03-24-2009 Council Work Session Packet

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� � CMP Part 3A. Environmental Protection Plan Since marshes and small lakes in the watershed aggregate nearly as much area as the main body of Lake Minnetonka, their potential for supplying water to the subsurface formations is appreciable. In addition, marshes provide diversity in the kinds of open space available within the region. They provide a habitat which is uniquely suited for certain birds and mammals. They can be utilized to provide storage of storm runoff with minimal disruption to their function as a habitat for wildlife and their ability to reduce the phosphorus input to the lake. Development Impacts on Wetlands. The historic problem has been that burgeoning urbanization has adversely affected the existence and the function of wetlands. The Harza Study showed that typical suburban forms of urbanization will lead to the pollution of the watershed and Lake Minnetonka because of the increased phosphorus load which would be in the surface water runoff. It is a documented fact that the amount of phosphorus in runoff increases with urbanization. When urban development occurs, the function of the natural drainageways and filtration system is adversely affected in three ways: The speed and quantity of the storm water runoff are increased as the absorption ability of the land is eliminated with hardcover (houses, driveways, roads, etc.). This increase in the speed and quantity of storm water runoff causes the third adverse effect, which is the increase of the amount of nutrients which are contained in the storm water runoff which now has less time in the natural marsh filtration system to be purified before entering the lake. Nutrients contained in dying vegetation, lawn fertilizers, and from other urban sources are discharged into the lake faster and in greater quantities as the level of urbanization increases. The Hickok report entitled "Storm Water Impact Investigation for the Metropolitan Council", November, 1972, revised February, 1973, showed that in an urbanized area, as much as 3.68 pounds of phosphorus per acre is generated versus 0.3 pounds per acre of discharge from a two acre minimum lot size zone as exists in rural Orono. Orono's Surface Water Management Plan of 1974, also done by Hickok, documented that Orono's existing rural wetlands could assimilate the rural phosphorus load but would be insufficient to handle an urban phosphorus load. In fact, Orono's existing urban wetlands were already overloaded. Thus, if rural Orono were to become urbanized, even at relatively low urban densities, phosphorus loading of Lake Minnetonka would increase to dangerous levels. Orono, however, must not rely solely on the ability of the natural filtration system of the marshes and drainageways to purify storm water so necessary for the preservation of Lake Minnetonka. Several �e� studies, one of which i-s was by the University of Wisconsin entitled "Effect of Marshes on Water Quality", concludesd that because of our freezing winter temperatures much of the filtration value of the natural marsh process is lost during the annual spring snow melt. City of Orono CommunitS�Management Plan 2008-2030 Page 3A-6