Numerical Modeling of Sediment Migration during Dam Removal

Current numerical sediment modeling strategies are presented in the context of dam removal. The capabilities and limitations of each strategy are analyzed and present needs in research are emphasized. It is shown that current state of the art modeling techniques do not sufficiently describe the complicated problem of sediment migration during dam removal. Based on the review, a new modeling methodology is presented that has the ability to track the quantity and velocity of sediment as it moves through the water course in steady and unsteady flow situations. The model can also track the migration of sediment attached contaminants. The model is applied to the Matilija and Battle Creek Dam removal projects. Matilija Dam is 160 feet in height and is almost completely full with sediment. The small flow in the river (only a few cfs) that it dams is interrupted by extremely high flow events every few years. Because of the relatively large population located near the river channel downstream there is concern of increased flood stage and geomorphic change of the river. Along Battle Creek, there are several diversion dams scheduled for removal. The two of greatest interest in terms of sediment management are approximately 10 to 15 feet high. There is very little development located near the river channel and therefore the risk to human populations is small. The main concern in the Battle Creek streams is the possible impacts on fish and fish hatcheries. These two projects are used to illustrate how the specific concerns of a dam removal project impact the modeling strategy. In addition, the new model proposed in this paper is compared with approaches that are more conventional.