Hydraulics of Vertical-Slot Fishways: Nonuniform Profiles

Abstract

Vertical-slot fishways (VSFs) are hydraulic structures which allow fish to swim around obstacles in rivers. These structures are subject to variations in discharge of either hydrological or operational origin, which result in nonuniform water depth profiles. These profiles are manifested as differences in the water drops across the slots (ΔH) and mean depths (h0) across the pools. Although nonuniform conditions are present in most VSFs, they are rarely considered in the design and evaluation of fishways. This study provides an introductory analysis of how nonuniform water depth profiles affect the hydrodynamics within the pools of VSFs. This study shows that flow patterns are controlled by changes in ΔH and h0 in addition to slope and other geometrical alterations, as previously suggested. Nonuniformity alters the flow structure in pools and the spatial distributions of hydrodynamic variables. Consequently, critical thresholds of hydrodynamic variables for fish may be reached in VSFs designed with recommended slopes when operating under nonuniform conditions.