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Eden Prairie Lakes Improvement Project

December 16, 2006

Work on restoring the natural level of Birch Island Lake will begin during the spring of 2007 says the Nine Mile Creek Watershed District (9MCWD). The District’s Board of Managers held a public hearing chaired by President LuAnn Tolliver on lake improvement projects at Eden Prairie City Hall on Thursday December 7th.

In attendence were a few home owners from the Cardinal Creek neighborhood, Jeff Strate of Friends of Birch Island Woods and EP City Environmental Coordinator Leslie Stovring and Parks Manager Stu Fox.

The normal flow of ground water to Birch Island Lake from the north in Minnetonka was cut off during the late 1980’s when the base for the Crosstown highway was constructed. (See related news stories on this website ).

Barr Engineering consultants said that with the installation of tile pipe along the north side of the Crosstown Highway east of Eden Prairie road, ground water and surface water will be collected and conveyed approximately 1500 feet directly to Birch Island Lake by a 1 foot diameter pipe. That pipe will be bored underneath the large wetland that lies between the lake and the highway.

Construction of a new rainwater detention pond on the west side of Eden Prairie Road north of Kurtz Lane and the upgrade of the existing detention pond between Edenvale Boulevard, Leslie Lane and Doriann Court will also begin. The goal is to fully restore the clarity of Birch Island Lake and its suitability for fishing, swimming and boating.

The Birch Island Lake restoration project is part of a larger package of water improvement initiatives that include reducing the phosphorous levels and algal growth in Birch Island Lake, Bryant Lake and Northwest and Southwest Anderson Lakes.

Excessive levels of phosphorus cause nuisance algae blooms in lakes.
Note: Blue-green algae is the foul-smelling green scum on lake and pond surfaces and filamentous algae is the hairy or moss-like algae that grows on weeds or rocks.

Most of the phosphorus is carried by storm-water runoff into the lakes. Sources include high-phosphorus lawn fertilizer, decaying leaves and grass, sediments washed into the street including car washing solutions, and duck, geese and pet waste.

The watershed district’s consultants (Barr Engineering) reported that each of the four lakes would be treated in a way which will address its own characteristics and sources of phosphorous.

Bryant Lake , for example, will be treated with alum and the large wetland within the Cardinal Creek Conservation Area wast of Interstate 494 will be restored. That wetland is drained by a small branch of Nine Mile Creek which flows into Bryant Lake

Alum treatments applied to lakes reduce algae growth by reducing the levels of phosphorus in the water that plants can absorb. Algae like most other plants, need phosphorus to reproduce and grow. Higher levels of phosphorus prompt more algae growth and cloudiness and the green scum that often appears during the summer. Non-toxic alum that is injected into a lake interacts chemically with phosphorus, trapping it as aluminum phosphate. At the bottom of the lake, alum prevents phosphorus from being re-released from lake-bottom sediments which include decaying plants. An alum treated lake has less phosphorus and less algae. Lake phosphorous levels can also be reduced by smarter residential lawn-care practices, stormwater runoff techniques and management of exotic waterplants.

Curllyleaf pondweed, an exotic in Northwest and Southwest Anderson Lakes, will be reduced by drawing down lake levels. The draw down could begin this winter and is expected to kill off much of the harmful plants which can not tolerate freezing. The effect of a drawdown may last only a few years and affect fish populations. Click here for a discussion of curlyleaf pondweed at the Minnesota Lake Association website.

Improvements to a rain water and stormwater detention pond near Prairie Lakes Dirve and a control flow gate between the Southeast lake (in Bloomington) and Southwest lake (in Eden Prairie) will also be taken on.

The 9MCWD managers are expected to approve the water improvement projects during its next meeting. The total estimated costs are $1,928,000. Of that, the Birch Island Lake level work will cost about $235,000 and the work on the two detention ponds about $170,000 for a total of $390,000. Work on Bryant Lake and the wetland will total about $990,000 and the work on the two Anderson Lakes about $530,000. Most of the costs of the project will be paid for by 9MCWD.

The City of Eden Prairie is one of Minnesota’s “Dirty Thirty,” ranking has 5th among Minneosta’s cities with the most polutted lakes. Click here for an Eden Prairie News story of what the City is being required to do.


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