McNary Dam Surface Fish Bypass

CLIENT: U.S. Army Corps of Engineers, Walla Walla District

The U.S. Army Corps of Engineers (USACE) operates four hydroelectric projects on the Lower Snake River. Each project includes multiple fish passage routes including conventional turbine intake screen bypass routes, spillway passage, and surface passage weirs at spillways. At McNary Dam, the USACE is investigating a new surface fish passage route that includes the addition of ogee crest weirs above the turbine intake units. The fish would pass over these weirs and into the existing ice and trash (I&T) sluiceway and then be diverted downstream into the tailrace.

NHC constructed and tested a 1:20 scale sectional model of two powerhouse units of McNary Dam. The purpose of the project was to test the addition of surface passage weirs over one or two bays of Unit 13 for a prototype test where the USACE would construct one weir as a pilot project. Due to the complex hydraulics in the existing I&T sluiceway, including a 40-foot drop in one section, a physical model was required to develop the design. The model includes a section of the forebay, Units 13 and 14 of the powerhouse, I&T sluice channel, gatewell slot fish passage orifices, I&T sluice drop, and I&T sluice chute. NHC tested two different weir configurations and several modifications to the I&T sluiceway channel system.