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N C.' 4l:I" C"';, :\",-" ;o.:,"J '--' Portions of the interiors of Roller Gate Nos. 1, 2, and 3 were sandblasted and coated with Amercoat 325 coal tar epoxy. c: 4. All-American Canal Desilting Basins Operation of the All-American Canal Desilting Basins was normal. The number of basins in operation varies according to the All-American Canal diversion requirements. When the basins were out of operation, they were inspected, and required maintenance work was performed. The sediment load removed by the basins and returned to the river as sampled by the District is shown on Table Nos. 4 and 5 of this report and amounts to 494,920 tons for the year. The District is continuing its practice of opening and closing the desilting basin bypass gates to the All-American Canal once each week to check operating conditions. This operation sluices a minor quantity of sediment deposited in the channel above the gates into the All-American Canal. The 10-foot diameter internal gear in clarifier No. 12, basin 3 failed in April 1980 and was replaced in February 1981. The District believes failure was due to unbalanced loading as a result of one arm being about 2 inches higher than the opposite arm. A new spare 10-foot diameter internal gear is to be ordered. Wear of the sludge pipes which carry sediment from the basins to the river continues to be a major maintenance item for the District. In 1975 and 1976, the District placed a lining consisting of a 50-50 mixture of sand and cement welded with Sika Latex along the bottom of several of the pipes. Some of this lining has given good service while others have failed because of the lack of bonding of the lining to the steel pipe. Replacement and repair of the lining is being made with a 50-50 mixture of sand and an epoxy compound. 5. All-American Canal and Drains Flow in the All-American Canal was considerably higher than normal during January 1981 due to upstream release of water greater than diversion requirements, Operation of the check structure at station 48+50 was normal all year. During low flow stages the check gates are lowered to control the water elevation in the bypass channels which carry water from the desilting basins to the All-American Canal, The check gates are raised to free flow position during high flow periods. Maintenance activities on the All-American Canal returned to a routine nature and the canal is considered to be in excellent condition. Maintenance of drains was also of a routine nature during the year. and the drains are in excellent condition. The annual centerline profile of the All-American Canal completed in December, shows the canal to be in good condition. Sediment deposits have raised the bottom elevation of the All-American Canal, but not enough to cause operational problems. 8