Northern Prairie Wildlife Research Center
Culverts should be at least 30 inches (preferably 48 inches) in diameter and 6 feet long. The choice of culvert diameter is a trade-off between resistance to tipping and weight. A 30-inch diameter concrete culvert with 3-inch walls weighs about 2,200 pounds for a 6-foot section. Since heavy equipment is required to move large culverts, installation requires either a dry wetland basin, or thick, solid ice. Culverts should be placed on end so that 3 feet remain above the high water line after they have settled into the soft bottom. If installed over the ice, a hole must be cut so the culvert rests on the pond bottom. Locations and densities of culverts should be similar to hay bales. Culverts should be filled with good soil, either from the surrounding uplands or the pond bottom, and should be heaping full to allow for soil settling. The fill level must be checked after the first year, and periodically thereafter, to insure that the fill has not settled more than 3 inches below the rim or the goslings and ducklings that hatch in the culvert will be trapped. Fill soil can be seeded with preferred grasses or natural vegetation allowed to grow.
Because geese nest earlier than mallards and trample all the vegetation around their nest sites, a baffle may have to be installed on the culvert if use by nesting mallards is desired. For baffle construction details, see "Mallards - Culverts".