NZ Living Wall

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.

This picture is looking downstream. The impinging point for high flows will be about where the rock is being placed.

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.

The same bend with rock toe & wood incorporated. From this secure base we will construct a “live wall” built from compost berms & geogrid for a reinforced soil wall.

The geogrid (biaxial) is laid back a meter then wraps the face of three compost berm “lifts” (about 18″ or 0.5m)

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.

As my friend David Derrick says, “Be the water”! Imagine the high water, another meter high hitting the wood, and rock toe. It (the water) will try to undercut the bank but instead maintain the long pool, we hope!

Here is an upstream view of the completed living wall transitioning into an “engineered, log” undercut bank, sometimes called a lunker structure. This log structure might more accurately be called a “modified New Zealand log lunker”! Notice also just downstream is a newly completed Newbury Rock Riffle. The crest of the riffle is actually a modified cross vane, so I call it a “viffle”!

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.

The Modified New Zealand Log Lunker almost completed. Looking upstream 

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! )


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