|Abstract:||Floods occurred in Texas during, June, July, and November 1940 that exceeded known stages on many small streams and at a few places on the larger streams. Stages at several stream-gaging stations exceeded the maximum known at those places since the collection of daily records began.
A storm, haying its axis generally on a north-south line from Cameron to Victoria and extending across the Brazos, Colorado, Lavaca, and Guadalupe River Basins, caused heavy rainfall over a large part of south-central Texas. The maximum recorded rain of 22.7 inches for the 2-day period June 29-30 occurred at Engle. Of this amount, 17.5 inches fell in the 12-hour period between 8 p.m. June 29, and 8 a.m. June 30. Light rains fell at a number of places on June 28, and additional light rains fell at many places within the area from July 1 to 4. During the period June 28 to July 4 more than 20 inches of rain fell over an area of 300 square miles, more than 15 inches over 1,920 square miles, and more than 10 inches over 5,100 square miles. The average annual rainfall for the area experiencing the heaviest rainfall during this storm is about 35 inches.
Farming is largely confined to the fertile flood plains in much of the area subjected to the record-breaking floods in June and July. Therefore these floods, coming at the height of the growing season, caused severe losses to crops. Much damage was done also to highways and railways.
The city of Hallettsville suffered the greatest damage of any urban area. The Lavaca River at that place reached a stage 8 feet higher than ever known before, drowned several people, destroyed many homes, and submerged almost the entire business district. The maximum discharge there was 93,100 second-feet from a drainage area of 101 square miles.
Dry Creek near Smithville produced a maximum discharge of 1,879 second-feet from an area of 1.48 square miles and a runoff of 11.3 inches in a 2-day period from a rainfall of 19.5 inches.
The area in the Colorado River Basin between Smithville and La Grange, amounting to 550 square miles, had an average rainfall of 19.3 inches, of which 11.5 inches appeared as runoff. The maximum discharge at La Grange was 182,000 second-feet, with much the greater part coming from below Smithville. This is probably a record-breaking flood for the area between Smithville and La Grange, but stages as much as 16 feet higher have occurred at La Grange. Heavy rainfall over the east half of Texas November 21-26 caused large floods in all streams in Texas east of the Guadalupe River. The maximum recorded rainfall for the 2-day period November 24-25 was 20.46 inches at Hempstead, of which 16.00 inches fell in 24 hours or less. The storm occurred during the period November 20-26, with the greater part of the rain falling November 23-25. During the period November 20-26, rainfall in Texas amounted to more than 15 inches over an area of 3,380 square miles, and ‘to more than 10 inches over an area of 17,570 square miles. The average annual rainfall for the area in Texas experiencing more than 10 inches of rain during this storm ranges from 501 inches on the east border of the State to 35 inches near the west edge of the area. The study of this storm for the purposes of this report is limited to the San Jacinto River Basin, which had an average rainfall of 13.6 inches. This basin has an area of 2,791 square miles above the gaging station near Huffman and is typical in topographic and hydrologic features of much of eastern Texas. The stage reached at the gage near Huffman was about 1 foot higher than known before, the maximum discharge was 253,000 second-feet, and the runoff from the storm amounted to 8.8 inches.
The November flood came after crops had been harvested, and its damage was mainly the destruction of highways and railways and the drowning of livestock. The storage reservoirs on the Colorado River located well upstream from the storm areas herein studied had very little effect on