452.a. Stormwater Management Regulations (SMR)

Possible Points: 380 points for the element.

Purpose of Element: Development is inevitable. As populations grow and change, additional space is needed to house, employ and provide services to members of the community. Development is typically associated with an increase in impervious surfaces. The expansion of these areas can increase the total volume of runoff entering into a community’s stormwater infrastructure, rivers, lakes and streams. The purpose of this element is to reward communities for implementing regulations that require developers to manage stormwater runoff from new developments onsite such that increases in the frequency and severity of flooding are prevented.

In general, several types of stormwater infrastructure can be used to reduce runoff created by new development. Stormwater detention ponds, stormwater retention ponds and site-scale green infrastructure (i.e. bioswales, pervious pavers, rain gardens and vegetated ponds) can all be implemented to reduce runoff volumes and peak flow rates. For more information on green infrastructure techniques that could be used, reference the US EPA’s Green Infrastructure webpage. Users can find state-by-state design manuals, information on operations and maintenance, introductory, intermediate, and advanced modeling tools, and funding opportunities.

Communities are credited based on their performance in four sub-elements, which reward them for:

1. Clearly stating the size and type of development that is regulated (SZ),
2. Specifying the design storm(s) that the community requires developers to use when they model pre- and post-development peak flow rates and volumes (DS),
3. Requiring low impact development techniques to be used to meet the requirements of DS (LID), and
4. Having the authority to require the owners of private stormwater management infrastructure to properly maintain their facilities (PUB).

The stricter the regulations are, the more credit a community can receive. For example, in order to receive full credit for the first two sub-elements, all development must be subject to stormwater management regulations, and the 100-year storm must be used in the design process in order to ensure that pre- and post-development peak-flow rates and runoff volumes are equal at the very least. For more information, see pages 450-4 - 450-13 of the CRS Coordinator’s Manual.

Impact Adjustment: The impact adjustment for this element is calculated by taking the ratio of area of all watersheds that contribute flow to the community to the area of the watersheds that are subject to the community’s stormwater management regulations or the regulations of another community in the watershed.

Under several circumstances, portions of these watersheds can be excluded from impact adjustment calculations. First, if the area of the watershed is 50 square miles or greater at the point where it enters the community’s jurisdiction, the area of the watershed upstream of the community can be excluded from impact adjustment calculations. Second, if an upstream flood control structure effectively reduces the size of the watershed by controlling the base flood, these areas can be excluded from impact adjustment calculations. Examples of a flood control structure that would qualify for this criterion include dams and flood control reservoirs like the Elmhurst Quarry. Third, areas that are unlikely to be developed like national and state parks and forests or large tracts of privately-held land that are enrolled in conservation easements or have otherwise been dedicated as open space can be excluded from impact adjustment calculations.

One additional critical factor that should be taken into account is that a community can count areas outside of its jurisdiction in their calculation of the total area that is impacted by its stormwater management regulations if it is able to demonstrate other communities in the upper reaches of the watershed have implemented creditable stormwater management regulations and watershed management programs. For more information, see pages 450-11 - 450-12 of the CRS Coordinator’s Manual.

Potential to Double Count Credit: None.

Degree of Difficulty - Documentation: Medium. The documentation requirements for this element are minimal. In order to take credit for this element communities must provide their ISO/CRS coordinator with copies of relevant ordinances, permits that demonstrate that the community’s stormwater management regulations are being enforced, a copy of the community’s impact adjustment map, and other relevant materials. That said, communities without access to a staff person or a contractor with the GIS expertise necessary to complete the impact adjustment calculations and mapping for this CRS element, may have limited credit earning potential. The CRS does have a minimum impact adjustment value of 0.15 that can be used. The community could also produce an estimate, but their ISO/CRS technical reviewer must agree with said estimation for it to be used in credit calculations. See page 450-13 of the CRS Coordinator’s Manual for more information.

Degree of Difficulty - Implementation: Medium. Implementation and enforcement of stormwater management regulations will require a community to have a professional engineer on staff or on contract to assist with enforcement and permitting. The adoption of creditable stormwater management regulations could also be met with opposition from community members. As a result, the degree of difficulty associated with implementing this CRS element is medium.

Tips for Success:

1. Wisconsin Sea Grant has created a publication aimed at helping communities to evaluate their codes and update them in ways that facilitate the use of green infrastructure. Communities interested in implementing stormwater management regulations can use this guide to evaluate their existing codes, and identify key places where changes can be made in order to encourage the use of green infrastructure.
2. Visit neighboring communities that already have experience implementing this CRS element or a similar initiative. Learning from the experiences of others can help communities avoid pitfalls and make informed decisions.

Co-benefits Associated with this Element: The most obvious benefit associated with this element is flood risk reduction. Requiring all new development include some kind of on-site mechanism to mitigate its impact on the rate and/or volume of stormwater runoff can help ensure new developments do not significantly impact flood risk.

The benefits associated with the implementation of these regulations go far beyond just flood control. Communities that require low-impact development to be implemented increase infiltration within the community. This can lead to reduced runoff volumes, slower runoff velocities and increased groundwater recharge. In addition, low-impact development can reduce the amount of pollutants that make it into receiving waterbodies, meaning high-quality aquatic habitat can be maintained. Vegetated detention ponds are also sometimes used as playing fields for local sporting events. Implementing multi-functional stormwater infrastructure like this can increase recreational opportunities for the community.