Along the banks of the Pend Oreille River, about 100 miles north of Spokane sits Boundary Dam, one of Washington's most dependable sources for clean, renewable energy. Its six turbines provide up to half of Seattle's total power requirements. The Boundary Hydroelectric Project operates on a Federal Energy Regulatory Commission license that would expire in 2011. Seattle City Light contracted with Tetra Tech, Inc. and HTI to conduct fish entrainment and habitat connectivity studies in support of its relicensing application.

One goal of these recently completed studies 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 HTI Model 244 Multi-Frequency Digital Split-Beam Echo Sounders.

The split-beam systems provided high temporal and spatial sampling coverage at each potential fish passage route, quantifying fish entrainment 24 hours a day, 365 days per year, over a 2 year period. The study results were used to estimate fish passage at the powerhouse and spillway under different operating regimes on an hourly, daily, diel and seasonal basis. Fish direction-of-movement, size, velocity, vertical approach distributions and other parameters are also summarized from the hydroacoustic data.

“Boundary Dam is a challenging site”, explained Peter Barton, fish and aquatics study coordinator for Boundary's relicensing team. HTI is proud to work with Seattle City Light at the Boundary Hydroelectric Project.