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but with a flow-through system without in-system storage and with the limited number of check structures, significantly more frugal operation is not feasible in light of delivery and water surface elevation control requirements. Histori- cally, with 74 open laterals, it was possible to spill a small quantity of water down each lateral rather than concentrate the spills at the canal spillways. Administrative water in a lateral was more readily available to irrigators' along the laterals when an order was placed for water. This form of operation can optimize the use of water while not requiring frequent adjustment of canal spillway structures. Reduction of river diversions would reduce the amount of administrative spills but does not provide the ability to meet the ever-changing irrigation demand. One aspect of operation which makes canal diversion adjustment difficult is the amount of time for a diversion adjustment to be delivered to the end of the system. Due to the canal configuration, it routinely takes about 3 days for an increased flow adjustment at the river diversion to reach the end of the system. The system takes about 2 days to respond to a decrease in flow. So, if there is a surplus of water within the system, it would take up to 2 days to decrease the flow into the canal and by that time the surplus may no longer exist. Temporarily deviating from the focus of this paper and addressing the legal implications of the water management practice, the question arises at whether this is a reasonably efficient management practice. This issue has been addressed by the Colorado Water Conservation Board as follows: "What "reasonably efficient practices" means is central to state- ments about the efficiency and waste involved in irrigation water use. A common understanding is that beneficial use is a flexible concept which tolerates whatever degree of "inefficiency" is present in the prevailing irrigation methods of an area. Courts will likely be reluctant to require innovations with private in- vestment that force any advance beyond those prevailing meth- ods. Likewise, the State Engineer can probably not require state-of-the-art irrigation systems in an effort to reduce irrigation water diversions."' Current Water Management Closed pipelines have resulted in a major difference in administrative spill patterns because closed pipe systems cannot be used as spillways. Conse- quently, administrative spills are confined to the remaining open laterals and ' Colorado Water Conservation Board. January 22, 1992. AN ANALYSIS OF WATER SALVAGE ISSUES IN COLORADO. Steve Miller. p. 6.