In 2012 the Clackamas Soil and Water Conservation District implemented a stream restoration project on Milk Creek, a tributary and major stream in the Lower Molalla River watershed. The purpose of the project was to enhance in-stream habitat for juvenile salmonids and resident fish by improving habitat complexity, creating resting places for fish during high flows, and enhancing the riparian vegetation along the creek. Milk Creek is home for several Molalla Basin fish species: Chinook and coho salmon, winter steelhead, cutthroat trout, and Pacific lamprey.
The main purposes of the District’s Milk Creek project:
- Improve habitat for local salmon, steelhead and trout
- Slow the velocity of the water during high flows
- Reduce bank erosion in the project area
What are we trying to achieve in this project?
Milk Creek was eroding the banks at our project site, and fish habitat was impaired. Historically, splash dams were used on Milk Creek to transport logs downstream. This practice probably scoured the creek to bedrock many years ago, flushing gravel and woody material out of the system.
So, one of the goals of the project on Milk Creek was to move the water velocity away from the eroding bank and add a substantial amount of dead and growing wood to the system. This will reduce bank erosion and restore vital habitat for salmonids.
Why is large woody debris so important?
A limiting factor for salmon and steelhead habitat in Milk Creek is a lack of large wood in the stream — the result of past forestry practices that harvested large trees, and from the removal of riparian trees to make way for agriculture and residential development.
Loss of large wood has caused reductions in stream complexity, which means the ability of the stream to gather and hold gravel suitable for spawning is impaired. It also means fewer deep pools that cool the water and provide resting places for fish.
Another result of the lack of large wood in the system increased stream flow velocity, and faster water scours the channel bottom and erodes the bank. In fact, portions of Milk Creek are scoured down to bedrock. Cobble sits in the floodplain, but is lacking in areas of the stream where it is needed by salmon.
What is up with the logs sticking out of the stream bank?
Compared to the rock rip rap that was placed along the bank some years ago, the log matrix is better able to deflect water to the middle of the stream, protect the bank, reduce water velocity, and collect and deposit gravel and woody debris. A log matrix, in this case, is the anchoring of logs in the stream bank at various angles.
Restoring the native vegetation completes the process.
To restore native vegetation to the site required that we first controlled invasive weeds like Himalayan blackberry and Japanese knotweed. This is a time consuming, but very important step to give the native vegetation a chance to grow without competition from the invasive weeds.
After invasive control a riparian buffer was planted on seven acres along both sides of the stream, adjacent to the log structures. Establishing a healthy riparian buffer will, over time, help to reduce stream temperature, provide homes and a food source for native wildlife, and be a long-term source of large wood for Milk Creek.
Thank you to all of our partners!
Pete and Carrol Haushalter – landowners
Joe and Jen Herrera – landowners
Oregon Watershed Enhancement Board
Clackamas County Soil and Water Conservation District
Oregon Department of Transportation
Oregon Department of Environmental Quality
USDA Natural Resources Conservation Service
National Oceanic and Atmospheric Administration – National Marine Fisheries Service
Molalla River Watch