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<br />Guide For Approximate Zone A Areas <br /> <br />Developinq BFEs <br /> <br />'S <br />c <br />o <br />(J <br />OJ <br /><n <br /> <br />~ <br />'" <br />D- <br />ID <br />III <br />IJ.. 3600 <br />(J <br />:0 <br />:J <br />2- 2750 <br />Q) <br />Ol <br />~ <br />aI <br />.c <br />(J <br />., <br />o <br />-'" <br />aI <br />Q) <br />D- <br /> <br />Discharge-Drainage Area Curve <br /> <br />10000 <br /> <br /> I I I <br />-- I -+-1- <br />_. I <br /> I , <br /> t i' k <br />- - '-=1=1=1 I .7 <br />- -1- -1-,- lJf I <br />--H~ I <br /> 'I I f , <br /> I I <br /> Ii , <br /> I 1 ill , I i I <br /> I I <br /> I I I , <br /> , I II i i <br /> I I <br /> I I III! I <br />1 8. 10 '12,0 10 <br /> <br />1000 <br /> <br />o <br /> <br />Drainage Area (Square Miles) <br /> <br />Figure 21 - 100-year Discharge Estimates for <br />site A and site B <br /> <br />Reqression Equations <br /> <br />Another methodology that can be used for determining <br />discharges for approximate Zone A areas is the application of <br />the appropriate regression equation found in a U.s. GeOlogical <br />Survey publication (Water Resources Investigation or Open File <br />report) . A list of these publications applicable to each <br />State is in Appendix 4. The U.S. GeOlogical Survey has also <br />released Version 1.1 of the National Flood Frequency Computer <br />Program. The National Flood Frequency Program contains the <br />regression equations for all of the continental United States. <br /> <br />The use of regression equations involves the determination of <br />specific variables for a watershed (drainage area, mean annual <br />precipitation, forest cover, stream slope, etc.). Regression <br />equations are based on actual stream gage data and are usually <br />developed to determine discharges for the 2-year event up to <br />the 100-year event (for purposes of determining the BFE, <br />determine the 100-year discharge). <br /> <br />V-19 <br />