5. Water Sensitive Urban Design (WSUD) for Treatment of Storm Water Runoff

Limited water availability and steadily increasing urban population have resulted in higher water demand, particularly in urban areas. Water scarcity or poor quality can lead to adverse health effects, water-borne diseases, and even casualties if the event is acute. For effective water management, the treatment of wastewater and its reuse plays a crucial role. A substantial volume of water received as rainfall runs off unutilized, contaminating the receiving water bodies in many cases. The first rain scavenges pollutants and flushes contaminants from the catchment making the water non-usable without treatment. Some treatment units like gross pollutant traps (GPT), wetlands, rain-garden, vegetated swales, etc., are the significant components of Water Sensitive Urban Design (WSUD) and can be used to remove the physical-chemical impurities from storm water runoff. These units have been used to remove the suspended/floating impurities, organic load (BOD), nutrients (nitrogen and phosphorus), heavy metals, hydrocarbons, and even pathogens (coliforms). There has been a wide application of WSUD in developed countries, but it is relatively less popular in developing/poor countries due to several factors. India, the second most populous country of the world with only 2.4% of geographical area, receives non-uniformly distributed precipitation (3880 BCM) mostly during 3–4 months of monsoon, and requires a strong and effective WSUD for conserving water. Suitable technique of WSUD can be applied individually or in combination depending upon the quality of runoff and feasibility of treatment. Design considerations such as type of vegetation and hydraulic conductivity of filter needs attention initially before its application. The lower operation and maintenance cost, no energy input, and formation of non-toxic metabolites make it sustainable. An effective WSUD not only conserves water, it also favours improved urban hygiene, better air quality, carbon sequestration, and healthy ecology.