Smaller, narrower lots also help reduce the need for pavement in driveways and walks, as in Figure 3. Clustering enables a better relationship between impervious surfaces and natural drainageways, too. Runoff from impervious surfaces now flows slowly over pervious, vegetation-covered areas, soaking into the soil, which filters out some of the pollutants before the storm water reaches lakes, rivers and streams. Greater use is made of drainage devices such as ditches and swales. Costs are lowered because curbs and storm sewers are no longer needed.
More rainfall is directed toward the replenishment of ground water.
The development generates a smaller volume of runoff moving more slowly toward the bodies of water receiving it. Management of Storm Water Facilities in Cluster Developments and Open Spaces Preservation of natural drainage systems and the use of overland swales for storm water require a different approach to maintenance and repair than traditional storm sewer systems. Most of all, this type of storm water network requires maintenance of living plants and occasional removal of sediment. This in turn requires a management organization designed and funded for that purpose. Public works departments are one alternative for managing these natural drainage systems.