Hydraulics of Resting Pools for Denil Fishways

Abstract

This paper presents the results of an exploratory laboratory study on the hydraulics of fish resting pools that are built between two Denil fishways, making a full turn or arranged in a folded-back pattern. These experiments show that the flow from the Denil entering the pool diffuses as a surface jet, with an increased growth rate, possibly because of the circulation and turbulence in the pool. This diffusing jet impinges on the backwall and dives into the pool. The flow formation in the vicinity of the outflowing Denil appears to occur in a relatively small region. The energy dissipation in the pool is significant. To provide some resting areas for fish ascending the multiple Denils, it is necessary to provide some depth below the common invert of the two Denils. Some suggestions have been made for determining the size of these resting pools.