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The Colorado River in Grand Canyon: How Fast Does It Flow?

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Grand Canyon Monitoring and Research Program The Colorado River U.S. Department of the Interior U.S. Geological Survey in Grand Canyon: How Fast Does It Flow? Opening the jet tubes at Glen Canyon Dam on March 26, 1996, released from Lake Powell a con- trolled flood of water that traveled down the Colorado River in Grand Canyon. How fast did the water move? How long did it take for water to reach a particular point along the river? The answers to these questions are important because the speed of river water affects the amount of physical and chemical changes, such as warming by sunlight, that the water will undergo as it moves downstream. Also, very fine particles and substances dissolved in the water travel along with the water, and the speed of the water tells us how fast these move downstream. How is the Water Speed Athough the dye is easy to see where it is first put into the river, it quickly mixes with the much larger mass of river water and becomes invisible. The highest concentration Measured? at sampling sites was between 5 and 35 parts per billion. One part per billion is about equal to one drop in a backyard swimming pool. One way to measure the speed of water is to tag it with a harmless Glen Paria Canyon 114° UTAH ° ° ° substance that is easily identified and 37° 113 112 Ri Dam 111 ve measured with the proper instruments. ARIZONA r River Lees Ferry These substances are called water tracers gin PAGE and are commonly used in both ground Vir water and surface water to track the water movement. A fluorescent dye NEVADA ARIZONA developed specifically for this purpose Lake Grand Mead Canyon Ri has been used in surface-water studies v National e for many years because it is safe and C Park r L C o i l t 36° o readily detectable at very low o Pearce t l Ferry r le o a Co concentrations. r d a o lo d To make a measurement, dye is put D ra o Gneiss Canyon ia CALIFORNIA mo do into the river as nearly as possible at a ARIZONA Cr nd ee single point and time. Samples of river k Ri water are collected at sites of known ve EXPLANATION r distances downstream as the dyed water R FLAGSTAFF i v DYE-SAMPLING SITE passes. The samples are measured using e r an instrument designed to detect the very PHOENIX 35° FLAGSTAFF small amounts of dye present. The speed 0 50 MILES of the center of mass of the dyed water is TUCSON determined from the data and represents ARIZONA 0 50 KILOMETERS the average speed of the water through the reach for the discharge during the Dye movement was tracked by sampling the water and measuring the dye measurement. concentration at eight sites during the controlled flood. When Dam Releases are 5 Constant, Water Moves Fastest reach Faster at Higher Dam Releases than at Lower 4 Releases Measurements of water speed have Slowest reach Lees Ferry downstream been made in the Colorado River 3 between Glen Canyon Dam and Lees Ferry at three different dam releases , IN MILES PER HOUR Fastest reach within the operating range of the powerplant at the dam —5,000, 15,000, 2 and 23,000 ft3/s. At the lowest releases, TER SPEED Slowest reach water moved through the reach at an A to Lees Ferry average speed of 0.7 mph, taking a little less than 1 day (22 hours) to travel the Example 1 /s 15 mi between the dam and Lees Ferry. 3 At the highest releases, water moved at VERAGE W Glen Canyon Dam A 2.3 mph and took about 7 hours to travel the same distance. The speed of water 15,000 ft was found to be directly related to the 0 0 10,000 20,000 30,000 40,000 50,000 magnitude of dam releases. DAM RELEASES, IN CUBIC FEET PER SECOND The speed of water downstream from Lees Ferry has been measured at two dam 3 Water speed from the dam to Lees Ferry has been measured at three dam releases—15,000 ft /s in 1991 and releases and downstream from Lees Ferry at two releases. Wa ter moves a little 45,000 ft3/s during the controlled flood of more slowly upstream from Lees Ferry than downstream. We can use the results March 1996. At 15,000 ft 3/s, the water to estimate the average water speed for a range of constant discharges. For moved at an average speed of 2.3 mph example, the data indicate that at 30,000 ft 3/s water would flow downstream from Lees Ferry at a little more than 3 mph. and took 41/2 days to travel the 235 mi from Lees Ferry