Micromanagement of Stormwater for Wet Weather Control

Urban areas often suffer from excess stormwater runoff into storm, sanitary, and combined sewers. Such difficulties are especially problematic in built-up older areas. Examples of these wet weather problems are: 1) basement flooding caused by surcharging of combined and⊘or sanitary sewers; 2) overflow of combined and⊘or sanitary sewers and resulting pollution of receiving waters; 3) excessive peak flow at wastewater treatment plants; and, 4) nonpoint source pollution and surface flooding caused by stormwater runoff.To be more precise, the preceding wet weather problems are often caused by peak rates of stormwater runoff, not necessarily by the runoff volume. Wet weather flooding and pollution problems would often not occur, or would be much less severe, if the peak flows could be lessened. Peak flows are often the principal culprit, not the volume of stormwater runoff.The concept of the micromanagement of stormwater, an approach that has now been successfully used in several communities, is to temporarily store stormwater in many and varied locations on the surface (off-street and on-street) and, as needed, below the land surface, near to the source. “Near to the source” means to store the stormwater as close as possible to where it falls as precipitation and certainly prior to its entry into the combined, sanitary, or storm sewer system. The idea is to accept the volume of stormwater runoff into the sewer system but greatly reduce the peak rate of entry of stormwater.Numerous components comprise a micromanagement system. They must be imaginatively tailored to the specific physical situation. Examples of system components are: 1) downspout disconnection to slow down, more widely distribute and temporarily intercept stormwater; 2) off-street surface storage of stormwater (conventional detention⊘retention) with regulated outflow; 3) on-street surface storage with regulated outflow achieved by an optimum combination of on-street berms and catchbasin flow restrictors; and, 4) sub-surface storage of stormwater with regulated outlet control using restrictors. These subsurface storage facilities range from oversized sewer segments to large tanks.Because the micromanagement of stormwater is a relatively unusual approach, especially when it includes the intentional temporary and controlled flooding of streets, its usefulness is best illustrated with a case study. The 8.6 square mile community of Skokie, Illinois will be used to illustrate the technical, nontechnical, and economic aspects of stormwater micromanagement.The test is in the doing. As described in the paper, a stormwater micromanagement project is solving community-wide basement flooding problems at great cost savings. In addition, there has been widespread citizen acceptance and the innovative project has received some external funding. Furthermore, potential difficulties have not occurred. That is, there have been no vehicular traffic (including emergency vehicle) problems, pavement has not deteriorated, icing has not occurred and there has been no excessive maintenance.