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<br />32.4 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />E. Steo ~. Collect field data at point of quantification on <br />ungaged stream and determine bankfull discharge. Measure <br />channel cross-sectional area and water surface slope at bankfull <br />stage. If this cannot be done while the stream discharge is at <br />bankfull, measure channel cross-sectional area and approximate <br />water surface slope using the bankfull stage indicators <br />described in Section 36.3. From these data calculate discharge <br />at bankfull (QB) stage using the general relation developed in <br />step 4. <br /> <br />As an alternative, the Manning and continuity equations may be <br />employed to calculate bankfull discharge. However, the <br />interpretative difficulties associated with the roughness <br />coefficient required by the Manning equation should be carefully <br />considered before embarking on such a course of action. <br /> <br />F. Steo 6. Proceed to Section 32.8, A. Common Step 1. <br /> <br />~ _ Method B. Use Method B in those situations where gaged <br />sites and all points of quantification can be visited for <br />measurements of bankfull width. <br /> <br />A. Steo 1. <br /> <br />1. Secure the following data from the representative gage <br />station and all suitable gage ~tation records. <br /> <br />a. Channel width vs. discharge or water stage vs. discharge <br />relations. <br /> <br />2. Secure for the representative gage station the <br />following. <br /> <br />a. <br />record. <br />b. <br /> <br />Duration table of daily values summary for the period of <br /> <br />c . <br /> <br />Mean annual discharge. <br />Daily mean hydrograph data for the period of record. <br /> <br />B. Steo 2. Determine bankfull discharge and baseflow for <br />representative gage station. Using either field measurements of <br />discharge or hydraulic geometry relations (or cross-sectional <br />area data) with the stage-discharge curve from the representa- <br />tive gage station; determine the discharge at the bankfull <br />(QR) stage. Us~ng depth ratios, stage, or cross sectional <br />area determine discharge at the baseflow (Q ) stage. (Note: <br />Baseflow stage is the water surface elevati&rt associated with <br />the discharge that just fills the thalweg or inner berm <br />channel.) <br /> <br />*-FSH 4/89 AMEND 3-* <br />