to Gneiss Canyon, which is 10 mi downstream from Diamond Creek. At that same dam release, water 5 flowed at an average speed of only 1.6 mph from the dam to Lees Ferry. Downstream from Lees Ferry, water traveled almost twice as fast (4 mph) at 3 3 45,000 ft /s as it had at 15,000 ft /s. 4 Average for 45,000 ft3/s dam releases Flow is Faster in Some Reaches than Others 3 The water mo ves through the reaches defined by dye-sampling sites faster or slower than the average speed depending on the channel shape and slope of the particular reach. For TER SPEED, IN MILES PER HOUR 2 Average for 15,000 ft3/s dam releases measurements made at both 15,000 and A W 45,000 ft3/s, water moves more slowly Little Colorado River than average from Lees Ferry to the Little Colorado River, 61 mi Marble Canyon Grand Canyon downstream, and about equal to or 1 faster than average from that point 0 50 100 150 200 250 downstream. The slowest reach DISTANCE DOWNSTREAM FROM LEES FERRY, IN MILES downstream from Lees Ferry was in Lower Marble Canyon, which is just Water speed through reaches defined by sampling sites was less than the average upstream from the Little Colorado for Marble Canyon and equal to or greater than the average for Grand Ca nyon for River. both constant dam releases measured. 30,000 Lees Ferry The difference in speed of the water 15,000 Dye and the discharge wave caused the water injected to move through some reaches faster and Wave 1 Wave 2 Wave 3 0 others more slowly than when releases 30,000 Little were constant. The measured water Center Colorado of dyed speeds during the rapidly changing 15,000 River water releases were higher than those measured during the constant 15,000 f t3/s Wave 1 Wave 2 Wave 3 0 release for the reaches in which the dyed 30,000 Gneiss Center of water moved with the higher, faster part Canyon dyed water of the discharge wave and lower for 15,000 those in which it moved with the lower, Wave 1 Wave 2 Wave 3 slower part of the wave. Averaged over DISCHARGE, IN CUBIC FEET PER SECOND 0 6 7 8 9 10 11 the whole 235 mi measured, the speed for rapidly changing releases was the MAY 1991 same as that measured during the constant 15,000 ft3/s release. Discharge waves move downstream faster than the water. For example, in May 1991, the discharge waves produced by rapidly changing dam releases moved through the canyon in about 12/3 days, whereas the water took about 41/3 days to travel the 235 miles How has Knowledge of the from Lees Ferry to Gneiss Canyon. The dye was injected at Lees Ferry into the discharge wave labeled wave 1 (top graph). Wave 1 passed the Gneiss Canyon Water Speed Helped? sampling location on May 8, whereas the dyed water passed that location late on May 10. Knowledge of the speed of Colorado River water in Grand Canyon will help How do Rapidly Changing managers make decisions needed to Releases Affect the Speed protect the unique natural resources. The when dam releases changed from speed of water through a reach is one 3 3 of the Water? 3,250 ft /s at night to 26,600 ft /s at factor that controls the amount of time 3 midday and averaged 15,000 ft /s over the water is exposed to light. Knowledge We’ve seen that the speed of water each 24-hour period. Dye was released of the water speed has helped to provide released from the dam is higher for higher at Lees Ferry not long before the peak of an understanding of light-dependent dam releases when releases are constant the discharge wave reached that point. processes, such as photosynthesis and throughout the dye measurement. When By the time the dyed water had reached respiration of aquatic plants, in the reach dam releases change rapidly during the the Little Colorado River mouth, 61 mi between the dam and Lees Ferry. Also, day, as they normally do for production downstream, it was moving with the because water speed is controlled in part of electricity, a wave of water is produced trough of the same discharge wave. At by channel roughness, which is very that moves downstream, but the water Gneiss Canyon, 235 mi downstream difficult to measure directly , itself moves more slowly than the surface from Lees Ferry, almost three discharge measurements of water speed provide a wave. waves had passed the Gneiss Canyon means to determine values of this A measurement of water speed was water-sampling location before the dyed important channel characteristic.
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