Fluvial Modeling ofVentura River Responses to Matilija Dam Removal

摘要

A plan has been made to remove Matilija Dam on the Ventura River. With dam removal, the delta in the reservoir and the downstream channel are expected to undergornmajor changes in morphology. The FLUVIAL–12 model was employed to simulaternreservoir and river channel responses after the dam removal. As the first step, the modelrnwas calibrated using the Ventura River data to establish its validity. In calibration, thernmodel was used to simulate the fluvial processes starting from the time of damrncompletion. The simulated sediment deposition above Matilija Dam matches closelyrnwith the measured deposits by the U. S. Bureau of Reclamation.rnA large amount of sediment has been stored in the reservoir; some of the storedrnsediment will be transported downstream after the dam removal. An importantrnconsequence of dam removal is the major increase of sediment release to the riverrnchannel downstream. The sediment supply to the downstream reach is not only from thernstored sediment in the reservoir but also from natural sediment inflow from the upstreamrnwatershed. Therefore, sediment supply to the downstream reach will exceed the naturalrnsediment flow before the dam presence. This situation tends to overload the downstreamrnreach with sediment to result in excessive deposition. The amount of sediment releasernfrom the area above the removed dam is closely related to the changes in reservoirrnmorphology. It is necessary to model changes in channel bed profile and in channelrnwidth during erosion in order to determine the amount of sediment removal. The amountrnof sediment release may not be simulated using an erodible-bed model but it may berndetermined using an erodible boundary model.