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<br />54 <br /> <br /> <br />OOlS',;) <br /> <br />The above meaaurementa are typical of moat areas and it can be <br /> <br />expected that the seepage loss rates at any stock pond will fall within <br /> <br />the limits shown. As with evaporation, the total seepage loss from a <br /> <br />pond will depend on the area covered by the water, and the design of <br /> <br />the stock pond can therefore have an important bearing on both kinds <br /> <br />of los ses, with the minimum to be expected with a low ratio of water <br /> <br />area to pond contents. <br /> <br />. MethodsJorredudng stock pond seepa.ge are, in general, simi- <br /> <br />lar to those which mi$ht be used in land treatment to increase runoff. <br /> <br />Essentially, the objective in each .case is the same, i. e., reducing <br /> <br />permeability of the surface soils. Use of impernieable blankets to <br /> <br />reduce seepage around the dam is a common practice. These are <br /> <br />generally placed around the abutments and the upstream base of the <br /> <br />dam. The blankets may be formed by compaction'of selected earth <br /> <br />. layers or by'paving with soil cement or asphalt mixes. Bentonite <br /> <br />clays generally have proved effective for this purpos-e and are c.om- <br /> <br />monly used where available at reasonable cost. Commercially <br /> <br />sacked bentonite generally is too expensive for stock .pond treatment <br /> <br />but local supplies of impure grade can be sub"tituted where avail- <br /> <br />able. As the bentonite may lose its effectiveness if the stored water <br /> <br />contains calcium sulphate, the possible chemical content of the water <br /> <br />to be stored should be considered in deciding on the method of pond <br />treatment. <br />