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<br />-8- <br /> <br />1 . Dams of the sealing clay or bentonite are placed in the dry <br />canal---close enough together for adequate ponding of the entire canal <br />section. <br />Z. A small head of water is run into the dry canal so that the <br />following procedure takes place slowly: <br />a. Water ponds behind first upstream dam of bentonite. <br />b. As water tops first dam, the break-out process is <br />assisted by shovelling bentonite into the water rushing through the break. <br />c. The muddy water formed in this manner is ponded <br />behind the second dam. <br />d. The process of ponding, over-topping and wash-out <br />of clay dams is repeated through successive downstream dams. <br />3. As an annual maintenance procedure a small amount of clay <br />is waShed into the treated reach. (Usually about 10 percent of initial amount.) <br />In all insta;Li.aUonr. an effort has been made to plan the installations <br />. (including follow-up maintenance treatments) for a time when the seepage <br />losses are at the highest level. Some canals gain water during some parts <br />of the irrigation season and lose water from the same sections at other <br />times. Obviously, if a gain of water is occurring, the deposition of bentonite <br />in the canal bed will be retarded since it cannot swim against the now of <br />water. <br /> <br />The amount of clay used in the installations has been in the range of <br />1 to 5 Ibsl sq. ft. of wetted surface area in the treated reach--open rocky <br />materials requiring the higher amounts and fine sandy materials the lower <br />amounts. The amount of clay used and the frequency of repeat maintenance <br />treatments depends directly on the stability of the canal bed and banks. In <br />the absence of definite proof that the follow-up treatment is not needed, a <br />10 percent (of original amount) treatment is recommended for inclusion in <br />the first water into the canal for the next two irrigation seasons. <br /> <br />1036 <br />