Well here is the "living wall" built on a rock toe. The purpose for this structure is to protect a tree we need to save while maintaining a long, rather deep pool. As mentioned before, one of the ways Lucas Creek has historically dissipated its' energy is undulations in it's long stream profile (pools and glides). This pool in the bend is pretty important to maintain.
The treatment for steep banks is a rock toe and maybe some incorporated large woody material (remember, the other historic energy dissipator is woody debris). When impinging flows hit hard, immovable objects the flows generally go down and scour. That is just what we want for aquatic habitat, a nice sustainably maintained scour pool with overhanging wood maybe.
Come winter time, the living wall - the compost socks and geogrid facing, will be hydromulched. IECA Member, Robert Coulson, RST Environmental Solutions Ltd., has has much experience building and vegetating these compost sock/reinforced walls, especially successful repairing failed road embankments. Robert often incorporates willow brushlayering in his solutions. Unfortunately, willow species are not native to New Zealand therefore willow must be kept out of the Lucas Creek Biotechnical Restoration.
We will also build several Newbury Rock Riffles along this 800m stretch. Rock riffles are a environmentally-sensitive grade control structure and we are using them to ensure that future incision of Lucas Creek will be arrested. They are also strategically placed to maintain the pool and glide profile. Newbury Riffles are well described in the NCHRP Report 544 - Environmentally-Sensitive Channel and Bank Protection Measures (2005) or also available in ESenSS. www.esenss.com.
Stay tuned, next entry will show compost blanket being installed and the first-ever rock vane to be built in New Zealand (maybe in the entire Southern hemisphere! )