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,.''''' r.._ ~..J" .. oJ J 0 PER A T I (I NAN 0 ~I A I N TEN A NeE " 37 I stalled in a section of the 48-inch diameter pipe to release air trap- ped in the line at high flows, During December 1948, the walls of four transition structures were raised 18 inches using concrete blocks in order to provide protection against flooding during storms. Precast concrete bulkheads were constructed and installed in three transition structures at the outlets for future barrels, thus provid- ing additional freeboard. Two highway crossings of the San Diego aqueduct were made during September and October 1948 in Rainbow Pass near the San Diego County line by the contractor on the reconstruction of {J, S. Highway 395. The work was under the supervision of the State Highway Department and included reinforced concrete incasements placed around the pipe in accordance with District requirements, A n extensive growth of underwater grass in San J aeinto reser- voir led to the construction in the District shops at La Verne, of a mowing device mounted on a boat. Gra~g cutting was started in October 1948 and was continued through November, The cut grass was removed from the edges of the reservoir, and after drying was burned. During April 1949, an electronic fish screen was installed at the reservoir outlet for the purpose of preventing small fish from entering the pipe line. After considerable adjusting by the manu- facturer, the screen appeared to be operating successfully. O}Je-rat-io-n of cit-rw:: mid wal-iw.t. grOl!C~ The District in September 1948 acquired an additional five acres of land planted to citrus trees on which it is planned to construct future units of the softening and filtration plant, Sixty-two acres of citrus and 22 acres of walnut groves are now owned by the Dis- trict and operated under the supervision of the chief operation and maintenance engineer. Normal operation include8 cultivating, pruning, irrigating, fertilizing, spraying, and dusting. Eighty-five young trees were planted to replace old nonproductive trees. The abnormally cold winter increased the cost of operation because heavy firing was necessary on two nights and light firing was needed on six other nights. In spite of the heating for protection against freezing, i-\ome injury to orangeR and lemons occurred in the colder parts of the groves, causing a considerable loss of lemons, The yield of oranges was higher than for several years, compen- sating for some slight frost injury to this crop. A bumper crop of walnuts was harvested.