CEIE 340 FINAL EXAM PACKET

CEIE 340 FINAL EXAM PACKET - Peak-Discharge Estimation...

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1 Water Resource Engineering CEIE 340 Sayedul H. Choudhury, Ph.D. Peak-Discharge Estimation Today’s Topics square6 Introduction square6 Single-Return-Period Equations square6 USGS Urban-Peak-Discharge Formulas square6 Index-Flood Estimation square6 Moment Estimation square6 Rational Method square6 Procedure square6 Runoff Coefficient for Nonhomogeneous Areas square6 Designs on Subdivided Watersheds
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2 Today’s Topics (Cont’d) square6 The Soil Conservation Service (SCS) Rainfall- Runoff Depth Relation square6 Conceptual Model square6 Runoff depth Estimation square6 The SCS Graphical-Peak-Discharge Method square6 The Ia/P Parameter square6 Peak-Discharge Computation square6 Pond-and-Swamp Adjustment square6 Limitations square6 Slope-Area Method of Discharge Estimation square6 Peak-Discharge Envelope Curves square6 Regionalization of Hydrologic Variables Hydrologic Cycle Peak-Discharge
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3 Instances of Peak-Discharge Estimates Single-Return-Period Equation square6 Determines Peak-Discharge for ungaged areas square6 Takes the following form: square6 Use multiple regression analysis after logarithmic transformation square6 Example variables: drainage area, channel slope, channel length, precipitation, drainage density, etc p b p b b b p X X X X b q K 3 2 1 3 2 1 0 =
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4 USGS Regression Equations square6 National Flood Frequency (NFF) Program square6 Link: http://water.usgs.gov/software/nff.html square6 Scientists analyzed gage data to derive a set of equation for each region square6 A State by State list of documents providing the detail of Regional Regression Equations square6 NFF is also a software which implements the Regional Regression Equations NFF Example: Virginia square6 Reference: The National Flood-Frequency Program— Methods for Estimating Flood Magnitude and Frequency in Rural Areas in Virginia, 2000 Q 2 = 179A 0.655 Q 5 = 317A 0.644 Q 10 = 438A 0.641 Q 25 = 626A 0.640 Q 50 = 793A 0.640 Q 100 = 984A 0.641 Q 200 = 1200A 0.643 Q 500 = 1535A 0.646 Northern Piedmont Q 2 = 2.4A 1.005 Sl 0.852 Q 5 = 4.0A 0.999 Sl 0.884 Q 10 = 4.9A 1.005 Sl 0.932 Q 25 = 6.0A 1.016 Sl 0.998 Q 50 = 6.8A 1.024 Sl 1.044 Q 100 = 7.6A 1.033 Sl 1.088 Q 200 = 8.3A 1.042 Sl 1.130 Q 500 = 9.2A 1.055 Sl 1.185 Coastal Plain
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5 USGS Urban-Peak-Discharge Formula Disadvantages of Single- Return-Period Equations square6 A separate equation must be fit for each return period requiring significant work square6 Because of random variation, the fitted coefficients may show irrational variation providing irrational estimates (e.g. a smaller for peak flow estimate for a larger return period when applied to an area different from the calibration site).
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6 Index-Flood Mehtod square6 Avoids the problems with single-return- period equations method square6 Consists of a prediction equation for one return period and a set of multipliers to be used for other return periods q T = k T q i square6 For example, q 2 = 139.8 A 1.049 S 0.5371 F -0.9255 q 10 = 1.994q 2 and q 100 = 4.013q 2 Development of Regression Equations: Moment Estimation square6 Steps: square6 Obtain the annual-maximum flood series for each gage square6 Perform flood-frequency analysis using the data from each gage square6 Compute the mean, standard deviation, and
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