Some options to minimise the effects of dams on water quality and mahinga kai.
When the natural flow and seasonal variations of a waterway are interrupted by a dam extreme care must be taken to maintain the amount of water needed to support healthy ecosystems. The amount of water needed is called environmental flow, which considers maximum and minimum flow levels to support a healthy ecosystem. Failure to provide an environmental flow can have serious consequences for water quality and mahinga kai.
The following options can be considered as minimum requirements for existing dam structures:
- Identify minimum flows that can be sustained by a waterway.
- Calculate the maximum amount of water that can be taken from a waterway based on minimum flows.
- Review and adjust flow and water levels when needed.
- Facilitate effective and species specific upstream and downstream passage for fish migration using ramps, ladders, and spillways on existing structures.
- Divert fish away from intake screens and outlet pipes as these damage fish.
- Use fish protection measures like collection buckets to return fish into the river.
- Monitor fish migrations to provide optimal conditions during migration - e.g., regulate when and how you use the water available at certain times of the year and avoid extreme temperatures (above 25 degrees).
- New structures need to incorporate methods for fish passage and natural flow.
The following need to be considered as minimum requirements for water storage dams:
- Regulate minimum and maximum flow levels in rivers and lakes above and below dams or barriers so that there is sufficient habitat for fish and invertebrate life.
- Maintain natural channels and depth - create natural meanders, low flow channels and rest areas for mahinga kai species.
- Prevent temperatures from reaching lethal or extreme levels due to low flow or water levels.