Dane County Starts Multi-Year Project to Help Yahara Lakes Better Handle Heavy Rains, Reduce Lake Flooding Risk

May 21, 2020
Ariana Vruwink, 608-267-8823
County Executive, Land & Water Resources

Hydraulic Dredging Kick-Off Marks Start of 11 Miles of Sediment Removal to Improve Management of Lake Levels During High Water Periods

Today, County Executive Joe Parisi joined Land and Water Resource Department staff at the Lottes Park Boat Launch in Monona to announce that Dane County has officially begun the first phase of its Yahara Chain of Lakes Sediment Removal Project. This first phase of the project kicked off this week, with dredging equipment now in the water, working between Lakes Monona and Waubesa. The County hopes to remove approximately 40,000 cubic yards (or more than 3,000 dump truck loads) of sediment in the project’s first phase. The $3.25 million project will help improve water flow, flood storage capacity, and fish and wildlife habitat in the Yahara Lakes.

“We are excited to kick off this first phase of our flood mitigation initiative in the Yahara Chain of Lakes,” said Dane County Executive Joe Parisi. “Climate change will continue to bring heavy rains to our area. With this initiative, we hope to improve the flow of water through the Yahara Lakes system and help mitigate future flooding risk.”

Currently, water comes into the Yahara Chain of Lakes faster than it goes out—taking two inches of rain over two weeks to leave the Yahara Lakes system. The efficient movement of water downstream can be undermined by sediment loading. While sediment movement is a naturally occurring process, accumulation of sediment in the Yahara River and Lakes is greatly increased by human activity, including urban development. It is estimated that over 8.5 million pounds of sediment enter the Yahara River and Lakes each year from urban runoff.

Last month, Dane County released its community-wide Climate Action Plan, which included newly published climate modeling by UW-Madison scientists. The modeling predicts southern Wisconsin will continue to get hotter and wetter over time. When looking at rainfall patterns, the modeling indicates it is highly likely that large precipitation events will continue to increase in frequency and intensity.

This location between Lakes Monona and Waubesa is one of six sites the County will target in five phases to improve water flow, with each phase being carried out as Dane County secures permitting. Dredgit Corporation was awarded the $3.25 million contract for Dane County’s first phase of the project last December. The goal is to complete the majority of the dredging by late summer, pending any changes related to the COVID-19 pandemic.

The project will use hydraulic dredging to remove between two to three feet of sediment about 50 feet wide and approximately 1.5 miles long. The material will be pumped approximately 3 miles away using a series of booster pumps to land owned by the Madison Metropolitan Sewerage District (MMSD). MMSD is allowing Dane County to utilize its land for the duration of the project. A dewatering basin will be built on this land to collect the sediment.

The type of sediment removal that will take place during this project is comparable to the County’s “Suck the Muck” initiative. Nearly a month after historic rainfall in the summer of 2018, water levels on Lake Monona were still 8 inches higher than Lake Waubesa. Sediment removal in this location could improve water quality, habitat, navigation, and the rate at which water leaves the Yahara Lakes in the wake of heavy rains.

In addition to this investment, County Executive Parisi has included money in his 2020 budget to create a sediment removal crew and purchase the equipment needed for the County to do its own hydraulic sediment removal. This will ensure for years to come that Dane County has the equipment and staff expertise in-house to manage work demands created by the new realities that pose unique challenges to a quickly growing area with diverse water resources.

The 2020 budget also includes $5 million to purchase equipment needed for sediment removal work and the staff to carry out the job. This will add 4 new positions dedicated to Yahara Chain of Lakes sediment removal work in the Land and Water Resources Department. The County hopes this investment will accelerate its work to increase capacity and water flow in the Yahara Lakes.