What is this Lucas Creek Project all about you might ask!
Well Lucas Creek drains a large watershed that happens to be one of the fasted growing areas in the Auckland area. New shopping malls, the huge new Rugby Stadium, and a good part of the Motorway are just some of the developments. On the good note, North Shore City Council and Auckland Regional Council (ARC is also the ultimate regulatory authority here) are implementing considerable Low Impact Development (LID) development standards. They are way "ahead" of us in California. But the point is, Lucas Creek is and will continue to experience higher and more frequent flood type flows.
So the main purpose for this project is to "re-fit" the creek to accept new flow regimes and to maintain water quality, enhance aquatic habitat, and develop a sustainable regional park area. All the goals center around Lucas Creek operating in a Proper Functioning Condition (PFC). PFC criteria asks can the stream system pass water (low and high), sediment, bedload etc., in a way that is naturally sustainable. A good question to ask is how did the stream dissipate excess energy in the past, e.g., rocks, meanders, large woody debris, pools/riffles, access to flood plains, or car bodies and refrigerators !!
Back to what we are doing. We are working over 800m long stretch this phase and we are going to widen Lucas Creek. It has already incised about 2-3m and the high flows rarely go out of bank. It is not functioning properly now and can only get worse with continued urbanization. The bottom width, low flow, will be roughly doubled to 4-5m. There are a couple of wide radius inner bends that will have large, low terraces (point bars) built. Next is the installation of really cool, naturalized grade control structures - Newbury Rock Riffles, will arrest any future incision. They will also provide good substrate, encourage pools and riffles and ...... that will be shown and discussed next week!!
Good news, while it rained last night and a bit today, the creek has stayed pretty clean. The most turbidity we saw today came during the mid day rain but the murky water came above our site, probably the Motorway upstream!! One of the other neat things is we are demonstrating NEW and Effective BMPs, alternatives to silt fence, like fiber rolls (installed with Caltrans-approved Type 2 installation - rope and stake method), and compost silt socks (half chips/half aged compost). These worked GREAT last night, and unlike silt fence, could be moved around today!
The pictures taken today show the completion of a "living wall" with rock toe. This is our "model" treatment for how we might treat other steep outer bends (versus the low, wide and terraced inner bends). We also introduced some salvaged Large Woody Debris as that is how this clay/silt soft-bottomed stream historically dissipated energy.
Also, upstream, two large excavators and an off road dump are "hogging out" soil (got dirt!) for a flood terrace there. Our operators are so good, keeping a 1 meter berm between them and the live stream - not a clod has fallen in!!