PREDICTING CHANNEL MORPHOLOGY FOLLOWING DAM REMOVAL USING HISTORIC CHANNEL CONDITIONS

One of the most critical issues surrounding dam removal is the fate fo the sediment stored in the impoundment. The quantity of the sediment transported out of the former impoundment has profound implications for the stability of downstream structures as well as for local biota. The conditions of the channel prior to the construction of a dam may serve as an indicator of the conditions to which the channel will return when the dam is removed, and thus provide an estimate of the (1) likely planform and profile the new channel may adopt, (2) areas needing sediment stabilization, and (3) quantity of sediment that will be transported downstream from the impoundment following dam removal. We collected sediment cores from an impoundment in southern Wisconsin and used thse data to reconstruct historic channel conditions in terms of channel morphology, location, and bed-load and suspended-load caliber. Post-removal morphology was then compared to pre-dam morphology. Preliminary analysis of these data, and those available from other dam removal studies, suggest that post-removal channels do not necessarily follow pre-dam channel alignment or profile. Such observations are in stark contrast to the common assumption that post-removal channels will return to pre-dam conditions.