The Design and Use of Detention Facilities for Stormwater Management Using DETPOND Robert Pitt, Ph.D., P.E., DEE Environmental Engineer © 2002 R. Pitt and J. Voorhees Detention ponds are probably the most common management practice for the control of stormwater. If properly designed, constructed, and maintained, they can be very effective in controlling a wide range of pollutants and peak runoff flow rates. There is probably more information concerning the design and performance of detention ponds in the literature than for any other stormwater control device. Wet detention ponds are also a very robust method for reducing stormwater pollutants. They typically show significant pollutant reductions as long as a few design-related attributes are met. Many details are available to enhance performance, and safety, that should be followed. Many processes are responsible for the pollutant removals observed in wet detention ponds. Physical sedimentation is the most significant removal mechanism. However, biological and chemical processes can also contribute important pollutant reductions. The extensive use of aquatic plants, in a controlled manner, can provide additional pollutant removals. Wet detention ponds also are suitable for enhancement with chemical and advanced physical processes. This course will use the DETPOND stormwater detention pond model (model and complete documentation included) to evaluate and design stormwater detention ponds for a wide range of conditions. DETPOND is based on the same modeling approach used in SLAMM, but provides more detail to enable more effective evaluations. This course also includes extensive documentation of successful pond designs and approaches. This material is excerpted from: Pitt, R. Stormwater Quality Management, Part Two: Treatment of Stormwater. CRC/Lewis. Boca Raton, FL. Publication forthcoming. Introduction........................................................................................................................................................................................4 Expected Detention Pond Performance ....................................................................................................................................5 Potential Detention Pond Problems ...........................................................................................................................................5 Wet Detention Pond Design Guidelines to Minimize Potential Problems .........................................................................5 Required Stormwater Detention Pond Maintenance..............................................................................................................6 Basic Wet Detention Pond Design Guidelines ........................................................................................................................6 Wet Detention Pond Costs ..........................................................................................................................................................7 Pond Size Calculation..................................................................................................................................................................7 Background........................................................................................................................................................................................7 Multiple Benefits of Detention Facilities .................................................................................................................................8 Dry Ponds ......................................................................................................................................................................................9 Wet Detention Ponds ...................................................................................................................................................................9 Extended Detention (Combination) Ponds...............................................................................................................................9 Roof Storage................................................................................................................................................................................10 Up-Sized Pipes............................................................................................................................................................................10 Underground Rock-Filled Detention.......................................................................................................................................10 Use with Other Controls ............................................................................................................................................................10 Examples of Detention Pond Performance ............................................................................................................................11 Chemical Assisted Sedimentation.......................................................................................................................................11 Full-scale Demonstrations....................................................................................................................................................15 Oil/Water Separators..................................................................................................................................................................19 Gravity Separation.................................................................................................................................................................20 Coalescing Plate Interceptor Oil/Water Separators..........................................................................................................21 Imp ingement Coalescers and Filtration Devices ..............................................................................................................22 Maintenance of Oil/Water Separators ................................................................................................................................22 Performance of Oil/Water Separators for Treating Stormwater....................................................................................23 10-1 Problems With Wet Detention Ponds..........................................................................................................................................24 Safety of Wet Detention Ponds....................................................................................................................................................24 Nuisance Conditions in Wet Detention Ponds and Degraded Water Quality ..................................................................26 Attitudes of Nearby Residents and Property Values ............................................................................................................26 Maintenance Requirements of Wet Detention Ponds...............................................................................................................27 Routine Maintenance Requirements .......................................................................................................................................27 Mowing....................................................................................................................................................................................27 Debris and Litter Removal...................................................................................................................................................27 Inspections ..............................................................................................................................................................................28 Sediment Removal from Wet Detention Ponds....................................................................................................................28 Problems with Contaminated Sediments in Wet Detention Ponds...............................................................................29 Vegetation Removal from Wet Detention Ponds..................................................................................................................29 Detention Pond Costs .....................................................................................................................................................................30 Guidelines To Enhance Pond Performance................................................................................................................................33 Insect Control and Fish Stocking.............................................................................................................................................33 Aquatic Plants for Detention Ponds........................................................................................................................................33 Locating Ponds............................................................................................................................................................................41 Pond Surface Area and Shape ..................................................................................................................................................46 Pond Water Depth......................................................................................................................................................................46