Hydroacoustic Sampling Illuminates Fish Passage at Boundary Dam

Boundary Dam, one of Washington’s most dependable sources of renewable energy, is located on the Pend Oreille River about 100 miles north of Spokane. Its six turbines generate up to half of Seattle’s power requirements.

The Boundary Hydroelectric Project operates on a Federal Energy Regulatory Commission license that was set to expire in 2011. Seattle City Light contracted with Tetra Tech and Innovasea to conduct fish entrainment and habitat connectivity studies to support its relicensing application.

The goal was to estimate the number, size, species and timing of fish that may be entrained through the dam’s turbine intakes and spillways. To describe fish passage through the powerhouse and spillways, Seattle City Light employed turbine netting in conjunction with two multi-frequency digital split-beam echo sounders from Innovasea.

The split-beam systems provided high temporal and spatial sampling coverage at each potential fish passage route, quantifying fish entrainment continuously over a two-year period. The study results were used to estimate fish passage at the powerhouse and spillway under different operating regimes on an hourly, daily and seasonal basis. The hydroacoustic data also summarized the fish’s size, velocity, vertical approach distributions and direction of movement.