Yahara River and Lake Flooding

Thursday, August 23, 2018 - 12:42pm

Additional information on flooding developments

Dane County Lakes management is forced to increase the amount of water coming out of Lake Mendota at the Tenney Dam and that is taking place now. In addition, they intend to open the locks channel to release more water this afternoon. At this point, Dane County staff is estimating that the Yahara River through the isthmus will go up another 3” to 6” over the next 24 hours. Yesterday it went up about 5 inches. A three inch rise is expected for Lake Monona over the next 24 hours.

The level of the water in Lake Mendota has to be brought down to provide room for the rains that are predicted Friday and into next week. If this isn’t done, the dam at Tenney would almost certainly be compromised. A failure of the dam would cause devastating flooding along the Yahara River, in the Isthmus and the lands surrounding Lake Monona.

Certain low lying areas of the isthmus are now at the same elevation as the elevation of the Yahara River. What that means, is that the water in the streets is a back water of the Yahara River. The storm inlets and pipes are the only way to drain the street. When it rains, instead of water draining into a dry pipe, the water entering the pipe has to push water out of the pipe. This makes the storm sewer much less efficient. The rain predicted for Madison on Friday and into next week is a significant concern. Urban flash flooding will occur more readily if the rain that falls is intense. More rain will only make the Yahara River and the Madison lakes rise further. Residents should avoid parking in low lying areas.

The City is making sand and sand bags available for residents and business owners to fill and use to protect their property. Bag and staff are available at the Tenney Beach parking lot, Commonwealth Development at 913 East Main, the Olbrich boat landing and other sites. The City is taking measures to protect City Facilities as well.

East Johnson St is closed at Tenney Park. Lane closures on East Washington Ave are going to be necessary. Full closure is a possibility.

More information will follow in our press releases and press conference at 1:00 p.m. today. cityofmadison.com/flooding is also an appropriate way to access up to date information


  • Katie Crawley, Mayor’s Office(608) 266-4611
  • Rob Phillips, City Engineer(608) 266-4751
  • Brian Smith,Traffic Engineering(608) 261-9625