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Ecowrappin'
Impoundment Wetland Creation
Tuesday, December 9, 2003
There are two basic needs in creating wetlands. You must have an adequate source of water and you must be able to contain it. Throughout most areas of Lambton and Chatham-Kent, we have clay soils that are ideal for holding water. We also live in a part of the country where precipitation is greater than the annual evaporation. That explains why an excavated pond will fill with water, given enough time. After that, the water level will go down during the hot summers, but is usually filled again by the next spring.Excavated ponds, when constructed to maximize wildlife use, are an important method in maintaining a part of the extensive wetland habitats that once existed in South West Ontario prior to settlement. They are of benefit to virtually all wildlife from insects to large mammals.
It is important to realize that excavating a pond is an expensive way to create wetlands. Ducks Unlimited Canada assists landowners who want ponds with technical advice on how to construct them in the most wildlife friendly way; and provided that advice is followed can offer an incentive grant after completion. This will cover 20% to 40% of the construction costs. This type of assistance includes an agreement with DUC to keep the wetland for a specified number of years.
A more cost effective method of wetland creation is dependant on the existing contours of a site. If water can be contained on a site by moving a small amount of earth, the cost per area of wetland is dramatically reduced. This typically takes place at the top of a watershed, at the upper end of a relative flat basin or gully that can be bermed to retain water.
It is important to have these sites surveyed to know exactly how large a wetland is going to be created; to establish an operating level at which to set the control structure; and to ensure that your wetland does not flood onto a neighbour's land.
In addition, it is necessary to determine the watershed area and the volume of water that may drain into, and through, your wetland. This is crucial to sizing the water control and conveyance structure that will allow surplus water to pass through, yet maintain the desired wetland level. If the control and conveyance structure is too small, heavy runoff will rise quickly above the operating level and may overtop and damage the berm.
Each site has its own characteristics, but some general principles are: all berms must have a minimum top width of 10 feet and side slopes should be a minimum of 3:1. Outlet pipes through the berm must have a seal or seepage collar installed to stop water from seeping along the outside of the pipe and weakening the berm.
Never just start pushing earth to the site to build. The topsoil must be stripped and stockpiled. The mineral subsoil should be exposed and the mineral soil core of the berm should be keyed into this mineral soil base. This procedure often exposes abandoned field tiles, or gravel seams, that may drain your pond. Any organic material (topsoil) left under the berm is a poor seal and water may continue to weep through if all topsoil is not removed during construction. The stripped topsoil can be spread over the completed berm and other disturbed surfaces and seeded to grasses and legumes.
There are a variety of fixed and adjustable control structures that can be used. Costs will vary but if properly sized for the job and installed with care they should function correctly and last for years.
Darrell Randell works for Ducks Unlimited Canada as a Conservation Programs Specialist in South West Ontario. Before that he was a Lambton County Pork Producer for 25 years. He served 2 terms on Sombra Township Council, 1994-2000, and is currently a councillor in St Clair Township. He is a past president of the Lambton County Federation of Agriculture. He was a founding member of the Rural Lambton Stewardship Network and served as chairman of that group from 1995-2003. He and Nancy have 3 grown children, each of whom they are extremely proud.
