On-site detention refers to a stormwater management practice that involves temporarily storing and slowly releasing stormwater runoff on-site. It is implemented to mitigate the impact of increased runoff caused by urbanization and development. Here are some aspects related to on-site detention:

  1. Stormwater Management: On-site detention systems are designed to control and manage the volume and flow rate of stormwater runoff. They help reduce the peak flow of stormwater that would otherwise be discharged rapidly into downstream drainage systems, streams, or rivers, which can lead to flooding, erosion, and water quality issues.
  2. Detention Basin: The primary component of an on-site detention system is a detention basin. It is a constructed or natural depression that temporarily stores excess stormwater during rainfall events. Detention basins are designed to have a predetermined capacity, allowing them to capture and retain a specified volume of runoff.
  3. Design Considerations: The design of an on-site detention system takes into account factors such as the catchment area, rainfall intensity, desired detention volume, and local regulations. Engineers use hydrologic and hydraulic calculations to determine the optimal size and configuration of the detention basin to achieve the desired level of stormwater management.
  4. Outlet Structure: On-site detention systems are equipped with outlet structures that control the release of stored water. These structures typically consist of control gates, weirs, or orifices that regulate the discharge rate, allowing the water to be released slowly over time. The controlled release reduces the downstream impact of stormwater runoff and helps mimic natural hydrological patterns.
  5. Water Quality Considerations: On-site detention systems can also incorporate water quality treatment components. These components, such as sediment traps, filter systems, or vegetated swales, help remove pollutants and sediment from the stormwater runoff before it is released. This improves the quality of the discharged water and helps protect downstream ecosystems.
  6. Maintenance: Regular maintenance is essential to ensure the proper functioning of on-site detention systems. Maintenance activities may include periodic inspection of the detention basin, removal of accumulated sediment or debris, and inspection of outlet structures. Adequate vegetation management is also important to prevent overgrowth and ensure the effective operation of the system.

On-site detention is an effective stormwater management strategy that helps mitigate the adverse impacts of increased runoff in developed areas. By temporarily storing and controlling the release of stormwater on-site, it reduces the risk of downstream flooding, erosion, and water pollution. Proper design, construction, and maintenance are crucial for the long-term effectiveness of on-site detention systems.