Stormwater Ponds In Montgomery County

January 1, 2021
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What are They and Why are They There?

You may have wondered what all these ponds are throughout Montgomery County.  In most cases they are stormwater ponds and their purpose is to: 1) hold water that runs off the land during rainstorms (stormwater runoff) allowing pollutants such as sediment, oils, grease, lawn fertilizer and metals to settle out and 2) release water at a slow rate which helps prevent erosion in the receiving stream.

Stormwater Ponds Come in all Shapes and Sizes!

Stormwater ponds come in all shapes and sizes, from large regional ponds, such as the Crabs Branch stormwater pond, to small neighborhood ponds, such as the Montgomery Manor stormwater pond.  Regardless of their size, they all provide environmental benefits by improving water quality and reducing erosion in our streams.

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Stormwater ponds are just one way that stormwater runoff is managed in Montgomery County.  To learn about other stormwater management practices used in Montgomery County visit the Department of Environmental Protection (DEP) website.

Maintenance of Stormwater Ponds

Over time, sediment builds up and pipes that bring stormwater into and out of the ponds deteriorate, reducing their ability to hold water and improve water quality.  Therefore, maintenance of stormwater ponds is critical to ensure they continue to function as designed.  DEP provides inspection and maintenance of stormwater ponds throughout the County.  This effort is funded by the Water Quality Protection charge.

Stormwater Pond Retrofits

Some stormwater ponds, that need major repairs, are included in the County’s Capital Improvement Program (CIP) for a complete renovation or retrofit.  These ponds are often in poor condition, have significant safety issues and can be redesigned to provide greater environmental benefits.  Sixty-seven (67) stormwater ponds have been retrofitted in Montgomery County since 2010.

Kemp Mill Stormwater Pond Retrofit

One stormwater pond retrofit project recently completed is the Kemp Mill stormwater pond Located in the Kemp Mill area of Montgomery County, at the end of Somersworth Way.  Before the retrofit, this was a dry pond, meaning it was dry most of the time and only held water during and after storms.  The Kemp Mill stormwater pond, originally constructed in 1986, captures stormwater runoff from 31 acres of the nearby residential community.  The metal riser structure (in the picture below) had rusted over the years and needed to be replaced in order to continue to function.

The riser in a stormwater pond is like the drain in your bathtub, all water collected in the pond leaves through the riser structure.  A pipe connected to the riser structure conveys water through the embankment to a nearby stream.

Kemp Mill Stormwater pond Before Retrofit

The Kemp Mill stormwater pond retrofit project converted the pond to a wet pond that includes a shallow marsh wetland. Improvements include:

  • The metal riser was replaced with a concrete one and the pipe conveying water through the embankment was relined with a heavy duty plastic pipe for many decades of extended service life.
  • To prevent water seepage, safety improvements were made to the embankment.
  • The pond bottom was regraded to form deeper pools and shallow areas where aquatic plants were planted.

The end result is a wet pond where stormwater entering follows a winding path through the pools and shallow marsh where pollutants settle out of the water and the plants help remove some of the pollutants.  The plants also provide shade that helps keep water temperature low, an important factor for the living criters both in the pond and the receiving stream.  The trees, shrubs, grasses and aquatic plants that were planted in the shallow marsh wetland and on the pond side slopes provide other environmental benefits as well such as habitat for birds, insects and various pollinator species and carbon sequestration.

Kemp Mill Stormwater Pond After Retrofit

The Kemp Mill Stormwater Pond is just one of many ponds in Montgomery County that have been transformed to provide improved water quality treatment, extended service life and a community amenity that current and future residents can enjoy.  Residents neighboring the Kemp Mill pond have expressed their appreciation for the improvements to DEP staff on several occasions.  As of March 2021,  DEP is working on designs for seven (7) stormwater pond retrofit projects and constructing three (3) projects in Montgomery County.

For information on these and other completed projects visit DEP’s Watershed Restoration Projects website.

Author: Doug Marshall, Project Planner, Division of Watershed Management, Construction Management Montgomery County Dept. of Environmental Protection

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