Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Survival of fish passing downstream at a small hydropower facility (#72)

Stephen Amaral 1 , Benjamin Coleman 1 , Jenna Rackovan 1 , Kelly Withers 2
  1. Alden Research Laboratory, Inc., Holden, MASSACHUSETTS, United States
  2. Brookfield Renewable, Marlboro, Massachusetts, United States

Hydropower dams can negatively impact upstream and downstream migratory fish populations in many ways, such as blocking access to upstream habitats and causing injuries or mortality during downstream passage.  For downstream passage at projects in the USA, federal regulators and agencies responsible for oversight of hydropower facilities typically require assessment studies and mitigation to address negative impacts with a primary goal of minimizing fish impingement and turbine entrainment and mortality.  In order to assess impacts of downstream passage of fish populations at a unique, small hydro project on the Mississippi River, impingement and entrainment rates, Obermeyer gate passage, spillway gate passage, turbine survival, and total downstream passage survival were estimated.  It was determined that 85% of fish passing downstream at the project would be small enough to pass through the bar spacing of the trash racks and 15% would be physically excluded. When 55% of river flow enters the turbine intake channel, the total project survival rates were estimated to be 77.3% with an Obermeyer gate bypass rate of 10% to 96.6% with a gate bypass rate of 90%. Therefore, any impacts to local fish populations resulting from the operation of the project are expected to be negligible and inconsequential.