Project Profile: Native Grasses and Innovative Technology
There’s a certain risk associated with changing what is apparently not broken. Examples abound, from New Coke to the Ford Edsel to the Arch Deluxe, McDonald’s “burger with the grown-up taste.” Don’t remember that last one? Exactly-some things are best left as is.
In 1999, in an effort to beautify a pair of islands on the campus’s Lyman Lakes, Carlton College decided to dredge and clean up the lake. When the dredging was complete, the shoreline grasses that had protected the two islands in the center of the lake were gone, replaced instead with traditional turf grass. This provided a park-like setting around the islands that was neat and manicured for the future enjoyment of anyone at the college. No one ever envisioned, however, the impact of that well-intentioned act: Gradually the current of the small stream that travels through this lake on to the Cannon River, coupled with the wave action from the wind, ate away a good portion of the islands’ shoreline. To restore that area, the college contracted with two of the Twin Cities’ foremost experts in that field: Windscapes and Prairie Restorations Inc. Windscapes’ blower truck technology and use of Filtrexx FilterSoxx, coupled with Prairie Restorations’ knowledge of native plants and their beneficial uses, have both minimized the impact of the project on the environment during construction and restored the area’s pristine beauty.
Wave Power
Located about an hour south of the Twin Cities of Minneapolis-St. Paul, MN, Carleton College consistently ranks among the top 10 liberal arts colleges in the country and offers one of the state’s most picturesque campuses. One of its defining features, Lyman Lakes, was dug in 1916. The material from the excavation was used to create a pair of islands that over the years have become a popular recreational gathering spot for the student body.
According to Chuck Joswiak of Windscapes in Inver Grove Heights, MN, all of the goals of the 1999 dredging project were noble. “Truth be told, most people probably would rather look at maintained turf than the taller native shoreline grasses that originally stabilized the edge. But, because turf grass has such a shallow root structure, when it was windy and waves would beat against the shoreline, the roots weren’t deep enough to hold the soil in place. Eventually, large chunks of turf and soil began disappearing-I’d guess 8 to 10 feet of shoreline on each island area was lost due to that erosion.”
Third One’s a Charm
To restore the area, Carleton College put out a request for proposals to area firms and chose Prairie Restorations, a Cannon Falls, MN, company with which it had worked in the past.
“We actually do quite a bit of work for the college,” says John Pauley, site manager. “We were happy to get the project, but, after looking around at the situation, I began to second-guess how we were going to do it. The lake was to be drained as low as it could go, so I thought we would either have to use traditional equipment like loaders and dozers and deal with the mess they would create, or wait until winter when we could drive on a frozen lake bottom. Neither was very attractive to us.”
Pauley says he then thought of a third option: getting material to the island using blower trucks from Windscapes. He says the two companies had worked together on other projects in the past and felt that was definitely the way to go. “I contacted Chuck, and together we came up with what you see here today.”
Going the Distance
The plan for recovering the Islands at Carleton College started with placement of stakes to establish boundaries and elevations, followed by laying of a geogrid membrane directly on top of the sandy soil of the lakebed to act as something of an anchoring mechanism for the bottom two layers of FilterSoxx.
“In other similar projects we’ve done using filter socks as we did here, we would add gravel to that bottom mix,” says Joswiak. That would give us the weight we need to help hold the sock in place and protect the newly placed material from any type of wave action or “˜bounce.’ At Carleton, that wasn’t possible, because of some of the distances that we had to push the material.”
Those distances-as much as 300 feet-prompted Windscapes to add irrigation piping in the area crossing the lake in order to ease the blowing process a bit. “The piping reduces friction, making some of those long distances we had to push the mix a lot more doable. It was a challenge, but the pipe moved the material fine, and the geogrid and filter sock combination held it in place nicely.”
Stakes, Blankets, and Socks
While the amount of shoreline being reclaimed varied from area to area, generally speaking, Windscapes was restoring about 8 to 10 feet of new island at the base, then tapering back to the original grade in incremental lifts.
“We first laid the geogrid and put a coir blanket in front of that to minimize the risk of any more of the original soil leaching away,” says Joswiak. “Once we had the coir blanket laid, we filled and placed our first sock. For this job, we used a heavy-duty 12-inch Filtrexx filter sock filled with a topsoil/compost/sand mix. We did, however, go with a little looser knit mesh material in the sock-it’s our HD version-which makes it easier for the roots to go through and anchor down into the subsoils.”
With the sock in place, Joswiak’s crew backfilled the area between it and the original island shoreline, compacted it (taking that original 12-inch sock down to about 8 inches), and made ready the second lift, this one set back about 6 inches.
“In a sense, our approach was very much like building a retaining wall,” he says. “The sock filled with our soil mix is acting as the front face of the wall and helps to contain the soil. To further stabilize the two lower lifts, we took that coir blanket and the geogrid and wrapped both materials all the way back to the island and pinned them about 3½ feet deep with L-shaped rebar stakes. This was necessary, again, because the base sock lifts had no gravel in them as they normally would, and we needed something to help hold them in place for the first few seasons until the plants could do that job. Finally, the top two layers, which were not wrapped with the geogrid and coir blanket, are actually filled with a blend consisting of 25% compost and 75% pulverized topsoil, which is perfect for plant establishment.”
Roots Run Deep
The choice of vegetation was critical to the success of the project; for that, Prairie Restorations’ expertise was key. According to John Pauley, the base plantings were the most important of all.
“For the base, we chose bulrush and other shallow-water-loving aquatic plants, which thrive in these conditions and, when mature, will offer a root structure that is easily 3½ to 4 feet deep. That will provide both a strong natural anchor and the protection needed to avoid any further erosion to the islands’ shoreline. The base layer socks offer the perfect medium for growing, so all we did was poke a hole in the sock material, insert the plant plug, and let nature do the rest.”
Pauley is confident that once the plants establish themselves and take over, the problem with the island shoreline will be resolved. As proof, he cites the adjacent lake shoreline, which was planted with native plant communities. “Those areas are doing just fine and showing no signs of erosion. We expect that will be the case with the islands as well.”
For the remainder of the plantings, Pauley chose a range of wet meadow sedges and flowers: plants that thrive in an area where their “feet” are wet, but the whole plant is not underwater.
“All told, there will be more than 15,000 plants in by the time this project is wrapped up,” he says. “We grow a lot of our own plants. But for big orders of specialty plants like this, we also buy them from native plant nurseries.
Shared Strengths
Pauley says that the shoreline restoration has been an outstanding project from a number of different perspectives. “We are reclaiming an area that was quickly washing away; we are reintroducing native species to the island areas; and, by teaming up with Windscapes, we are able to bring in about 1,800 cubic yards of soil mixture with a lot less environmental impact than a traditional construction project. It’s really been a great project.”
Windscapes’ Joswiak echoes that sentiment and cites a philosophy shared by the two companies as a large reason the Carleton College project went so smoothly.
“If this tough economy has proved anything, it is that solid customer service, doing the job right, and attention to detail on the job will win new customers and keep existing ones coming back. We’ve always believed that, and have found Prairie Restorations to be on the same page with us. Our two companies work extremely well together, we both enjoyed it, and as a result, Lyman Lakes is on its way to regaining its former beauty. I’d say everyone won out here, including the environment.”