The earthen dam on the outskirts of this Williamson County city certainly does not look flimsy. At 35 feet high and nearly a third of a mile long, it has done a reliable job of holding back floodwaters on Chandler Branch, a normally placid tributary of Brushy Creek, for more than 50 years.

But in a worst-case flood, like what Hurricane Harvey unleashed on parts of Texas in August, or even a flood a bit more than half as severe, Chandler would turn into a monster, eventually surging over the top of what’s known as Upper Brushy Creek Dam 10A. When rushing water and earth meet, water usually wins, and the dam would almost certainly breach, resulting in the uncontrolled release of the impounded water, more than 500 million gallons.

That would swamp a miles-long area stretching southeast into Round Rock that includes 306 houses, eight multifamily buildings, 19 commercial properties and 14 road and railroad crossings, according to a study commissioned by the Upper Brushy Creek Water Control and Improvement District. Interstate 35, about 4 miles downstream, would be under nearly 6 feet of water.

Dam 10A is one of several hundred substandard dams upstream of populated areas in Texas that violate state law intended to guard against dam breaching, or failure, in catastrophic floods, an investigation by the American-Statesman has found.

Those include six city-owned dams in Austin, as well as others in Central Texas, a region that has experienced some of the heaviest rainfall events in the world. The adequacy of hundreds more dams that could put people in harm’s way is unknown because they haven’t been studied. All told, Texas has 7,229 dams, more than any other state.

Few people who could be at risk are aware of the hazard of living in what engineers call the potential inundation zone, which includes areas well outside the 100-year flood plain.

“We’ve lived here about 19 years, and I have never heard of this,” said Teresa Jones, president of the homeowners’ association in Jester Farms, one of several Round Rock neighborhoods east of I-35 and along Chandler Branch that would be threatened by the failure of Dam 10A. “I definitely want to look into this further.”

The Statesman’s investigation also found:

• Development in potential inundation zones is with few exceptions unregulated by local, state and federal authorities. As a result, construction of housing, businesses and roads puts those structures at risk from dams, like 10A, built decades ago to a less stringent standard for agricultural land and therefore never intended to protect populated areas. In a case of one step forward and two steps back, federal, state and local governments have spent millions of dollars to upgrade some of these dams even as development continues below other once-rural dams.

• Lack of public awareness about the hazards posed by dams is no accident. After the terrorist attacks of Sept. 11, 2001, federal and state officials, citing security concerns, have restricted the ability of news organizations and the public to obtain information about the hazards posed by many dams.

• In a departure from national norms, the Texas Commission on Environmental Quality, which regulates and inspects dams, applies stricter safety standards to those whose failure would be expected to cost seven or more lives than it does to dams whose collapse could possibly cost up to six lives. The latter can get by in some cases by being capable of handling just half of a worst-case flood.

• A state law passed by the Legislature and signed by then-Gov. Rick Perry in 2013 permanently exempts 45 percent of the dams in Texas from inspections and other safety requirements because of their relatively small size and rural locations. Although more than 90 percent of these dams would not be expected to cause loss of life if they failed, 231 of them are in the up-to-six-deaths-are-possible category.

The Statesman previously investigated dam safety in 1997, finding an alarming state of neglect and inadequate oversight in Texas. At that time, nearly two-thirds of dams above populated areas had not been inspected for at least five years. Formal emergency action plans had not been developed by dam owners for 94 percent of dams that should have had them. And the state’s dam safety team had dwindled to six employees from more than 40 in the early 1980s.

Twenty years later, the Commission on Environmental Quality’s dam safety team has 30 employees and a $2.3 million annual budget. Eighty percent of dams whose failure would put people at risk — not counting the exempted ones — have been inspected in the last five years, and 77 percent of dams under the commission’s oversight have submitted emergency plans. The Federal Emergency Management Agency cited the stepped-up inspections and planning as one of the nation’s “success stories” in its report to Congress last year on dam safety.

Experts nevertheless describe dam safety in Texas as an increasingly urgent matter.

“More people are at risk from dam failure than ever, despite better engineering and construction methods, and continued deaths and property losses from dam failures are to be expected,” the state environmental commission warns in its “Guidelines for Operation and Maintenance of Dams in Texas.” It adds, “Risk is high because people have been allowed to settle below dams in potential inundation zones.”

