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<br />OQlo8l <br /> <br />32.8--2 <br /> <br />, <br /> <br />WATER INfORMATION MANAGEMENT SYSTEM HANDSOOK <br /> <br />.1. If using the duration table of daily values summary from <br />United States Department of the Interior (USDI) Geological <br />Survey data sources, divide the cfs values given in the listed <br />table classes by the calculated bankfull discharge (QS) to <br />develop a ratio for each listed flow class. <br /> <br />2. Construct the flow-duration curve (normalized) by <br />plotting the calculated ratio values versus the corresponding <br />percent time value that a given class cfs value is equaled or <br />exceeded. Connect plotted points with a smooth curve. <br /> <br />The shape of a flow-duration curve 1s largely determined by the <br />hydrOlogic and geologic characteristics of the watershed it <br />represents. If the ordinate (y) axis is normalized by an <br />indexing discharge (bankfull), the flow-duration curve may be <br />used to describe the behavior of ungaged watersheds which have <br />similar hydrologic and geOlogic characteristics. This concept <br />is employed in the procedure for the purpose of constructing the <br />channel maintenance flow hydrograph for the ungaged point(s) of <br />quantification. <br /> <br />B. Common Steo 2. Identify Q , Q , Q , and Q ratios <br />and their durations on the no~mal!zedLtlow-dur~tion curve and <br />calculate rise-recession ratios and durations. <br /> <br />1. Bankfull Discharll:e (Q). The ratio value of 1.0 is <br />the point on the y-axis of th~ flow-duration curve which <br />represents bankfull discharge. Extend a horizontal line from <br />this point to its intersection with the flow-duration curve. <br />Extend a vertical line from this intersect down to the x-axis <br />and read the value for the percent of time bankfull discharge is <br />equaled or exceeded. This time increment, converted to days, <br />becomes the duration of bankfull discharge. <br /> <br />2. Mean Annual Dischar~e (Q). Locate along the flow- <br />duration curve the point which r4presents the ratio value of <br />QA/QB (QA is identified from representative station data). <br /> <br />3. Saseflow Discharll:e (QL1)' Locate on the flow-duration <br />curve the point which represents the ratio value of Q /Q <br />..~~~~~1ut:;~~~~~~'f~ed.f:,.ODt-representa ti.'Ve ~tat.ion- data ah~/o~ <br /> <br />4. Lowflow Discharll:e (Q ). <br />curve the point which repres~fits <br />(Ql.,/QS) (QL2 is identified from <br />dan) . <br /> <br />Locate on the flow-duration <br />the lowest ratio value of flow <br />representative station <br /> <br />Note: QL2 represents the flow with the highest exceedance <br />value. <br /> <br />*-FSH 4/89 AMEND 3-* <br />