Scientific Investigations Report 2005-5022

Initial-Phase Investigation of Multi-Dimensional Streamflow Simulations in the Colorado River, Moab Valley, Grand County, Utah, 2004

By Terry A. Kenney


A multi-dimensional hydrodynamic model was applied to aid in the assessment of the potential hazard posed to the uranium mill tailings near Moab, Utah, by flooding in the Colorado River as it flows through Moab Valley. Discharge estimates for the 100- and 500-year recurrence interval and for the Probable Maximum Flood (PMF) were evaluated with the model for the existing channel geometry. These discharges also were modeled for three other channel-deepening configurations representing hypothetical scour of the channel at the downstream portal of Moab Valley. Water-surface elevation, velocity distribution, and shear-stress distribution were predicted for each simulation.

The hydrodynamic model was developed from measured channel topography and over-bank topographic data acquired from several sources. A limited calibration of the hydrodynamic model was conducted. The extensive presence of tamarisk or salt cedar in the over-bank regions of the study reach presented challenges for determining roughness coefficients.

Predicted water-surface elevations for the current channel geometry indicated that the toe of the tailings pile would be inundated by about 4 feet by the 100-year discharge and 25 feet by the PMF discharge. A small area at the toe of the tailings pile was characterized by velocities of about 1 to 2 feet per second for the 100-year discharge. Predicted velocities near the toe for the PMF discharge increased to between 2 and 4 feet per second over a somewhat larger area. The manner to which velocities progress from the 100-year discharge to the PMF discharge in the area of the tailings pile indicates that the tailings pile obstructs the over-bank flow of flood discharges. The predicted path of flow for all simulations along the existing Colorado River channel indicates that the current distribution of tamarisk in the over-bank region affects how flood-flow velocities are spatially distributed. Shear-stress distributions were predicted throughout the study reach for each discharge and channel geometry examined. Material transport was evaluated by applying these shear-stress values to empirically determined critical shear-stress values for grain sizes ranging from very fine sands to very coarse gravels.




Purpose and Scope

Description of Study Reach

Flood-Frequency Analysis

Model Development

Data Acquisition Methods

Topographic Data

Hypothetical Channel Geometries

Model Boundary Conditions

Model Calibration

Over-Bank Drag Coefficient

Model Limitations

Simulation Results

Water-Surface Elevation

Water-Surface Elevation for Existing Channel Geometry

Water-Surface Elevation for Hypothetical Channel Geometries

Velocity Distribution

Velocity Distribution for Existing Channel Geometry

Velocity Distribution for Hypothetical Channel Geometries

Shear-Stress Distribution

Shear-Stress Distribution for Existing Channel Geometry

Shear-Stress Distribution for Hypothetical Channel Geometries

Future Work


References Cited

This report is contained in the following file:

SIR2005_5022 (23 mb)

Send questions or comments about this report to the author, Terry A. Kenney ( 801.908.5046.

For more information about USGS activities in Utah, visit the USGS Utah District home page.

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