Stop this disaster!

It is now common practice to use large, similar sized, rip-rap (boulders) to manage downstream erosion at structures.

Above is typical example of a recent culvert upgrade where extensive rock armouring has caused water to be sub-surface and spread over a wide area during most flows, making upstream migration almost impossible for most fish.

The rubber strip and rope were added afterwards to try to help with fish passage.

We need your help to share ideas on how to better provide fish passage while still meeting erosion control requirements.

– Discussion Paper- 

The challenge – maintaining fish passage through rock armouring, especially  during low lows.
Below is a concept that may provide passage for small fish, while still achieving erosion control.
A series of precast channels maintain a flow path that may be completely covered with large rocks, providing gaps remain between individual rocks.

Installation process

1. Excavation as part of structure installation
2. Suitable geo-textile laid
3. Precast channel fitted to apron at outlet. Also baffles fitted on apron
4. Rock rip-rap placed either side of ramp
5. Channel covered with rock rip-rap

Points to consider:

– Channel design
– Installation
– Cost
– Durability
– Effectiveness (short and long-term)
– Planting