On August 20-21 2018 heavy rainfall impacted western Dane County including parts of Madison, Middleton and communities along Black Earth Creek (PDF). Large amounts of rainfall occurred over a short period of time which overloaded the capacity of stormwater drainage infrastructure, resulting in rapid or flash flooding. The flash flooding damaged roads/bridges (e.g., Highway 19 in the Village of Black Earth), residential and commercial property, and recreation trails (e.g., Middleton).
Developed areas contain roads, buildings, parking lots, and other impervious surfaces. These surfaces reduce the amount of water that soaks into the ground and therefore increases water runoff. The water runoff travels through storm sewer drains and pipes. The storm sewer drains, bridges, and other infrastructure have limited capacity and are often not designed to accommodate water from extreme events such as August 20-21.