Developing Wetlands: Development

Once an appropriate site is selected, the next step is proper wetland development. Most marsh sites need only low-profile levees for flooding of shallow water areas. Generally, levees should have 4-to-1 slopes (or flatter) on the front and back slopes, depending on the marsh's location. Levees that are subjected to occasional flood water should be less steep with a minimum of a 6 to 1 slope. Flatter slopes will also help minimize muskrat damage to levees if the wetland is flooded throughout the summer months Levee heights will depend on the depth of water and the topography of the site, but at least 18 inches of freeboard (height of levee above water level) is necessary so the levee is protected from wave action and water-logging. The minimum top width of the levee should be four feet - 12 feet if used as a road. For vehicular access, the levee should be compacted sufficiently to prevent rutting, which will create a future maintenance expense. Emergency spillways built into the levee are important if periodic flooding occurs or if there is a large drainage area above the wetland. To prevent erosion of levee slopes, levees should be seeded immediately after construction is completed. Switchgrass is an excellent grass for this purpose. When construction is finished, maintain levees by mowing or burning to prevent growth of woody plants. Levees should also be checked annually for muskrat, groundhog or beaver damage.

Image Right: Water for a wetland can be pumped from a stream or well.

The area from which soil is taken to build a levee, called a borrow area, can be located inside or outside the flooded area, depending on your intended use and the soil type. Locating the borrow area inside the levee can deepen the wetland, provide a diversity of water depths and vegetation and provide interior drainage. However, borrow areas require a lot of water to re-flood so the water supply should be sized accordingly. Borrow areas outside the wetland area will mean less pumping and provide more uniform water depths within the wetland. These borrow areas outside the levee can also be important for amphibians and other wetland wildlife as breeding and nesting areas.

A variety of water control structures are available for managing water levels in wetlands. The objective for the wetland is also an important consideration in determining the type of control structure. Regardless of the type used, it should have the capability to hold water and also have the ability to provide drainage of the wetland. Wetlands are dependent on fluctuating water levels to maintain their productivity. Wetlands constructed without the ability to draw the water down become unproductive and are often difficult to manage. Listed below are several types of control structures along with a few examples for developing small wetlands.

To avoid a violation of wetland protection laws, you may need a permit from the Corps of Engineers and permission from the Natural Resource Conservation Service before beginning construction. Your local Corps of Engineers and NRCS offices should be contacted to determine if these provisions apply to the site you have selected for wetland development. For further information see Wetlands and the Law.

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