Restoration Toolbox
Wetland restorationists have assembled a "bag of tools" over the years. Which combination of tools you use will depend on your site, your resources, and your goals.
Ditch Plugging- Many wetland sites have a ditch or several ditches that drain the wetland. The quickest and least expensive option for reversing the harmful effect of the ditch is to plug it at the lowest point. By pushing an earthen plug into the ditch, the drainage stops and water backs up in the wetland. Current recommendations are to plug at least 150 feet of ditch if the soils are organic and 100 feet if soils are mineral. The plug should rise 33 percent above grade for organic soils and 20 percent above grade for mineral soils to allow for soil settling. A gentle slope with at least an 8:1 ratio, where for every 8 feet of width the level goes up a foot, is best. In some instances ditch plugs require periodic extensive maintenance to ensure that they remain functional.
Filling Ditches and Recontouring- Back filling the entire ditch is an alternative to a plug. In most cases filling may result in a more effective and permanent restoration of site topography and hydrology than simply plugging the ditch. Typically, ditches are rimmed by soil berms, called spoil banks (or spoils), made up of the earth excavated when the land was ditched. Spoils can be on one or both sides
of the ditch and create an unnatural rise in topography that serves as a barrier to water flowing across the site. The spoil piles can harbor invasive plants such as glossy buckthorn, reed canary grass, or other upland weeds, and are a conduit for predators to readily enter and traverse the wetland. Depending on the size and depth, a ditch may have a negative hydrological impact on the wetland due to its water storage capacity. To return the site to its historic topography, ditches are filled with the spoils from the sides of the ditch. Ditch filling is perceived as more costly than using a plug. The actual cost per acre is less, however, because more wetland can be restored using a ditch fill than with a ditch plug alone. Once completed the filled ditch does not usually require further maintenance, as may a ditch plug.
Disabling Drain Tile- Drain tiles are perforated, hollow tubes buried underground, usually in an array of parallel tile lines 2 to 5 or more feet deep. As water infiltrates into the soil, it collects in the tile and drains off site to a ditch or stream. As long as drain tiles function, they are very efficient at water removal. If your site contains drain tiles you need to locate and disable them. The original farmer, NRCS, county land conservation office, or excavation firm that placed the tiles may have a tile map for the site. If no tile map exists, search the ditches for outlet pipes. Once the lines are located, remove them and fill the trench. Clay tiles can be crushed and reburied. Most tile lines drain to a ditch so if you fill, re-grade the ditch, and remove or destroy the line, you will double your chances of successfully restoring the original hydrology. It is equally important to disable the "soil conduit", the space created by compacted soil surrounding the tile lines that forms a distinct channel.
Stream Channelization and Realignment- Most sites that feature stream channelization and realignments included other drainage techniques. A meandering stream may have been realigned and its channel straightened, widened and deepened, as well as tiled or ditched. In such sites you may be able to restructure and restore the original waterway using old aerial photos and the topography of the site as guides. Reconfiguring a stream requires experienced assistance. Any stream work will require Wisconsin DNR permits. Your local Wisconsin DNR water management specialist can guide you through the permit process. Extensive erosion-control practices will be required to ensure that sediments washing in do not become a problem.
Berms, Dams, Dikes, and Levees- Berms, dams, dikes, and levees are all earthen embankments constructed to contain water. These will be referred to here collectively as berms. These structures must be properly designed to prevent failure due to over-topping, seepage, sloughing, or collapse. Berms often are used to increase water levels in a wetland above historic levels to create open water. They also can protect a neighboring property from flooding. Berms require maintenance to control muskrat damage and to guard against erosion caused by heavy rains. Another issue with berms comes from elevated water levels inhibiting the germination of native vegetation where the seed bank is adapted to shallower water. A spillway must be properly engineered if included in the berm design to establish a maximum water level. You will undoubtedly need a Wisconsin DNR permit to construct a berm.
Water Control Structures- Water control structures control flows into and out of a wetland. Such structures include spillways, pipes with drop inlets, and stoplog water controls. A spillway, a low point in a berm, provides an escape for excess water above the designed level. Stoplog and drop inlet water control structures also control water levels on the site, but give the owner/manager of the property more control over filling or draining the area. Berms in conjunction with water control structures can be used temporarily to control invasive species and to manage for a native plant community. Long-term reliance on water control structures as the sole alteration of hydrology is cost-prohibitive and does not restore self-sustaining wetland systems.
Scrapes- Many small "pothole" or scrape wetlands are being constructed, often in clusters, in croplands across the state. On suitable sites, topsoil is stripped away to expose sub-surface soils, which are removed to create a berm. Then the topsoil, comprised of wetland soils and the seed bank, is redistributed over the surface of the newly formed basin. On some sites, eroded topsoil deposited in a former wetland depression in the field can be scraped out, uncovering the original wetland soils. On other sites wetland soils or wetland seed banks may be nonexistent. These pothole wetlands often create suitable wetland habitat for waterfowl and amphibians. Clusters of scrapes should vary in size, shape and depth to create habitat diversity. Purple loosestrife and reed canary grasses commonly move into these sites after a few years. Scrapes provide an appropriate remedy in some situations, but in the long term they may not become self-sustaining wetlands. A small scrape constructed within an area that could support a much larger restoration does not realize the full potential of the site.
>> Planning a Restoration Project page 2
Content for our restoration webpages is excerpted from WWA's Wetland Restoration Handbook for Wisconsin Landowners, 2nd Edition (2004) by Alice L. Thompson and Charles S. Luthin. Both editions of the Handbook have
won the Wisconsin Library Association's Distinguished Document
Award. To learn more about this publication and order a copy, see WWA's publications list. To download PDF versions of Handbook chapters, visit Wisconsin DNR's website.
WWA thanks Wisconsin Coastal Management Program for providing funding support for our wetland restoration outreach efforts, including development of these webpages.
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