WSP00353

• File Number: 8240.200.43.H.2
• Description: Grand Valley/Orchard Mesa -
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/11/1993
• Title: Analysis of the Orchard Mesa Check Operation Under Current and Historic Stream Administration Practices
• Water Supply Pro - Doc Type: Publication

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The Check is a feature of the OMID's water system located below the Orchard Mesa Power Canal
south of the Coiorado River (see Figure 1). It consists of three radial gates and a by-pass canal
constructed in the common afterbay of the Orchard Mesa Power Plant and Orchard Mesa Pumping
Plant. When the radial gates are lowered, the level of water being discharged into the afterbay
rises until it is forced to flow upstream through the 1,200 foot by-pass channel. The water
discharges to the Colorado River at a location upstream of the GVIC's point of diversion. This
discharge, which would have otherwise entered the river below GVIC's diversion is effectively used
twice; once in the power and pumping plants and again in the GVIC's diversion canal. This
operation helps satisfy the GVIC demand thereby reducing the amount of the Cameo call. With
full implementation of the Check, the Cameo demand can be reduced to approximately 1,700 cfs.

HISTORIC OPERA TION OF THE CHECK

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The USA and OMID do not maintain records of the amount of water flowing through the Orchard

Mesa Check. Accordingly, the volume and duration of water in the Check had to be calculated

through a water balance model of the Cameo demand. Based upon the information assembled for

the investigation, a study period of 1945 through 1990 was selected. This period included the

operation of Green Mountain Reservoir and contained representative average, wet and dry water

years.

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The water balance model utilized daily streamflow records of the Colorado River and Plateau Creek

together with actual diversions by the GVWUA, OMID and USA. This information was used in a

water balance equation to solve for the amount of water flowing in the Check. The equation is

expressed as:" '

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Check (cfsl = Streamflow at Cameo Gage' Diversions by Government High!ine Canal
+ Streamflow at Plateau Creek Gage - Diversions by GVIC

If the equation produced a negative value, it represented flows that were available to GVIC through

implementation of the Check. In other words, if there was not sufficient water available in the

Colorado River below the Grand Valley Diversion Dam to explain the actual diversions recorded by

GVIC, the difference in flow must have originated from unrecorded water entering the river at the

Check structure. Figure 2 graphically displays the equation used to solve for the amount of water

in the Check.

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