A storm drain, storm sewer, surface water canal/sewer, or storm sewer is an infrastructure designed to drain excess rain and groundwater from impassable surfaces. Paved streets, car parks, parking lots, footpaths, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems.
Most motorways, freeways, and other congested roads, as well as towns in areas with heavy rainfall leading to flooding, and canals receive water from street gutters in coastal towns with normal storms. Channels from houses and buildings are also connected to the storm drain. Many storm drainage systems are gravity drains, which carry untreated sewage into rivers or streams so pouring hazardous materials into sewers is not acceptable.
Storm drains can sometimes not withstand heavy rainfall or rainfall during storms. Inundated canals can cause basement and street flooding. Many areas require detention tanks inside the property, These temporarily stop the flow during heavy rains and limit the outlet flow to the open sewer. This reduces the risk of open sewage flowing. Some storm drains deliberately mix sewage in the case of sewers or accidentally mix it with sewage.