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Ecology and Management of Islands, Peninsulas and Structures for Nesting Waterfowl

Wetland Enhancement Design and Construction Techniques

Dennis McDonough, R.P.E.
Ducks Unlimited Great Plains Regional Office
Bismarck, ND 58501

Islands and peninsula cutoffs are two types of effective wetland enhancement projects designed and constructed by Ducks Unlimited. The recommended location criteria for all islands is that islands must be at least 100 yards from the normal shoreline in 18-36 inches of water and placed so that the fetch of the prevailing wind is at a minimum. The island shape and orientation to the prevailing winds must combine to minimize the island area exposed to attack by wave erosion. The design settled height of the island shall be at least three feet above normal pool levels. Off site borrow areas shall be located, excavated and shaped so that the finished borrow area becomes part of the wetland basin. Islands that are constructed with an off site borrow shall have a 10 foot wide berm constructed at the normal pool elevation to aid the development of a vegetative wave erosion barrier. The topsoil from off site borrow is placed on all disturbed areas (borrow and island) above the normal pool level. Peripheral borrow sites generally do not have sufficient topsoil to strip and stockpile therefore topsoil placement is not required.

Island construction techniques vary with the location of the borrow site (peripheral or off-site) and the construction season. The most economic island construction occurs when dry conditions prevail and using a dozer in a peripheral borrow area. Winter construction of islands requires removal of ice from the borrow area and the base of the island. Summer construction in wet conditions requires construction of an access road for an off-site borrow or the use of a dragline or excavator on mats with a peripheral borrow.

Peninsula cutoff excavations are 100 yards wide and have a functioning water depth of 3 feet. The soil from the cut is placed on the new island not higher than 3 feet above normal pool level and spread no closer than 100 yards to an adjacent shore. Topsoil from the cutoff is placed on the disturbed areas on the new island. Peninsula cutoffs are usually completed in the winter due to the frost conditions required to support the construction equipment.

Peninsula cutoff fence design requires that the fence location first be stripped of all topsoil. After the topsoil is removed excavation of the trench for the burial of mesh may begin. The trench is backfilled to natural ground with material that is not frozen and free of organics. Topsoil is not placed over the trench excavation only over other disturbed areas no closer than 12 inches to the fence. The completed fence has one hot wire four inches above natural ground and one hot wire at the top of the fence. The fence is charged by a solar panel, wet cell battery and charger system that can deliver up to 8000 volts. The fence must extend into open water a minimum of 50 feet or into 3 feet of water. The fence in the water shall be standard galvanized cattle panels wrapped in galvanized square mesh. The panels are temporary and must be removed prior to freeze up and reinstalled immediately after ice out. It is recommended that the fence be inspected weekly when functioning and that the solar panel and charger be dismantled before freeze-up.

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