We received heaps of thoughtful feedback from engineers and ecologists regarding the last mail-out, so we have summarized the comments below. The projects in question are typically the often steep outfalls from culverts or other structures, as opposed to stream restorations or realignments.
Treatment of rock armoring feedback:
- Ideally surface-flow should be maintained with nature-like meanders.
- There is some evidence that small fish can make their way up through the gaps between the rocks but it is not ideal.
- Finer material may need to be added if it is unlikely to be transported and deposited by natural processes.
- Appropriate geo-textiles may need to be used. These may need to be impermeable.
- Adding of finer material will need to be managed to ensure large rocks still interlock.
- Armoring may need to extend further as velocities may be higher when all water is at the surface and the suface is less rough.
- Provision should be made to include vegetation within and overhanging.
- Precast channels can be designed to meander.
- If precast channels are used then the joints would need to be flexible and water-tight similar to the floating ramps.
- Precast channels would need to be anchored to ensure they do not tip and spill water over the sides.
This useful link to a very comprehensive Urban Storm Drainage Criteria Manual was shared by Iain Smith
https://udfcd.org/wpcontent/uploads/uploads/vol1%20criteria%20manual/08_Open%20Channels.pdf