The commission declined to make any of its officials available for an interview, but it responded in writing to questions submitted by the Statesman. “TCEQ is not aware of any dams that are under threat of imminent failure,” the agency said, adding that it has no plans to revise its rules “at this time.”

No one has died as a result of a dam failure in Texas since 1989, when a man drowned as he drove down a road that had been flooded after the Nix Club Lake Dam in Rusk County, in East Texas, collapsed in a storm.

There have been dozens of failures since then, including four East Texas dams that washed out as a result of Hurricane Harvey and its aftermath — three in Tyler County and one in Newton County. Sixteen other dams sustained damage from Harvey, including five in Fayette County, southeast of Austin.

Runoff from Harvey’s 50 inches of rain flooded thousands of houses in Houston as the reservoirs behind the Addicks and Barker dams swelled, and thousands more flooded downstream from the dams’ releases. The dams themselves held up, although they have been considered at risk of failure for years, with the Army Corps of Engineers, which owns them, struggling to secure sufficient funding from Congress. Dozens of lawsuits have been filed over the flooding. State regulators have no authority over the Corps of Engineers and other federal dams.

A question of standards

Dam safety specialists are troubled by the Legislature’s exemption of what are now 3,232 dams, or 45 percent, from safety requirements, as well as the environmental commission’s weaker standards for dams with a lower potential death toll.

“Texas’ current dam policies, including the exemptions of dams, place priority on lessening the burden of dam owners rather than on the safety of the public living downstream of a dam,” said Travis Attanasio, former vice president for professional affairs for the American Society of Civil Engineers’ Texas Section. He was chairman of that organization’s 2017 dam safety report card for Texas, which gave the state a grade of “D,” indicating the dam infrastructure is “poor and at-risk,” he said.

In the vast majority of states, any dam that would be a threat to life if it failed is considered a “high-hazard potential” dam. But not in Texas, where dams that could kill up to six people if they collapse receive the midlevel rating of “significant-hazard potential.” No loss of life is expected if a low-hazard dam fails.

The exemptions from inspection and other oversight under House Bill 677, which passed the Legislature with only one no vote in 2013, include 231 significant-hazard dams, according to the environmental commission.

Proponents of the measure, including representatives of ranching and farming groups, told lawmakers that dam owners were having to spend upwards of $100,000 in studies and improvements per dam. At the time, the exemptions were approved by the Legislature, 57 of the significant-hazard dams being exempted were deemed by the commission to be in poor condition, according to an analysis by the House Research Organization.

To qualify for the exemption, a dam must be outside a city in a county with a population under 350,000 and impound less than 500 acre-feet of water, or 163 million gallons.

“Generally accepted guidelines state that should a dam failure have the potential for killing one person, then that dam should be maintained as a high-hazard potential structure,” said Lori C. Spragens, executive director of the Association of State Dam Safety Officials.

Like the association, the Federal Emergency Management Agency and the Corps of Engineers define such dams as high hazard.

The Texas commission said it would inspect an exempt dam that was the subject of a complaint and would raise a dam’s classification to high hazard if aerial photographs or field observation revealed downstream development.

The commission declined to disclose the hazard classifications of individual dams, citing a 2005 opinion by the state attorney general’s office that declared such classifications and emergency plans — which include maps of potential inundation zones — confidential because they identify “particular vulnerabilities of critical infrastructure to an act of terrorism.” The Statesman was able to determine the hazard classification of some dams by interviewing local officials, obtaining documents and conducting online research.

“A majority of people living below a dam have no idea what could happen,” Attanasio said, adding that dam safety and funding would be a higher priority “if people truly knew the consequences of not maintaining even significant-hazard dams.”

Brushy Creek a case study

Perhaps no watershed in Texas better illustrates the challenge as well as the progress in addressing dam safety than Brushy Creek, in southern Williamson County and southwestern Milam County. Forty-six dams were built from 1959 to 1976 under standards for low-hazard dams. Now, thanks to rapid urbanization, more than half are high-hazard dams, and the trend is expected to continue.

