A low rock ramp downstream of a culvert will help prevent hanging outlets and other erosion problems by slowing down the flow of water at the outlet.
To allow fish passage, build your rock ramp the width of the stream and take care that your rock placement doesn't cause water to back up in the culvert at high flows.
Large rocks are placed across the stream bed to form a zigzag stairway. This will slow water flow and form small pockets of still water and eddies in which fish can rest. Make sure there is at least one clear channel of water that meanders through the rock ramp at low stream flows.
The cross section of the rock ramp from bank to bank should form a shallow ‘v' shape to help ensure suitable water depths for fish at a variety of flows.
A rock ramp fish pass, with rocks forming a zigzag pattern across the stream bed to reduce flow and provide pockets of still water/eddies where fish can rest as they move upstream.
For more information please contact our land management team on 0800 002 004.
Thanks to Greater Wellington Regional Council for sharing their ‘Fish-friendly culverts and rock ramps for small streams' brochure concept and Horizons Regional Council, Manawatu, for their fish and culverts photos.