*This is an excerpt from Pond Building: A Guide to Planning, Constructing & Maintaining Recreational Ponds, ANR – 1114.
The process of choosing a pond site is at least as important, if not more so, than the actual construction process. Selecting a pond site involves more than arbitrarily deciding to “put it over yonder,” just as building a pond involves more than just “digging a hole.” Unfortunately, many sites are not suitable for ponds. Minor problems may be correctable at some sites; other sites are doomed for failure no matter how well the pond is constructed. To have a reasonable chance of a good pond, the prospective pond owner should be aware of the basic criteria necessary for a site to be suitable for pond construction. These criteria include the safety of the location, the water-holding capacity of the soil in the pond, the geologic makeup and topography of the site, and the characteristics of the watershed or drainage area.
During the planning stages, do not overlook the possibility of dam failure and the resulting damage from the sudden release of water. If possible, do not locate your pond where failure of the dam could cause loss of life; injury to people or livestock; damage to residences, industrial buildings, railroads, or highways; or interrupted use of public utilities. If the only suitable pond site presents one or more of these hazards, hire an engineer experienced in pond design to reduce the possibility of failure from improper design or construction.
Be sure that no buried pipelines or cables cross the proposed pond site. They could be broken or punctured by the excavating equipment, which can result not only in damage to the utility but also in injury to the operator of the equipment. If it is necessary to use a site crossed by pipelines or cable, you must notify the utility company before starting construction and obtain permission to dig. Before beginning any construction, it is always wise to contact the local utilities and appropriate government offices to determine if any underground lines or pipes cross the site. This will also reduce the chance that the pond might violate right-of-way agreements. Avoid sites under power lines. The wires may be within reach of a fishing rod held by someone fishing on the pond.
Ponds, like any body of water, attract people so there is always a chance of injury or drowning. No matter what the purpose of the pond, you can never tell what a small child passing by might do. While individual states or local governments may not have laws governing the design, construction, or operation of a pond, you may be liable in the case of injury or death resulting from use of your pond whether you authorized such use or not. This is particularly important if you intend to open your pond to the public and charge a fee for its use. You may realize that you will need to protect yourself with liability insurance coverage.
If the pond is to be used for swimming, guards must be installed over pipe openings. All undesirable trees, stumps, brush, rubbish, junk, and fences that might be hazardous to boats or swimmers should be removed. Mark safe swimming areas, and place warning signs at all danger points. Lifesaving devices should be properly located to facilitate rescue operations should the need arise.
Soils in the Pond
The composition of soils in Alabama is highly variable. Soils range from almost pure sands in the Coastal Plain to heavy clays in the Black Belt. Variation in soil texture can vary with depth and can change drastically over short distances. The suitability of a pond site depends on the ability of the soils in the reservoir area to hold water. The soil should contain a layer that is impervious and thick enough (usually a 2-foot minimum) to prevent excessive seepage. Soils made of clay or silty clay are excellent for ponds; sandy clays are usually satisfactory. Coarse-textured sands and sand-gravel mixtures do not hold water well and are unsuitable for ponds.
If there is poor soil over a portion of the pond bottom, you can sometimes make it impervious by importing and compacting a good-quality clay soil or by incorporating bentonite clay into the pond bottom. However, sealing pond bottoms can be very expensive (see Leaky Ponds). If soils are determined to be questionable, choosing a secondary pond site with good soils may be the best alternative.
The soil profile under the proposed dam is also very important to the ultimate success of the water-holding ability of the pond. Over time, the ponded water can seep beneath the constructed dam. Therefore, the dam and its foundation must be sealed with impervious soil material to prevent seepage beneath the dam (see Cutoff Trench and Dam Core).
Tip to Remember: The importance of careful site selection and proper construction cannot be overemphasized as means of keeping seepage losses to a minimum. Cutting corners in these areas will often come back to haunt the pond owner. The use of after-the-fact seepage reduction methods ranks as only a distant second choice when compared to doing it right the ﬁrst time.
Some areas with limestone deposits, such as the Tennessee Valley and Wiregrass region of Alabama, are especially problematic as pond sites. There may be invisible crevices, sinkholes, or caverns in the limestone below the surface soil. Building in these sites may result in a badly leaking pond. In addition, many soils in these areas are granular and remain highly permeable even when wet. Pond sites in limestone areas should be thoroughly investigated using both geologic and laboratory analyses before the construction of a pond is planned. Although there are no guarantees, a good indication of the suitability of a pond site in one of these areas (or any area) is the degree of success others in the immediate vicinity have had with farm ponds.
The topography, or lay of the land, determines the ultimate construction cost of the pond more than any other single factor. For economic reasons, try to locate the pond where the largest storage volume can be obtained with the least amount of earth fill for a dam.
A good site is usually one where a dam can be built between two ridges crossing a narrow section of a valley that is immediately downstream of a broad section of valley. This permits a large area to be flooded. Such sites also minimize the area of shallow water in the pond, which can be undesirable.
