Soil Bags Preserve History
Pat Dixon is co-owner with his wife Colleen of Dixon Shoreline LLC in Portage, WI, a family business he inherited after his father died in 1994. “I kept getting telephone calls, so we started up again,” he says.

With an emphasis on water quality and erosion and sediment control, the company tries to stay ahead of the curve on new regulations and products, Dixon says, adding that it was among the first to install soil bags. “We use bioengineered soil stabilization for erosion and sediment control on hillsides and shorelines. I have done thousands of installations.”

Veteran Gil Layton, who acted as technical advisor to the project, spent 38 years with the Wisconsin Department of Transportation and has been involved in erosion control and stormwater programs for 44 years.

In an August 2009 project, Dixon and Layton used Agrecol’s Envirolok geotextile fabric bags. “They grab and have good bursting strength,” Dixon says. The site, on Lake Mendota north of Madison, WI, involved a 50-foot cliff where the hillside had started to wash out and the homeowner’s backyard had started to collapse. “We used earth anchors, geogrid, and Envirolok soil bags with permeable drain tiles behind them.”

A residential lakeside property, the site was home to a 1,200-year-old Native American effigy mound in the shape of an eagle. With a 60-foot body, the entire mound covered 100 feet of the owner’s backyard. According to authorities, about 10,000 such mounds once existed in Wisconsin. Only a small fraction of these earthworks remain today, and most of those were tampered with at one time or another. The failure of this cliff had already started to affect the effigy mound, which prompted the homeowner to proceed with the project.

To prepare the site, workers removed 20 cubic yards of soil by hand, using a pulley system and buckets to move it uphill. “It took eight hours a day, with many men, for several days,” Dixon says. “We laid the first soil bags at the base, then went up 2 feet, wrapped the next course in geogrid, and put in earth anchors to connect the two and tie the system back into the cliff. We did the whole thing in 2-foot stages, putting drain tiles behind to alleviate hydrostatic pressure. The hillside was so steep that we had to use rock-climbing harnesses for safety.” Dixon says placing the bags is more than a mechanical process. “You have to work with the contour of the slope. It’s all handwork, and you have to feel the hill. It’s almost like artwork.”

The next step involved hydroseeding the site with a native mix. “We brought in a hydroseeding tank on a 26-foot work barge so we could work from the water and more easily access the site,” Dixon says. “We applied the mix of seed, tackifier, and hydroseed mulch as a cover crop for germination. Then we harnessed up and planted 2,800 plant plugs by hand.”

Layton says Wisconsin regulatory agencies are reluctant to allow hard armor along a waterway above the ordinary high water mark. “Therefore, we were telling the owner that a ‘green’ system was our only alternative.”

Dixon says the cliff, a one-quarter-to-1 slope, was the steepest project he had ever done: “Probably the steepest anywhere.” He praised the Envirolok bags. “They are individual units, so they add strength to the hillside; they are much better than sediment logs on steep slopes. We used 2,500 individual bags.”

Why did the hillside fail in the first place? “There’s usually a reason for shoreline erosion,” Dixon says. “It can be due to bottom, groundwater flow, or overland stormwater runoff flow at the top. In this case it was mainly overland flow. We redirected the downspouts and tiled them in to flow away from the slopes. We also directed the runoff from the yard to a catch basin on the site and redirected it toward the lake with an underdrain system.”

As a retired journeyman lineman, Dixon has traveled the country, always dealing with nature. Wherever there is a problem, there is a way to fix it. This is Dixon’s mantra. “You can always find a solution. We work with Mother Nature, not against her. Rock is not always the answer. Much of our erosion is caused by man. From the DNR to the counties with their zoning administration, good regulations are doing their job. We need to value native plants and clean water and become less dependent on foreign energy.”

About Envirolok, a product of Agrecol Corp. headquartered in southern Wisconsin, Layton says,” There’s a right place and a wrong place for every product out there. In this case, we were not allowed hard armor and there is nothing comparable to the Envirolok wall system when a vegetated or ‘green’ system is required. The bags are filled with 80% sand and 20% topsoil. The sand, or mineral-type soil, prevents settlement of the system, which is a common cause of failure with compost-filled systems when used on steep slopes. This was erodible clay soil, so we also tied the system back into the native soil as deep as possible using geogrid and earth anchors. This was a unique site; we used native plants with their deep roots, 10 to 15 feet, to enhance the structural value of the wall as they grow.”

Author's Bio: Mary Ellen Hare is a writer in Granville, OH.

Photo: DIXON SHORELINE Soil-filled geotextile bags, earth anchors, andgeogrid stabilized a 50-foot cliff near Lake Mendota. The backyard of the residence above the cliff had started to collapse

For the entire article click here