2002-06-26 CC Packet - Laserfiche WebLink

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. . Retentioft-Sw;tems - "Werponcts Following the recommendations ofthis BMP section, by providing deep inlet and outlet zones or multiple pools, will usually result in designs that are robust enough to handle the winter and spring conditions without special consider- ations. However, runoff volume from spring snowmelt events can be very large, often the largest-volume event of the year. Ponds designed to function effectively in summer are often disrupted by winter and spring ~vents. Inspection and maintenance during spring runoff should be a consistent feature of stormwater treatment systems in cold climates. Sequencing Wet ponds may be constructed in the early phases of a development project, in order to treat site runoff during construction. If the basin is used as a sediment trap during construction, all sediment deposited during construction should be removed before normal operation begins. Construction t As with other stormwater BMPs, soils, depth to bedrock, and depth to water table must be investigated before designing a wet pond. At sites where bedrock is close to the surface, high excavation costs may make wet ponds infeasible. If the soils on site are relatively permeable or well drained, it will be difficult to maintain a permanent pool. In this situation, it may be necessary to line the bottom of the wet pond to reduce infiltration. All local, state and federal permit requirements should be established prior to initiating the pond design. De- pending on the location of the pond, required permits and certifications may include wetland permits, water quality certifications, dam safety permits, sediment and erosion control plans, waterway permits, local grading permits, land use approvals, etc. Since many states and municipalities are still in the process of developing or modifying storm water permit requirements, the applicable requirements should be confirmed with the appro- priate regulatory authorities. . Pond systems can perform well in cold climates because many modification options are available to increase their effectiveness in frigid and snowy conditions. Many ofthese modifications address the problems associ- /..<1 with nipe ~berts, 1991 and CWP, 1997). ~ Maintenance~ ( \ . Maintenance is required for the proper operation of wet pon!is. Plans for wet ponds should identify owners, piuties responsible for maintenance, and an inspection and maintenance schedule for wet ponds. , --,. . Once constructed, the wet pond should be inspected after several storm events to confirm drainage system functions, bank stability, and vegetation growth. Problems should be addressed immediately. Accumulated trash and debris should be removed from the side slopes, embankment, emergency spillway and weird trash gates as often as needed (at least twice during the growing season). Accumulated sediment in the forebay should be inspected at the same time. Wet ponds should be inspected at least twice per year during the growing season to ensure that they are operating as designed. Potential problems that should be checked include; subsidence, erosion, cracking or Metropolitan Council I Barr Engineering Co. 3-263.