Reclamation Information Sharing Environment (RISE)

We present in this geospatial data the work that was conducted of a series of geomorphic and hydraulic studies to assess changes in the Bighorn River, including geomorphic mapping, tracing the displacement of RFID-tagged gravels, and hydraulic modeling. The first studies in 2009-2010 followed a period of drought marked by lower releases from the dam; findings include: (1) the Bighorn River lost significant geomorphic diversity following dam closure, indicated by loss of active channel area, side channels, islands, and unvegetated bars; (2) the Bighorn River was not incising; (3) the frequency of moderate peak flows (<10,000 cfs) likely aggraded side channel entrances; and (4) modeled flows of the maximum allowable release were unlikely to excavate aggraded material at side channel entrances. In 2019, we reassessed the river following a wetter decade with prolonged high flow releases. The high flows resulted in bank and mid-channel island erosion, which provide the only source of gravel to the river. The majority of gravel tracers seeded at the entrances to four side channels were found close to the seeding location, or completely flushed through the channel. One possibility is that it is more difficult to mobilize gravels at the crest of side channel entrances than it is to mobilize farther downstream. High flows did remove vegetation and aggraded sediment at many channel entrances, most often reopening overflow channels. However, many side channels continued to become disconnected from the main channel- requiring higher flows on the Bighorn River to form a connection.