When land is developed, the natural hydrologic system is altered. Impervious surfaces such as rooftops, driveways, streets and parking lots all prevent rainwater from soaking into the ground and increase the amount and rate of stormwater runoff. Development and urbanization in a watershed can dramatically increase the amount of stormwater runoff as illustrated below. This effect is further exacerbated by drainage systems such as gutters, storm sewers and lined channels that are designed to quickly carry runoff to rivers and streams.
Increased stormwater runoff volume and higher peak flows can result in more frequent and severe flooding events, and well as significant stream channel erosion. This problem is compounded by building and filling in floodplain areas, which cause flood heights to rise even further. In a watershed with rapid development, properties and structures that had not previously been subject to flooding may now be at risk.
Communities in the Metro Water District are helping to minimize potential flooding due to future growth by both addressing the stormwater impacts from new development & redevelopment, and by regulating floodplains based on projected future land use conditions. Please see the Model Ordinance for Post-Development Stormwater Management for New Development and Redevelopment and the Floodplain Management / Flood Damage Prevention Model Ordinance, respectively, for more information.