Stormwater Management Facility Parts
August 25th, 2015
Written by Industry Expert, J. Wesley Allen, Environmental Scientist
Stormwater management rules and regulations were formalized in the 1990’s, developing from the Clean Water Act. While a lot of things have changed and continue to change in stormwater management, being informed on what your stormwater pond is designed to do and what its design elements, or parts, are, is key to understanding and implementing a sustainable maintenance and pond management program for your community, property, or commercial facility.Today, more and more stormwater management is done with a variety of Best Management Practices (BMPs), such as infiltration basins, bio-infiltration areas, bio-swales, and rain gardens, but we still see a large number of stormwater management “wet” ponds or “dry” detention basins. These ponds are designed to hold water, capture sediment and pollutants, and then release the water slowly to mimic run-off from the site before development. These ponds not only function as stormwater management facilities, but are often designed as key features in communities. Most of these ponds have similar basic parts:
POND EMBANKMENTTypically, stormwater ponds have an embankment surrounding them. Part, or all, of the embankment acts as a dam to keep the water in the pond. The embankment is usually sloped and should be stabilized with herbaceous vegetation and grasses. Large trees, animal burrowing, and exposed soils can lead to erosion and failure of the embankment. A beneficial vegetative buffer can also be allowed to grow. Buffers can help reduce sediment and nutrient loading in the pond, while providing greater stabilization for the embankment. Buffers should be composed of herbaceous vegetation and be kept free of invasive species and trees.
OUTLET STRUCTUREThese structures are designed to hold and release the water from the stormwater pond at different rates based on the amount of rainfall or run-off. They are mostly concrete structures now, but older ponds may also have galvanized steel structures or other types of pipe risers. Outlet structures may also have trash-racks on the low-flow (bottom orifice) and overflow (top of the structure). Trash racks need to be secured and kept in place. Outlets and the associated trash-racks should be kept free of trash, debris and vegetation. They also need to be checked for any structural weaknesses or leaks that could jeopardize the function of the system.
INLETSAn inlet is an area, often a pipe, that conveys run-off from surrounding paved areas and property to the stormwater pond. Inlet pipes are typically concrete, high strength plastics, or galvanized steel. Where inlets enter the pond there are rip-rap (stone) dissipaters or aprons designed to reduce run-off velocity to prevent erosion and catch sediment and debris before it enters the pond. The inlet should be periodically checked for sediment buildup in the pipe. The rip-rap dissipater should also be kept free of vegetation and checked for erosion or sediment build-up. Sediment, invasive vegetation, or erosion at inlet areas can cause drainage issues and reduce the life-span of the pond.
FOREBAY Forebays may be located at inlet areas. They are small zones segregated from the rest of the pond by rip-rap, stone gabions or earth embankments. The purpose of a forebay is to collect sediment before it enters the rest of the pond, making maintenance and sediment removal easier. Forebays need to be check for sediment build-up to function properly. They should also be kept clear of trees and invasive vegetation. EMERGENCY SPILLWAY The emergency spillway is a cut-out in the top of the basin’s embankment where water can leave the pond during an extreme storm or rain event. These areas can be stabilized with concrete, rip-rap or herbaceous vegetation. The emergency spillway should be kept clear of trees, sediment, and debris. They need to be checked for any erosion or structural weaknesses.
SAFETY BENCH Depending on the age and jurisdiction of your stormwater pond, it may have safety benches. There are normally two benches, one is one foot above and one is one foot below the permanent pool of the pond (normal water level). They are designed to prevent someone from falling into deep water if they fall near the edge of the pond. These areas should be kept free of trees and invasive vegetation and stabilized with grass and/or beneficial wetland plants.
It is important to note that design elements may differ in some ponds and stormwater BMPs, but by recognizing these basic pond parts, you can work with a stormwater management professional to develop an annual pond maintenance and management plan that keeps your stormwater area functioning properly and reduces longterm capital expenditures.
Design elements and regulations will also differ from jurisdiction to jurisdiction, so it is important to work with a certified stormwater BMP inspector when developing stormwater inspections and maintenance programs. Contact your local pond professional to discuss your pond or to schedule an inspection. .
Contact the experts at 888-480-LAKE (5253) for all of your lake, pond and fisheries management needs.
J. Wesley Allen is an Environmental Scientist with SOLitude Lake Management. Since 1998, SOLitude Lake Management has been committed to providing full service lake and pond management services that improve water quality, preserve natural resources, and reduce our environmental footprint. Lake, pond and fisheries management services, consulting, and aquatic products are available nationwide. Learn more about SOLitude Lake Management and purchase products at www.solitudelakemanagement.com.