DryWell

A drywell is an underground drainage structure designed to receive surface runoff and allow it to infiltrate into the surrounding soil. It is a form of infiltration-based stormwater management and is used to reduce surface runoff, lower peak flows, and promote groundwater recharge. In some regions, a drywell is also called an infiltration well or leaching well.

Construction and design typically involve a cylindrical or box-shaped chamber made of concrete, plastic, or masonry. The chamber is placed underground and connected to an inlet conduit that carries runoff from roofs, pavements, or other surfaces. The interior is often perforated or surrounded by a permeable wall, with gravel or crushed stone backfill to facilitate percolation. A filter fabric or geotextile may line the backfill to limit sediment entry, and an overflow or outlet is provided to manage excess water. A protective grate or lid covers the top and prevents debris entry while allowing access for maintenance.

Operation hinges on soil permeability. Drywells are effective in areas with moderate to good infiltration capacity and are used to infiltrate relatively clean runoff. They require pretreatment to remove sediment and pollutants; otherwise clogging and reduced performance can occur. They are not suitable where the groundwater is shallow, where soils are clayey or have low infiltration rates, or where runoff could introduce contaminants to sensitive receptors.

Maintenance and regulation vary by jurisdiction but commonly include periodic inspection, sediment removal, and ensuring free flow into and out of the chamber. Drywells are one option among green infrastructure practices for managing stormwater on site.