FIGURE LIST OF ILLUSTRATIONS 1 Pressure and temperature at various altitudes.. 2 Radius of curvature... 3 Motion on the earth.. 4 Motion in a plane tangent to the earth. 5 Normal annual rainfall, eastern United States. 6 Excessive precipitation data, sample form. . 7 Number of stations used in studying excessive precipitation. 8 Periods of record of stations in quadrangles 3-D and 4-C.. 9 Periods of record of stations in quadrangles 9-E, 9-F, and 10-E. 10 Periods of record of stations in quadrangles 12-B, 12-C, 12-D, and 12-E. 11 Periods of record of stations in quadrangles 12–F, 12–G, 12–H, and 12–I. 12 Periods of record of stations in quadrangles 12-J, 15-E, 15-G, and 15–J. 13 Isopluvial chart for 15-year period and 1-day rainfall. 14 Isopluvial chart for 15-year period and 2-day rainfall. 15 Isopluvial chart for 15-year period and 3-day rainfall . 16 Isopluvial chart for 15-year period and 4-day rainfall . 17 Isopluvial chart for 15-year period and 5-day rainfall. 18 Isopluvial chart for 15-year period and 6-day rainfall. 19 Isopluvial chart for 25-year period and 1-day rainfall. 20 Isopluvial chart for 25-year period and 2-day rainfall. 21 Isopluvial chart for 25-year period and 3-day rainfall. 22 Isopluvial chart for 25-year period and 4-day rainfall. 23 Isopluvial chart for 25-year period and 5-day rainfall. 24 Isopluvial chart for 25-year period and 6-day rainfall. 25 Isopluvial chart for 50-year period and 1-day rainfall. 26 Isopluvial chart for 50-year period and 2-day rainfall. 27 Isopluvial chart for 50-year period and 3-day rainfall. 28 Isopluvial chart for 50-year period and 4-day rainfall. 29 Isopluvial chart for 50-year period and 5-day rainfall. 30 Isopluvial chart for 50-year period and 6-day rainfall. 31 Isopluvial chart for 100-year period and 1-day rainfall. 32 Isopluvial chart for 100-year period and 2-day rainfall. 33 Isopluvial chart for 100-year period and 3-day rainfall. 34 Isopluvial chart for 100-year period and 4-day rainfall. 35 Isopluvial chart for 100-year period and 5-day rainfall . 36 Isopluvial chart for 100-year period and 6-day rainfall. 37 Aggregate years of record in each quadrangle..... 38 Maximum 1-day rainfall recorded in each quadrangle. 39 Maximum 2-day rainfall recorded in each quadrangle.. 40 Maximum 3-day rainfall recorded in each quadrangle. 41 Maximum 4-day rainfall recorded in each quadrangle. 42 Maximum 5-day rainfall recorded in each quadrangle.. 43 Maximum 6-day rainfall recorded in each quadrangle. 44 Frequency of excessive precipitation in quadrangle 3-D. 45 Frequency of excessive precipitation in quadrangle 9-E. PAGE 37 41 44 45 51 67 69 72 73 74 75 76 86 86 87 87 88 88 89 89 90 90 91 91 92 92 93 93 94 94 95 95 96 96 97 97 98 103 103 104 104 105 105 107 107 46 Frequency of excessive precipitation in quadrangle 12-J.. 47 Frequency of excessive precipitation in quadrangle 15-E. 48 The 160 great storms arranged in order of size. 108 108 .Facing 116 49 The 160 great storms arranged by season of occurrence. Facing 118 120 124 55 Great storms over southern states during February, March, and April... 125 56 Great storms over southern states during May, June, and July. . . . . 126 57 Great storms over southern states during August, September, and October 127 58 Rainfall map for maximum day, storms of December 1895, March 1897, and April 1900.... 51 Great storms over northern states during February, March, and April... 121 52 Great storms over northern states during May, June, and July. . . . . 122 53 Great storms over northern states during August, September, and October 123 54 Great storms over southern states during November, December, and January.. 134 59 Rainfall map for maximum 2 days, storms of October 1869, December 1895, March 1897, and April 1900.... 135 60 Rainfall map for maximum 3 days, storms of December 1895 and April 1900..... 136 61 Rainfall map for maximum 4 days, storm of December 1895.. 62 Rainfall map for maximum day, storms of July 1887, May 1894, June 1899, and September 1905...... 137 139 63 Rainfall map for maximum 2 days, storms of July 1887, May 1894, June 1899, and September 1905. ... 64 Rainfall map for maximum 3 days, storms of July 1887, May 1894, June 1899, and September 1905... 140 ... 141 65 Rainfall map for maximum 4 days, storms of July 1887, May 1894, June 1899, and September 1905... 142 66 Rainfall map for maximum 5 days, storms of July 1887, May 1894, June 1899, and September 1905.... 143 67 Rainfall map for maximum day, storms of September 1894, March 1902, August 1903, and October 1903. 146 68 Rainfall map for maximum 2 days, storms of September 1894, March 1902, August 1903, and October 1903.. 147 69 Rainfall map for maximum 3 days, storms of September 1894, March 1902, and August 1903.... 148 70 Rainfall map for maximum 4 days, storms of March 1902 and August 1903 149 71 Rainfall map for maximum day, storms of May 1889, July 1897, July 1900, and November 1906... 152 72 Rainfall map for maximum 2 days, storms of May 1889, July 1897, July 1900, and November 1906.. 153 73 Rainfall map for maximum 3 days, storms of July 1897, July 1900, and November 1906....... 154 74 Rainfall map for maximum 4 days, storm of November 1906. 75 Rainfall map for maximum 5 days, storm of November 1906. 155 156 76 Rainfall map for maximum day, storms of June 1905, July 1908, August 1908, October 1908, June 1909, and October 1910.... 158 77 Rainfall map for maximum 2 days, storms of July 1908, August 1908, October 1908, June 1909, and October 1910..... 