CLIPA White Paper - Lake Maintenance Plan

Our investigation shows that the North basin would only need to be dredged once every 5 years. We recommend and identify funding for a Deschutes Watershed management plan that addresses sediment management upstream as part of a comprehensive sediment management strategy. When implemented, the costs for dredging Capitol Lake could be reduced and the timing could be extended considerably. (It should be noted we are not advocating a shift in costs from the state to the local level, but a cost sharing program consisting of a public/private partnership.)

 

CLIPA strongly advocates for the restoration and protection of the entire lake, consisting of the three basins (South, Middle or “Mid,” and North – we capitalize each to draw attention to each individual basin). We recognize the State’s inaction to maintain the lake through routine dredges has resulted in the South basin turning into a wetland. We somewhat reluctantly support the continuation of the South basin as a wetland if: (1) funds are not sufficient to return this basin into a lake; (2) a Deschutes Watershed plan and the predesign studies clearly indicate the benefits of this wetland to the system as a whole, and; (3) this wetland be incorporated into an overall watershed and lake strategy to provide for the needs to the ecosystem and community, such that it is properly maintained and enhanced for habitat and other appropriate uses.

 

CLIPA recognizes the Mid basin has at least three possible courses that it may follow:

It is important to note that this decision does not need to be made until later in the first decade, after further study, experience from the North basin maintenance dredge, and coordination of a Deschutes Watershed plan.

 

With respect to the latter two alternatives, we first recommend considering Percival Cove as a dredged material disposal site (see “Alternative Considerations”), but should the Mid basin be (partially) converted into a wetland, we strongly recommend dredging spoils not be placed along the western shore (or either shore for that matter) at any time, as this would preclude the optimal development of a wetland. Optimal development of a wetland for multiple purposes, whether for part or all of the Mid basin, would suggest creating a south to north “island,” with streams running along either side. A walking bridge could be constructed to access this area once it was built up enough, for the purposes of trails and interpretation.
(See Figure 1 – Maintenance Dredging Method, includes a sketch of option #2 only for illustrative purposes)

 

With respect to aspects the predesign study might include, the EIS Alternative “Lake/River Wetland With Trap” should also be considered regarding the “trap” concept. However, a sediment trap located in the Middle basin in the pathway of the moving river current may only have a trapping efficiency of 25% according to the 1997 Entranco Study, and reiterated in the 2008 Moffatt & Nichol Dredging Report (page 36).

 

We are intrigued as to whether relocating the “trap” to the southerly section of the North basin would provide a more effective and efficient location. In our White Paper and Financial Projections, we consider the center of North basin, and thus North basin itself, to act as the sediment “trap” until further study indicates otherwise.