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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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Building a beach is a job best left to nature. © David Larson

June 2004

Finding equilibrium

Beaches as an engineering challenge.

Lisa Gaumnitz


Building a beach is a job best left to nature.
© David Larson

Contents

Shifting sands and advancing science are spurring a sea of change in how Wisconsin protects its Great Lakes beaches.

Where experts once urged coastal property owners to use gigantic boulders, cement walls and other heavy-duty structures to stem erosion and stabilize bluffs, they're now counseling them to let nature take its course.

"We've come to realize that we can't always engineer a solution to many processes, like erosion. We can only live with them," says Gene Clark, a University of Wisconsin-Sea Grant coastal engineering specialist based in Superior. "The brute force approach seldom works."

He and other experts are not only converts to the idea that "hard armoring" with cement and boulders is futile in many cases, but that some beach erosion is necessary and fighting it can backfire.

"You want a little bit of erosion because that supplies the sediment needed for the system to be healthy," says Alberto Vargas, who coordinates an interagency Coastal Hazards Workgroup for the Wisconsin Coastal Management Program. "Nature tries to find an equilibrium, so sand will come from one place and be deposited in another. It cycles and it circulates.

"The problem occurs when you change one of the elements in this equation. Sand supply is one of the elements, and we have a sand-starved coastline in Wisconsin."

That paucity of sand results from Wisconsin's highly erodible coast – 80 percent is comprised of highly unstable materials and so are erosion prone. Human actions exacerbate the erosion.

Erosion

Addressing erosion starts with understanding how Great Lakes and Wisconsin beaches formed. This story was laid out in "Living on the Coast," a 2003 Sea Grant and U.S. Army Corps of Engineers publication that describes how glaciers entered the region about million years ago, forming, advancing and receding as many as 15 times until the last glaciation 25,000 to 10,000 years ago.

With each cycle, the glaciers carved the lake basins deeper and as they melted, left behind till, a mixture of sand, silt and clay. Each layer was composed of different materials, with sand and gravel deposited between them. Surface water and drainage between these layers makes them very unstable, and they are exposed in eroding banks and bluffs as high as 100 feet in many places along the shore.

Storm waves carve sand from beaches, ridges and banks. In Wisconsin, the bluffs have eroded about a foot a year in some places, so that in the last 10,000 years, they've eroded miles.

"That's what feeds the beaches," says Al Lulloff, a DNR water management engineer. "But people have been putting in hard armoring and cutting off the supply of sand."

Historically, and into the present, people wanted ports, cities and homes on the water, but Wisconsin has few natural harbors. So communities created manmade harbors by filling in lakebeds, building on them and protecting them with hard armor such as breakwaters, seawalls and groins (structures built perpendicular to the shore to stabilize a beach by holding its sand in place).

The number of groins and other armored shore protection along Lake Michigan's coast has grown significantly in recent decades as demand for coastal property has grown. The shore along Racine and Kenosha counties is peppered with groins as property owners vie for scarce sand. Proposals from developers farther north seek to erect structures that create "pocket beaches" along Port Washington's sand-starved coast.

Structures like groins placed perpendicular to the shorelines trap sand that would otherwise drift down the shoreline. Milwaukee, where a wastewater treatment plant and other facilities protected by hard armoring are stockpiling sand, is starving the Racine and Kenosha coastline areas of sand. That in turn has spurred an armor buildup.

Consequently, beaches that once provided some natural protection by dissipating the energy of storm waves are now starved of sand. As a result, the lakebed is more exposed than ever to wave energy and erosion that accelerates, undercuts and undermines even large expensive structures.

This consequence of armored shore protection really hit home for scientists and some homeowners in the mid-1980s. High water levels in the Great Lakes and other U.S. coastal waters caused huge chunks of bluff to give way and homes slid into the water. These eye-opening examples started to turn the tide against structural shore protection – at least among those who have made their careers out of mitigating coastal hazards.

From "Help Yourself" to "Living on the Coast"

That shift in mindset is apparent in differences between "Living on the Coast" and the Corps of Engineers publication it replaced, "Help Yourself," published in 1978. Implicit in the title was the idea that an individual property owner and protect their shoreline. The message made clear with "Living on the Coast" is that you need to look beyond your individual property and often work together.

Old shoreland protection manuals promoted structural solutions to beach erosion. "Now we stress natural practices first and structural methods only as a last resort," says Clark.

Natural practices begin with staying out of nature's way – not building on erosion prone property. Other natural practices include restoring native vegetation to the shoreline to stabilize bluffs or banks and managing stormwater runoff so it doesn't run over the edge of a bluff and down the face of the slope.

Clark counsels figuring out why a bluff or beach is eroding. Do waves, high water levels, vegetation removal, poor stormwater drainage practices, poor siting of septic system fields, or a combination, cause their problems?

"Once they realize that the bluff instability may be from their actions, they realize that by restoring vegetation and managing stormwater, may slow the problem," Clark says.

Armoring the shore can be appropriate when it would be very expensive or impossible to relocate buildings vulnerable to falling into the water, or when climate changes bring high water, intense storms or more frequent storms.

Mike Friis, manager of the Wisconsin Coastal Management Program (WCMP), says there are public settings where traditional shore protection can be necessary and appropriate.

Part of his program's mission is to provide public access to Wisconsin's coastal resources, a mission that can help communities offer marinas, boardwalks, public beaches and other facilities that might require armoring to protect the community's investment.

"You have to weigh offering those recreational opportunities with any potential impacts," Friis says. Without access to the waters, people don't develop an appreciation or an understanding of its importance.

But Friis stresses that the grants WCMP provides to help pay for public access projects are reviewed by technical experts to weigh public benefits, environmental impacts and costs. "We make sure the public entity understands the consequence of its activity."

Looking ahead by stepping back

Wisconsin is improving its ability to predict where erosion will occur and how fast through research funded by the WCMP's interagency Natural Hazards Workgroup. For the last decade, that group, which includes DNR, Wisconsin Emergency Management, the State Cartographer's Office and UW Sea Grant, has worked to minimize damages due to coastal hazards.

"We're trying to determine the easiest, most affordable way to track erosion so we can plan for the future and give good advice to people who live on the shoreline or want to live on the shoreline," Vargas says.

One research projects that's wrapping up involves Lulloff's work to use aerial photos of the coastline taken every decade over the last 50 years to help build a model that more precisely predicts erosion rates at different stretches of the coast.

"Erosion is sporadic. Our estimate that the Lake Michigan shore is eroding one foot a year doesn't mean it erodes one foot a year every year – it could be that a 40-foot chunk falls off after one big storm – and the rate will be higher or lower in different spots."

The project will result in maps that define risk areas, and can help guide how far buildings need to be set back from the water to be on stable ground, Lulloff says. That distance could be as far as 250 feet along some highly erodible bluffs, and much less in other areas. Lulloff and other coastal experts hope the results can increasingly steer development along the Great Lakes shore and help the property owners learn to live with the coast, not manipulate it.

"Recognize that your property encompasses an eroding bluff. Stay back and let it do its thing," Lulloff says. "It's really, really expensive to stop the erosion process, it's a long-term investment, and you may be causing a problem for yourself and your downdrift neighbors."

Lisa Gaumnitz is a public affairs manager for the DNR's Water Program.