Courtesy Austin History Center, Austin Public Library, CO8484-A
The 1935 flood produced this historic scene of a houseboat washing over the old Austin Dam in Austin. |
 eventy years ago this summer, just as the newly created Lower Colorado River Authority was setting up shop, the Colorado River of Texas experienced the first of what are arguably the basin's three worst floods of the 20th century.
Photographs and news accounts of the floods that occurred in 1935, 1936 and 1938 are still powerful in their depiction of Colorado River floodwaters: farmlands swept clean of buildings, livestock and families; a houseboat washing over a dam; Austin citizens watching as the river splits their city in two. While the lower Colorado River basin has experienced powerful floods in recent years, those events pale in comparison to the catastrophic floods of the 1930s. Nothing like them has occurred since LCRA completed building Mansfield Dam upstream of Austin in 1941. One of six dams built by LCRA that form the chain of Highland Lakes on the Colorado, Mansfield is designed to store the Hill Country floodwaters that routinely ravaged Austin and other downstream communities. But while the Highland Lakes dams have prevented some floods and moderated others, they haven't completely eliminated the threat of flooding in the basin. And according to some LCRA experts, it's not a question of if but when the basin again will experience a flood like those of the 1930s.  "We've been lucky so far, because there have been several catastrophic floods that have danced around our basin in recent years," said LCRA chief meteorologist Bob Rose. "But one day, our luck will run out."  | | LCRA Corporate Archives, W00470 |  | | LCRA Corporate Archives, W00472 | Llano River (top): A 42-foot crest on the Llano River during the 1935 flood washed out the bridge at Llano, forcing residents to ferry across the river until the state highway department completed a new bridge the following year.
San Saba (bottom): The 1938 flood inundated much of San Saba, as seen in this aerial photo. The flood was the largest of record for the San Saba area.
Click images for larger photos. | 1935 flood produced historic image
The lower Colorado River basin is known as "Flash Flood Alley" for good reason. More than 80 major floods have been recorded since the early 1800s, often with devastating results. A 1900 flood destroyed the Austin Dam, which was considered a technological marvel of the time, and floods destroyed a replacement dam in 1915. Flooding in 1913 merged the mouths of the Colorado and adjacent Brazos rivers, forming a lake 65 miles wide. The 1930s floods surpassed these events. All three floods of the 1930s were caused by rains totaling as much as 51 inches in the western Hill Country over the Llano River watershed upstream of Austin. Much of the land in this region has thin soils that are easily saturated and, along with steep slopes, easily convert heavy rain into runoff. The 1935 flood was caused by almost 20 inches of rain that fell throughout the upper central basin and the Hill Country in early June. That was on top of nine-inch rains that saturated the basin in late May. The rains swelled Hill Country tributaries including the Llano, which peaked at a record 375,000 cubic feet per second (cfs) at Castell before floodwaters swept away the gauge. (For perspective, in early July of what has been an almost rain-free summer so far, streamflow on the Llano was at about 80 cfs.) With no effective flood-management system on the Colorado River (the 4-month-old LCRA was getting its oars in the water, so to speak, by securing federal funds to build its dams), the Llano and upper Colorado floodwaters combined with those of the Pedernales and swept into Austin, where the river crested at 50 feet, just one foot below an all-time peak in 1869, with a peak flow of 481,000 cfs. The floodwaters inundated the downtown district, washed out the Montopolis Street Bridge downstream, and left as many as 3,000 homeless. And on its June 16 front page, the Sunday Austin American-Statesman published a picture of a houseboat washing over the Austin Dam — an iconic image that even today illustrates the unchecked power of the Colorado. 1936, 1938 floods devastated farms, communities
The basin didn't fare much better with the floods that followed in 1936 and 1938. The 1936 flood was created by two major storms in summer and early fall totaling 51 inches over the watershed of the Concho River, a tributary of the Colorado. At San Angelo, the Concho floodwaters washed away 300 buildings. After the flood runoff entered the Colorado, it imperiled hundreds of farm families in Coleman and McCulloch counties and inflicted most of its damage between Ballinger and Kingsland, where several bridges were destroyed, livestock drowned, farm houses flooded and fields swept clean. At Austin, the volume of floodwaters was more than double that in 1935, swelling the river for nearly a three-week period. The July 1938 flood nearly shut down LCRA, which had just completed Buchanan Dam the year before. Rains of up to 25 inches fell over a 10-day period at the storm's center near Brady, upstream of Buchanan. LCRA opened 22 of Buchanan's 37 floodgates (still a record) to pass through floodwaters, which would go on to claim property and crop losses in the Columbus area totaling more than $3 million (about $39 million in today's dollars). Casualties, still unverified to this day, included 12 deaths in the Austin area and more than 4,000 homeless. The flood attracted nationwide interest and triggered federal and state investigations, with the state water engineer recommending a higher elevation for Mansfield Dam (then under construction) and installation of a system of rainfall and river gauges in the basin to warn LCRA of floods. (The gauges were the forerunner of LCRA's modern-day electronic Hydromet system.) Recent floods not as severe as those of the 1930s
