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<br />5 <br /> <br />CWCB Construction Fund Grant Application <br />Grand Valley Water Management Project <br /> <br />relatively low. Diversions into the canal system are used to flush and load the system and to meet <br />any early irrigation demand. Typically, irrigation demand increases quickly and by early- to <br />mid-Maya full demand can be expected. With few exceptions, the canal runs at or near capacity <br />until irrigation demand begins to decrease around mid- to late-August. From late-August to the <br />end of October the amount of diversion gradually decreases but is generally higher than irrigation <br />demand to keep the canal water surface elevation at required levels. Certain water surface levels <br />are required in the canal to provide water service to high lands adjacent to the canal and to <br />prevent damage to pipe laterals that can be caused by air entering the pipelines. The air that <br />enters the pipeline can become trapped when the pipe inlets lose submergence and then are <br />suddenly resubmerged. This trapped air can cause dangerous pressure surges in the pipeline. <br /> <br />Diversions in excess of demand can be administratively spilled at the six canal spillways or <br />through the open laterals. About 60,000 acre-feet/year of water are administratively spilled. This <br />may seem high but with a flow-through system without in-system storage and with the limited <br />number of check structures, precise matching of demand to supply is not feasible in light of <br />delivery and water surface elevation control requirements. Historically, with 74 open laterals, it <br />was possible to spill a small quantity of water down each lateral rather than concentrate the spills <br />at the canal spillways. Administrative water in a lateral was more readily available to irrigators' <br />along the laterals when an order was placed for water. This form of operation can optimize the <br />use of water while not requiring frequent adjustment of canal spillway structures. Reduction of <br />river diversions would reduce the amount of administrative spills but does not provide the ability <br />to meet the ever-changing irrigation demand. <br /> <br />One aspect of operation which makes canal diversion adjustment difficult is the amount of time <br />for a diversion adjustment to be delivered to the end of the system. Due to the canal <br />configuration, it routinely takes about 3 days for an increased flow adjustment at the river <br />diversion to reach the end of the system. The system takes about 2 days to respond to a decrease <br />in flow. So, if there is a surplus of water within the system, it would take up to 2 days to decrease <br />the flow into the canal and by that time the surplus may no longer exist. <br /> <br />Potential Water Management <br /> <br />In order to manage water more efficiently, it is necessary to make canal adjustments quickly to <br />meet demand and maintain canal water surface elevation with a reduced flow of water in the <br />canal. To meet the ability for quick response, in-system storage and canal automation have been <br />evaluated; and to maintain water surface elevation, additional checks are proposed. The amount <br />of water which could be conserved through these efforts is about 28,500 a.f per year. <br />