Extended Detention Basins & Facilities in MD, VA, DC, NC & CA

By acting as a temporary storage basin for stormwater runoff, extended detention facilities are an important part of managing stormwater quality and quantity following a significant weather event. They hold rainwater after large storms to help prevent flooding and soil erosion. The most common locations for extended detention basins include commercial and industrial development sites where increased runoff is expected. Standard detention basins can also be converted to extended capacity if needed.

At first glance, extended detention basins may look like nothing more than a simple ditch. However, multi-stage construction is designed to detain runoff for an extended period, allowing contaminants to settle to the bottom while clean water empties into a larger water source, such as a river.

To make sure they operate as intended without adversely affecting erosion, flood control volumes, and outflow rates, extended detention facilities must follow a recommended maintenance plan. The experienced stormwater management engineers at iSTORMWATER offer the services you need to avoid violations and fines.

Learn more about the requirements for maintaining your aboveground stormwater reservoirs. Then, contact iSTORMWATER at (443) 699-2828 to schedule an extended detention facilities inspection in Maryland, Virginia, Washington, DC, North Carolina, and California.

Extended Detention Facility Maintenance Requirements

The effectiveness of an extended detention basin largely depends on the maintenance it receives. Here are the requirements to keep in mind when formulating your extended detention facilities’ inspection plan:

General Maintenance Tips for Detention Basins

All extended detention basins must be inspected for excessive debris and sediment buildup at least twice a year. The specific components that require attention include:

  • Inlets
  • Basin bottoms
  • Trash racks
  • Outlet structures
  • Low flow channels
  • Riprap or gabion aprons

Sediment should only be removed when conditions are dry. All debris removed from the basin must be disposed of or recycled in accordance with federal, state, and local waste regulations.

Treating Vegetated Areas of Extended Detention Basins

Many extended detention facilities contain vegetative cover. If this applies to your basin, regular mowing and trimming are required. Grass should be mowed at least once a month during the growing season, and all vegetated areas must be inspected at least once a year for erosion, scour, and unwanted growth. Further regulations apply if you’re interested in adding or restoring vegetation. For example, fertilizer and pesticide use should be avoided whenever possible.

Structural Components of Detention Basins

The sides, bottom, and other structural components of your extended detention facility must be inspected at least once a year. Repairs may be necessary if the contractor finds any of the following problems:

  • Cracking
  • Subsidence
  • Spalling
  • Erosion
  • Deterioration

Other Maintenance Criteria

A properly functioning extended detention facility should drain within a maximum allotted time. Failure to do so could result in a loss of runoff storage volume, mosquito breeding, and difficulty maintaining the bottom of the basin.

To prevent these problems, the maintenance plan should make a note of the normal drain time. Then, if a significant increase or decrease is observed, measures must be taken to improve the function of the basin. The factors that may require attention include:

  • Outlet structure
  • Underdrain system
  • Groundwater level
  • Tailwater level

Call iSTORMWATER at (443) 699-2828 our fill out our form for top-rated extended detention basin services in the DMV, California, and North Carolina!

Schedule an Extended Detention Basin Inspection in MD, VA, DC, NC & CA

Don’t put your property at risk by neglecting your extended detention facilities. Choosing iSTORMWATER as your stormwater management consultant ensures compliance with applicable codes and regulations to help you avoid costly fines. Working with us also means you’re doing your part to keep public wilderness areas safe for people and animals alike.

For help creating a customized stormwater preventative maintenance plan or to schedule your next extended detention facilities inspection, please give us a call at (443) 699-2828. Our service area includes Washington, DC, and the surrounding areas in Maryland and Virginia. We also serve North Carolina and California!


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Incredible stormwater management service. The owner John consulted on a property I manage and ended up saving us thousands of dollars in environmental fees from the government. Now, our property is compliant with the EPA and we have a great partner to keep us maintained on storm water regulations over time.

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