Even with the Highland Lakes dams in place, the risk of flooding along the Colorado continues today. The basin has experienced five severe floods since 1991, including the "Christmas Flood" of that year, which pushed Lake Travis (the reservoir created by Mansfield Dam) to its all-time high elevation of 710.4 feet above mean sea level (ft. msl), about four feet below the Mansfield Dam spillway. Even so, the floods of the 1930s would have been worse. If they occurred today, based on studies by LCRA and the U.S. Army Corps of Engineers, they would have sent the level of Lake Travis over the spillway of Mansfield Dam — something that never has happened. The elevation of the Mansfield Dam spillway is 714 ft. msl. "A flood like the one in 1935 would have raised Lake Travis to an elevation of about 717 ft. msl, and a flood like the one in 1938 would have raised Travis to about 722," said LCRA senior engineer Melinda Luna. Potential catastrophic floods have "danced around us"
Even more worrisome is how close the lower Colorado basin has come in recent years to experiencing floods that would have rivaled those of the 1930s. For example, the 1998 flood that devastated communities along the Guadalupe River could have done the same to the lower Colorado basin, had the storm's center shifted only 85 miles to the northwest into the Hill Country. Had that happened, according to an LCRA study, the storm's 20-plus inches of rain would have resulted in a one million cfs peak flow on the Llano (almost three times the 1935 record), a 50-foot rise on Lake Travis that would have pushed it over the Mansfield Dam spillway, and downstream flooding that would have forced the mouths of the Colorado and Brazos rivers to merge, as in the 1913 flood. A worse impact would have come from a storm like Tropical Storm Allison, which swamped Houston in 2001 with rains of up to 37 inches. According to an LCRA study, a Hill Country storm like Allison would have pushed Lake Travis 26 feet above the Mansfield Dam spillway, forcing LCRA to open all 24 of the dam's floodgates — something that has never happened. (The most that have been opened at one time was six, during a 1957 flood.) Downstream, the river would have risen as high as 59 feet at Bastrop, 34 feet above flood stage. "Major storms like these have danced all around our basin," said Rose. "A small change in weather currents easily could have shifted any of these storms into the Colorado basin, creating floods like those of the 1930s. One day, we will get one of those floods, and it will affect a basin that is much more heavily populated and urbanized than seven decades ago." A 1930s-style flood would afflict a basin that has more than quadrupled in population over the past seven decades — from about 229,000 in 1930 to almost 1.1 million in 2000 in the 10-county LCRA district that encompasses the lower Colorado River basin, according to U.S. Census figures quoted in the Texas Almanac. Much of that growth is in or near the floodplains of the Highland Lakes, Colorado River and major tributaries. A matter of when, not if
Anticipating that unlucky day, LCRA has completed a decade-long $52 million upgrade of the Highland Lakes dams. It is building out its Hydromet system, with plans to add 46 rain and streamflow gauges by 2008, many of them in the basin's northwest and southeast fringes to provide earlier alert of trouble. Most of the basin now has access to local round-the-clock broadcasts of NOAA Weather Radio, thanks to transmitters installed and maintained by LCRA. And LCRA is helping basin communities update floodplain information. "LCRA is doing everything we can to prepare for a catastrophic event," said Roy Sedwick, LCRA floodplain management coordinator. "But people need to remember that the risk of floods in the Colorado River basin will never be completely eliminated. Residents who live in or near a floodplain need to understand that they are at risk of being flooded, and they need to take the appropriate steps to protect themselves." Those measures include building or retrofitting your home or office to minimize flood damages (or better yet, not building in a floodplain); purchasing flood insurance; planning a safe escape route in the event of floods; and buying and using a weather or all-hazards radio. "We've been fortunate these past seven decades not to have suffered a flood of the magnitude like those of the 1930s," Sedwick said. "But we know a flood that size will occur, and everybody needs to be ready for it when it happens." John Williams is a senior writer and editor for LCRA. Contact him at john.williams@lcra.org. |
