The Floods in Central Texas in September, 1921
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DEPARTMENT OF THE INTERIOR ALBERT B. FALL, Secretary UNITED STATES GEOLOGICAL SURVEY GEORGE OTIS SMITH, Director Water-Supply Paper 488 THE FLOODS IN CENTRAL TEXAS IN SEPTEMBER, 1921 BY C. E. ELLSWORTH Prepared in cooperation with THE STATE OF TE?A8 WASHINGTON 0OYERNMENT PRINTING OFFICE 1923 ADDITIONAL COPIES OF THIS PUBLICATION MAT BE PROCURED FKOM ' THE SUPERINTENDENT OF DOCUMENTS GOVEKNMENT PRINTING OFFICE WASHINGTON, D. C. AT 15 CENTS PER COPY PURCHASER AGREES NOT TO RESELL OR DISTRIBUTE 1ES3 COPY FOR PROFIT. P.UB. RES. 67, APPROVED MAT 11, 1923 V CONTENTS. Page. Introduction_________________ 1 Acknowledgments_________________ _ _ ___ _ _ 2 Area covered by the storm__________ _ _ _ 3 General features _ _ _ __ _ _ _ 3 Topography and geology-______ ___ _ _ _ _ _ 3 Damage caused by flood ___ 4 Precipitation ________________, ___________________ 7 Maximum discharge per square mile _ : _ _ 13 Flood flows_________________-__-_ - _ 14 Brazos River flood______________ _ _ _ 14 General features___________________________ 14 Determination of flow ________ ______ _______ 16 Little River and tributaries______________________ 17 General features__________________________ 17 Determination of flow_______________________ 18 Little River below junction .of Leon and Lampasas rivers 19 Little River at Cameron______________________ 20 Salado Creek near Salado________________: 22 San Gabriel River at Georgetown________________ 24 Brushy Creek at Round Rock______________ __ 27 Colorado River flood_______________________________ 29 Guadalupe River flood____________________________ 31 The flood at San Antonio_________________________ 33 General features_____________________________ 33 Determination of discharge_______________ ___ 37 Previous floods__________________________________ 46 General features of flood of 1913______________________ 46 Brazos River_________________________________ 48 Colorado River__________________ __________,___ 49 Guadalupe River- _____________ ____________ 51 San Antonio River _____________________ ______ 53 Index________ _________________ _____________ 55 in IV CONTENTS. ILLUSTRATIONS. Pas* PIATE I. Map of central Texas, showing drainage basins and total rain fall September 7-11, 1921_____________________ 4 II. A., View of Little River valley below junction of Leon and Lampasas rivers; B, View of Little River at Gulf, Colorado & Santa Fe Railway crossing near Cameron, Tex., at crest of flood _________________________________ 20 III. A, View across Little River valley near Cameron, Tex., from Marlow Bridge; J5, View up Salado Creek from Jones mill, near Salado, Tex__________________________ 20 IV. A, View down San Gabriel River valley below Georgetown, Tex.; B, View up Brushy Creek near Round Rock, Tex______ 20 V. A, Bridge across San Antonio Ri3ver near Pioneer Mills after flood of September 9-10, 1921; B, Bridge across San Antonio River at Romana Street, San Antonio, Tex., after flood of September 9-10, 1921____________________^__ 44 VI. A, Water-stage recorder at South Alamo Street, San Antonio, Tex.; B, South Alamo Street Bridge, San Antonio, Tex., after flood of September 9-10, 1921_______________ 44 VII. Map of San Antonio, Tex., showing area flooded, September 9-10, 1921 ______________________________ 44 VIII. A, View of San Antonio River showing slope stretch used in determination of maximum discharge during flood of Sep tember 9-10, 1921; B, View from right bank near center of slope stretch shown in A_________________ _ _ 44 . Map of San Antonio River and tributaries in vicinity of San Antonio, Tex., showing drainage basins and total rainfall, September 8-10, 1921__________________^__.___._ 8 2. Gage-height graph of Little River at Cameron, Tex., during flood of September, 1921___________ _ 21 3. Gage-height graph of San Antonio River and San Pedro Greek at San Antonio Tex., during flood of September 9-10, 1921 40 4. Rating curves of San Antonio River at South Alamo Street Bridge, San Antonio, Tex_______ 42 5. Mean cross section of San Antonio River used in determination of discharge at maximum stage of flood of September 9-10, 1921____________._____________-_ 44 IV THE FLOODS IN CENTKAL TEXAS IN SEPTEMBER 1921. By C. E. ELLSWORTH. INTRODUCTION. Heavy rainfall over a large area in south-central Texas from Sep tember 8 to September 10, 1921, produced great floods which caused the loss of at least 224 lives and damage to property amounting to more than $10,000,000. The most destructive flood in Texas prior to 1921 occurred in December, 1913. That flood, which is described on pages 46-47, caused the loss of 177 lives and destroyed prop erty valued at more than $8,500,000. The most densely populated and most highly developed com munity affected by the flood of 1921 was the city of San Antonio, where 51 lives were lost and property worth more than $3,000,000 was destroyed. It was the disaster at San^Antonio that received the most widespread notice in the press, though the aggregate loss of both life and property in other