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<br />OOlG99 <br /> <br />36.2--4 <br /> <br />WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK <br /> <br />(al 8eginning at the QB/QB ratio point on the flow-duration curve <br />(ex. 2), a vertical line is extended from the 1.0 ratio level down to <br />intersect the 0.90 ratio level. From this intersect, a horizontal line is <br />extended to intersect the f10w-duration curve. This becomes the first step <br />of the rise-recession flow component. The duration in days of this <br />component is calculated by reading the corresponding percent time increment <br />limits of the step and converting this percent to days. (For example, 1.7a <br />to 2.2a or 0.5a which is equivalent to a duration of 1.82 days.) <br /> <br />(b) Succeeding rise-recession steps and their duration are determined <br />in a similar fashion. (that is, a vertical line is extended from the 0.90 <br />curve intersect point down to intersect with the 0.80 ratio level, then a <br />horizontal line is extended from this point to intersect the flow-duration <br />curve. This becomes the second rise-recession flow step.) <br /> <br />(c) Proceeding in the above manner,. the last flow-duration curve <br />intersect occurs at the QA/QB point on the flow-duration curve. A <br />vertical line from this last f1ow-duration .intersect point is drawn to <br />intersect the percent time scale. <br /> <br />(d) Multiply the calculated durations by 0.5. The product represents <br />the rise-recession durations which will be required. Next, 1 day, <br />representing the recession limb duration, is subtracted from each <br />rise-recession duration having a magnitude equal to or greater than 2 <br />days. The remainder represents the duration for the individual rise step. <br /> <br />c. Basef10w. <br /> <br />A vertical line is drawn from the Qll/QB ratio point to the x-axis. <br />The duration (unadjusted) of the basef10w component is the percent time <br />increment between the last recession step and this time scale intersect <br />point (in this example 26a to 91.5a or 65.5a1. <br /> <br />The QL2/QB ratio point represents an estimate of the flow rate which is <br />used to calculate the amount of basef10w that may occur during the <br />remaining percent time increment (that is, from the QLl/QB intersect <br />pOint to the end of the time scale). This f10wrate and its duration are <br />used to estimate the total volume contained in the basef10w component. <br /> <br />Step 2. Representative Gaged Station Maintenance Flow Estimation Worksheet. <br /> <br />a. Bankfull flow (row labeled QB in ex. 3): <br /> <br />(1) Read the percent time limits (as decimals) of bankfull duration <br />from the f10w-duration curve (ex. 2) and record in column 1. <br /> <br />(2) Calculate the percent time increment (as a decimal) and record in <br />column 2. <br /> <br />) <br />