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<br />001536 <br /> <br />32.5--2 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBODK <br /> <br />Step 2 - Determine bankfull discharge and baseflow for representative gage <br />station. Using either field measurements of discharge or hydraulic geometry <br />relations (or cross-sectional area data) with the stage-discharge curve from <br />the representative gage station, determine the discharge at the bankfull <br />(QB) stage. Using depth ratios, stage, or cross sectional area determine <br />discharge at the baseflow (QLl) stage. (Note: Baseflow stage is the water <br />surface elevation associated with the discharge that just fills the thalweg or <br />Inner berm channel.) <br /> <br />Step 3 - Calculate or measure bankfull discharge for all suitable gage' <br />stations. Using channel width vs. discharge, water stage vs. discharge, or <br />field measurement, calculate or measure bankfull discharge for all suitable <br />gage stations. <br /> <br />Step 4 - Measure bankfull width at the representative station and all suitable <br />gage stations. Procedures for measuring bankfull width are presented in <br />Appendix C. It is imperative that these guidelines be followed in field <br />determinations. Avoid areas such as beaver dams, road encroachments, bedrock <br />or braided reaches, meander benches, debris jams, and other channel <br />modifications or features which limit the channel's ability to adjust. The <br />value used is an average of at least three measurements along uniform stream <br />reaches. <br /> <br />Step 5 - Develop general relation. Using the data from Steps 1 and 4 regress <br />bankfull width against drainage area using watersheds in similar area-weighted <br />elevation zones to develop a relation of the form: <br />WB = f(DA) <br /> <br />where: <br />We = <br />f(DA) = <br /> <br />bankfull active channel width <br />some functional relationship of drainage area <br /> <br />This relation will be developed for as many elevation zones as the user <br />chooses. Alternatively, if the data are not stratified by elevation zones the <br />user may develop a relationship of the form W = f(DA, E} where E = elevation. <br /> <br />Step 6 - Develop general relation. Using the representative and all suitable <br />gage station bankfull width measurements developed in Step 4 and bankfull <br />discharge measurements of Steps 2 and 3, develop a relation which takes the <br />form: <br /> <br />where: <br />QB <br />a,Wg <br /> <br />QB = aWR <br /> <br />= bankfull discharge <br />= bankfull active channel top width <br />= coefficient and exponent <br />