Experiments on Channel Evolution due to Dam Removal in Taiwan

Due to safety concerns and habitat restoration for landlocked salmon, a 13-m high check dam on Chijiawan Creek was removed in late May 2011 in Taiwan. We conducted experiments to understand channel evolution of different scenarios. We further compared our experimental results of riverbed elevation changes with the analytical solutions derived from the diffusion equation and field dynamics as well after the creek experienced the first flood event. The results indicated that magnitude of discharges and notch size are dominant factors in resulting channel evolution. While the largest differences between grain size distribution are associated with discharge, the largest differences in net change in upstream volume are associated with notch size. While the theoretical equation could help understand the channel change after dam removal, it only explained the evolution closer to the dam. The physical experiments, on the other hand, provided insights especially with regard to comparing alternative proposed management actions. The discrepancies between predicted and actual outcome highlight more needed inputs for future dam-removal assessments.