Figure 1: Diagram of a good basin design; this design emphasizes shallow slopes and depths (each line represents one foot of depth), and good shoreline features. Adjacent uplands are seeded to native grasses.
- Depth and slopes. Waterfowl and most other wetland wildlife species need shallow water. When filled with water, your dugout should be no more than 4 feet deep. In mid-summer, much of your dugout should be less than 3 feet deep. Your pond should generally have the following depths when it is full (as in spring):
Steep slopes prohibit growth of desirable vegetation, encourage erosion, and reduce wildlife use. Grade the slopes of your basin as flat as possible, 10:1 (horizontal:vertical) or flatter if possible. The bottom of the pond should have variable, undulating depths. This allows an interspersion of vegetation and open water, which is attractive to waterfowl. Some biologists prefer to construct dugouts with one deep side to ensure water availability and allow for viewing of waterfowl. Figure 1 shows an example of a good basin design from the perspective of slopes and depths.
Water Depth (feet) Percent of Pond at this Depth Likely Result 0 - 1.5 25 - 40 wet meadow and mixed emergent vegetation; usually dry by July 1.5 - 3 25 - 50 cattails and emergent vegetation/open water; dry in drought 3 - 4 < 20 mostly open water/submerged aquatic plants; dry in severe drought
- Size. Wildlife will use all sizes of wetland, but bigger is usually better. In building a pond for waterfowl, consider a minimum size of 2500 square feet (equal to a square with 50 foot long sides). Larger, irregularly shaped ponds are preferred.
- Shoreline features. A pond that has an irregular shoreline and many points and bays is more attractive to waterfowl and most other wildlife than a dugout with a straight shoreline. Plan your dugout to have as much shoreline as possible, as in Figure 1.
- Number and distribution. For nesting waterfowl, your dugout should be near an existing shallow marsh for brood-rearing purposes. If you have adequate space and funding, you can consider digging more than one dugout. In general, two closely spaced small dugouts will receive more use than one larger dugout. If you construct more than one pond, space them about 100 to 300 feet apart. Ponds can be closer if tall vegetation screens the ponds from each other (breeding ducks are territorial and won't tolerate others of the same species if they can see them).
- Islands. Dugouts are generally too small to include an island. Studies have shown that unless islands are 300 feet or more from shore, duck nests are almost certain to be destroyed by predators. As an alternative, use nest baskets, boxes or floating rafts for nesting. A floating log, anchored in place, provides an excellent site for waterfowl and turtle loafing. (Note: Canada geese will nest successfully on small islands near shore; however, because of the current abundance of Canada geese and potential nuisance problems, the DNR does not encourage providing nest sites for this species.)
- Spoil. Excavating a pond means you end up with a lot of soil removed from the dugout; this is called "spoil". When excavating in an existing wetland, remove the spoil from the wetland. Placing the spoil in the wetland can trigger the need for a permit. Check with the appropriate agencies (see list at end) to determine if you need a permit.
The top 6"-12" will probably be black topsoil (or peat, if excavating an existing wetland), high in organic matter. This should be saved separately for later spreading over the excavated bottom (see section 7). The remaining soils should be moved to an upland site and spread evenly. It is important that this material be removed from the wetland basin and not piled adjacent to the dugout. The edge of the dugout should have a continuous slope below and above the water surface, as shown in Figure 2.
Figure 2: Cross section of wetland bottom showing smooth, shallow grade at waterline and undulating bottom contours. See a larger version of this diagram.
Finally, all disturbed uplands and spread spoil should be seeded to native grasses for a minimum of 150 feet around the dugout. This will provide optimal cover for wildlife, minimize weed growth, and prevent the spoil from eroding back into the basin. Providing 4 acres of upland nesting cover for each acre of wetland is best for duck production. For optimal waterfowl habitat, do not plant trees near your dugout; these serve as predator perches and dens, and will reduce waterfowl use. Use nest boxes to attract wood ducks. Remember to get any necessary permits before you start digging! (See the section on Permits, below.)
- Final treatment. In general, the clay and sand underlying most mineral soils are less fertile and may not support adequate plant growth. In order to establish a food chain in your dugout, it may be necessary to provide an organic base (your county soil and water conservation district can provide advice). If needed, this can be accomplished by spreading 4"-6" of black topsoil over the entire excavated area. This can be the topsoil originally removed from the site when digging started. Another technique is to spread 2"-6" of clean upland hay over the excavated surface. Both can be used simultaneously. Do not use topsoil that previously had reed canary grass or purple loosestrife growing on it. Also, do not use reed canary grass hay. Once covered with water, either of these bases will quickly allow vegetation and insects to grow, providing the building blocks for a desirable marsh.
It's not absolutely necessary to plant aquatic plants in your basin -- they will generally establish themselves naturally in time, given a suitable site. However, wetland plant communities left to establish on their own tend to have lower plant diversity and lower overall quality. Landowners interested in establishing a diverse, high quality wetland plant community should consider seeding and planting. See the references in the "Additional Resources" section for more information.
In general, a bulldozer or scraper is best for constructing ponds as they can be fairly precise in "sculpting" the landscape. A backhoe (power shovel) or excavator can do a good job, and a dragline can produce fair results. The nature of your project will likely determine to a large degree exactly which equipment is used. Use a dozer, scraper, or backhoe for dry sites. If it's a wet site, a backhoe or dragline must be used. Minimize the disturbance to existing vegetation around the dugout or undesirable weed growth will be encouraged.