10-08-08 Council Agenda - Laserfiche WebLink

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ATTACHMENT 5 Dear Little Canada Resident, Over the last several months the City has been discussing the water quality of Savage Lake with area residents and the Watershed District due to concerns expressed regarding a perceived decline in the water quality of the Lake over the last number of years. These discussions have resulted in the development of an action plan to investigate key factors affecting the Lake. One of these factors is the water quality of the stormwater runoff that enters the lake. Natural, pervious surfaces such as lawn and boulevard areas account for a small portion of the stormwater runoff, but the vast majority of the runoff is generated by the impervious surfaces, i.e. streets, driveways, roofs. In review of the surrounding area that ultimately drains into Savage Lake, it appears the area to the south and southwest of the lake is adequately pretreated by the wetland in the northeast corner of Demont Avenue and Lakeshore Avenue. However the areas to the west, north, and southeast are largely untreated at this time. The streets within these areas are Jackson Street, the portion of Old County Road C adjacent to Jackson Street, Australian Avenue, Bluwood Avenue, Lake Street, Rose Avenue, and Savage Lane north of Rose Avenue. What can be done? As indicated above, several areas do not have any treatment of stormwater prior to discharge into Savage Lake. To address this issue, the City is interested in constructing rainwater gardens along the streets that currently do not have treatment. The City has been utilizing rainwater gardens for stormwater treatment since 2005 on its street reconstruction projects to meet the new water quality standards required when streets are improved. They have been found to be the most cost effective means for treatment of street runoff. When adequately sized and designed the rainwater gardens typically provide 100% treatment of the first 1-inch of runoff from the impervious street surface and meet all current stormwater treatment standards for water quality discharge on a new construction site. What is a Rainwater Garden? A rainwater garden is a small depression typically 20-30 feet long by 15-20 feet wide adjacent to the street that stormwater runoff is directed in to. The typical depth for a rainwater garden is approximately 1 to 2 feet and they are planted with water tolerant native plants to make them appear to be a flower or shrub garden. During a rain event, the rainwater garden will accept runoff until it is full of water (standing depth of 1 to 2 feet) at which point water will continue down 21