Post-Construction Runoff Controls
In addition to a Post-Construction Runoff Model Ordinance, this website contains ordinances from around the country:
The management of stormwater runoff from sites after the construction phase is vital in controlling the impacts of development on urban water quality. The increase in impervious surfaces such as rooftops, roads, parking lots, and sidewalks due to land development has a number of effects on aquatic systems. First, increases in imperviousness create a corresponding increase in the total volume of stormwater runoff from a site . This increase in runoff volume leads to degradation of stream channel habitat and increases in the occurrence of flooding. Heightened levels of impervious cover have also been associated with stream warming and loss of aquatic biodiversity in urban areas. Runoff from impervious areas can also contain a variety of pollutants that are detrimental to water quality, including sediment, nutrients, road salts, heavy metals, pathogenic bacteria, and petroleum hydrocarbons . Efforts to control the impacts of imperviousness and stormwater runoff are typically in the form of structural and nonstructural management practices that either prevent initial pollutant loadings or detain and treat stormwater to reduce pollutant levels and control the volume of runoff.
The main goal of a stormwater management ordinance for existing development is to limit surface runoff volumes and reduce water runoff pollution loadings. To create the most effective ordinance possible, the following sections are required in any stormwater runoff ordinance. First, language referring to a guidance manual for BMP design and implementation is necessary. This design manual is created by a designated stormwater management agency and contains information on sizing criteria, performance criteria, and guidance on selection and location of BMPs. By referring to the current version of a design manual, the ordinance will not need to change to reflect new technological advances or changes in stormwater management experiences within a community. Changes are instead incorporated into the design manual and the ordinance simply states that you use the criteria in current design manual. Second, the ordinance should have language requiring that all development projects include a post-construction stormwater management plan. The ordinance should include information on what the contents of an acceptable plan are and who is responsible for operation and maintenance. The operation and maintenance section will include a mechanism for inspection of all stormwater control practices. For examples of stormwater operation and maintenance ordinances, including a model ordinance that deals with inspection issues, click here. A final requirement is language explaining the mechanisms for enforcement of the requirements of the ordinance, including the civil and criminal penalties that may apply.
There are other ideas that can be included in an ordinance to improve its ability to control stormwater runoff. The ordinance could include what nonstructural and structural stormwater practices are allowed within the community. Communities may also wish to add language regarding on-site stormwater requirements and whether off-site treatment is an option. The example ordinances provided here include language dealing with each of the issues above, and communities should examine each ordinance for the language that is appropriate for their stormwater program.