Over the years, 19 of the Upper Brushy Creek water district’s 23 dams, all of which are high hazard, have been modernized, said Ruth Haberman, the district’s general manager. Dam 7 in Cedar Park, which forms the lake at Brushy Creek Lake Park and is traversed by the Brushy Creek Regional Trail, is in the midst of a $20 million upgrade to withstand a worst-case storm of 44 inches in 24 hours.

Improvements are being designed for another of the district’s dams, and one needs no upgrading. That leaves Dam 10A, which in the event of a collapse would inundate parts of several Round Rock neighborhoods, including Jester Farms, Chandler Creek and Legends Village. The dam and the small lake it forms occupy an easement on a large parcel of land west of I-35 and southwest of Georgetown owned by the Texas Crushed Stone Co., which operates a quarry.

“It looks pretty stout to someone who’s been around it for 50 years,” said Bill Snead, the company’s president, adding that it would be “a good idea” to make it safer.

Haberman said the district conducts periodic “table-top” exercises with local emergency management officials to keep them updated on its dams. What’s more, anyone buying property in the district is required under state law to sign off on a notice advising the purchaser that the district has taxing authority. The Upper Brushy district goes beyond that requirement, adding a paragraph in bold type stating that the property “may or may not be within an inundation easement or downstream of a District-owned flood control structure” and encouraging buyers to contact the district for more information. Few people bother to do so.

The Texas environmental commission raised Dam 10A’s classification from low hazard to high hazard last year, according to the district’s annual report. It could be five years before the process of submitting grant applications, preparing designs and fortifying the dam, likely by raising it three or four feet, is completed at a cost of millions, Haberman said.

The Upper Brushy district has been able to fix its dams and prepare an emergency plan covering all 23 because voters in 2002 authorized a tax of 2 cents per $100 of property value, which now generates about $7 million a year. The district has also obtained federal and state grants. Voters in the Lower Brushy Creek Water Control and Improvement District refused to grant taxing authority, which makes it much more difficult to fund improvements, said James Clarno, the district’s general manager. Three of the district’s 23 dams are classified as high hazard and two as significant hazard.

Lower Brushy Creek Dam 32, just east of Coupland, is being reconstructed at a cost of $1.7 million, thanks to federal and state grants cobbled together by the district. The district also secured $1.3 million in grants to improve Dam 20, whose failure would flood several houses and a wastewater treatment plant in Thorndale; construction on that project is expected to begin in the spring.

Dam 29, just south of Taylor, is a different story, with no immediate prospects of funding an upgrade. It rises 37 feet and extends for nearly half a mile, forming a lake on Battleground Creek, a tributary of Brushy.

In a worst-case storm, Battleground’s flow would spill over the top of the dam, breaching it and sending a 16-foot-high wave rushing toward a home, three barns, a state highway and three county roads. An analysis by an engineering firm concluded that as many as 11 lives would be at risk.

John Kitsmiller, whose house would be in harm’s way and who keeps longhorns and horses on his property, isn’t losing any sleep over it. “We’ve been here 11 years,” he said. “We’ve never had anything close to worrying about.”

The Lower Brushy Creek district has an emergency plan for Dam 32, a draft plan for Dam 20 and no plans for Dam 29 and two others for which they are required. Clarno said it can cost $25,000 to prepare a plan, including a map of the breach inundation zone.

A ‘whopping big rain’

What, exactly, is a worst-case flood? It varies by location, topography and other characteristics. Even frequently dry watersheds sometimes “catch a whopping big rain” that puts a stream “up on its hind legs to roar,” as the late Texas novelist Elmer Kelton put it in “Pecos Crossing.”

The technical term is “probable maximum flood” based on the most severe weather and water conditions “reasonably possible,” according to the environmental commission. Such a flood is a function of the “probable maximum precipitation,” which the National Weather Service defines as the theoretical greatest depth of rain for various lengths of time at a particular location.

“Hurricane Harvey was akin to what we expect a (probable maximum precipitation) storm to look like at large area sizes and long durations,” said Bill Kappel, chief meteorologist and president of Colorado-based Applied Weather Associates LLC, which produced a study last year on such worst-case scenarios for the environmental commission.

The study found that probable maximum precipitation figures were highest near the Texas coast and along the Balcones Escarpment, a region of elevated terrain arcing southwest from Waco to Austin and San Antonio and then west to Del Rio. The escarpment, which marks the edge of the Hill Country, “is home to some of the largest recorded rainfalls in the world,” thanks to “the effect of topography on an already moist, unstable air mass,” the study noted.

