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I <br />in pipe. The canal is concrete lined and has four check structures which can <br />maintain the upstream water surface elevation regardless of canal flow. <br />West End Government Highline CgO The last 8 mi. (13 km) of <br />canal is called the West End Government Highline Canal (West End). The <br />design capacity of the beginning of the West End is 160 ft-/s (4.5 m3/s). It <br />delivers water to 9 laterals and about 5,200 ac (2,100 ha). All the laterals in <br />the West End have been placed in pipe. The canal is membrane lined and has <br />four check structures which can maintain the upstream water surface elevation <br />regardless of canal flow. <br />WATER MANAGEMENT IN THE GARKELD GRAVITY DIVISION <br />Only the relevant aspects of canal operation regarding the potential for water <br />management will be discussed. Operation of the current system is described <br />by the manager of the GVWUA as an art. The intricacies and "art" of daily <br />operations are extensive. This art is developed through years of observation of <br />how the system responds to various conditions. It is through this experience <br />that the manager makes daily decisions on how the canal should be operated. <br />And it is the accumulation of this observed knowledge that makes the science <br />of water management unwelcome and difficult. <br />Historic Water Management <br />During the early part of the irrigation season, about 1 April through 1 May, <br />there is usually an abundant supply of water in the Colorado River. During <br />this period, irrigation demand is often relatively low. Diversions into the <br />canal system are used to flush and load the system and to meet any early <br />irrigation demand. Typically, irrigation demand increases quickly and by <br />early- to mid-May a full demand can be expected. With few exceptions, the <br />canal runs at or near capacity until irrigation demand begins to decrease <br />around mid- to late-August. From late-August to the end of October the <br />amount of diversion gradually decreases but is generally higher than irrigation <br />demand to keep the canal water surface elevation at required levels. Certain <br />water surface levels are required in the canal to provide water service to high <br />lands adjacent to the canal and to prevent damage to pipe laterals that can be <br />caused by air entering the pipelines. The air that enters the pipeline can <br />become trapped when the pipe inlets lose submergence and then are suddenly <br />resubmerged. This trapped air can cause dangerous pressure surges in the <br />pipeline. <br />Diversions in excess of demand can be administratively spilled at the six canal <br />spillways or through the open laterals. It has been estimated that 60,000 acre- <br />feet/year (74 Mm') of water are administratively spilled. This may seem high