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In Northeastern Illinois Many developments utilize wet basins as landscaping ameniti es. Detentio n basins designed to store large run- off volumes (e.g., the 100- year event) are more effec- ti ve than small er ones which drain relatively quickly. In some cases, advance water- shed planning identifies the most effective location for a basin and requires develop- ers to contribute funds for it in lieu of constructing on- site detention. Figure 2-2 Effect of Urbanization on Runoff Stormwater management requirements for detention are generally found in ordi- nances governing subdivi- sions and other new devel- opments. Minimum require- ments for stormwater man- agement regulations have been set by the Metropolitan Water Reclamation District (Cook County) and the DuPage and Lake County stormwater management committees. The county programs have coordinated the water quantity requirements with water quality criteria to reduce the pollutant loads of stormwater runoff. Stormwater regulations are addressed by individual communities in the other counties. NA. TURAI.. GROUND COVER 2Q'Il.SH-lLLOW NFI-TRAflON 35' - 50,", IMPERVIOUS SURFACE 10.. ~ 20.. IMP!!RVIOUS SURFACE 10' SHALLOW INFIl TI~ATIOH !.. OEEP -*I.Tl'IATION 75' ~ 100'" IMPEIWKJUS SURFACE Source: Stormwater Management: A Guide for Roridians, Florida Dept. of Environmental Regulation, p.16 Appropriate for: All new developments. Problems: Continued maintenance is needed after the developer leaves. For more information: Guidance is available from the Metropolitan Water Reclamation District, the county stormwater management committees, and the Northeastern Illinois Planning Commission. References include Model Stormwater Drainage and Detention Ordinance and Stormwater Management. 2.1.7 Watershed measures The run-off of rain water can be slowed down on the ground by vegetation, -terraces, -.contonr plll"'irg no-till fann practices, and other measures. Delaying surface water on its way to the channel increases infiltration into the soil and controls the loss of topsoil from erosion and the resulting sedimentation. Another type of watershed measure is to protect areas that hold water. Many watersheds have wetlands, depressions and other natural storage areas. If these are preserved from development, it reduces the impact of paving areas less important to stormwater management