|
<br />VOL, 31, NO, 2
<br />
<br />WATER RESOURCES BULLETIN
<br />AMERICAN WATER RESOURCES ASSOCIATION
<br />
<br />APRIL 1995
<br />
<br />MEASURED AND PREDICTED VELOCITY AND LONGITUDINAL DISPERSION
<br />AT STEADY AND UNSTEADY FLOW, COLORADO RIVER,
<br />GLEN CANYON DAM TO LAKE MEADl
<br />
<br />Julia Badal Graf2
<br />
<br />ABSTRACT: The effect of unsteadiness of dam releSBe8 on velocity
<br />and longitudinal dispersion offlow was evaluated by injecting a flu-
<br />orescent dye into the Colorado River below Glen Canyon Dam and
<br />sampling for dye concentration at selected sites downstream. Mea.
<br />Burements of a 26-kilometer reach of Glen Canyon, just below Glen
<br />Canyon Dam, were made at nearly steady dam releases of 139, 425,
<br />and 651 cubic meten per second. Measurements of a 380-kilometer
<br />reach of Grand Canyon were made at steady releases of 425 cubic
<br />meters per second and at unsteady releases with a daily mean of
<br />about 425 cubic meters per second. In Glen Canyon, average flow
<br />velocity through the Bwdy reach increased directly with discharge,
<br />but dispersioD was greatest at the lowest of the three flows mea-
<br />sured. In Grand Canyon, average flow velocity varied slightly from
<br />subreach to BUbreach at both steady and unsteady flow but was Dot
<br />significantly different at steady and unsteady flow over the entire
<br />study reach. Also, longitudinal dispersion was not significantly dif-
<br />ferent during steady and unsteady flow. wng tails on the time.con-
<br />centration curves at a site, characteristic of most rivers but not
<br />predicted by the one-dimensional theory, were not found in this
<br />study. Absence of tails on the curves shows that, at the measured
<br />flows, the eddies that are characteristic of the Grand Canyon reach
<br />do not trap water for a significant length of time. Data from the
<br />measurements were used to calibrate a one-dimensional flow model
<br />and a solute-transport model. The combined set of calibrated flow
<br />and solute-transport models was then used to predict velocity and
<br />dispersion at potential dam-release patterns.
<br />(KEY TERMS: flow velocity; longitudinal dispersion; steady flow;
<br />unsteady flow; tracers; water policy/regulation/decision making;
<br />Glen Canyon Dam; Colorado River.)
<br />
<br />INTRODUCTION
<br />
<br />Measurements of velocity and longitudinal disper-
<br />sion of flow in the Colorado River below Glen Canyon
<br />Dam (Figure 1) were made in October 1989 and May
<br />1991 to evaluate the effects of channel geometry and
<br />unsteadiness of flow on these fundamental flow char-
<br />acteristics, The measurements are a key part of a
<br />
<br />program of data collection to support the development
<br />of physically based flow and transport models of the
<br />river by the U,S, Geological Survey (USGS), Mea-
<br />sured velocity is used to estimate bed roughness for
<br />flow-routing models developed as part of the overall
<br />program (Flow and Sediment Transport in the Col-
<br />orado River Between Lake Powell and Lake Mead,
<br />J, D, Smith and S, M, Wiele, written communication,
<br />1992; A Discharge Model of the Colorado River
<br />Through the Grand Canyon, S, M, Wiele and J, D,
<br />Smith, written communication, 1993),
<br />USGS data collection and model development are a
<br />part of an interagency, interdisciplinary study, the
<br />Glen Canyon Environmental Studies (GeES), coordi-
<br />nated by the Bureau of Reclamation (BOR), The goal
<br />of the study is to provide managers of the dam and
<br />downstream resources the means to predict the
<br />effects of different dam-release patterns on the ripari-
<br />an system downstream from the dam, Flow and trans-
<br />port models are important to the GCES because
<br />assessment of effects of dam operations on all other
<br />components of the riparian environment depend on
<br />the ability to predict river stage and fluid and sedi-
<br />ment transport that result from specified dam releas-
<br />es, Information from this and other GeES research
<br />has been incorporated into an Environmental Impact
<br />Statement (EIS) on dam operations ordered by the
<br />Department of the Interior and submitted to the Sec-
<br />retary of the Interior in March 1995, To aid in the
<br />evaluation of potential dam-release patterns that is a
<br />part of the EIS, velocity, and dispersion data were
<br />used to calibrate existing flow and solute-transport
<br />models and the calibrated models used to predict
<br />velocity and dispersion for two of the dam-release pat-
<br />terns under evaluation,
<br />
<br />IPaper No. 93145 of the Water Resources Bulletin. Dl8cuuiona are open until December 1, 1995.
<br />2Research Hydrologist. U.S. Geological Survey, 375 South Euclid Avenue, Tucson. Arizona 85719.
<br />
<br />265
<br />
<br />WATER RESOURCES BULLETIN
<br />
<br />t'1!:
<br />. : ~
<br />.. ~
<br />~~~.' '
<br />
<br />: ~.
<br />
<br />"
<br />:-"':,'$.,'
<br />.' ~',,-:.:
<br />"'...
<br />
<br />,,'."
<br />
<br />",
<br />
<br />~;~i ~.,'
<br />'~."""
<br />~]<:[j'
<br />~~!:~
<br />
<br />-:':,.~ ;
<br />
<br />"
<br />
<br />"
<br />
<br />,.~' .
<br />'.; :.~.
<br />
<br />(~ ~~~.~
<br />:~~>
<br />
<br />,~'<'
<br />WJ;~:
<br />~~/~;)::
<br />
|