Fiscal Note
No Fiscal Impact
Title
Requesting Dane County and the City of Madison convene a technical work group to study strategies for reducing the risk of future high lake level events and flooding on the Yahara River and the Yahara Lakes.
Body
Lakes Mendota and Monona are at water levels well above the WDNR ordered summer maximums much of the summer in a typical year. This year is no exception. In the months leading up to the August 20, 2018 storm that devastated parts of western Dane County, the Madison lakes were already well above their summer maximum elevation. The August 20 storm caused the lakes to rise to critical elevations. Lake Monona rose to 10 inches above the 100 year flood elevation and high water on the Yahara River caused road closures within the lower lying areas of the isthmus, including one of the three arterials traversing the east isthmus. In addition, there were lane closures on East Washington Ave (US 151) due to flooding.
With the Tenney Dam, located where water exits Lake Mendota into the Yahara River, water elevations on Lake Mendota can be well controlled. Unfortunately, there is little that can be done to control water levels on Lake Monona in a flooding situation, because the capacity of the Yahara River downstream of Lake Monona is limited. This sets up a situation where water must be released out of Lake Mendota to preserve the integrity of the dam but the water coming into Lake Monona can’t leave at a rate high enough to prevent a significant rise in water level on Lake Monona.
The Yahara River through the east isthmus between Lake Mendota and Lake Monona has good capacity but the capacity of the river does become problematic when the discharge rate is extremely high. High release rates from Lake Mendota combined with high water levels on Lake Monona create a significantly higher profile on the river and this increases the potential for flooding, especially flash flooding when storm sewers, filled with water, are unable to quickly drain water away.
If no changes are made, it is not a matter of if Lake Monona and the Yahara River through the east isthmus will flood to the point of damaging homes and businesses, it is only a matter of when.
Therefore, the City of Madison is requesting that Dane County, along with the City of Madison, convene a technical work group to study appropriate operating orders for the Yahara chain of lakes and to study the necessary actions, both short and long term, to significantly reduce the risk of flooding in the future.
In 2008, the Yahara Lakes Advisory Group (YLAG) was formed to study lake levels. Around the year 2000 a similar group was also formed. In both cases, a recommendation to lower the lake levels did not appear on the list of recommendations. Many of the recommendations were valid however and should be explored further. At this time, there is a need to review and update the recommendations of the 2008 YLAG group and to study the suitability of the current WDNR lake orders including the suitability of the current summer mandated lake levels. There is also a need to create an implementation plan.
Now Therefore be it resolved, that the City of Madison hereby requests that Dane County, along with the City of Madison, convene a technical work group to investigate the suitability of the current Wisconsin Department of Natural Resources Lake Level Orders on the Yahara Lakes, to review strategies to reduce the probability of lake and river flooding in the future, and to provide a recommendation to petition the Wisconsin Department of Natural Resources to revise the current Operating Orders for the Yahara Lakes; and,
Be It Further Resolved, that the Group be charged with reviewing and updating the recommendations of the Yahara Lakes Advisory Group and creating an implementation plan; and,
Be It Finally Resolved, that City of Madison Storm Water Utility Staff, and other agency staff as necessary, are hereby directed to staff, represent the City of Madison on the technical work group, and to report back to the Common Council during the work group and present the final report for approval.