Surface-water quality and flow Modeling Interest Group
USGS, Water Resources Division
230 Collins Road
Boise, ID 83702-4520
Internet: ceberenb@usgs.gov
Phone: (208) 387-1303
Fax: (208) 387-1372
The U.S. Geological Survey has made indirect measurements to estimate peak discharge in streams for many decades. The slope-area method is the most commonly used indirect discharge measurement procedure. A new icon-driven procedure was developed to produce slope-area plots and slope-area computation (SAC) program input files using a portable computer in the field. The procedure requires a total station for surveying and recording field data, a 386 or higher portable computer with 4 or more megabytes of random access memory, the Quattro Pro 6 for Windows1 spreadsheet program, and the SAC computer program.
The slope-area method requires location and elevation of high-water marks and channel cross sections and identification and selection of roughness coefficients within a stream reach. Traditionally, high-water marks and cross sections have been surveyed using an automatic level, and the data have been recorded manually on field notesheets. These data subsequently were plotted onsite using a portable drafting table. If evaluation of the plots indicated a need to improve the definition of the geometry in the reach, additional high-water marks and (or) cross sections were surveyed and plots modified. These data were used to compute the discharge estimate in the office using a mainframe computer. These procedures were cumbersome and time consuming. Frequently, the important step of plotting the data in the field was not done because of insufficient time. Neglecting this step often resulted in poorly chosen locations for cross sections, which adversely affected the overall quality of the discharge estimate.
A new procedure permits automated data plotting and field computation of the discharge estimate. An electronic total station is used to survey and record data in the field. Each surveyed point is labeled with a specific prefix. For example, the label "X2-10" describes the tenth surveyed point of the second cross section. Data can be downloaded into a Quattro Pro 6 for Windows spreadsheet at any time as the survey progresses. Plan-view and cross-section plots can be created and viewed on the computer monitor at any time by selecting predefined icons on the menu bar. Once the field crew is satisfied that the geometry is adequately defined, selection of another icon generates a SAC input file that can be saved in ASCII format. The input file is used with the SAC computer program to calculate the discharge estimate in the DOS environment. Total time required to download data from the total station to the spreadsheet, create plots, and compute discharge is much less than traditionally required to plot data and compute discharge estimates. Because high-water marks and cross sections can be readily incorporated at any time, this procedure can improve the overall quality of the discharge estimate. The procedure would benefit from the use of a portable printer, but such a printer is not essential.
1Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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