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San Pedro River near Charleston The bed material is mainly hard conglomerate overlain by deposits that range from sand to angular and rounded boulders 2 to 3 ft (610 to 920 mm) in diameter. The material surrounding the boulders has a median grain size of 1.2 mm (fig. 14C). At the upper end of the reach, conglomerate projections are exposed across the entire channel. The projections are several feet across, and many stand 2 to 3 ft (610 to 920 mm) above the average bed level. Grass and small brush grow along bars at the channel sides. The stream is perennial, and flow is umegulated. Two other channel reaches also were used to verify roughness coefficients for this same discharge measmement. These reaches were in sections of the stream where the bed was primarily composed of sand-sized material and was considered highly unstable. Owing to the uncertainty of charmel geometry during peak flow (D.E. Click, hydrologist, U.S. Geological Survey, written commun., 1964), these reaches were not included in this report. Table 21. Flow data and computed roughness coefficient, San Pedro River near Charleston Reach location: Drainal!e area: Bed-material size: Channel descriution: Remarks: Latitude 31"37'33", longitude 110010'26". Reach is just downstream from streamflow-gaging station 09471000, San Pedro River near Charleston (Aldridge and Garrett, 1973). 1,234 mil. See channel description. Date of flow Roughness coefficient 08-t4-64 Discharge, in cubic feet per second Rating Fair 7,550 0.048 Table 22. Average-reach properties, San Pedro River near Charleston l Date Area, in square feet Top width, Hydraulic Mean velocity, in in feet radius, in feet feet per second Froude Total length, Total fall, Water-surface number in feet in feet slope 08-14-64 t,268 276 4.62 0.44 0.0048 293 1.42 5.9 San Pedro River near Charleston 55