Fish Passage Design for Ecological Connectivity to a Stormwater Facility
Stormwater Conference
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Designing stormwater facilities to provide fish passage is becoming increasingly important as stakeholders and communities realise the benefits of improving water quality, ecology and amenity values, and the impact of developments on threatened native freshwater fish.
The stormwater facility for the Burlington Lifestyle Village in Christchurch provides stormwater treatment using first flush wet ponds, a conventional wetland and floating wetlands within a wet pond. The inclusion of wet ponds provided an opportunity to enhance ecological value by providing a new habitat for native freshwater fish.
Fish access through culverts is vital for allowing fish movement into upstream waterways and stormwater facilities. However, structures used for flow control for stormwater basins are typically of a small diameter with resulting flow velocities exceeding the threshold at which freshwater fish passage is achievable. An added challenge was a requirement to provide 0.5 m flood storage above the wetland in a 2% AEP 48-hour event in accordance with the Styx Stormwater Management Plan but not inundate the wetland in all events up to a 10% AEP magnitude.
All new structures were designed to provide fish passage for native freshwater species from the downstream Styx River receiving waterway to the new stormwater facility and further upstream into Barclays Drain, whilst also ensuring the stormwater treatment and partial flood storage objectives were achieved.
This paper presents some of the fish passage structures designed for this site. This includes culverts with orifice plates designed to control outflow rates and allow fish passage, spoiler baffles constructed within the invert of culverts and ramped fishways with rock baffles in the base to slow flow velocities and provide small pools for fish to rest. The culvert spoiler baffles and rock baffles were designed to slow flow velocities and then optimised for the site constraints based on two-dimensional hydraulic modelling.