measerr(1) U.S. Geological Survey (wrdapp) measerr(1) NAME measerr - A program for determination of error in individual discharge measurements ABSTRACT The uncertainty, or standard error, for individual measurements of stream discharge is computed based on a root-mean-square error analysis of the individual component errors. The component errors include errors in the measurement of width, depth, and velocity, and in computation procedures. The error in measurement of velocity include the uncertainties introduced by the measurement instrument, the pulsation of flow in natural rivers, the vertical distribution of measurements, and oblique flow. This error analysis can be used to evaluate the uncertainty for most discharge measurements made with the vertical axis, cup-type current meter. The procedures do not apply to other types of current meters or other methods such as dilution gaging or ultrasonic methods. A USGS study indicates that standard errors for individual discharge measurements can range from about 2 percent under ideal conditions to about 20 percent when conditions are poor and shortcut methods are used. Some conditions, such as wind, ice, boundary effects, flow obstructions, improper equipment, as well as incorrect measuring procedures and carelessness, can result in larger errors than indicated by the error analysis. METHOD The standard errors computed are at the 68 percent level of significance (one standard deviation from the true value). That is, 68 percent of the measurements made under similar conditions are expected to differ from the true value by less than one standard error. The MEASERR program computes an estimate of the standard error by computing the standard error of the individual error components, and then combining these errors in a root-mean-square error analysis to compute the overall standard error of the current- meter discharge measurement. HISTORY Version 2.5 1994/04/19 - code clean-up and minor bug fixes Release V930501 - version for use on DOS-based and the Data General AViiON computers Release B91.1.0, 6/91, author David Yancey, designed by Robert W. Meyer, for Prime minicomputers, language: Fortran 77 DATA REQUIREMENTS The program prompts the user for all necessary input and alerts the user to acceptable ranges of input data. The required input data include: 8- or 15- digit station identifier, optional textual description of the measurement station, the measurement number, the channel width, the cross-sectional area, the measured mean velocity, the current-meter type, if horizontal flow were present, the average observation time, the number of verticals measured, the number of points measured in the vertical, the measurement type (waded, 7 Jul 1998 1 measerr(1) U.S. Geological Survey (wrdapp) measerr(1) suspended, or acoustic), and the channel-bed type. MEASERR can also retrieve input from discharge-measurement data from a WATSTORE OUTWAT retrieval. Required data not in the OUTWAT retrieval are prompted for. Input data are expected in the U.S. customary units. OUTPUT OPTIONS The program displays the computed standard error and stores the results in a text file. This file contains a summary of the input data, computed standard error, and corresponding qualitative rating (excellent, good, fair, or poor) for each discharge measurement. SYSTEM REQUIREMENTS MEASERR is written in Fortran 77 with the following extensions: use of integer*2 declarations and use of adjustable size concatenation of strings. MEASERR uses ANSI escape sequence to position text on the screen and thus requires terminal emulation that supports these escape sequences (for example, VT100 on UNIX-based systems and ANSY.SYS loaded for DOS-based systems). Generally, the program is easily installed on most computer systems. The code has been used on UNIX-based computers and DOS-based 386 or greater computers having a math coprocessor and 1 mb of memory. DOCUMENTATION Sauer, V.B., and Meyer, R.W., 1992, Determination of error in individual discharge measurements: U.S. Geological Survey Open- File Report 92-144, 21 p. REFERENCES Pelletier, P.M., 1988, Uncertainties in the single determination of river discharge: a literature review: Canadian Journal of Civil Engineering, v. 15, no. 5, p. 834-850. TRAINING Used in surface-water field and records techniques courses taught at the regional level. CONTACTS Operation and Distribution: U.S. Geological Survey Hydrologic Analysis Software Support Program 437 National Center Reston, VA 20192 h2osoft@usgs.gov Official versions of U.S. Geological Survey water-resources analysis software are available for electronic retrieval via the World Wide Web (WWW) at: http://water.usgs.gov/software/ and via anonymous File Transfer Protocol (FTP) from: water.usgs.gov (path: /pub/software). 7 Jul 1998 2 measerr(1) U.S. Geological Survey (wrdapp) measerr(1) The WWW page and anonymous FTP directory from which the MEASERR software can be retrieved are, respectively: http://water.usgs.gov/software/measerr.html --and-- /pub/software/surface_water/measerr If you would like to obtain the price of and (or) order paper copies of USGS reports, contact the USGS Branch of Information Services at: U.S. Geological Survey Branch of Information Services Denver Federal Center, Box 25286 Denver CO 80225-0286 To inquire about Open-File Reports or Water-Resources Investigations Reports: Tel: 303-202-4210; Fax 303-202-4695 To inquire about other USGS reports: Tel: 303-202-4700; Fax 303-202-4693 7 Jul 1998 3