Colorado River Ecology and Dam Management Proceedings of a Symposium May 24-25, 1990 Santa Fe, New Mexico (1991) / Chapter Skim
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Sediment Transport in the Colorado River Basin
Sediment Transport in the Colorado River Basin
Pages 54-74
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From page 54... ...
Large reservoirs were constructed on each of the three major headwater tributaries during the early 1960s. Daily sediment transport and water discharge records collected at gaging stations in the Colorado River basin over the past 60 years demonstrate that an appreciable change in the hydrology of the Colorado plateau occurred about 1941, and they describe the pre- and postdevelopment hydrologic conditions.
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From page 55... ...
Beginning in 1925, the suspended sediment concentration was sampled daily at two gaging stations in the Colorado River basin: the Colorado River near Grand Canyon, Arizona, and the Colorado River near Topock, Arizona. Over the subsequent 5 years, the sediment-sampling network was expanded to four additional gaging stations located on the
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From page 56... ...
NEW MEXICO _ 25 6\o&~° '~! .4 -- ' FIGURE 4-1 Mean annual runoff and sediment load at selected gaging stations in the Colorado River basin, 1941-1957.
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From page 57... ...
By 1957, during the peak of reservoir construction, the suspended sediment concentration was being sampled daily at 18 gaging stations, each of which eventually had a record length exceeding 10 or more years. This network is the most extensive and detailed description of sediment transport in a large drainage basin ever collected.
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From page 58... ...
Thus, the suspended sediment concentrations reported by the studies cited above are surely less than the actual concentrations. Although the methods were rudimentary and relatively few samples were collected, some of the fundamental characteristics of sediment transport processes in the Colorado River basin were deduced by these early investigations.
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From page 59... ...
Various laboratory and field comparisons, including these conducted at the San Juan River at Bluff and the Colorado River near Grand Canyon, suggest that the Colorado River sampler would undersample the true concentration by a few to several percent. The number of daily sediment sampling sites operated during each year from 1925 to 1990 in the Colorado River basin upstream from Lake Mead is shown in Figure 4-2.
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From page 60... ...
Conversely, most of the sediment is contributed by the semiarid parts of the basin in southeastern Utah and adjacent States. The mean annual water discharge and sediment discharge measured during the period 1941-1957 at 11 gaging stations in the Colorado River basin upstream from Lake Mead are compared in Figure 4-1.
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From page 61... ...
The largest of these tributaries, notably the San Rafael, Paria, Chaco, and Little Colorado rivers are shown in Figure 4-1. The portion of the Colorado River basin that lies upstream from Grand Canyon and downstream from Jensen, Utah, on the Green River, Cisco, Utah on the Colorado River, and Shiprock, New Mexico, on the San Juan River contributed about 59 million tons/year on an average, or about 69% of the basinwide sediment discharge, but supplied only 15% of the basinwide water discharge.
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From page 62... ...
cn or LL ~ 1,000 on G us 500 Z O LL CD 2.0 I en ~ 1 a: ILL 3: 1.0 I O 0.5 o COLORADO RIVER ECOLOGY AND DAM MANAGEMENT 800.000 COLORADO RIVER AT LEES FERRY 1947-1957 3 WATER DISCHARGE Qma=450 m3/s ~3 SEDIMENT LOAD _ QSE D = 66 X 10 6 TO N S . _ 600.000 DA = 279,400 km2 ; , ~ V ~~ ~ ~200.00000 PARIA RIVER AT LEES FERRY 1948-1976 Qma = 0.72 m 3/s _ QsED = 3.02 X 10 6 TONS/YR D A = 3,652 km 2 L.~ _ ~ _L ~ z m G ~ ~ ~ ~ ~ ~ 111 ~ ~ ~ Z 11 20,000 1 0,000 O 40,000 LL llJ on 30,0OO I c FIGURE 4-3 Mean monthly water and sediment discharges of the Colorado River and Paria River at Lee's Ferry, Arizona.
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From page 63... ...
The relationship of annual runoff and suspended sediment loads recorded at the Colorado River near Grand Canyon between 1925 and 1957 is plotted in Figure 4-4. The mean annual suspended sediment load of the Colorado River near Grand Canyon was 195 million tons/year during the period 1925-1940 compared with 85.9 million tons/year during the period 1941-1957.
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From page 64... ...
64 COLORADO RIVER ECOLOGY AlID DAM MANAGEMENT 550 _ / ~500: o ~ 400 ~ ~ , ~300 200~ as ~47~ 57s2 two 44 54 o I I I I 1 1 1 1 10 I 1 1 1 1 1 1 1 20 RUNOFF (in billion cubic meters) FIGURE 4-4 Relationship of annual runoff to annual sediment load in the Colorado River near Grand Canyon, 1926-1940 and 1941-1950.
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From page 65... ...
The mean annual flood of the Paria River since 1942 is 106 m3/s, or 55% of mean annual flood, 220 m3/s, recorded prior to 500 r o a' 100 Q a)
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From page 66... ...
An identical reservoir located at different sites in the Colorado River basin would have very different downstream effects on sediment transport and deposition.
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From page 67... ...
Prior to the construction of a dam in Flaming Gorge, a quasi-equilibrium condition appears to have existed downstream in the Green River channel; that is, over a period of years, the transport of sediment out of a given river reach equaled the supply of sediment into the reach. Since regulation by Flaming Gorge Reservoir began in 1962, the mean annual sediment discharge at downstream gages has decreased substantially.
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From page 68... ...
As described above, the mean annual sediment load of the Colorado River at Lee's Ferry during the period 1941-1957 was 66.1 million tons/year. This gaging station is located only 23 km downstream from Glen Canyon Dam, and there are no significant tributaries to the intervening reach.
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From page 69... ...
A comparison of mean annual sediment load during the period 19411957 indicates that the sediment load at the Colorado River near the Grand Canyon exceeded the sediment load at the Colorado River at the Lee's Ferry by about 20 million tons/year, see Figure 4-1. The difference between the quantity of sediment supplied by the Paria and Little Colorado Rivers, which represent 93% of the intervening drainage area, and the increase between the Lee's Ferry and Grand Canyon gages can be explained by (1)
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From page 70... ...
Using this approach, the estimated mean annual sediment load of the Colorado River near Grand Canyon is approximately 11 million tons/year under present conditions, compared with 85 million tons/year during the period 1941-1957, immediately prior to the construction of Glen Canyon Dam. In contrast to the situation on the Green River downstream from Flaming Gorge Reservoir described above, the decrease in mean annual sediment load in the Colorado River near Grand Canyon is not solely due to a decrease in relatively large discharges.
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From page 71... ...
At this time, we do not understand any of these topics well enough to determine precisely the range of stream~low that will maintain and, we hope, enhance occurrence of sandbars through the Grand Canyon reach. CONCLUSIONS Long-term daily sampling of suspended sediment transport began in the Colorado River basin at the Grand Canyon gage in 1925.
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From page 72... ...
Vast quantities of sediment were eroded by those floods, and large arroyos were formed in all of the tributaries draining the Colorado plateau. Suspended sediment concentrations at a given discharge as well as the annual sediment loads of the Colorado River and its major tributaries were substantially larger before than after 1941.
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From page 73... ...
The concentration of suspended sediment at the Colorado River near Grand Canyon at a specific discharge has decreased by a factor of 2.3 for commonly occurring flow. Since 1970, the mean annual sediment load of the Colorado River near Grand Canyon has been approximately 11 million tons, which is about the estimated contribution of sediment to the reach between Lee's Ferry and Grand Canyon.
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From page 74... ...
1965. Water resources of the Upper Colorado River Basin.
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