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<br />bed configuration in the transitIOn zone. A <br />discontinuity in stage-discharge relations may occur at <br />the transition between lower-regime and upper-regime <br />flow (Culbertson and Dawdy, 1964). <br />In upper,regime flow, the bed may have a plane <br />surface or it may have long smooth sand formations in <br />phase with the surface waves (Leopold and others, <br />1964, and Karim, 1995). These waves are known as <br />standing waves or antidunes where, during upper, <br />regime flow conditions, roughness can be much larger <br />than for plane,bed conditions (Simons and Richardson, <br />1966). As the size of the antidunes grow, the water, <br />surface slope on the upstream side of the waves <br />becomes steeper, and the antidune may eventually <br />collapse, Following collapse of antidunes, the flow <br />generally will shift back to plane,bed conditions, If the <br />anti dunes do not collapse, however, resistance to flow <br />can be about the same as for plane,bed conditions. <br />When antidune formation occurs in upper-regime flow <br />and the water and bed surfaces are in phase, the flow is <br />rapid or supercritical (Froude number> I; Simons and <br />Richardson, 1966, p, J9). <br />On the basis of criteria presented by Simons and <br />Richardson (1966) and Benson and Dalrymple (1967), <br />upper,regime flow conditions were exhibited for all <br />verification measurements that were made in sand, <br />dominated streams (sites 6 and 12, fig. I). In addition <br />to the uncertainties associated with changing boundary <br />conditions for sand channels, the possibility of <br />intermittent antidune formation and subsequent <br />collapse of the antidunes could result in intermittent <br />surging of the water surface along the banks of the <br />channeL The surges may result in super elevation of <br />high, water marks that normally are surveyed when the <br />flow subsides, This phenomenon occurred on March 6, <br />1995, about 1,000 ft upstream from the USGS <br />streamflow'gaging station at Hassayampa River near <br />Morristown, Discharge was about 9,000 ft3/s, and the <br />authors witnessed trains of large antidunes (about 6 ft <br />from trough to crest) that were forming and collapsing <br />at regular intervals, The collapse resulted in a surge of <br />the water surface along the channel banks of more than <br />I ft in elevation, Following collapse of the anti dunes, <br />the flow would return to plane, bed conditions until <br />another train of antidunes formed. <br />Intermittent surging of the water surface causing <br />super elevation of the high, water marks along the <br />channel banks complicates the task of obtaining <br />accurate and representative water-surface elevations <br />for n,verification measurements made in sand <br /> <br />channels, and may introduce errors into the hydraulic <br />computations, The accuracy of the verification <br />measurements that were made in sand channels, <br />therefore, was qualified according to the potential <br />amount of error resulting from difficulties in obtaining <br />accurate water,surface elevations and channel, <br />boundary configuration. <br /> <br />PRESENTATION OF VERIFIED <br />ROUGHNESS COEFFICIENTS <br /> <br />A total of 37 verified n values are presented for <br />discharge measurements at 14 separate stream <br />locations in Arizona. Data for 4 of the 14 sites are from <br />Aldridge and Garrett (1973), and data for Salt River <br />below Stewart Mountain Dam is from Barnes (1967). <br />General information is presented on the location of the <br />site, drainage area of the stream, date and discharge of <br />each measurement, computed roughness coefficients <br />for the reach, median size of bed material (if available), <br />concentration of suspended sediment (if available), and <br />a general description of the channeL Tabulated data <br />presented are from field surveys and hydraulic <br />computations. These data include average values for <br />area, top width, hydraulic radius, mean velocity, and <br />Froude numbers, The total reach length and fall in <br />water surface also are included, Plan,view sketches are <br />presented to show the location of the cross sections and <br />general shape of the channeL A representative cross <br />section is illustrated with water, surface elevations <br />shown for each flow. Information for two or more <br />discharges is available for most sites to show changes <br />in roughness with depth, The changes are demonstrated <br />by plots of Manning's n and hydraulic radius, The <br />assumption is made that hydraulic radius closely <br />approximates mean flow depth for each of the sites. <br />Color photographs are presented for each study reach <br />to be used as a comparison standard to aid transfer of <br />results to sites with similar channel and hydraulic <br />characteristics. Selected photographs also show flow <br />conditions at the time of the measurement The average <br />water level correspouding to the measured flow is <br />indicated in certain photographs by a horizontal rod, <br />The frame of the square grid (painted orange) in several <br />photographs has an outside dimension of 1.5 ft and an <br />internal grid spacing of I in, <br /> <br />10 Verification of Roughness Coefficients for Selected Natural and Constructed Stream Channels in Arizona <br />