People inexperienced in pond design and construction sometimes think that ponds are always excavated to store water. In reality, excavated ponds are the most expensive to construct per volume of water stored. Therefore, always consider a site where the water is stored above ground behind a small earthen dam.
For ponds in which surface runoff is the main source of water, the contributing drainage area, or watershed, must be large enough to fill and maintain adequate water in the pond during droughts. However, the drainage area should not be so large that expensive overflow structures are needed to bypass excess runoff during storms.
Some characteristics of a watershed that directly affect the yield of water are the slope of the land, soil infiltration, and plant cover. These interrelated factors are variable and site specific. There are no set rules for determining the exact size watershed needed to fill and maintain a given size pond. However, there are some rules of thumb that can be used. For example, some watersheds containing mostly pasture with heavy clay soils may need only 5 acres of land while a sandy watershed in a wooded area may need 30 acres or more of land to contribute runoff for each surface acre of ponded water. A good rule of thumb is to have about 15 acres of watershed for every pond surface acre.
If the drainage area is too small in relation to the pond size, the pond may not adequately fill, or the water level may drop too low during extended periods of hot, dry weather. Shallow water contributes to excessive aquatic weed problems and potentially to fish kills from low dissolved oxygen when average depth is less than
Ponds with excessive drainage areas can be difficult to manage for fish production. They tend to be muddy, silt-in rapidly, and have erosion problems in the spillway area. Runoff from oversized drainage areas can flush out the nutrients and much of the microscopic plant and animal life (the plankton) that form the base of the food chain for fish, thus lowering pond productivity. Fish, particularly grass carp if present, may also leave the pond during overflow from heavy rains. Contamination of ponds with wild fish from either upstream or downstream sources is more likely when watershed size is excessive.
To avoid potential pollution of pond water, select a location where drainage from farmsteads, feedlots, sewage lines, dumps, industrial and urban sites, and other similar areas does not reach the pond.
For the planned depth and capacity of a pond to be maintained, the inflow must be reasonably free of silt from an eroding watershed. The best protection is adequate erosion control on the contributing drainage area. Land under permanent cover of trees or grasses is the most desirable drainage area. If such land is not available, treat the watershed with proper conservation practices to control erosion before constructing the pond.
Water Sources and Quality
The three sources of water for filling ponds are rainfall runoff, groundwater, and surface water, each of which has advantages and disadvantages.
The primary source of water for embankment ponds is rainfall runoff from the drainage or watershed area surrounding the pond. Rainfall runoff can be an excellent free source of water, depending on the physical and chemical characteristics of the watershed. The best runoff water source for ponds is a watershed containing undisturbed, well-vegetated cover such as timberland or grassland. Avoid unvegetated watersheds because of the potential for excessive muddiness and premature siltation of the pond. Watersheds containing concentrated livestock feeding areas or overfertilized pastures can result in problems due to excessive nutrients and other contaminants entering the pond. Watersheds with cropland receiving regular pesticide applications are of concern because of the potential for pond contamination from runoff or spray drift. Ponds receiving runoff from cropland should have a good buffer zone of grass or sod between the cropland and the pond to serve as a filter for potential soil erosion and pesticide runoff.
Groundwater pumped from wells, where available, can serve as either a primary water source for a levee or excavated pond or as a supplementary source to ponds with inadequate watersheds or excessive seepage. Advantages of well water include the absence of wild fish and, generally, good water quality. Disadvantages include construction cost and maintenance, potential inadequate water yield, and pumping costs.
Surface water from nearby springs, streams, rivers, or reservoirs that have good water quality can be used as a pond water source. Water pumped from these sources should be filtered to remove wild fish, fish eggs, and larvae. However, it is difficult to prevent wild fish from contaminating a pond that is supplied by surface water. Withdrawal of water from a public source such as a permanent stream or reservoir may require a permit, and the amount of water may be limited depending on state or federal regulations.
Potential pond sites in Alabama will sometimes include land areas classified as wetlands. Wetlands include marshes, swamps, and shallow areas that pool water seasonally and support wetland-type plants, such as bulrush, cattails, cypress trees, and other plants associated with wet soils. Wetlands are among the most biologically productive natural ecosystems in the world. They provide many benefits including food and habitat for fish and wildlife, flood protection, natural products for human use, water quality improvement, and opportunities for recreation, education, and research.
If wetlands are present on a pond site, they must be identified before beginning construction of the pond. Federal wetland provisions under the Clean Water Act and the no-net-loss of wetlands policy do apply to private landowners who are considering constructing ponds in areas considered to be wetlands. Always check with the U. S. Army Corps of Engineers (USACE) or the USDA Natural Resources Conservation Service (NRCS) before construction to determine which specific law or regulation may apply to you. In some cases, it may be necessary to obtain a permit or additional planning assistance.
If wetlands are present (depending on the assessment by the USACE), locating an alternative pond site without significant wetlands may be the best alternative. That way, paperwork, cost of mitigation, and possible litigation can be avoided. Most importantly, the wetland and its benefits to the environment will be preserved.