Mitigation Measures for Fish Passage in Culverts in Australia :
Turbulence Manipulation, Fish Kinematics and More...
Séminaire Hubert CHANSON
- Professor in Hydraulic Engineering - University of Queensland Brisbane Australia
Jeudi 24 novembre à 13 h 30
Culverts are road crossings passing underneath an embankment (e.g. roadway, railroad) to allow continuous flow of water. Numerous waterway culverts are installed worldwide. Culvert designs are diverse, using various shapes and materials determined by stream width, peak flows, Stream gradient, and minimum cost. For the past two decades, concerns regarding the ecological impact of culvert crossings have led to an evolution in their design. In some cases, the environmental impact on fish passage may affect the upstream catchment with adverse impact on the stream ecology, because the installation of road crossings can limit the longitudinal connectivity of streams for fish movement. Common culvert fish passage barriers include excessive vertical drop at the culvert outlet (perched outlet), high velocity or inadequate flow depth within the culvert barrel, excessive turbulence, and debris accumulation at the culvert inlet. Higher culvert exit velocities may also increase perched outlet fall heights (fish barrier) with increased scour hole development downstream. One of the primary ecological concerns regarding culvert crossings is the potential velocity barrier to upstream fish passage resulting from the constriction of the channel as illustrated in Figure 1. In an effort to minimize the impact of culvert crossings on stream ecology, several jurisdictions have developed guidelines to ensure that their design will allow for the upstream passage of fish. In Canada, these guidelines are based on a number of criteria including average flow velocity and minimum embedment depth. In Australia, national recommendations provide little guidance, merely indicating that water depth should range between 0.2 to 0.5 m with bulk velocity less than 0.3 m/s during base flows, thus yielding uneconomical culvert designs. For culvert rehabilitation applications where fish passage may be a concern, baffles installed along the invert may provide a more fish-friendly alternative, provided that adequate culvert discharge capacity is maintained.
In Australia, small native fish species have body length less than 150 mm with sprint speed less than 0.6 m/s. Their limited performances constitute a major challenge for culvert design. In this seminar, physical modelling was conducted for a range of configurations typical of standard box culvert. Experiments were performed to assess the response of fish to turbulence and turbulence manipulation in the new UQ Seddon Bio-hydrodynamics laboratory. The project focuses on the development of simple solutions, which could be used to retrofit of existing box culverts, embedding both hydrodynamic and biological considerations.
- Fig. 1 - Culvert operation during medium rainstorms in Brisbane, Queensland, Australia - Outlet of culvert beneath Cornwall Street, Stones Corner on 31 Dec. 2001 around 6:10 am