Poorly designed instream structures (including culvert pipe, weirs, and dams) are a significant contributing factor in the declining populations of New Zealand’s native freshwater fish.
If these structures are not designed, installed, and maintained correctly, they can disrupt fish lifecycles by creating barriers to fish passage and preventing fish moving up and downstream and to the sea.
Good fish passage design for an instream structure ensures:
- Efficient and safe upstream and downstream passage of all aquatic organisms and life stages resident in a waterway with minimal delay or injury
- Diversity of physical habitats and hydraulic conditions (rapids, backwaters, and areas of slow flow for example)
- The structure provides no greater impediment to fish movements than the adjacent stream reaches
- Natural processes like the movement of sediment and debris to continue
- Structures have minimal maintenance requirements and are durable.
To ensure the culvert pipe design meets New Zealand’s Fish Passage Guidelines, any instream structure should be designed to avoid vertical drops, water that is too shallow, high water velocities, excessive turbulence, sharp corners, overhanging edges, and smooth substrates.
Simple Solution: Large Culverts.
One of the simplest solutions for an instream pipeline structure that can meet the guidelines for fish passage is the installation of a large culvert that is buried to a sufficient depth, so it simulates the stream environment around it in terms of the channel width, depth and slope.
With a large culvert pipe that is buried to the right depth, you can retain the bank-line inside the culvert and ensure you have the natural substrate (such as pebbles, gravel, silt or plants) present throughout the culvert too.
In using this design, you are aiming to offer the same water depths, resting areas and basic habitat that is present in the rest of the river or stream to enable fish species to easily pass and complete their lifecycle.
As outlined in the New Zealand Fish Passage Guidelines it is important that any instream structures are durable and have minimal maintenance requirements.
P&F Global’s EUROFLO® pipes are one option for instream pipeline structures: made from high-density polyethylene (or HDPE) the pipes are maintenance and rust-free, robust (they are one of the strongest plastic pipes on the market) and they come in a range of sizes up to 2100mm in diameter.
If you have a dam, weir or creek that needs a culvert talk to your local Think Water store about doing the right thing for our environment and keeping our fish population healthy.