A dry pond, sometimes known as an extended detention pond, serves as a critical component of stormwater management systems, designed to effectively mitigate the impact of urban development on natural water cycles. Unlike traditional ponds, a dry pond is characterized by its intermittent or dry state under normal weather conditions, only becoming inundated during periods of heavy rainfall or storm events.

A dry pond, also called an extended detention pond, is a stormwater management facility that temporarily holds runoff during storm events and remains dry between rain events. Unlike a wet pond, which maintains a permanent pool of water, a dry pond fills only during rainfall and drains completely within a designed drawdown period, typically 24 to 72 hours.

The primary purpose of a dry pond is to address and manage stormwater runoff in urban and suburban areas. Here’s a short overview of its key objectives:

Stormwater Detention: A dry pond acts as a temporary storage facility for stormwater runoff, allowing the controlled collection and gradual release of excess water. During heavy rainfall, the pond temporarily fills, retaining the water and preventing immediate discharge into downstream water bodies. This detention function helps to reduce the risk of flooding and erosion.

Sedimentation and Filtration: As stormwater flows into the dry pond, the slowed velocity facilitates the settling of suspended sediments. This process promotes sedimentation within the pond, preventing these particles from reaching downstream water bodies and maintaining water quality.

Water Quality Improvement: By temporarily holding stormwater runoff, a dry pond allows pollutants and contaminants to settle, promoting natural processes of filtration. This results in improved water quality as the pond acts as a buffer, reducing the influx of harmful substances into rivers, lakes, or other receiving waters.

Peak Flow Reduction: The controlled release of stormwater from the dry pond helps to manage peak flow rates. By slowing down the discharge, the pond minimizes the risk of downstream flooding, erosion, and infrastructure damage. This is particularly crucial in areas prone to intense rainfall and flash floods.

Groundwater Recharge: During dry periods, when the pond is not actively collecting stormwater, the permeable bottom allows water to infiltrate the ground. This promotes groundwater recharge, contributing to the overall sustainability of local aquifers and maintaining a balanced water table.

Enhancing Urban Green Spaces: Dry ponds are often incorporated into urban planning to serve dual purposes. In addition to stormwater management, they contribute to the creation of green spaces within urban areas, providing aesthetic value, recreational opportunities, and habitat for local flora and fauna.

Dry pond plays a vital role in sustainable stormwater management by providing a controlled and environmentally conscious solution to the challenges posed by increased urbanization. It helps safeguard against flooding, erosion, and water pollution, contributing to the overall health and resilience of ecosystems in urban environments.

Regular Inspections of dry ponds are crucial to ensure proper functionality, address potential issues, and maintain effectiveness in managing stormwater runoff. Begin by establishing a routine inspection schedule based on local regulations, the design specifications of the dry pond, and environmental conditions. Inspections by a licensed professional should occur at least annually, and you can supplement that schedule with more frequent inspections after significant storm events.

To inspect your dry pond, perform a visual assessment of the entire dry pond area, including the embankments, inlet and outlet structures, and the pond bottom. Look for signs of erosion, sediment buildup, vegetation health, and any structural damage. Make a note of excessive sediment that can reduce the storage capacity and diminish the pond's effectiveness. A professional can help you evaluate if sediment removal or dredging is necessary based on the design specifications. You can also inspect the health and density of vegetation within the dry pond. Healthy vegetation is essential for stabilizing the pond's banks, enhancing sediment filtration, and promoting overall ecosystem health. Identify and address any issues with invasive species.

You can also examine the inlet structure for debris, blockages, or damage that might impede the flow of stormwater into the pond. Similarly, inspect the outlet structure and spillway to ensure it is functioning correctly and regulating the discharge as designed without any erosion issues..

Maintain detailed records of your inspection findings and any profession inspection reports you get, including photographs, measurements, and any necessary corrective actions. This documentation is valuable for tracking changes over time and demonstrating compliance with regulatory requirements.

By conducting regular and thorough inspections, stakeholders can address issues promptly, prolong the life of the dry pond, and ensure its ongoing effectiveness in managing stormwater runoff and maintaining water quality. Regular inspections also contribute to the sustainability and resilience of the overall stormwater management system.

In Virginia, DEQ requires annual inspections of privately owned stormwater BMPs, including dry ponds, by a licensed professional or someone holding the DEQ Stormwater Inspector Certification. Inspection records must be retained for a minimum of three years. Similar requirements apply in Maryland, North Carolina, and other states within Exact Stormwater's service territory. Our inspection teams frequently encounter issues with dry ponds throughout Virginia and North Carolina, including sediment accumulation in the forebay, erosion on the embankment slopes, and debris blocking the low-flow orifice.

