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<br />32.5--2 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />A. Steo 1. <br /> <br />1. Secure the following data from the representative gage <br />station and all suitable gage station records. <br /> <br />a. Channel width vs. discharge or stage vs. discharge <br />relations. <br />b. Drainage area of watershed above gage. <br />c. Area-weighted mean elevation of watershed above gage. <br /> <br />2. Secure for the representative gage station the <br />following. <br /> <br />a. <br />record. <br />b. <br />c. <br /> <br />Duration table of daily values summary for period of <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 />(Q ) stage. Using depth ratios, stage, or cross sectional <br />ar~a determine discharge at the baseflow (Q ) stage. (Note; <br />Baseflow stage is the water surface elevati&J associated with <br />the discharge that just fills the thalweg or inner berm <br />channel.) <br /> <br />C. Step ,. Calculate or measure bankfull discharge for all <br />suitable gage stations. Using channel width vs. discharge, <br />water stage vs. discharge, or field measurement, calculate or <br />measure bankfull discharge for all suitable gage stations. <br /> <br />D. Steo 4. Measure bankfull width at the representatLve <br />station and all suitable gage stations. Procedures for <br />measuring bankfull width are presented in Section 36.3. It is <br />imperative that these guidelines be followed in field determina- <br />tions. Avoid areas such as beaver dams, road encroachments, <br />bedrock or braided reaches, meander benches, debris jams, and <br />other channel modifications or features which limit the <br />channel's ability to adjust. The value used is an average of ~t <br />least three measurements along uniform stream reaches. <br /> <br />E. Step S. Develop general relationship. Using the data from <br />Steps 1 and 4, regress bankfull width against drainage area <br />using watersheds in similar area-weighted elevation zones to <br />develop a relation of the following form. <br /> <br />*-FSH 4/89 AMEND 3-* <br />