Numerous features of the natural landscape trap runoff and allow rainwater to filter into the ground. Wetlands and ponds can retain significant volumes of water; forests and grasslands absorb water freely. These natural features remove pollutants and slow the rate of surface runoff. Land development often eliminates features that moderate stormwater runoff, may expose soil to erosion, and may exacerbate other negative impacts. It is, therefore, important for the MS4 to inventory, evaluate and characterize the natural, land use and development characteristics of the area. This characterization helps to establish a realistic stormwater management programs whose goal is to maintain pre-development runoff conditions.