Fish-friendly – at normal water levels, the floodgate stays open. (Photo: Ron Ovenden, NIWA)
Fish-unfriendly – a traditional Waikato floodgated stream with trapped sediment, stagnant water, and aquatic weeds. (Photo: Jacques Boubee, NIWA)
Floodgates and stopbanks play an important role in protecting productive farmland and housing during floods and spring tides. Unfortunately, floodgates also hinder the passage of fish such as whitebait and mullet. The good news is that a new fish-friendly gate has been designed by a NIWA-led team, and is now ready for installation.
The design, based on a simple ballcock mechanism, can be easily attached to existing structures. As well as enabling fish passage, the fish-friendly gate should allow more natural water flow conditions behind the gates, improving water quality and enhancing conditions for fish. Improving water flow will have other benefits, including reducing the proliferation of aquatic plants. Plants can trap sediment, restrict water flow, and need expensive regular spraying and/or digger use to clear them. Stagnant water behind existing floodgates often looks and smells unpleasant, and can harbour mosquito larvae.
The fish-friendly gate is likely to cost less than $3,000 to buy and install. The development team included Opotiki engineer Kelly Hughes, Environment Waikato, Environment Bay of Plenty, and collaborators from New South Wales. Sites in the Waikato will be the first to have the gate installed.