|Langston University Aquaculture|
Conserving Water In Ponds
By Kenneth Williams
MANY PONDS ARE vulnerable to severe water loss during drought. Fortunately, there are steps we can take to increase the water storage efficiency of ponds and reduce the likelyhood of dry ponds in times of drought.
The first step toward water conservation is to closely examine the pond for sources of water loss. Willow and other tree species that grow on pond dikes can remove significant amounts of water from the pond through transpiration, a plant process that draws water up into the roots and out through the pores of the leaves into the air. Most trees should be removed from pond banks although some large trees may be left for the shade and beauty they provide. It is best to remove all trees from the pond dam, not only because water is readily lost through transpiration but more importantly, many trees will have rotted roots that provide channels for water to work its way into the dam. water channels weaken the dike and may allow water to seep through it. Small seeps can quickly become large leaks when rains fill the pond. As the pond fills with water and becomes deeper, the water pressure on the seep hole increases, forcing more and more water through the hole. Erosive force of the water can rapidly enlarge a small leak or even lead to a complete failure of the dam. Leaks in pond dikes can be expensive to repair. It's usually a good idea to repair small leaks before they become a problem.
Water storage capacity of ponds with extensive areas of shallow water can be improved if they are drained and deepened. The shallowest area in a pond should be at least three feet deep. This depth of water will slow growth of aquatic plants which can take up a large amount of pond volume, effectively reducing the water storage capacity of the pond.
Most ponds are filled by rainfall run-off from their watershed. An eroded watershed washes sediments into the pond with each rain, reducing pond volume and the useful life of the pond. A well planted watershed improves pond water quality by removing sediments. Reduced sedimentation increases the pond life span by maintaining the pond's volume, which also helps insure the pond maintains water during periods of drought.
The pond can capture more rainfall by increasing the watershed acreage. This can be accomplished by cutting a small ditch that gently angles upslope from the pond. The ditch will funnel water into the pond from a wider area than the naturally, accessible watershed. However, if these furrows catch too much water the pond may regularly overflow resulting in failure of the dam.
Furrows or ditches are easily made with a single bottom plow. Soil should be thrown down slope from a six inch furrow. It can be smoothed with a box blade or shovel. Grass will soon cover the exposed soil. These furrows greatly increase run-off water available to the pond and allows it to fill quicker with less rainfall. Grass cover will help prevent sediments from washing into and muddying the pond or eroding the watershed.
Ponds filling with eroding soil are usually muddy and their water storage capacity is reduced with each pulse of sediments. This problem can be solved by constructing a small sediment retaining pond above the main pond. Most of the water that enters the main pond from run-off can be directed to enter the sediment retention pond first. Much of the suspended soil particles settle out in this pond before the water enters the main pond. The two ponds are connected by a grass covered spillway or large, 12-16 inch pipe. The pipe should be 2-3 feet below the top of the retention pond dam.
Wind breaks located to block prevailing winds help conserve pond water by reducing the rate of evaporation.
Oklahoma normally has an evaporation rate of 3-4 feet of water per year. This amount nearly equals, or in many areas of the state, exceeds annual precipitation. The wind break should be placed far enough away from the pond so that it does not send roots into the pond or it's dikes; and aligned perpendicular to the prevailing summer winds.
Water Level Maintenance
Water can be maintained at a constant level in ponds provided with a water supply other than watershed run-off. To conserve water and reduce energy costs of pumping water in these ponds, maintain water levels below the maximum allowed by the stand pipe. This practice allows rainfall to be collected in the pond directly or from runoff with little or no loss from the drain pipe. How much below maximum level the pond is filled depends upon season, weather patterns, evaporation rates, location, water holding ability of the pond, size of fish in the pond and weight of fish.
Many commercial fish producers in the Mississippi delta use the 6/3 rule in their levee ponds. This management technique allows pond water level to drop six inches below the stand pipe before additional water is pumped into the pond. The pond is then filled to three inches below the stand pipe level. The remaining three inches are used to catch available rainfall which reduces the amount of water taken from the aquifer and lowers pumping costs.
The 6/3 rule is a good starting point for water conservation in most Oklahoma ponds. Actual water levels at the stand pipe will have to be adjusted for local conditions. Pond water levels can drop after fish harvest in late fall to a level that takes advantage of most of the precipitation of winter and early spring. If a new crop of fingerlings are stocked in spring the water level can remain somewhat lower than normal until most of the spring rainy season is over. The fish will be small at this time and may benefit from diminished pond size because feed will be more readily found. Final spring rains can fill the pond to capacity. Most water will be pumped into the pond in mid and late summer. At this time water level is kept low enough to take advantage of summer showers. Runoff rains are not as likely at this time of year and the 6/3 recommendation is adequate for most ponds. During fall, evaporation rates are reduced, rains increase and less water has to be pumped into ponds, however, levels should remain high because fish will be near maximum weight and feed consumption may be high.
Ponds that are drained and dried after fish harvest are best worked as early as possible to take advantage of late winter precipitation to help refill the pond.
Ponds that are primarily filled from watershed runoff are able to fluctuate more during winter and spring because heavy rains may raise water levels a foot or more in these ponds. It is possible to let water levels drop as much as 12 to18 inches before pumping water into the pond and then only to a level about six inches below the stand pipe
Water Conservation Checklist
All these measures may not be practical for a particular pond or fish farm. Use the management techniques that are most adaptable to local conditions to gain the maximum savings in water, energy expenditure and capital.
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