<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
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