Stormwater Ponds Explained - Retention or Detention? - Dry or Wet?

Here is a great resource we found online from Montgomery County in Maryland.

By  •  • 4 minute read

Here is a great resource we found online from Montgomery County in Maryland. We wanted to share this great info to help stormwater pond owners in Charlotte, Asheville, Greenville, and Spartanburg understands what their responsibilities and how stormwater ponds function.

What are wet and dry ponds?

A pond is a type of stormwater management facility designed to collect rainwater and pollutants and prevent downstream flooding. Wet ponds always have a pool of water. Dry ponds only have water after a storm event.

Most ponds located throughout your county are stormwater management ponds, even ones that are community amenities. Ponds can have many different designs, including ponds with concrete channels, dry ponds with sand filters on the pond bottom, and ponds that provided wetland habitat around the edges.

Why are ponds important?

• Remove pollutants • Improve health of streams and rivers • Help to make our waters fishable and swimmable

Why is it important to keep your pond maintained?

Unmaintained ponds may:

  • Not remove pollutants as intended, sending polluted water to streams and rivers
  • Become filled with sediment and debris, so water cannot be stored in the facility, which may lead to downstream flooding and erosion
  • Look unsightly with excessive growth of unwanted weeds or algae
  • Cost more to fix problems if left unchecked
  • Lead to a dam breach if overgrown vegetation and trees compromise the pond safety over time. This would cause flooding and damage to surrounding properties and adjacent homes.
  • Have inlet and outlet areas blocked by excessive growth or debris. This will cause water to back up or pond on adjacent properties. As rainwater flows over hard surfaces and lawns, it picks up pollutants such as sediment, trash, pesticides from lawns, nutrients from fertilizer or pet waste, and oil and grease from cars. Ponds can help to reduce this pollution.

How will I know what maintenance is required?

Montgomery County regulations require that you perform ongoing routine grass cutting, trash removal, and vegetation management of your stormwater facility. If the work described below is not done regularly, you could receive a notice of violation.Pond Maintenance

Grass Cutting

Mow grass in the pond area at least twice a year

  • Downstream slope of dam
  • Top of the dam
  • Upstream slope of dam (dry pond only)
  • 25 feet around the control structure (dry pond only)

The most commonly forgotten non- structural maintenance is mowing and removal of trees and woody vegetation on the downstream slope of the embankment.

  • Inlet channels, around headwalls, and pipes within pond area (where safe and accessible)
  • Outlet channel

Vegetation Management

Manually remove all trees and woody vegetation in the following pond areas at least twice a year

  • From the top and upstream and downstream slopes of the dam
  • From inlet and outlet channels
  • Within 25 feet of the control structure
  • From channels, headwalls, and pipes into the pond area

Do not apply herbicides, fertilizers, or pesticides in or around the pond. If manual removal of invasive weeds has been ineffective, limited applications of aquatic friendly herbicide may be applied by a qualified professional certified by the State of Maryland.

Trash Removal

Remove trash and debris from all areas in and around the pond monthly

• For wet ponds, any trash in the water should be removed safely by professionals

Other Preventive Maintenance

As needed

  • Know the pollutant sources on your property and try to reduce or eliminate the pollutants at the source
  • Notify DEP if beaver activity or animal burrowing is observed
  • Prevent trees and woody vegetation from growing in these areas
  • Seed and cover adjacent areas of bare soil to prevent erosion

Other Maintenance

Inspect and perform as needed

  • Notify Montgomery County police if graffiti is observed
  • Verify all pond safety signs are in place

These basic actions will keep your facility working correctly and prevent more serious repairs, which will save you money in the long term.

• Inspect the facility after every major storm and contact DEP if you are concerned

Why do you most people believe stormwater ponds will take care of themselves?

Taking care of your lake or pond is not a luxury, it’s a necessity. As your local pond management professionals, we’ve been there. Let us help guide you as a member to protect, plan, and preserve your pond or lake if you live in the Charlotte NC, Asheville NC, and Greenville SC areas.

Get started. Become a member today!


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