Milk Creek is home for several Molalla basin fish species: Chinook and Coho salmon, winter steelhead, cutthroat trout, and Pacific lamprey.
A limiting factor for salmon and steelhead habitat in Milk Creek is a lack of large wood — a result of past forestry practices that harvested large trees, and from the removal of riparian trees to make way for agriculture and residential development.
What are we trying to achieve in the Milk Creek project?
The main purposes of the District’s Milk Creek project are:
- Improve habitat for the local salmon, steelhead and trout;
- Slow the velocity of the water during high flows; and
- Reduce bank erosion in the stream reach of the project.
Our work has focused on returning large wood to the stream while protecting eroding banks.
Here’s what we wrote in one grant application:
The project is on Milk Creek, a major stream in the Lower Molalla River watershed in western Clackamas County. Work will take place on three adjacent private properties on both sides of the creek. Milk Creek is a primary production stream for coho, listed spring chinook, listed winter steelhead, and resident cutthroat trout. Assessment, TMDL, and salmon recovery plans for the Molalla and Milk Creek watersheds recommend riparian and in-channel restoration, sediment reduction, large wood placement, and restoration of channel hydrology.
Watershed issues this project will address: lack of in-stream habitat, simplified channel structure, changes in stream hydrology, sediment inputs from bank erosion, high water temperature, and need for watershed stewardship education of local residents.
Proposed solutions: bank shaping; placement of a vegetated log matrix; removal of invasive non-native vegetation; heavy planting of native trees, shrubs, and cuttings; outreach and education.
Success measured through: photopoints, plant surveys, water sampling, pebble counts (gravel deposition), landowner response to workshops and site tours.
Lack of large wood impacts the stream, banks, and fish
Loss of large wood has caused reductions in stream complexity, which means the ability of the stream to gathers and hold gravel suitable for spawning is impaired. It also means fewer deep pools that cool the water and provide resting places for fish.
Loss of large wood has also contributed to 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.
Photos taken on December 5, 2012
These photos collected today help to show the current state of the large log structures. Also available are numerous photo galleries of the Milk Creek project showing the various stages of construction.
Difficulties encountered during construction
The construction phase of the project — completed in September 2012 — included bank shaping and installation of large wood structures. These large wood structures were challenging to design and install. Over several years the streambed in the area where the engineered log matrix was to be installed had become scoured down to bedrock.
When Aquatic Contracting LLC began preparing the site for the vegetated log matrix, it became apparent that it would be impractical, if not impossible, to embed the logs with attached roots (“rootwads”) into the streambed as proposed in the design, because the streambed was bedrock.
Initial design gets redesigned
Subsequently, the contractor, District staff, and engineers from the Natural Resources Conservation Service and the National Oceanic and Atmospheric Administration worked to come up with a solution. Significant revisions were made to the project design to make it easier to install the rootwads. At the same time, the revised design improved the effectiveness and structural stability of the vegetated log matrix.
The willingness of the various partners to take a team approach allowed the structure to be redesigned quickly, supporting a quick, successful installation within a very limited in-water work window.
Structures are tested by high water
The flood late in November 2012 tested the structures! This fall we’ve been experiencing very heavy rainfall which has resulted in high water levels in our local streams and rivers. Milk Creek has been no exception.
One good thing about floods is that they give us an opportunity to check out how the in-stream structures are working and the effects they have on the creek. The vegetated log matrix was designed to resist forces due to buoyancy, drag, and flow during a range of common storm events. The matrix includes a combination of large logs projecting into the stream.
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.
Recent storm events have allowed us to see that the installed structures remained intact, moved the highest water toward the middle of the channel, and even captured some debris that floated down during peak flows. Our monitoring cameras at the site captured before, during, and after photos of the event. One of the engineering team members visited and took video of the high water, then posted the video on YouTube.
What comes next?
The next phase in the Milk Creek project is to plant a riparian buffer on six 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.
To restore native vegetation requires that we first control invasive weeds like Himalayan blackberry and Japanese knotweed. Native riparian trees and shrubs will increase the complexity of the riparian buffer, shade the stream, and enhance wildlife habitat. Approximately ten thousand native trees and shrubs will be planted at the site early in 2013.