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OfilG7~ 32.6--1 , WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK where, W f(~A) WB = f(DA) = bankfull active channel width and = some functional relationship of drainage area Develop this relationship for as many elevation zones as chosen. Alternatively, if the data are not stratified by elevation zones, develop a relationship of the following form. W = f(DA, E) where, E = elevation. F. Steo 6. Develop general relation. Using the representative and all suitable gage station bankfull width measurements developed in Step 4 and bankfull discharge measurements of Steps 2 and 3, develop a relation which takes the following form. b QB = aWB bankfull discharge, bankfull active channel top width, coefficient, and exponent. where, QB = W~ = = b = G. Steo 7. Calculate drainage area, area-weighted mean elevation or other appropriate variables for regression with bankfull width. For the points of quantification calculate drainage area and area-weighted mean elevation. Other variables may be more appropriate in some areas. If such is the case, measure those variables for both the gage station watersheds and for the watersheds above the points of quantification. H. Steo 8. Calculate bankfull discharge (Q ) for points of quantification using the data from Step 7 anH the relations developed in Steps 5 and 6. I. ~~. Proceed to Section 32.8, A. Common Step 1. ~~ - Method D. Use this method in those situations where field visits to gage stations and points of quantification cannot be made. This method uses the relationship between bankfull discharge and its recurrence interval. While the method describes the use of a log-Pearson type III 1.5 years recurrence interval peak discharge, daily mean discharges and/or a different recurrence interval may be used if more appropriate. The decision to use daily mean discharges and/or a recurrence interval other than the 1.5 years value should be based on an examination of the representative gage station data. The data *-FSH 4/89 AMEND 3-*