GEOMORPHIC AND HYDROLOGIC CHANGES IN THE EAST FORK WHITEWATER RIVER FOLLOWING LOW-HEAD DAM REMOVAL, RICHMOND, IN

We assessed sediment movement and water quality parameters in the East Fork Whitewater River following the September 2023 removal of a 2-m high weir dam. Suspended sediment associated with dam removal moved through the survey area almost immediately, resulting in a sediment peak visible on a USGS stream gauge 4 km downstream approximately 11 hours after removal began. To study the fate of coarser sediments that made up the bulk of the former dam pool and determine how riverbed and channel morphology changed following dam removal, we resurveyed 12 cross sections and a long profile of the channel bed using total stations in July-August 2024. River velocity and water quality parameters were also measured throughout the study area.

We found that the large pool behind the dam no longer exists, and the channel in that area has become much narrower and shallower, with riffles developing as the channel bed equilibrates to a new base level. In spite of significantly increased water velocity in the vicinity of the former dam pool, water quality parameters including dissolved oxygen concentrations and temperature have not improved. Most of the sediment previously stored behind the dam has been deposited in pools and runs within 350 m of the former dam, although we measured deposition up to 750 m downstream.

In the approximately 10 months between dam removal and our survey, the watershed experienced multiple high-flow events, but none larger than a 2-yr flood that occurred on 11 April 2024. We conclude that dam pool sediment moves even at relatively low discharges in the initial year following dam removal, and hypothesize that sediment movement will require larger and larger flows to mobilize with increasing time after dam removal.