediment waves in natural and experimental channels, and should be applicable to cases of sediment released from a dam.