It’s all about water over the dam

I am writing about the Sheboygan Marsh and the cattail problem that Gary Henschel wrote about last week. Gary is right that history is a great teacher. The history of water levels on the Sheboygan Marsh and the drawdowns are detailed in the Sheboygan Marsh Management Plan – found on the county web site – in the planning and resource department, see link below. There is also a frequently asked questions document (2nd link).

Mgmt Plan - pdf file: showdocument?id=5102

FAQ: showdocument?id=7679

In brief, after the marsh was drained (1912 – 1921, by digging 21 miles of ditches and blasting out the final part of the natural limestone dam near MM); the marsh laid drained until WPA (works proj- ects administration) built the dam in 1938 (to the same level as before it was drained). By 1952 records indicated they were having problems with vegetation floating into the dam. In 1968 they conducted a drawdown and put in the 5-foot diameter bypass to allow drawdowns because of –“cattail problems”. We continued to have problems with floating cattails and have had intermittent drawdowns since 1984.

As you can see, the problems with floating cattails didn’t just start with the drawdowns since 1984. You can also see that keeping levels up for 30 and 16 years didn’t stop floating cattails from happening. What has changed is the frequency - as changes in the watershed and more frequent large rainfall events have exacerbated the problems. Hybrid cattails have also invaded the marsh and added to the problem.

There is a 133-square mile watershed that flows through the 65-foot wide dam and 5-foot diameter bypass tube. Prior to draining the marsh and removing the natural dam, there was a natural spillway where there are now roads and parking lots. Some fluctuation in water levels was part of the natural hydrologic regime but humans have modified both the dam area and the watershed resulting in increasing amplitudes of these fluctuations.

Trying to lower water levels prior to ice out is problematic for a number of reasons. First it is very difficult to operate the bypass when things are still frozen. Any significant rains combined with the spring thaw makes keeping water levels down very difficult. Also, lowering water levels while snowmobilers and 4-wheelers are still using the marsh would cause more dangerous ice conditions.

“The Sheboygan County 2013 Management Plan Update” (first link above) provides a very comprehensive review of the Sheboygan Marsh - including the geological history, management history and water resources. Pages 11 - 22 covers water level management, with a lot of good information on the past that explains why these drawdowns have to be done. There are many opinions on water level management options for the marsh and they are also discussed (pages 16 - 22).

There are also some opinions about the historic (at the time of European settlement) water levels on the marsh, that continue to be offered - as you could say “alternative facts”. That is one of the reasons there is so much information in the Management Plan on how the “historic” (prior to drainage) water levels were determined. The information includes the topographic survey that we did from the lime kiln area to the dam (comparing levels to the information in the 1905 thesis by engineering students Peterson & Sinz), vegetation and other references noted in the original land surveys from the mid 1800s and soil type information. If this sparks your curiosity, read pages 33 - 41 (Mgmt Plan).

I appreciate the opportunity to share my perspective. I worked for the Wisconsin DNR for over 37 years and we worked with Sheboygan County on the management of water levels on the Sheboygan Marsh. The WDNR and Sheboygan County plan on conducting a drawdown this summer. As I discussed above - the large watershed and the changes to outflow area, makes this a challenge on both ends - drawing it down and reflowing it. Add in unpredictable large rain events and the limited capacity to bypass water and you can see the challenges…and why I am happy to just be an observer this time!

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