Project Name

Harkens Lake Restoration Alternatives Analysis (NEW)

Watershed and Stream Assessments
Client / Agency
Greenbelt Land Trust
Oregon Watershed Enhancement Board, Meyer Memorial Trust, Bonneville Power Administration
Willamette River near Monroe, Oregon
2011 - 2013
Project Description
The Greenbelt Land Trust, with funding provided by the Oregon Watershed Enhancement Board, Meyer Memorial Trust, and Bonneville Power Administration, retained River Design Group, Inc. to complete a floodplain inundation investigation and restoration alternatives analysis for the Harkens Lake area northeast of Monroe, Oregon. Harkens Lake is a relict channel of the Willamette River that has been modified by two U.S. Army Corps of Engineers’ revetments, multiple low water crossings, and agricultural land uses. Under the current conditions, Harkens Lake is backwatered by the Willamette River during winter and spring flows. As the system no longer experiences sufficient flow-through due to the upstream disconnection from the Willamette River, sedimentation and vegetation encroachment have degraded habitat for native species including juvenile Chinook salmon and steelhead.

Project goals include gaining a better understanding of floodplain inundation patterns and developing restoration strategies for improving connectivity between the Willamette River and Harkens Lake, enhancing aquatic habitat in Harkens Lake for juvenile salmonids and other native species, and maintaining existing levels of landowner access throughout the property.

The floodplain inundation investigation included relating observed water surface elevations at five staff gages in the Harkens Lake area, to measured river discharge at the U.S. Geological Survey Harrisburg gage on the Willamette River. Developed stage-discharge relationships were used to predict floodplain inundation extents at multiple discharges. Inundation patterns and existing floodplain topography were assessed to determine possible cost-effective restoration actions that would achieve the project goals.

Five restoration alternatives were prepared for the property. Although the alternatives are presented as discrete alternatives, elements of each alternative may be selected by the stakeholders to maximize ecological and socio-economic outcomes. Additional stakeholder discussions will be necessary to identify the preferred suite of restoration actions which will then be developed during the project design phase.
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Predicted floodplain inundation at the Harkens Lake site associated with increasing river stage.
Willamette River bank conditions adjacent to Harkens Lake.
Water control structure at the downstream extent of Harkens Lake is operated to affect water surface elevations in Harkens Lake. The restoration alternatives provided suggestions on addressing this structure.
A rock sill forms the outlet from Harkens Lake to the Willamette River. The Willamette River overtops the sill and backwaters Harkens Lake.
Installing staff plates at Harkens Lake. Staff plates were used to monitor floodplain inundation to better understand river-floodplain connectivity.
A Harkens Lake staff plate during a January 2012 high water event.