THE FLOODS IN CENTRAL TEXAS IN SEPTEMBER, 1921

[Pages:72]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 September 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 property valued at more than $8,500,000.

The most densely populated and most highly developed community 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 Little 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

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FLOODS IN CENTRAL TEXAS IN SEPTEMBER, 1921.

results. In addition to the-measurements made on the streams mentioned 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 comprehensive 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 Geological 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 information 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 newspapers 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 acknowledgments 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 rendered 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, Georgetown, Austin, San Marcos, New Braunfels, and San Antonio is under cultivation. As the soil is fertile and the conditions for farming are otherwise favorable, this area is one of the most densely populated and highly developed in the State. Much of the land northeast of that line is also under cultivation, but to a less extent than that to the southeast, because the soil is thin and less fertile and the country is more broken and hilly. A large percentage of the land in both areas that is not under cultivation is covered with a fairly thick growth of post oak and stunted cedar, such as the thin soil is capable of supporting.

TOPOGBAPHY AND GEOLOGY,

The axis of the area of maximum rainfall followed closely the Balcones escarpment, which is the dividing line between the Rio Grande Plain, on the southeast, and the Edwards Plateau and Grand Prairie region, on the northwest. The Balcones escarpment is the result of an enormous geologic fault that extends across the entire State from Red River to the Rio Grande. It marks a sudden change of topography from the gently sloping Rio Grande Plain, which stands at an elevation of about 500 feet, to the eroded plateaus, which range in elevation from 1,000 to 2,000 feet. In passing from the plateau to the plains the streams have cut deep channels, which have steeper grades than those on either side of the

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FLOODS IN CENTBAL TEXAS IN SEPTEMBER, 1921.

escarpment. The prevailing rock is limestone of the Cretaceous period. It is overlain principally with clay soil. In the area northeast of the fault zone the soil is thin and considerable areas of rock are exposed, but in the area southeast of it the soil is deeper and rock is seen at few places except along the banks of some of the streams.

Except for the loss in the city of San Antonio, the greater part of the total loss occurred in the rural districts, where crops were destroyed and roads and bridges were washed out. Owing to conflicting opinions concerning the amount and the value of the crops destroyed it is impossible to determine accurately the damage caused in the rural districts.

One item of loss for which no estimate is here given, and which can not be determined with reasonable accuracy, is the loss of soil from farm lands by erosion or by being covered with deposits of sand and gravel. Such losses undoubtedly aggregate millions of dollars. Walter E. Davis, agricultural demonstration agent for Travis County, stated that the loss of soil was much greater, than the loss of crops but that he could not estimate the total loss for the county. The loss of soil in Travis County was probably much greater than in any other, because much of the cultivated land in this county has a steeper slope than the average in the rest of the area covered by the storm. The damage was due largely to erosion by the rains that fell directly upon the land. The water attained scouring velocities before it left the fields and entered the usual stream channels. The crops, principally cotton and corn, were washed away with the soil; the devastated area ranged from narrow strips in some places to wide areas in others.

Mr. T. S. Etenderson, of Cameron, estimated that more than 75,000 acres of farm land in Milam County was flooded by the overflow from Little River and its tributary, San Gabriel River. More than half of the area overflowed had been planted in corn and cotton, which were practically a total loss. Cultivated land covering thousands of acres that lay above the area flooded by overflow from the river was also greatly damaged by the torrential rain falling directly upon it or by the scouring action of the water as it flowed over the fields. The total loss of crops was at least $1,000,000. The loss of live stock was $60,000, and the damage to houses, fences, and miscellaneous farm structures was $20,000. Mr. Giles L. Avriett, county auditor, estimates the loss and damage to bridges and highways at $100,000, about equally divided between the two items.

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