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<br />00lGJ4 <br /> <br />36.1--6 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />4. Watershed area and area-weighted mean elevation are the watershed <br />characteristics which best correlate with bankfull stage channel top width. <br /> <br />5. If unavailable in gage station records, bankfull stage channel <br />top width is to be the average of measurements of no less than 3 points at <br />gage stations utilizing bankfull indicators. and the surveyor's level and <br />stadia technique. <br /> <br />6. Ungaged basin characteristics are to be developed from standard <br />USGS 7 1/2 minute (1:24000) quadrangles; <br /> <br />7. Bankfull discharge is calculated through the use of the station <br />stage-discharge relation and the extrapolation of bankfull discharge <br />stage, defined at an uncontrolled section, to the station staff gage. <br /> <br />Following is the stepwise analysis: <br /> <br />Step 1 - The needed data are found in exhibit 1. <br /> <br />Step 2 - Using station records for the representative station(s) and/or <br />field measurements, bankfull and baseflow discharges are determined. The <br />results of this step are: <br />QB . 173 cfs <br />QLl = 5.0 cfs <br /> <br />Step 3 - Using the methods described in Appendix C, three bankfull width <br />(WB) measurements are made and averaged at the representative and all <br />suitable stations. <br /> <br />Step 4 - Using maps and/or photos, watershed area, area-weighted mean <br />elevation, or other watershed characteristics variables are measured for <br />the point(s) of quantification (ex. 1). <br /> <br />Step 5 - Using the station data for the representative and all suitable <br />stations and the data resulting from step 3, the following functional <br />relation is developed: <br /> <br />WB = 227.8DAO.52E-l.89 <br /> <br />Step 6 - For all suitable stations bankfull discharge is measured or <br />calculated using measured channel cross-section area, stage or width and <br />station records (as in step 2). <br /> <br />Step 7 - Using the bankfull width values measured in step 3 and the Q~ <br />values calculated in steps 2 and 6 the following regression equation lS <br />developed: <br /> <br />QB = 6.53W~.07 <br />