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Storm drainage systems collect excess rainwater from urban areas through gutters, canals, and pipes. They can be integrated into sewage systems or separate. Effective drainage is crucial to prevent flooding and contamination from pollutants. New policies aim to improve separation techniques and permeable surfaces.
Storm drainage is any system designed to drain excess rain or flood water from urban watersheds. These systems typically consist of networks of gutters, canals and underground pipes that collect the excess water that accumulates on roofs, streets, parking lots and sidewalks during storms. This stormwater inflow is then fed into the area sewer system or a dedicated storm drain.
Stormwater runoff in urban areas has always been a problem in urban areas, and drainage systems have been an integral part of city planning and architecture for thousands of years. For example, runoff from a one-acre parking lot is about 16 times that of a similarly sized lawn. The runoff figures for an average sized city are staggering and require an effective storm drainage system to prevent constant destructive flooding. Sewage is often just as dangerous as sewer with the cocktail of waste, fuel, oil, fertilizer, pesticides and heavy metals it collects in urban watersheds. This requires storm drainage to be environmentally safe and effective at removing water.
These drainage systems generally fall into two categories. The former sees runoff removed via an existing sewage system. The second uses a dedicated arrangement of pipes or channels that keeps rainwater separate from the sewage system. Both use a system of drainage points throughout the catchment area that collect runoff from roofs, sidewalks, streets and parking lots. These drainage points are usually located in front of a curb or flat on basin surfaces.
Curbside drains usually rely on the convex profile of the road surface to direct rainwater to the drain. Flat drains are typically located in specially designed troughs that funnel runoff into them. Both usually feature some sort of trap immediately below the entrance to remove sediment and debris and to prevent sewer gas and rodents from escaping. From these drainage points, the rainwater will then enter the sewer or a dedicated storm drainage system.
Combined sewers are generally unable to accommodate both the regular flow of sewage and rainwater during heavy rains and rely on storage tanks and ponds to handle the sudden influx of water. For this reason, dedicated storm drain systems are considered better options; combined sewers are usually only found in areas where systems were installed prior to the 1930s. Dedicated systems discharge runoff into seas, rivers and lakes or into dry wells and retention ponds. Because the water from these systems returns to the groundwater untreated, they often feature drain point grates decorated with messages discouraging people from dumping waste down the drains.
Protecting the environment from rainwater contamination is becoming a major concern for many authorities; As a result, storm drainage policies are constantly being reviewed. These revisions include permeable catchment surfaces that allow runoff to seep into the ground before entering the system. Improved separation techniques have also been instituted to remove hazardous waste from stormwater to minimize the environmental impact of stormwater drainage.
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