Need help with your dry pond? Exact Stormwater provides certified inspection, maintenance, and installation services across 12+ states. Call (804) 302-5151 or contact us to schedule a consultation.

Maintaining a dry pond is essential to ensure its continued effectiveness in managing stormwater runoff, preventing flooding, and promoting water quality. Regular maintenance helps address potential issues, extends the life of the pond, and contributes to its overall functionality. Here’s how to maintain a dry pond:

Periodically remove accumulated sediment from the bottom of the pond, paying particular attention to the forebay areas where sediment is most likely to accumulate. Never let sediments fill more than 50% of the forebay capacity, as this will improve effectiveness, preventing sediment migration into the rest of the pond, which can get expensive to remove. Sediment removal helps maintain the pond’s storage capacity and prevents the buildup of pollutants. Trees that love water, like willows, will tend to grow in the soft, damp soils in the bottom of a dry pond, and these should be regularly removed or mowed to prevent them from getting too large.

Regularly inspect the inlet structure for debris, blockages, or any issues that may impede the flow of stormwater into the pond. Similarly, check the outlet structure to ensure it is functioning correctly, regulating the discharge as designed.

Check for Erosion: address any areas suffering from erosion promptly by implementing erosion control measures such as erosion matting, riprap, or other stabilization measures.

Keep detailed records of maintenance activities or other corrective actions taken. This documentation is valuable for tracking changes over time, demonstrating compliance with regulations, and informing future maintenance efforts.

By following a proactive and systematic approach to dry pond maintenance, you can preserve the pond's effectiveness, promote environmental sustainability, and contribute to the overall health of the surrounding ecosystem. Regular inspections, timely repairs, and adherence to design specifications are key to the successful maintenance of a dry pond.

Dry pond maintenance typically includes mowing and vegetation management on the embankment and bottom, sediment removal from the forebay and main basin, inspection and clearing of the outlet control structure, and erosion repair on side slopes and the emergency spillway. Exact Stormwater provides comprehensive dry pond maintenance services including annual maintenance plans tailored to each facility's specific conditions and regulatory requirements.

For dry ponds with embankment erosion or slope instability, HydroTurf turf reinforcement mats provide a durable, low-maintenance solution for slope stabilization that supports vegetation growth while preventing future erosion.

Building a dry pond or an extended detention pond can be as simple as excavating a large depression into the landscape, but is often far more involved. Most dry ponds include special features like forebays, aquatic or safety benches, primary and emergency spillways, and a low-flow orifice with a trash rack. All of these features work together to create a best management practice that’s both safe for you and the folks downstream, and effective at removing pollutants from the runoff that enters the pond.

Dry ponds are usually constructed with mild side slopes (4-5 feet of horizontal distance for every 1 foot of vertical change), and getting good vegetation established quickly will prevent those slopes from eroding into the pond.

If you or your contractor are in the process of building a dry pond, be sure to ask them about what features are being included so that you can make sure the finished product looks great and performs as expected.

A dry pond holds stormwater temporarily during rain events and drains completely between storms, leaving a dry basin. A wet pond maintains a permanent pool of water year-round. Dry ponds are primarily designed for flood control and peak flow reduction, while wet ponds provide both flow control and water quality treatment through sedimentation in the permanent pool. Both types require regular inspection and maintenance to remain functional and compliant. You can learn more about wet ponds on our wet pond guide page.

Inspection frequency varies by state and local requirements. In Virginia, DEQ requires annual inspections of privately owned dry ponds with records retained for three years. In North Carolina, SCM inspection reports must be submitted by June 30 each year. In South Carolina, post-construction BMPs require inspection every three years. Exact Stormwater performs certified inspections in all of these states and can provide written reports suitable for regulatory compliance. Call (804) 302-5151 to schedule your inspection.

A neglected dry pond will gradually lose its ability to detain stormwater effectively. Sediment accumulates in the basin and forebay, reducing storage capacity. Vegetation becomes overgrown or dies, exposing soil to erosion. The outlet structure can become clogged with debris, causing uncontrolled overflow during storms. In regulated jurisdictions, failure to maintain a dry pond can result in a Notice of Violation from the state environmental agency, potential fines, and mandatory corrective action at the owner's expense.

The property owner or the entity identified in the stormwater maintenance agreement (often an HOA or property management company) is responsible for maintaining the dry pond. In most states, this responsibility is established during the site development process and recorded as a deed restriction or maintenance covenant. Exact Stormwater works with property managers and HOAs to establish annual maintenance plans that keep facilities compliant and functioning properly.