Evaluating Stream Restoration Options after Dam Removal Using HEC-RAS

The liability associated with obsolete or aging dams combined with concern over the impediments to natural fish passage have created an environment where many agencies are seriously looking at dam removal as a viable option. However, years of sediment deposition in upstream reservoir areas mean that more than just the impacts of dam removals must be evaluated. Once the dams are removed, the streams will create channels through the sediments, scouring this material and carrying it downstream. Since this may create numerous problems with both the environment and the hydraulics, careful attention must be given to restoring the reservoir area. There is only one restoration option that both minimizes both the sediment impact downstream and the amount of upstream dredging that is necessary. This option is creating a stable upstream channel through the old reservoir. Established channel restoration techniques, however, have not been developed for creating a stable channel through old reservoir deposits. Through a combined effort of comparing channel morphology with stream's that have similar attributes and an analysis of the shear forces developed by the stream channel determined through a HEC-RAS model of the lake area, a suitable channel can be built.