Hydraulics of vertical slot fishways: Non-uniform 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 non-uniform water depth profiles, i.e. differences in the water drops across the slots (ΔH) and mean depths (h0) across the pools. Although non-uniform conditions are present in most VSFs, they are rarely considered in the design and evaluation of fishways. The aim of this work is to provide an introductory analysis of how non-uniform 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. Non-uniformity 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 non-uniform conditions.