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<br />001587 <br /> <br />32.6 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />Step 7 - Calculate drainage area, area-weighted mean elevation or other <br />appropriate variables for regression with bankfull width. For the points <br />of quantification calculate drainage area and area-weighted mean <br />elevation. Other variables may be more appropriate in some areas. If such <br />is the case, measure those variables for both the gage station watersheds <br />and for the watersheds above the points of quantification. <br /> <br />Step 8 - Calculate bankfull discharge (QB) for points of quantification <br />using the data from Step 7 and the relations developed in Steps 5 and 6. <br /> <br />Step 9 - Proceed to Sec. 32.8, Common Step 1. <br /> <br />32.6 - Method D. Use this method in those situations where field visits to <br />gage stations and points of quantification cannot be made. The method <br />utilizes the relationship between bankfull discharge and its recurrence <br />interval. While the method describes the use of a log-Pearson type III <br />1.5 years recurrence interval peak discharge, daily mean discharges and/or <br />a different recurrence interval may be used if more appropriate. <br /> <br />The decision to use daily mean discharges and/or a recurrence interval <br />other than the 1.5 years value should be based on an examination of the <br />representative gage station data. The data set and recurrence interval <br />most nearly approximating the bankfull stage discharge of the <br />representative gage station should be the chosen alternative. <br /> <br />Step 1 <br />a. <br />b. <br /> <br />- Secure the following data from the representative gage <br />Duration table of daily values summary. <br />Mean annual discharge. <br />Daily mean hydrograph data for the period of record. <br /> <br />station: <br /> <br />c. <br /> <br />From the representative and all suitable gage stations secure the following <br />data: <br />d. Drainage area of watershed above gage. <br />e. Area-weighted mean elevation of watershed above gage. <br />f. Other watershed characteristics if appropriate. <br />g. Log-Pearson type III 1.5 years return interval peak flow (daily <br />mean flow and/or other return interval if appropriate). <br />h. Log-Pearson type III 1.5 years return interval, 7-day low flow (or <br />use the locally calculated return interval and duration which best <br />correlates to the flow which fills the inner berm, or thalweg channel). <br /> <br />Step 2 - Develop general relation. Regress the log-Pearson type III <br />1.5 years return interval discharge (QB) against drainage area for the <br />representative and all suitable gage stations using watersheds in similar <br />area-weighted mean elevation zones to develop a relation of the form: <br />QS = f(DA) <br /> <br />where <br />Qe = log-Pearson 1.5 years return interval flow <br />f(OA) = some functional relationship of drainage area <br /> <br />In No. 3 <br />8/28/87 <br />