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<br />001584 <br /> <br />32.4 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />where: <br />QB = bankfull discharge <br />AB = channel cross-sectional area at bankfull stage <br />s = water surface slope at bankfull stage <br />k,x,y = constant and exponents. <br /> <br />Step 5 - Collect field data at point Qf quantification on ungaged stream <br />and determine bankfull discharge. Measure channel cross-sectional area and <br />water surface slope at bankfull stage. If this cannot be done while the <br />stream discharge is at bankfull, measure channel cross-sectional area and <br />approximate water surface slope using the bankfull stage indicators <br />described in Appendix C. From these data calculate discharge at bankfull <br />(QS) stage using the general relation developed in step 4. <br /> <br />As an alternative, the Manning and continuity equations may be employed to <br />calculate bankfull discharge. However, the interpretative difficulties <br />associated with the roughness coefficient required by the Manning equation <br />should be carefully considered before embarking on such a course of action. <br /> <br />Step 6 - Proceed to Sec. 32.8 Common Step 1. <br /> <br />32.4 - Method B. Use Method B in those situations where gaged sites and <br />arr-points of quantification can be visited for measurements of bankfull <br />width. <br /> <br />Step 1 - Secure the following data from the representative gage station and <br />all suitable gage station records: <br /> <br />a. Channel width vs. discharge or water stage vs. discharge relations. <br /> <br />Secure for the representative gage station the following: <br /> <br />b. Duration table of daily values summary for the period of record. <br />c. Mean annual discharge. <br />d. Daily mean hydrograph data for the period of record. <br /> <br />Ste~ 2 - Determine bankfull discharge and baseflow for representative gage <br />sta 10n. Using either field measurements of discharge or hydraulic <br />geometry relations (or cross-sectional area data) with the stage-discharge <br />curve from the representative gage station. determine the discharge at the <br />bankfull (QS) stage. Using depth ratios, stage, or cross sectional area <br />determine discharge at the baseflow (QLl) stage. (Note: Baseflow stage <br />is the water surface elevation associated with the discharge that just <br />fills the thalweg or inner berm channel.) <br /> <br />Step 3 - Measure bankfull width at the representative gage station and all <br />suitable gage stations. Procedures for measuring bankfull width are <br />presented in Appendix C. It is imperative that these guidelines be <br />