Pond lining

  Lining of the pond helps in controlling seepage losses. Lining materials such as natural clay soils, bentonite, bituminous materials, soil-cement mixture, stone or brick lining, cement concrete chemical additives, asphalt compounds and polythene, rubber and plastic are commonly used. The lining using different materials is discussed below:

Puddling: Puddling of pond bottom through trampling by animal results in reducing the seepage loss. Addition of fresh cow dung at the time of puddling further improves the sealing of pores.

Clay blanket: Pond dug in the coarse textured soil provides clay blanket at the bottom resulting in reduced seepage. The thickness of the clay blanket varies with the depth of water impounded to avoid cracks in the blanket. A 25 cm thick clay blanket is strong enough to withstand the pressure of 3 m water column. Clay blanket should be kept in moist condition by covering it with mulches and regular sprinkling of water to avoid the development of cracks till the water is impounded. '

Bentonite treatment: Bentonite a fine textured colloidal clay is useful in sealing the pond. It swells 8 to 15 times its volume by water absorption. Bentonite is mixed with surface soil and the mixture is compacted. The compaction should be done in layers of 15 cm with optimum moisture level by using heavy roller, cattle or manual ramming in case of small pond. A well graded soil needs about 5 kg of bentonite per m' and up to 20 kg in sandy soils.

Addition of sodium salts: Soil deflocculates like sodium carbonate, sodium chloride and tetra sodium polyphosphate when added to the surface soil of the pond can considerably reduce the seepage rate. For these substances to be effective, the clay content of the soil should be more than 15 % and the cation exchange capacity (CEC) of the soil greater than 15 milli equivalents per gram. These parameters can be determined by soil testing. Of three salts, sodium carbonate is reported to be most durable. Sodium carbonate should be added at the rate of about 105 kg /m'at an interval of2-3 years to keep the lining effective.

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