areas far exceeded that at San Antonio. The total rainfall and the run-off per square mile of drainage area were much less in the basin of San Antonio River than in the basins of many other streams in the path of the storm. If the rainfall in the basin of San Antonio River had been as heavy as it was in much of the basin of Little River, in Bell, Milam, and Williamson counties, the destruction at San Antonio would have been so great as to make that actually suffered tKere seem insignificant. The United States Geological Survey, in cooperation with the Texas Board of "Water Engineers, made special determination of the flood flow of San Antonio River at San Antonio and of Little River at Cameron immediately after the flood. Several months later, determinations were made of the maximum discharge of Lit tle River near the junction of Leon and Lampasas rivers, of Salado Creek near Salado, of San Gabriel River near Georgetown, and of Brushy Creek at Round Rock. The amount available for the work was so small that measurements were made only on streams where the conditions were favorable for obtaining reasonably accurate 1 2 FLOODS IN CENTRAL TEXAS IN SEPTEMBER, 1921. results. In addition to the-measurements made on the streams men tioned above determinations of the flood flow at several regular gaging stations were made by routine methods. In the area north and east of Taylor, where the total rainfall exceeded 36 inches, the flood was so wide and was so much obstructed in its course down the valleys of San Gabriel River and Brushy Creek that the maximum discharge of those streams could not be determined with sufficient accuracy to make the determination valuable. The average annual losses in Texas by floods amount to several million dollars, and the people of the State are beginning to realize that its future prosperity must depend in large measure upon the wisdom with which they can control and utilize the streams. Over 30,000,000 acre-feet of water annually passes unutilized from the streams of Texas to the Qulf of Mexico, much of it in floods that cause great destruction. Good business sense demands that the floods of Texas be controlled and that the flood water be stored, so far as practicable, for the many uses for which it is needed. The Board of Water Engineers of Texas has planned a compre hensive study of the streams of the State and of the best methods of controlling floods and utilizing flood water. The report here presented has been compiled for the purpose of assembling under one cover all the essential information now available concerning the flood of 1921 and of giving a brief summary of the information available concerning previous floods. The report is in many respects incomplete, but it should be a valuable contribution to the body of information on floods that must eventually be compiled. ACKNOWLEDGMENTS. The steam-gaging work done in Texas by the United States Geo logical Survey is carried on in cooperation with the State Board of Water Engineers, consisting of John A. Norris, chairman; C. S. Clark, and A. H. Dunlap. This board allots a large part of the funds available for such work. Acknowledgments are due the United States Weather Bureau for practically all the data on rainfall, many gage heights, and much in formation about the storm and its effect; to Col. Edgar Jadwin and Maj. W. N. Vance, of the United States Engineer Corps at Fort Sam Houston, for their kindness in giving the writer access to their excellent unpublished report of the San Antonio flood; to C. Terrell Bartlett, for information that has been quoted freely from his published statements in engineering periodicals and local news papers regarding the flood at San Antonio; and to many county officials, engineers, railroad companies, residents, and the public press for statements of losses and other information which could AREA COVERED BY THE STOBM. O not have been obtained without their cooperation. Individual ac knowledgments are given throughout the report. In determining discharge of streams during the flood the .writer was assisted by C. E. McCashin, D. A. Dudley, R. G. West, and Trigg Twitchell. The office computations of discharge were made principally by C. E. McCashin and Trigg Twitchell, and assistance in assembling the matter and preparing it for publication was ren dered by Kate Casparis. AREA COVERED BY THE STORM. GENEBAL FEATURES. % The rainfall that caused the flood covered an elliptical area that includes nearly 10,000 square miles, whose longer axis extends southwestward along the Balcones escarpment from Temple beyond San Antonio, a distance of more than 150 miles. (See PI. I.) The larger streams that cross this area, all flowing southeastward, are Brazos, Colorado, Guadalupe, and San Antonio rivers. The counties within the storm area are Bell, Milam, Williamson, Travis, Hays, Comal, and Bexar. These counties contain much of the richest agricultural land in Texas. Practically all the area lying southeast of a line extending from Temple through Belton, George town, Austin, San Marcos, New Braunfels, and San Antonio is under cultivation.