The Williamson County town of Thrall saw 38 inches of rain in 24 hours in the Brushy Creek watershed in 1921; 93 people died in the county and floodwaters stretched 10 miles wide where Brushy empties into the San Gabriel River. In 1998, New Braunfels recorded 35 inches of rain in three days. And in 2015, three people in southeastern Travis County died in floodwaters from Dry Creek, which received more than 11 inches in six hours.

The National Weather Service years ago set 44 inches in 24 hours as the probable maximum precipitation for much of Central Texas. But the Applied Weather study, using updated records and taking local topography and other factors into account, refined those calculations and in some areas came up with lower 24-hour figures for the probable maximums — for example, 27.9 inches at the University of Texas campus and 33.6 inches at Cummins Creek in Fayette County, said John Mueller, state conservation engineer for the federal Natural Resources Conservation Service.

Harvey dumped upwards of 25 inches of rain on the Cummins Creek watershed, damaging five dams. The auxiliary, or emergency, spillway for Dam 30, about 3 miles northwest of Fayetteville, took the biggest hit. The spillway is a grassy area, wide and sloping, on one side of the dam that allows floodwaters to bypass the dam to the stream below instead of overtopping it.

Dam 30’s spillway now looks like someone set off dynamite, with gullies up to 20 feet wide, 15 feet deep and 90 feet long. It will have to be repaired because a subsequent flood could cause the gullies to grow, eventually eating into the crest of the spillway and increasing the flood threat downstream, Mueller said.

The Lee-Fayette Counties Cummins Creek Water Control and Improvement District No. 1 hopes to secure a grant from the conservation service to help pay for roughly $1.5 million in repairs to Dam 30 and the other four dams, said Kevin Ullrich, the district’s president.

All told, Harvey damaged 20 dams in Texas, including 11 classified as significant hazard. The environmental commission listed the 20 dams for the Statesman but declined to identify the 11 significant-hazard ones, citing the attorney general’s opinion relating to terrorism.

Pay now, or pay later?

Asked how much it would cost to bring all dams in Texas into compliance with safety standards, the Texas environmental commission replied, “It is difficult to give an accurate cost at this time.”

The Texas State Soil and Water Conservation Board estimates that it would cost $1.8 billion to upgrade 458 earthen dams that were built with financial and other assistance from the federal government decades ago and that do not meet high-hazard criteria that now apply.

“In a month or two it might be 468,” said Steve Bednarz, statewide programs engineer for the board. “It just continues to get bigger because of urban development around these dams.”

Since 2014, the board has received $34 million in funding from the U.S. Department of Agriculture’s Natural Resources Conservation Service and $17.3 million from the Legislature to parcel out for various projects, with 32 dams currently undergoing studies, design or construction. Such funding is not available for dams that are privately owned; they constitute more than half of the dams in Texas.

The city of Austin has spent about $5 million to upgrade four dams, including Great Northern just east of MoPac Boulevard near Far West Boulevard, said Stephanie Lott, a city spokeswoman. Design work is underway to upgrade Northwest Park Dam off Shoal Creek Boulevard and Old Lampasas Dam off Old Lampasas Trail. Preliminary engineering work is expected to begin for upgrades on four other dams within two to six years depending on the dam, according to city officials. Eleven other dams still need to be evaluated.

The Lower Colorado River Authority spent about $89 million between 1994 and 2005 to improve its dams along the Colorado River, and all six can safely pass a probable maximum flood, said John Hofmann, LCRA’s executive vice president of water.

The American Society of Civil Engineers’ report card for Texas recommends creation of a state loan or grant program for dam repair, abandonment or removal. It also urges the state, local governments and zoning boards to pursue regulation of development in breach inundation zones.

The state environmental commission said it provides requested information to the Legislature but does not lobby or suggest action. “Prohibiting development in an inundation zone is a local issue,” the agency said.

McKinney, north of Dallas, has not permitted residential development in inundation zones since 1998, but Michael Hebert, its assistant city engineer, said he’s not aware of another community in Texas with a similar ordinance.

“The chance of a breach is unlikely,” Hebert said. “The concern is, if something happens in the middle of the night, will you be able to get out of the house?”