MAGNITUDE AND FREQUENCY OF FLOODS IN THE UNITED STATES PART 7, LOWER MISSISSIPPI RIVER BASIN by J.L. Patterson Prepared by the U.S. Geological Survey 1964 WATER-SUPPLY PAPER 1681 TABLE OF CONTENTS Abstract Introduction Acknowledgments Description of the area River basins Topography Climate Flood-frequency analysis Records available Records not used in regional analysis Methods Flood frequency at a gaging station Types of flood series Flood-frequency curves Regional flood frequency Mean annual flood Adjustment to base period Test for homogeneity Composite frequency curves Mean annual flood relation Application of flood-frequency data Regional application Special application Mississippi River Limitations PLATES 1. Map showing gaging stations, hydrologic areas, and flood-frequency regions FIGURES 1. Map of conterminous United States 2. Frequency of annual floods 3. Adjustment to ratio to mean annual flood 4. Variation of mean annual flood with contributing drainage area in hydrologic areas 1-10 5. Variation of mean annual flood with contributing drainage area in hydrologic areas 11-16 6. Variation of mean annual flood with contributing drainage area in hydrologic areas 17-22 7. Variation of mean annual flood with contributing drainage area in hydrologic areas 23-27 8. Elevation-adjustment curve 9. Shape adjustment curve 10. Variation of mean annual flood with contributing drainage area on the main stems of Black River, Neosho River, Cypress Creek and Twelvemile Bayou, and North Canadian River 11. Variation of mean annual flood with contributing drainage area on main stems of Big Black River and Homochitto River 12. Relation of selected flood frequencies to drainage area, White River main stem 13. Relation of selected flood frequencies to distances above mouth, Arkansas River main stem 14. Relation of selected flood frequencies to contributing drainage area, Red River main stem 15. Relation of selected flood frequencies to contributing drainage area, Washita River main stem 16. Relation of selected flood frequencies to distance above mouth, Canadian River main stem 17. Relation of selected flood frequencies to contributing drainage area, Ouachita River main stem 18. Relation of selected flood frequencies to contributing drainage area, Yalobusha River main stem 19. Frequency of annual floods, Mississippi River main stem 20. Variation of mean annual flood with distance above Head of Passes, La., Mississippi River TABLES 1. Inventory of data for gaging stations used to define regional flood-frequency relations 2. Maximum stages and discharges at gaging stations not used to define regional flood-frequency relations 3. Peak discharges at miscellaneous sites and unusual floods at short-term gaging stations ABSTRACT This report describes methods by which the magnitude and frequency of expected floods for most streams in the lower Mississippi River basin may be determined. Flood data were used to define flood-frequency curves applicable to the area. Composite frequency curves were drawn showing the relation of mean annual floods to floods having recurrence intervals from 1.2 to 50 years. In some areas, it was found that the slope of the composite frequency curve varies with drainage area. An adjustment curve was defined for use in conjunction with the composite curve for these areas. Other curves express the relation of the mean annual flood to drainage-basin characteristics. By combining data from the composite and mean-annual-flood curves, flood-frequency curves may be drawn for streams in the lower Mississippi River basin not materially affected by the works of man. Neither of the two types of curves just mentioned should be extrapolated beyond the range defined by base data. Frequency curves, described in this report, were based on analysis of flood records collected at gaging stations having 5 or more years of record not materially affected by regulation or diversion. LizardTech's Djvu plug-in is needed to view these reports. CLICK HERE TO VIEW THE ENTIRE REPORT For questions or comments, contact K. Van Wilson.