Event Title

Fluvial Systems Tied Together Through a Common Base Level: Geologic and Geomorphic Response of the Dirty Devil River, North Wash Creek and the Colorado River to the Rapid Base Level Drop of Lake Powell

Presenter Information

Adam L. Majeski

Location

ECC 216

Event Website

http://water.usu.edu/htm/conference/past-spring-runoff-conferences

Start Date

5-4-2007 6:25 PM

End Date

5-4-2007 6:30 PM

Description

Lake Powell is created by Glen Canyon Dam, on the Colorado River. The drainage area above the lake encompasses ~107,700 mi2, collecting enough water to make Lake Powell the 2nd largest reservoir in the U.S and the current depocenter for 868,231 acre-feet (as measured in 1986) of sediment (Ferrari, 1988). Fifty-four percent of this sediment has accumulated in the Colorado River Delta, 32% in the San Juan River Delta, and the remaining 14% in smaller tributary arms (Ferrari, 1988). Also, the deltas of several reservoir tributaries, notably the San Juan and Dirty Devil Rivers, have extended to their confluence with the Colorado River in the main channel storage area (Ferrari, 1988). Since dam closure in 1963, the reservoir has experienced one transgression, filling to the top of its active storage (3700 ft) in 1980, and one minor regression from 1988 to 1993. The lake recovered by 1999, but this year also marked the beginning of the most significant flow deficit in the Colorado River basin in over 100 years (Webb et al, 2004). As a result, the lake dropped 150 ft over the subsequent 6 year period, and the delta sediments ~95 miles upstream of the dam, near the marina of Hite, were exposed for the first time. Since then, the Colorado River has been down cutting and reworking these sediments. Furthermore, delta sediments accumulating in side canyons and tributaries of the Colorado have been subject to exposure and reworking as well. Of particular interest are two tributaries, North Wash Creek and the Dirty Devil River, which join the Colorado at its delta near Hite. The Dirty Devil River shows significant sediment accumulation and it is one of the few tributaries whose delta extends to the main channel storage area of the Colorado River. North Wash Creek enters ~3 km downstream of the Dirty Devil River and contrasts it greatly; its delta does not extend to the Colorado River and its sediment accumulation has been minor by comparison. Therefore, the current lowered reservoir condition sets up a perfect natural laboratory to compare and contrast the response of these three different fluvial systems to the same drop in base level. By surveying channel slopes and cross sections, based on those established by Reclamation in 1986, the present state of these systems can be compared to similar historical records and to pre-dam topography. This will also allow volumetric analysis of deposited delta sediment in order to determine the amount mobilized and/or deposited. By observing photographs taken by several researchers, including John Dornwend, James Evans, William Vernieu, and myself, changes in delta morphology and sediment deformation over time can be viewed in a qualitative manner. Finally, by observing delta stratigraphy and associated grain-size distributions and bed-material size distributions, causes for differences in incision rates, and the presence or absence of lateral slumping, mud cracking, and slope failure can be inferred. Each piece of data will help to characterize each system, and through comparison and contrast with the others, it will become clearer which responses are dependent and independent of the size and physical characteristics of the river system.

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Apr 5th, 6:25 PM Apr 5th, 6:30 PM

Fluvial Systems Tied Together Through a Common Base Level: Geologic and Geomorphic Response of the Dirty Devil River, North Wash Creek and the Colorado River to the Rapid Base Level Drop of Lake Powell

ECC 216

Lake Powell is created by Glen Canyon Dam, on the Colorado River. The drainage area above the lake encompasses ~107,700 mi2, collecting enough water to make Lake Powell the 2nd largest reservoir in the U.S and the current depocenter for 868,231 acre-feet (as measured in 1986) of sediment (Ferrari, 1988). Fifty-four percent of this sediment has accumulated in the Colorado River Delta, 32% in the San Juan River Delta, and the remaining 14% in smaller tributary arms (Ferrari, 1988). Also, the deltas of several reservoir tributaries, notably the San Juan and Dirty Devil Rivers, have extended to their confluence with the Colorado River in the main channel storage area (Ferrari, 1988). Since dam closure in 1963, the reservoir has experienced one transgression, filling to the top of its active storage (3700 ft) in 1980, and one minor regression from 1988 to 1993. The lake recovered by 1999, but this year also marked the beginning of the most significant flow deficit in the Colorado River basin in over 100 years (Webb et al, 2004). As a result, the lake dropped 150 ft over the subsequent 6 year period, and the delta sediments ~95 miles upstream of the dam, near the marina of Hite, were exposed for the first time. Since then, the Colorado River has been down cutting and reworking these sediments. Furthermore, delta sediments accumulating in side canyons and tributaries of the Colorado have been subject to exposure and reworking as well. Of particular interest are two tributaries, North Wash Creek and the Dirty Devil River, which join the Colorado at its delta near Hite. The Dirty Devil River shows significant sediment accumulation and it is one of the few tributaries whose delta extends to the main channel storage area of the Colorado River. North Wash Creek enters ~3 km downstream of the Dirty Devil River and contrasts it greatly; its delta does not extend to the Colorado River and its sediment accumulation has been minor by comparison. Therefore, the current lowered reservoir condition sets up a perfect natural laboratory to compare and contrast the response of these three different fluvial systems to the same drop in base level. By surveying channel slopes and cross sections, based on those established by Reclamation in 1986, the present state of these systems can be compared to similar historical records and to pre-dam topography. This will also allow volumetric analysis of deposited delta sediment in order to determine the amount mobilized and/or deposited. By observing photographs taken by several researchers, including John Dornwend, James Evans, William Vernieu, and myself, changes in delta morphology and sediment deformation over time can be viewed in a qualitative manner. Finally, by observing delta stratigraphy and associated grain-size distributions and bed-material size distributions, causes for differences in incision rates, and the presence or absence of lateral slumping, mud cracking, and slope failure can be inferred. Each piece of data will help to characterize each system, and through comparison and contrast with the others, it will become clearer which responses are dependent and independent of the size and physical characteristics of the river system.

http://digitalcommons.usu.edu/runoff/2007/AllPosters/8