In November of 2021, the Dane County Executive signed into effect an amendment to Chapter 14 of the Dane County Ordinance, which governs erosion control and stormwater management. It updated the standards to help mitigate flooding by requiring peak rate control of the 200-year storm and added volume requirements for closed watersheds.
Effective November 15, 2021, the updated ordinance sets the minimum requirements for stormwater management in all cities, villages, and towns in Dane County. These changes will help to reduce the chance of localized and regional flooding, reduce the burden put on public drainageway and storm sewer systems, and contribute to improved water quality.
The ordinance aims to reduce or minimize adverse impacts of stormwater and snow melt runoff from land disturbing and land development activities. Runoff from disturbed land can be a significant source of both water quality and quantity issues. Updates to the ordinance are intended to address increasingly heavier and more extreme rainfall events occurring because of climate change as well as more intense development in the Dane County area. Key elements include:
- The peak rate of runoff leaving a site in the post-development condition must now match that of the predevelopment condition for all storms up to the 200-year, 24-hour design storm event (7.53 inches). The previous ordinance required up to the 100-year storm (6.66 inches).
- Redevelopment projects meeting certain thresholds must now treat the first ½-inch of stormwater runoff using green infrastructure.
- Development within closed watersheds (internally drained areas) must now comply with certain requirements to reduce the additional volume of runoff leaving the site because of the development, as compared to predevelopment conditions.
An overarching goal of CARPC’s Regional Development Framework is the community-established priority to promote growth that fosters community resilience to climate change. Adapting stormwater standards to account for climate change is an important aspect of becoming a more climate resilient region.
Efforts to improve water quality and increase resiliency to climate change have been ongoing across the region for several years. In 2020, the City of Madison made similar updates to their stormwater Ordinance. In 2017, a report titled “Reducing Increased Risk of Flooding”, prepared by a joint Stormwater Technical Advisory Committee convened by the Dane County Lakes & Watershed Commission and CARPC, included recommendations related to enhanced volume control and better management of stormwater in closed basin watersheds.
The updated county ordinance is available on the Dane County Land & Water Resources Department website. CARPC maintains an ArcGIS Online map of the region’s closed watersheds (internally drained areas), available in our Open Data Portal.
