Reverse flow tubes and their application in upstream fish passage

The purpose of this research was to evaluate reverse flow tubes (RFTs) and their ability to reduce velocities in open channel flow and provide suitable upstream fish passage. A RFT is defined as a pipe that introduces a countercurrent jet into an open channel. The momentum transfer between the countercurrent jet and the main channel flow increases the flow depth and decreases the average velocity. Because RFTs reduce the average velocity, placing the RFTs in series may have an application in upstream fish passage.; To test the concept, a tiltable flume was constructed in the laboratory and physical measurements were conducted. The flume was 24 ft long by 4 ft wide by 3 ft high. The flume had a maximum capacity of approximately 20 cfs with approximately 5 cfs for the reverse flow. A moveable wall within the flume allowed different channel widths to be tested. The flume width was varied from 18, 30, 36, and 48 inches. Flume slopes included horizontal, 1V:20H, 1V:10H, and 1V:8H. RFT nozzles included 6-inch and 8inch elbows and various orifices were tested to increase the momentum flux.; A one-dimensional hydraulic analysis was completed using the conservation of mass and momentum principles. A comparison of the predicted upstream depth compared with the measured depth in the physical tests showed reasonably good agreement for most of the flows. A numerical three-dimensional analysis using the Reynolds-Averaged Navier-Stokes equations was also completed on three different configurations, providing information on the velocity field.; Three-dimensional velocities were recorded using an acoustic doppler velocimeter. Velocities were collected over a specified grid and time-averaged for a minimum of 20 seconds. The velocities were plotted and show that the use of RFTs significantly reduces the time-averaged velocities and creates a velocity field that is hydraulically conducive to upstream fish passage.