Calibration of Walnut Gulch Supercritical Flumes

A new supercritical measuring flume is being used to gage sediment-laden ephemeral flows in steep channels. The transition from the natural channel to the straight modified trapezoidal measuring section of the flume consists of a cylindroid surface. The flume is kept free of deposition by a V-shaped floor which slopes in the direction of the flow. The head is measured at the midpoint of the straight section. Ten of these concrete flumes have been installed in the Walnut Gulch Watershed near Tombstone, Arizona. Eight of the flumes have already been calibrated with models in the laboratory. The largest has a bottom width of 120 ft and a capacity of about 26,000 cfs. This structure is the largest known pre-calibrated flume now in operation. The design of the flumes, the laboratory calibration data and some observations of their field operation are analyzed.