Stormwater Management in a Changing Climate

Successful management of the impacts of climate change on flood risk will require significant improvements in the stormwater ordinances that regulate land development. Ordinance requirements intended to prevent development-related increases in flood risk are generally enacted and enforced by local governments, as federal requirements pertain only to water quality and many states limit their requirements accordingly. The most obvious improvement needed is a new set of rainfall statistics that accounts for climate change. In addition, stormwater ordinances need to be upgraded to ensure that they are fully effective in preventing increases in flood risk due to failure to account for the various ways in which land development affects downstream flooding.

This talk focuses on a recent effort to strengthen local stormwater ordinances in Dane County, WI. The most notable aspect of this effort is the fact that flooding associated with the series of large lakes on the Yahara River is sensitive to increases in the volume of runoff, rather than the peak. As a result, the prevention of development-related increases in flood risk requires control of runoff volumes rather than peak runoff rates. The current state regulations require 90% control of runoff volumes. A recent task force has recommended that the County require 100% control. The committee also recommended the creation of a volume-trading program to encourage efficient construction of the infrastructure required to fully control runoff volumes. The recommendations were well received by County government. But before any action could be taken, the state legislature passed a resolution prohibiting any local government from exceeding the state stormwater volume-control requirements, even though those requirements focused on the impacts of development on water quality rather than on flooding. In spite of this roadblock, the County is exploring the logistics of a 100% volume-control program and identifying promising opportunities for volume trading. Major flooding on the Yahara Lake last summer has increased the likelihood that the prohibition on total volume-control will be reconsidered.