Agenda - 08-23-1993 - C 2 and C 3 attch

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Creating Optimum Conditions for Pollutant Removal and Treatment 14 4 renting a marsh at the inlet enhances the growth of vegetation and the trapping of sediment and other pollutants. Aquatic benches along the sides also encourage vegetation. The plants enhance pollutant removal by drawing nutrients from sediments. Algae attaches to these plants and can draw nutrients directly from the water. A created wetland is desirable, but consideration should be given to restricting vegetation to a confined area where it can be managed so the entire pond does not become a jungle of vegetation, cold blooded wildlife, and insects. The greatest initial settling occurs in the upper end of the pond where the larger, heavier particles fall out as the flowing runoff looses velocity as it enters the still water in the pond. For this reason it is necessary to provide a baffle or other structure near the inlet to concentrate sediment accumulation where it can be reached for periodic removal as part of maintenance. Consideration for Multiple Uses Careful evaluation and planning is needed since vegetation may make the pond unattractive for use as recreation and landscaping. If the pond is to be multipurpose, marshes and benches should be isolated from other areas to be used for fishing, boating, swimming, etc. Vegetation on or close to the dam should be discouraged and prevented through routine maintenance. Roots can weaken the dam, and vegetation attracts burrowing animals that can weaken it further. Thick vegetation makes maintenance more difficult, which may delay work and allow growth to spread further until major clearing is required. Refer to the sources listed in the references for more information and for suggested plants to establish in a pond. Safety A fence is required around the pond to control access. Gates sized for either pedestrian or vehicular access (for maintenance) should be installed at appropriate locations. At the designated access to a public right-of-way the gate must be wide enough to accommodate equipment needed to mow and otherwise maintain the pond and to excavate accumulated sediment when the time comes. The owner should consult with an attorney concerning liability for accidents, legal requirements for fencing and access, insurance, etc. Review of Pond Design A pond can have both positive and negative impacts on the natural environment and the development and review of the design will consider these impacts. However, develop of the site will have impact downstream with or without the pond, so the pond is necessary to mitigate the impact and contain pollutants before they are washed downstream. DRAFT 10 June 1993