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OJJ2GO 29 The accuracy of the original data can always 'be questioned. Any time that is read off a recorder chart' is likel)l to be different from the ~rue time by at least 15 minutes. This can be due to inaccurate clock speed, the recorder pen not precisely set on the chart, the chart paper advancing at an angle, etc. This office made numerOus spot checks of the recorder stations on the Arkansas and found several times that a chart would be one hour or mOre off from the true time. Ninety percent of the 1966-1970 data used for the release and shutoff curves fell within less than two hours of the Figure IV-I curves. Approx- imately 10 per cent of the data represented extremes; they were five hours or more away from the curve. These extremes may have been caused by in- accuracy in the original data. The basic analysis for Figure IV-I was based on the Granite and Pueblo gages. One and a ha I f hou,rs was added to the Gran i te gage to obta i n the release time from Twin Lakes.* Studies of travel time from Pueblo to the Colorado Canal were, used to complete the nomograph. Confirmation of the graph was then made by plotting Twin Lakes to Colorado Canal travel time for past data. Lacey"s (35) 1939-40 work consistently reported times of travel about 5 hours less for the Grani te to Pueblo reach than ,did the 1970 analysis. The discrepancy cannot be fully explained. The river channel characteristics have undoubtedly changed to some degree, for example, new bridges, different length, new diversion structures, etc. However, they would prohably not account for five hours. Lacey did not state that his times were based upon the first effect of the release or shutoff. Figure IV-I can Be used as an administrative guide to estimate travel times of large (200 cfs to 500 cfs) reservoir runs on the Arkansas River from the Twin Lakes area down to the Colorado Canal. It is our opinipn that most large reservoir runs will reach thF'headgates as estimated by Figure IV-l, plus or minus two hours. We,belleve time of travel for releases of less than 200 cfs can also be estimated by Figure IV-I. Theoretically, the smaller releases should take a little longer to traverse the river; however, no data was available to confirm this phenomenon. Figure IV-l is probably inaccurate for flows above 3,000 cfs at Canon City since at that stage the river is "over bank" in some areas and the river hydraul ic characteristics change more significantly. Rate of Openinq and Closinq Headqates. Some experimentation has been done in the past 20 years on releasing water in stages, that is, starting the run with 5~/' of the desired flow then 24 hours later opening the gates to 10~/, of the desired flow. This practice is believed to be inefficient as far as travel losses are con- cerned. For best efficiency in transporting and eventually diverting the water, the gates should be opened to the full amount at the beginning of the run.