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Home , Channel (geography), Little Colorado River, Paria River

U.S. Department of the Interior Monitoring Channel U.S. Geological Survey Storage in the Colorado Studies River in Grand Fact Sheet

Sandbars provide habitat for plants and measure the changes in channel sand about sand movement after individual wildlife along the in the storage caused by and the tributary floods. and are commonly the low releases from the dam in 1992 and only areas among cliffs and boulders 1993 (with daily maximum releases Sand Accumulates Below where river rafters can camp. As part of restricted to less than about 20,000 cubic the Canyon Environmental Studies, feet per second). The data collected also Tributary Mouths funded and coordinated by the Bureau of are being used to refine computer models When the Paria and Little Colorado Reclamation, the U.S. Geological Survey that can simulate the movement of sand , much of the sand they carry is monitoring the supply, storage, and through reaches of the river. quickly settles out in the main channel of movement of sand in Grand Canyon the Colorado River. With time the sand N National Park (fig. 1). Before Glen Channel Sand Storage is moves downstream. The monitoring Canyon Dam was built, an average of Monitored at More Than network supplies detailed information * -about 65, million tons of were 100 Sites about the areas of initial and : transported by the Colorado River into the the rate of sand movement through the park each year.- Because the dam now The Paria and Little Colorado Rivers river. In August 1992, the blocks the river, the only significant (fig. 1) contribute most of the sand that flooded with a peak of about ' $6Xtra?s of sediment for,, the park are enters Grand Canyon National Park; 1,270 cubic feet per second. The four sites and river| downstrearfi frorn the therefore, 34 monitoring sites were closest to the Paria River (fig. 1) were dam. The amount of sand-ttese established in the 7-mile reach of the measured before and after the flood. supply. varies "greatly from yjsar to year Colorado River just below the mouth of During the flood, discharge was measured but averages about 2,9 million tons" per the Paria River and 32 monitoring sites and seven suspended-sediment samples . Available data indicate that if dam were established in the 7-mile reach were collected automatically at the Paria releases \are managed properly this is below the mouth of the -gaging station 1.1 miles

113° 112° 111°

Figure 1. Location of study area and cross sections.

. enough sand to maintain sandbars and River. Forty other sites are distributed upstream from the mouth of the river. The other sand deposits in the park (Bureau of between these two rivers and farther Paria River flowed thick with sediment Reclamation, 1994 '-50-51). downstream. Measurements are made at from about 3:00 p.m. on August 23 until lijmd from tributaries^ is temporarily \ ch $ite at three key times during the 9:00 a.m. the next day. The total ' depositedX 'ifr- -- the river> channel,: *- : 5 during'I lowf - 'ear: hr- the winter, before the suspended sediment transported by the flows p^roduced^Jby - 'controlled dam floods in tributaries: in late spring or early flood was estimated to be 544,000 tons, of v releases. \A !.' controlled ~ flood \ of summer, after the flbpds; and in the fall, which 330,000 tons was sand. Much of appropriate]Sizeand\duration will scour, after the summer thunderstorm season. the sand was deposited in the river channel just below the mouth of the Paria sand"-and rebuild som^ s,ai|ibars. M 1 i. ; \ may"" be-;" measureds * - more "monitoringx;, stu4y .^^ae^esigned" -'to frequentiy) to collect.detailed information River. Sand accumulated at all four of the ~^^L^J x - "^ ..^'-^^^

Fact Sheet printed on recycled paper cross sections that had been measured on 1992 and 1993, releases from Glen deposition and will result from August 23. Parts of cross section p4, near Canyon Dam have been high enough to dam releases. To date (1995), we have the center of the channel, filled with redistribute large amounts of sand only been able to study flows of less than nearly 20 feet of new sand (fig. 2). A transported to the Colorado River channel 20,000 cubic feet per second, but the flood of this size or larger occurs on the by tributary floods. Just downstream from cross-section network will still be in place

100 200 300 400 500 100 200 300 DISTANCE FROM LEFT , IN FEET DISTANCE FROM LEFT BANK, IN FEET

Figure 2. A flood on the Paria River on August 23, 1992, Figure 3. A flood on the Little Colorado River in January deposited about 2,400 square feet of sand in the Colorado 1993 deposited about 5,300 square feet of sand in the River at cross section p4 (fig. 1) just downstream from the Colorado River at cross section a6 (fig. 1), downstream . Five months later, about 2,880 square feet of from the confluence. Three months later, only about 220 sand had been eroded from the main channel at the cross square feet of sand had been eroded. section and 317 square feet had been deposited in the eddy.

Paria River about once every 2 years. The the mouth of the Paria River, most of the when higher flows occur in the future. amount of sediment transported can vary sand deposited in the main part of the Data collected at that time will provide greatly. river channel during the flood of August detailed information about how floods In January 1993, a flood on the Little 1992 had been scoured out by January 23, scour and redeposit sand. Colorado River washed about 10,100,000 1993 (fig. 2). Sand did accumulate in the tons of sediment into the Colorado River, large eddy at this location during this Selected References about 4,600,000 tons of which was sand, time. The sand in the Colorado River enough to fill a channel an average of 400 deposited downstream from the mouth of feet wide with 10 feet of sand for about the Little Colorado River in January 1993 Bureau of Reclamation, 1989, Glen 5 miles. However, the sand was not also began to move downstream (fig. 3). Canyon Environmental Studies Final evenly deposited. Some cross sections The river bed changed more slowly in the Report, January. 1988: Bureau of below the mouth of the Little Colorado study reach downstream from the mouth Reclamation Report, 84 p. River had very little sand accumulation of the Little Colorado River than in the and some gained almost 30 feet (fig. 3). study reach downstream from the mouth Bureau of Reclamation, 1994, Operation This flood lasted about 3 weeks and had a of the Paria River, probably because a of Dam Draft Environ- peak flow of about 16,400 cubic feet per larger amount of sand had been deposited ental Impact Statement: Bureau of second. A flood with such a long duration there and because the Little Colorado Reclamation Report, 324 p. and high peak flow occurs on the Little River and other tributaries continued to Samuel M.D. Jarisen, Julia B. Graf, Colorado River about once every 50 supply some sand after the flood. years. Jonathan E. Marlow, and Gregory G. The cross-section monitoring provides Fisk information on changes in sand storage at For more information, please contact: Sand is Carried Downstream specific locations. Computer models U.S. Geological Survey by Dam Releases under development will make it possible 375 S. Euclid Avenue to compute changes in storage in river Tucson, AZ 85719 Cross-section measurements show that reaches in Grand Canyon National Park (602) 670-6671 even during; the restricted dam releases in and to predict where and how much sand

May 1995 FS-120-95