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32.8--3 WATER INFORMATION MANAGEMENT SYSTEM HANDBOOK 5. ~~~ssion~~: For ease of construction, to approximately mimic the natural hydrograph, and to reasonably construct the rise and recession segments of the channel mainte- nance flow hydrograph, this common step incorporates the follow~ng assumptions. a. Most sediment transport will occur during the period of flow which begins with the occurrence of mean annual discharge and continues through bankfull discharge. b. Sediment transport will be' provided for in the channel maintenance flow hydrograph if the constructed hydrograph includes bankfull discharge and one-half of the calculated rise-recession flow with most of this flow being distributed to the rising segment of the constructed hydrograph. c. A recession segment composed of a series of single day decrements in flow will generally prevent adverse streambank effects from rapid drawdown. If local data and professional judgement indicate the need, the hydrologist should modify this step to make allowance for situations which do not fit the above assumptions. Considering the segment of the flow-duration curve between the bankfull discharge (QB/QB) ratio point QA/QR ratio point (ex. 2), locate graphically the r~sing-recession flow steps as follows. that lies and the (1) Beginning at the Q /Q ratio point on the flow- duration curve, extend a ve~ti~al line down to intersect the 0.90 catio level. From this intersection, extend a horizontal line to intersect the flow-duration curve. This becomes the first step of the rise-recession flow component. The duration of this component is determined by converting to days and subtracting the percent time increment limits, in days, of the step (that is, the difference between the bankfull discharge time increment and the 0.90 flow-duration curve intersection point time increment). ___=___u___J2t~:~uc-c-eedin_g--rise-rece-ss~on steps,frid their durations are u"_, u.-uu---determined in If'similar fashion. For example, extend a vertical line from the 0.90 curve intersection point down to intersect . the 0.80 ratio lev~l, then extend a line horizontally to intersect the flow-duration curve. This becomes the second rise-recession flow step. (3) Proceed in the above manner, using 0.1 decrements in the y-axis ratio levels, until a decrement value falls below the QA/QB ratio. At the QA/QB ratio extend a horizontal *-FSH 4/89 AMEND 3-*