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<br />the Grand Canyon reach is less than is commonly
<br />found in other rivers.
<br />a The data fit a simple one-dimensional mixing
<br />model, without modifications to account for dead
<br />zones, better than data for many rivers for which
<br />measurements are available.
<br />a The absence of tails on the time-concentration
<br />curves show8 that retention time of water in eddies is
<br />very short - the eddies do not act as dead zones at the
<br />measured flows.
<br />a Differences from subreach to subreach in large-
<br />scale channel geometry and slope have a relatively
<br />small effect on flow velocity and longitudinal disper-
<br />sion.
<br />a Unsteadiness of flow affects the velocity through
<br />individual subreaches, but velocity over the entire
<br />380-kilometer Grand Canyon reach is not significant-
<br />ly different at steady and unsteady flow. Unsteadi-
<br />ness of flow does not appear to affect the rate of
<br />longitudinal dispersion significantly.
<br />a Greater longitudinal dispersion at low flow in
<br />the Glen Canyon reach may be caused by a change in
<br />the effective channel geometry. Similar channel-
<br />geometry changes probably also cause greater disper-
<br />sion at low flows than at high flows in at least some of
<br />the individual subreaches in the Grand Canyon reach.
<br />a One-dimensional unsteady-flow and solute-
<br />transport models calibrated with data from research
<br />flow periods provide a good fit with observed data and
<br />can be used to make predictions about solute trans-
<br />port.
<br />
<br />ACKNOWLEDGMENTS
<br />
<br />The study was done in rooperation with the Bureau ofReclama-
<br />tion and funding was provided through the Glen Canyon Environ-
<br />mental Studies. OARS, Inc" Angels Camp, California, provided
<br />logistical support for the field measurements - Mike Walker coordi-
<br />nated the support effort; Randy Fabres and Tim Deutschlander
<br />were the boatmen during the Grand Canyon measurements; and
<br />Denise Hogan, K.C, Deutschlander, and Monte Becker provided
<br />meals and other logistic support. Hatch Expeditions, Marble
<br />Canyon, Arizona, provided a raft Bnd boatman used for one dye
<br />injection in the Grand Canyon reach, Bernice Cobb and Dan
<br />LUDBford volunteered their time to help in the sampling. These
<br />measurements could not have been made successfully without the
<br />enthusiastic participation of these and the U.S. Geological Survey
<br />crew members. James F. Wilson, Jr. and Hjalmar W. Hjalmarson,
<br />U.S. Geological SUlVey, and Prof. Zdzi,law Mikulski and Dr. Arlur
<br />Magnuszewski, Warsaw University, reviewed the report. and made
<br />suggestions that improved it.
<br />
<br />WATER RESOURCES BULLETIN
<br />
<br />Graf
<br />
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