Dam Removal Effect on the Lower St. Regis River Ice Jam Floods

The Hogansburg Dam in Akwesasne, NY, on the lower St. Regis River, a tributary of the St. Lawrence River, was decommissioned and removed in 2016. The dam removal restored over 893 river km of migratory fish access. However, ice jams occurred on the lower St. Regis River in winter before and after the dam removal, which caused flooding in the St. Regis Mohawk Tribe Reservation. This study reviewed the historical ice-jam conditions in the lower St. Regis River and the effect of dam removal. A two-dimensional river-ice model, DynaRICE, capable of simulating the dynamic ice transport and jamming processes, was used to evaluate pre- and post-dam-removal conditions of the Hogansburg Dam on the ice-jam flooding in the St. Regis Mohawk Tribe Reservation. The study showed that the dam removal effect decreases as the breakup discharge increases. A potential mitigation scheme for reducing ice-jam floods in the Hogansburg area using ice booms was examined and recommended.