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Thursday, December 25, 2014 |  Madison, WI: 34.0° F  Overcast
The Daily
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Getting too high on the lake
Mendota's elevated water is a disaster waiting to happen

Russ Hefty paddles his kayak out to a floating chunk of sedge meadow connected tenuously to Cherokee Marsh - not by roots but by surface vegetation. A heavy rain or strong storm might be all it takes to make this chunk break off and float away, as have hundreds of acres of Lake Mendota marshland over the years.

"Sedge meadows are not supposed to be floating," explains Hefty, the city of Madison's conservation resource supervisor. "They're only floating because we've raised the water level of the marsh."

Hefty points out a clump of swamp loosestrife at the sedge meadow's edge. He tells a group of Madison residents gathered around in kayaks and canoes how, in shallower water, this plant would grow roots wherever its stem touched soil and thus spread out, increasing the meadow's chances of hanging onto the shore.

"But here," he says, "it can't spread laterally because the water's too deep."

For the last several years, Hefty and his crew have been working feverishly to save Cherokee Marsh from further erosion and possible complete destruction. They've planted thousands of tubers and water lilies, many in wire-and-wood cages that stretch for more than a mile along the shore.

In some places, these plantings have taken hold, extending the marsh. In others, the marsh has continued to wash away. Either way, Hefty's biggest challenge is Lake Mendota's artificially high water levels.

"We have two levels, high and higher, and both of them work against the ecology of the lake," says Hefty. He estimates that Lake Mendota is now 5.5 feet higher than when "we started mucking with it" - first with dams and then, in 1910, with the Tenney locks and dam.

The continual pounding of wind and water exacerbated by these higher levels has washed away vast areas of wetlands. Using aerial photos from 1937, Hefty has reckoned the loss since then at more than 275 acres (see map).

Higher water levels make it harder to maintain shoreline integrity, forcing lakefront property owners to use boulders and riprap to protect their properties. And twice in recent years (1993 and 2000), water levels have risen to where they threatened to overflow the lake, which could cause devastating flooding.

Warns Hefty, "We're operating on a two-strike count."

New floodplain maps produced by the>/b> state Department of Natural Resources (DNR) have added urgency to this issue. The maps raise Lake Mendota's flood elevation a full foot, to 853 feet. This underscores the increased risk of flooding and will force hundreds of homeowners on or near lakeshores to buy costly federal flood insurance.

The new maps also show that in a 100-year flood event the area around the Tenney locks would be overtopped. The city of Madison disputes this, but its own calculations add only about a half-foot of comfort.

If the lake overflows, water would pour from Mendota through the Yahara River to Lake Monona, which is managed to be about four feet lower. "Basements in Monona would be in serious trouble," says city engineer Larry Nelson. "We [Madison] would be taking some losses. Monona would take more."

In early May, Nelson wrote the DNR to challenge some aspects of its floodplain maps and, more important, to urge serious discussion about lowering the lake level. "[I]t is clear the management strategy must be modified or the locks and surrounding area must be raised," Nelson wrote.

Hefty would like to see the lake at least six inches lower, which would make "a huge difference" in helping marsh vegetation resist erosion and thrive. City engineering has suggested dropping the lake's summer target maximum a full foot.

"Somebody's got to address this in some way," says Greg Fries, a principle engineer with the city. "We've maxed out here."

And the less permeable the surface, the greater the risk, because more rainfall ends up in the lake. "As development proceeds to the north of Lake Mendota," says Fries, "this problem is going to get worse."

So there you have it. Artificially high water levels in Lake Mendota are causing environmental harm. They increase the danger of massive flooding, and could require that millions be spent to build up the shoreline at Tenney Park.

Lowering the lake would protect wetland and aid ongoing remediation efforts. It would reduce erosion and the need to fortify the shore. And it would make it less likely that folks in Madison and Monona might someday be able to swim in their basements.

So why isn't this idea being universally embraced as a wise thing to do?

Because artificially high water levels are favored by people with big boats, a constituency that wields tremendous power. Otherwise, they'd need longer piers or have to dredge the moorings at their lakefront properties.

"Some people would like to see higher water levels so they can get their boats into areas that would otherwise be too shallow," notes Sue Josheff, the DNR's point person for the watershed that includes Madison's lakes. And lower levels might harm habitat for northern pike and other species.

"Anytime we approach setting levels or changing levels, it's highly contentious," says Josheff. "We have to balance a lot of issues."

But, she adds, the DNR fully intends to "start the conversation" on the water levels in the Madison lakes, a difficult and time-consuming process.

It's a discussion that's long overdue. What's lacking, and clearly needed, is for the area's political leaders to prove their environmental credentials and heed the warnings now being sounded. That may mean standing up to some rich folks with big boats.

Don't hold your breath.

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