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Water Science and Applications



  • Paleohydrology
  • Floods

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  • 1821 Hydrology: Floods



Robust determination of stage and discharge: An example from an extreme flood on the Verde River, Arizona

R. P. Denlinger, D. R. H. O'Connell, and P. K. House

Depth-averaged models can simulate nearly all aspects of three-dimensional flow in rivers, yet are more efficiently applied to large areas. The assumption that fluid pressure is hydrostatic is found to provide a good approximation for shallow water flow over complex three-dimensional terrain. Here we compare depth-averaged flow simulations with data from two large floods that occurred on the Verde River, Arizona, in January and February, 1993. Using a combination of photogrammetric and geodetic data, we construct a 6 km by 3 km grid of a reach of the river that contains a USGS stream gage and a narrow bedrock constriction. Elevation accuracy is 0.05 m and grid accuracy is 0.2 m. In the study area the channel is bedrock-controlled and forms a right-angle bend followed by a constriction at Sheep Bridge. Water dammed by this constriction during the 1993 floods created a 3 m drop in water-surface elevation over a distance of 50 m. High velocities generated by this drop scoured the channel and built a large bar of boulders and cobbles that stretched across the channel 150 m downstream. Indicators of minimum water surface elevation, including mudlines, debris stranded on hillsides, and grass wrapped around trees were mapped at 45 sites along the channel. Discharge was monitored through a spillway at Horseshoe Dam, 15 km down-stream of the bridge, during the larger January flood, and stage and velocity were measured at the USGS Tangle Creek gage during the smaller February flood. High-water indicators near the gage are 0.07 m lower than the peak stage measured at the gage in January 1993. Peak stage and peak velocities exceeding 6 m/s lasted 4 hours during the January flood, justifying the use of a steady-flow model for the 6 km long reach. The flow simulations for a discharge of 3398 m3/s (120,000 ft3/s) and a Manning's n value of 0.038 agree closely with direct velocity and stage measurements at the gage, a direct measurement of discharge through the spillway, and with the distribution of high-water marks along the channel. Other combinations of discharge and Manning's n result in larger residual errors in model fits to high-water indicators, and cannot fit both the high water marks and the observed combination of stage and peak velocity at the Tangle Creek gage for the 1993 floods. Thus discharge and bed roughness are uniquely constrained using profiles of maximum inundation along the channel margins extending upstream and downstream from the constriction. The inclusion of surface velocity measurements is not required, but improves resolution and statistical confidence in peak discharge estimates.

Citation: Denlinger, R. P., D. R. H. O'Connell, and P. K. House (2002), Robust determination of stage and discharge: An example from an extreme flood on the Verde River, Arizona, in Ancient Floods, Modern Hazards: Principles and Applications of Paleoflood Hydrology, Water Sci. Appl., vol. 5, edited by P. K. House et al., pp. 127–146, AGU, Washington, D. C., doi:10.1029/WS005p0127.

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