7869 - Laserfiche WebLink

Home Browse Search

2.3 Operation During all but very low flow periods, the operation of the Grand Valley Irrigation Company diversion is typical of most run-of-the-river gravity diversion systems. The combination of the floodgates and the diversion dam are used to raise the level of the Colorado River to create sufficient head to divert 640 cfs through the GVIC headgates. Generally, diversions are at or near the 640 cfs level throughout the irrigation season which generally runs from April 1 through October 31. During the early portion of April, as well as, September and October, diversions may drop below 640 cfs as demand is less. However, due to physical constraints of the system, at least 580 cfs are needed to provide sufficient head in the main canal to fully serve users on the Grand Valley Highline canal. Flow in the canal is measured at a weir section approximately 500 feet downstream of the headgates. A continuous recorder and satellite uplink to the State Engineers office is located approximately 20 feet upstream of the weir section. When the canal flow is 640 cfs, the staff gage at the recorder house reads 4.10. This corresponds to an elevation of 4679.61. Two electrical switches, which are attached to a rod on a float in the recording house, activate an alarm whenever the stage in the canal is 0.2' above or below the 4.10 reading. These switches are also connected to a readout at the headgate with red and green lights. Based on the color of the lights, the dam tender knows whether to raise or lower the headgates. The flow into the canal is controlled by six 5.4' wide sliding headgates which are driven by electric motors. For optimum operation of the canal and downstream facilities, the system works best when there are several feet of head on the slide gates and the gates are operating in an orifice condition with the gates partially closed. This condition is satisfied when the water level is kept at or above the diversion dam crest. With the gates operating in this condition, fluctuations in the river level do not cause a significant increase or decrease in the canal level. In contrast with the gates operating fully open, changes in the river level result in significant changes in the canal discharge. This change can be accentuated throughout the system as downstream operators adjust their gates to the changes in the canal level and possibly over compensate. This is particularly true when the change is due to a spike caused by tributary inflows during the thunderstorm season. Based on a survey of water marks at the upstream side of the headgates and conversations with the 5