The site and design of the pond may be the most important factors controlling the profitability of the catfish farm. Ponds that leak, have irregular bottoms, or routinely suffer from a shortage of water will not produce a consistent crop of catfish.
Ideally, levee ponds built on flat land and filled with groundwater or surface water are more suitable for commercial catfish production. However, most Alabama terrain is rolling and not conducive to this kind of construction. Also, water supplies for filling levee ponds are often scarce and will eventually limit the use of the ponds. In hilly terrain, pond builders must take advantage of the natural formations by constructing dams across valleys between hillsides so that runoff from rainfall on the watershed will be stored behind the dam.
Water to fill and maintain watershed ponds usually comes entirely from runoff, although groundwater (wells) and surface water (springs, streams, and reservoirs) can also be used as supplemental sources. The ratio of watershed to water surface acreage should be large enough so that ponds fill and sometimes overflow during rainy months but drop no more than 2 feet during drier months. The best ratio of watershed to water surface varies according to the type of land on which the pond is built. For a watershed of heavy clay soil on open land, the best ratio is 5 acres of land for each surface acre of pond. For a sandy watershed in a wooded area, the best ratio is 30 acres or more of land for each surface acre of pond.
When a watershed is too small and unable to supply enough water to the pond, or an outside source of water is needed for filling during dry periods, water from wells, streams, or rivers can he pumped into the pond. Water containing wild fish should be filtered to avoid introducing these fish into your pond.
When ponds are built in series in a valley, less watershed is needed to maintain an acre of water. Before harvest, water can be pumped or drained from one pond to another for storage. This procedure not only allows a producer to refill, using the stored water, immediately after harvest, but it also eliminates the possibility of draining nutrients into nearby natural waters.
Good-quality soil that is at least 20 percent clay is necessary for building the core of dams. This includes clay, silty clay, and sandy clay soils. Soil should be sampled by frequent borings along a proposed dam site to determine if the clay foundation is large enough to build the dam.
Borings should also be taken from the proposed dam site and the shoreline to be sure there is enough clay to build the dam. Usually a good source of clay can be found in the hillside near the dam site. If such a source is available, using it to build the dam can add to the size of the pond. However, if removing the clay will uncover rock formations, sand, or gravel in the pond bottom, it is best to leave the clay in place.
Pond construction in limestone areas can be especially risky because of the possibility of underlying cracks and sinks which may cause the pond to leak. In areas where the soil of the proposed pond bottom could result in leaky ponds, soils should be bored to check for quality. Approximately four borings per acre are sufficient, unless there are variations in soil type in the pond bottom. Figure 2 shows the parts of a dam, including the core and drainage system.
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| Figure 2. Cross-section of a typical dam at the drain pipe. |
Topography will greatly affect the size and shape of a watershed pond. Generally, steep slopes in V-shaped valleys require dams of larger volume per water surface acre than sites with gently sloping hills and wide, flat valleys. So, ponds built in steep terrain usually cost more per pond acre than those built in gently rolling terrain.
Ideally, watershed ponds should be less than 10 feet deep at the drain. This depth allows the producer to harvest the pond without draining it. Deep ponds must be drained of much of their water before they can be seined for a complete harvest.
Some sites with gentle slopes and large flood plains allow for the construction of two-sided and three-sided watershed ponds (Figure 3). These ponds are usually constructed parallel to hills bordering a creek. Runoff is used as a water source, but the dam does not cross a hollow or draw. The great advantage of this kind of pond is that it is a "seine-through" pond: it does not have to be drained for harvest.
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| Figure 3. Diagrams of conventional hill ponds. | ||
The site for a watershed pond should be selected so that pipes and valves can be installed to drain the pond completely. The proposed shoreline should be excavated to provide a depth of at least 3 feet around the edge of the pond. Pond bottoms should be smooth and slope gently to the drain pipe. Remember, a poorly constructed pond with an uneven bottom will cause incomplete harvests.
Make sure that floods from nearby rivers will not flow over the dam or that floods within the watershed will not weaken the dam. Ponds constructed in flood plains should be located so they will not cause damage to adjacent property if flooding does occur. Information on floods and their 100-year potential is available from the U.S.D.A. Soil Conservation Service field office in each county.
After deciding on a dam site, mark off the permanent waterline and the potential flood-stage waterline of the proposed pond to make sure that water will not encroach on other property. Also, if the pond site contains 1 acre or more of wetland, the U.S. Army Corps of Engineers will require a permit before the pond can be constructed.
The curves in Figure 4 were developed by the Alabama Fish Farming Center for ponds built in West Alabama. The curves are estimates for data generated during 1987 and 1988. Cost estimates include clearing, earth fill, excavation, pipe and drain concrete, seeding, and road gravel. The term "sided" refers to number of sides of the dam. The measurements (such as "8 to 10 feet") refer to the maximum depth of water at the stand pipe. Each pond site is unique, and these curves should be used only for rough estimates and comparisons. In general, a large, shallow, one-sided watershed pond is relatively inexpensive to construct in West Alabama. A three-sided pond may cost about twice as much as a one-sided pond.
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Figure 4. Comparison of estimated construction costs (per acre) for typical hill ponds. |
To obtain expert assistance in building the right pond for your needs, contact the Soil Conservation Service (SCS) field office in your county. The SCS provides site evaluations, design layout, and construction assistance.
Additional information on the construction of a levee pond can be found
in the Southern Regional Aquaculture Center Publication No. 101, "Construction
of Levee-type Ponds for Fish Production." SRAC publications are available
from your county Extension agent or from the Extension fisheries specialists.