Modeling the impact of dam removal on channel evolution and sediment delivery in a multiple dam setting

Dam removal can generate geomorphic disturbances, including channel bed and bank erosion andassociated abrupt/pulsed release and downstream transfer of reservoir sediment, but the type and rate ofgeomorphic response often are hard to predict. The situation gets even more complex in systems whichhave been impacted by multiple dams and a long and complex engineering history. In previous studiesone-dimensional (1-D) models were used to predict aspects of post-removal channel change. However,these models do not consider two-dimensional (2-D) effects of dam removal such as bank erosionprocesses and lateral migration. In the current study the impacts of multiple dams and their removal onchannel evolution and sediment delivery were modeled by using a 2-D landscape evolution model(CAESAR-Lisflood) focusing on the following aspects: patterns, rates, and processes of geomorphicchange and associated sediment delivery on annual to decadal timescales. The current modeling studyrevealed that geomorphic response to dam removal (i.e., channel evolution and associated rates ofsediment delivery) in multiple dam settings is variable and complex in space and time. Complexity ingeomorphic system response is related to differences in dam size, the proximity of upstream dams,related buffering effects and associated rates of upstream sediment supply, and emerging feedbackprocesses as well as to the presence of channel stabilization measures. Modeled types and rates ofgeomorphic adjustment, using the 2-D landscape evolution model CAESAR-Lisflood, are similar to thosereported in previous studies. Moreover, the use of a 2-D method showed some advantages compared to1-D models, generating spatially varying patterns of erosion and deposition before and after damremoval that provide morphologies that are more readily comparable tofield data as well as features likethe lateral re-working of past reservoir deposits which further enables the maintenance of sedimentdelivery downstream.