Systems designed with convenience in mind quickly remove runoff water from areas such as streets and sidewalks because they're difficult to use when covered with water. Convenience facilities like storm sewers, technically referred to as minor systems, quickly remove the peak flow of a runoff resulting from typical small storms. Apart from temporary measures to control sediment in construction areas, water quality concerns in residential areas focus on the polluting substances washed from paved surfaces and carried into streams or other bodies of water during storms. Pollutants carried in runoff include sediments, nutrients, chemicals, disease-carrying organisms and heavy metals. Sources of these pollutants include grass clippings, leaves, eroded soil, fertilizer particles, oil and gasoline drippings, animal droppings, and metal flecks from vehicles.
Regulations require such ponds.
This results from zoning provisions that require minimum lot sizes and widths, and from local governments requiring developers to construct streets that serve every lot. The adverse effects of storm water management in traditional developments mainly occurs because of changes made to the character of the land surface. Developments introduce roofs and large areas of pavement, referred to as impervious surfaces, which substantially reduce the amount of rainfall soaking into the soil and substantially increase the amount of runoff. Because pavements and roofs have much less surface area to wet in a rainstorm compared to plant-covered lands, more water is also free to run off these simpler, impervious smooth surfaces. Because they are smoother, water also runs off them faster.