159 78 Rainfall map for maximum 3 days, storms of July 1908, August 1908, October 1908, June 1909, and October 1910.... 160 79 Rainfall map for maximum 4 days, storms of July 1908, October 1908, and June 1909...... 161 80 Rainfall map for maximum days, storms of July 1908, October 1908, and June 1909.... 162 81 Rainfall map for maximum day, storms of July 5-7, 1909, July 20-22, 1909, January 1913, October 1913, and October 1914.. 82 Rainfall map for maximum 2 days, storms of July 5–7, 1909, July 20-22, 1909, January 1913, October 1913, and October 1914.. 83 Rainfall map for maximum 3 days, storms of July 5–7, 1909, July 20–22, 1909, and January 1913. . . . . 165 166 167 84 Rainfall map for maximum day, storms of March 1913, December 1913, and July 14-16, 1916... 170 85 Rainfall map for maximum 2 days, storms of March 1913, December 1913, and July 14-16, 1916.. 171 86 Rainfall map for maximum 3 days, storms of March 1913, December 1913, and July 14-16, 1916. . . . . 172 87 Rainfall map for maximum 4 days, storms of March 1913 and December 1913, and for 1 day (July 16), storm of July 14–16, 1916. . 88 Rainfall map for maximum 5 days, storm of March 1913.. 173 174 89 Rainfall map for maximum day, storms of August 1915 and July 6–10, 1916..... 175 90 Rainfall map for maximum 2 days, storms of August 1915 and July 6–10, 1916..... 176 91 Rainfall map for maximum 3 days, storms of August 1915 and July 6-10, 1916.... 92 Rainfall map for maximum 4 days, storms of August 1915 and July 6-10, 1916...... 177 179 93 Rainfall map for maximum 5 days, storms of July 1912 and July 6–10, 1916 180 94 Time-area-depth curves for storms over northern states, 1-day period.... 182 95 Time-area-depth curves for storms over northern states, 2-day period.... 184 96 Time-area-depth curves for storms over northern states, 3-day period.... 186 97 Time-area-depth curves for storms over northern states, 4-day period.... 188 98 Time-area-depth curves for storms over northern states, 5-day period.... 190 99 Time-area-depth curves for storms over southern states, 1-day period.... 192 100 Time-area-depth curves for storms over southern states, 2-day period.... 194 101 Time-area-depth curves for storms over southern states, 3-day period.... 196 102 Time-area-depth curves for storms over southern states, 4-day period.... 198 103 Time-area-depth curves for storms over southern states, 5-day period.... 200 104 Form showing method of compiling storm data.. 105 Map illustrating method of platting storms. 106 Time-area-depth curves for storm of July 14–17, 1916.. 215 216 227 232 233 236 236 237 237 .Facing 238 245 107 Monthly and annual rainfall over eastern United States, 1888-1916. 108 Monthly and annual rainfall over 5 interior states, 1888-1916.. 109 Maximum departures of monthly rainfall, eastern United States. 110 Maximum departures of annual rainfall, eastern United States. 111 Maximum departure of monthly rainfall, 5 interior states.. 112 Maximum departure of annual rainfall, 5 interior states. 113 Chronological distribution of 160 great storms. . . 114 Relation between average greatest annual 24-hour rainfall and mean annual rainfall, Europe. . . . CHAPTER I.-INTRODUCTION ORIGIN OF THIS INVESTIGATION This report sets forth the results of what is probably the most extended study of storm rainfall that has ever been undertaken. When an engineering examination of the Miami Valley was begun, immediately after the subsidence of the great flood of March, 1913, for the purpose of determining the best plan for preventing damage by future floods, an investigation of rainfall and runoff conditions was one of the first lines of attack. Although the 1913 flood seems to have been by far the largest that has occurred in this valley since its first occupation by white settlers a little over 100 years ago, it was soon apparent that the records of daily discharge of the Miami River going back only to 1892, and the local rainfall records of somewhat longer duration, afforded but a poor basis for the determination of the most probable size, frequency, and distribution of future floods. The magnitude of the interests jeopardized by floods justified the use of an elaborate system of protection works if simpler ones could not be devised; and the valley is so densely populated, the areas subject to flood damage so separated and diverse, and the conditions affecting the development of plans so numerous and complicated, that only an extensive and costly system could adequately secure effective regulation. To meet this intricate situation it was necessary to determine not only the largest flood that could ever possibly occur, but also, so far as possible, the frequency of all smaller floods which would cause damage. In default of more extensive hydrological records in the Miami Valley, it seemed necessary to study the records of the whole region of the United States, which is at all similar in its situation with respect to rainfall and runoff conditions. Since runoff records are so scant in comparison with rainfall records in this country, it became evident that chief reliance had to be placed upon the latter alone in determining from past experience what is the most probable future distribution of extreme flood conditions. In beginning this investigation it was uncertain what geographic limits should be set to obtain the largest amount of useful and pertinent data. These limits at first were assumed to include the entire United States, but during the progress of the investigation it became apparent |