Modifications to a One-Dimensional Model of Unsteady Flow in the Colorado Riverthrough the Grand Canyon, Arizona

摘要

Calculations of the downstream progression and evolution of discharge wavesreleased from Glen Canyon Dam on the Colorado River through Grand Canyon have been based on hydraulic geometry derived from measurements made at a maximum discharge of 792 cubic meters per second. Predictions of downstream hydrographs for larger discharges, such as the controlled flood in March-April 1996, which reached a maximum release of 1,270 cubic meters per second, have been based on extrapolations of that hydraulic geometry. Data from the controlled flood have been used to extend the model to higher discharges using a method that differs from that used to determine hydraulic geometry in the original model. Scaling of the momentum equation shows that the wave is well represented by the kinematic-wave equation on the receding limb of the controlled-flood hydrograph. This procedure has yielded a modified hydraulic geometry for the model of flow in the Colorado River between Glen Canyon Dam and Lake Mead that has been extended to 1,270 cubic meters per second. A numerical method modified for higher rates of change in discharge and the new hydraulic geometry have improved the accuracy of the model for discharges greater than about 800 cubic meters per second.