Why is it Important to Manage Stormwater from Development Projects?
In the fall of 2014, DWSD conducted a comprehensive municipal code review as a part of Detroit’s Green Infrastructure Plan
implementation to meet multiple objectives:
- Assess the existing City stormwater development standards and their suitability to manage peak flows and volumes from development projects over a wide range of conditions.
- Evaluate specific language in the municipal code and the extent to which it enables, incentivizes or limits green stormwater infrastructure implementation and the multiple benefits green stormwater infrastructure can provide.
- Identify barriers to green stormwater infrastructure practices or strategies which may be authorized to reduce ratepayers’ drainage charge.
The review of Detroit's municipal code revealed that the City currently does not require new or redevelopment projects to manage stormwater post-construction. Impervious developed lands – such as roofs, parking lots and sidewalks – that do not allow rain water and snow melt to infiltrate into the ground increase the amount of stormwater that goes into the combined sewer system. This puts stress on the City’s infrastructure and impacts water quality when combined sewer overflows occur due to system overloading. In order to prevent this – and to comply with DWSD's permit requirements – the City is developing new regulations which will require development projects to manage the stormwater generated by the project site and revising existing code to help support and incentivize green stormwater infrastructure. An inter-departmental City technical advisory committee has been working with local stakeholders to accomplish these goals.
Stormwater Management on Development Projects
The City’s municipal code does not include any requirements for development projects to manage stormwater if they create or replace impervious cover. A new ordinance has been drafted which would require this type of management to mitigate infrastructure and water quality impacts. The proposed ordinance will require regulated projects to install controls which will manage the amount of stormwater which enters the city’s infrastructure and the rate at which this stormwater enters the system. Project applicants will be required to submit a post construction stormwater management plan which specifies how these controls will accomplish the required level of management. Implementation of this plan will be required during the project and proper operation and maintenance of the controls will be required after the project is complete.
Zoning Code Updates
The code review revealed that small revisions could be made to the zoning code to better allow multiple benefits to be achieved in landscaping areas (e.g., screening, breaking-up pavement, pedestrian safety, stormwater management, and open space) and to allow for the reduction of impervious area within off-street parking areas. Updates to the zoning code were proposed which will make it easier to use existing landscaped areas and recreational space to manage stormwater and to use pervious materials for off- street parking.