Potential errors associated with stage-discharge relations for selected streamflow-gaging stations, Maricopa County, Arizona

Potential errors were derived for individual discharge measurements and stage-discharge relations for 17 streamflow-gaging stations in Maricopa County. Information presented primarily consists of stage and discharge data that were used to develop the stage-discharge relations that were in effect for water year 1998. Accuracy of the discharge measurements directly relate to accuracy of the stage-discharge relation developed for each site. Stage-discharge relations generally are developed using direct measurements of stage and discharge, indirect measurements of peak discharge, and theoretical weir and culvert computations. Accuracy of current-meter measurements of discharge (direct measurements) depends on factors such as the number of subsections in the measurement, stability of the channel, changes in flow conditions, and accuracy of the equipment. Accuracy of indirect measurements of peak discharge is determined by the accuracy of discharge coefficients and flow type selected for the computations. The accuracy of indirect peak-discharge computations generally is less than the accuracy associated with current-meter measurements.

Current-meter measurements, indirect measurements of discharge, weir and culvert computations, and step-backwater computations are graphically represented on plots of the stage-discharge relations. Potential errors associated with the discharge measurements at selected sites are depicted as error bars on the plots.

Potential errors derived for discharge measurements at 17 sites range from 5 to 25 percent. Errors generally are greater for measurements of large flows in channels having unstable controls using indirect methods.