Agenda - Parks and Recreation Commission - 10/12/1989

Home

GENERAL DESIGN CONSIDERATIONS IN CREATING ARTIFICIAL WETLANDS FOR WILDLIFE The best solution to maintaining adequate wetland resources is to prevent disturbance to existing natural basins. When this is unavoidable, however, loss of natural wetland basins can be at least partially offset or be compensated for by construction of artificial basins. Based on our review of recent literature on the subject, we recommend that the following general design features be implemented, to the extent possible, when constructing an artificial wetland basin: 1. The wetland basin can be relatively small (0.5 acre), but, if at all possible, should be at least 1.0 acre in size. 2. A variable (rather than an even-sided) shoreline should be constructed if at all possible since it will increase the amount of shoreline per unit area and increase the waterfowl usage by providing isolated areas for feeding and loafing. 3. The bottom contour should be uneven and rolling, which will produce a variable water depth and allow for emergent vegetation growth on shallow areas throughout the basin. Water depth in shallow areas should be about 12-18 inches and about 3-4 feet in the deepest areas. The shoreline area should have a gentle (10:1 to 20:1) slope to provide for adequate vegetative growth, but also can be variable to provide small vegetative "fingers" and open "bays" and thus more edge. Vegetation growing in these shallower areas of the basin should produce vegetative islands and thereby increase interspersion or edge habitat. A 50% open water and 50% vegetation coverage of the wetland (including the emergent vegetation around the shoreline) will provide the greatest species richness and diversity. 4. The wetland should have a good clay seal to prevent leakage. In addition, we recommend that topsoil be placed on the bottom of the basin to provide a more suitable substrate for aquatic vegetation growth, which will quickly establish a detritus food chain and invertebrate abundance. Wetland basins lined-only with clay normally produce less vegetation, fewer invertebrates and lower numbers of waterfowl than those lined with both clay and topsoil. 5. On projects where existing wetlands are unavoidably impacted; when feasible, muck from existing wetlands should be placed in the bottom of the newly-created basin. This would provide the basin with a naturally-occurring seed bank and other material of high organic content. 6. It may be desirable to construct one or two small earthen islands within some newly-created wetland basins to increase diversity and provide an offshore nesting area for waterfowl and other wildlife. 7. After construction, a layer of natural or domestic~hay should be placed on the wetland substrate; this will allow a detritus food chain to become established more rapidly. 8. Re-establishing and maintaining an upland vegetative buffer area around the perimeter of the newly-created wetland basin will provide nesting habitat and help to ensure optimum waterfowl production occurs on these areas. If mowing of the vegenation around the wetland basin is necessary, it should be delayed until after August 1 if at all possible to avoid disturbance to waterfowl, upland game birds and other wildlife, during the nesting season. Ils