How San Antonio area is preparing before the next Harvey hits

San Antonio River Authority, city, county working to mitigate flooding

By Chris Shadrock - Web - News Producer

SAN ANTONIO - They are dates that evoke panic and fear in longtime South Texans: June 1997. October 1998. July 2002.

The memories of whole homes floating down rivers, Highway 281 under water and dozens of lives lost in raging floodwaters remain -- even though few physical scars from the storms do.

August 2017 was almost added to the list. Had Hurricane Harvey -- which roared ashore on the Gulf Coast of Texas on Aug. 26 -- shifted west by just 50 miles, it would have inundated the Alamo City. 

In the ensuing months, city planners in San Antonio have had to reckon with that near-miss -- and the questions it raised: Is the Alamo City ready for the kind of disastrous flooding that struck Houston? Could it happen here? What is being done? What more can we do?

Ultimately, as longtime residents and planners will say, it is a matter of when -- and not if -- another catastrophic flood hits.

Should a storm like Harvey hit our area, preliminary model results show that the Olmos Basin would receive enough water to fill the Alamodome 41 times, which equates to more than 23.3 billion gallons of water, officials with the San Antonio River Authority said. 

Learning the hard way 

Major changes began in earnest after the massive floods in 1998 and 2002. The city and Bexar County, seemingly caught off-guard, began making changes to better prepare the area for future floods.

The two floods combined killed 40 people across South Texas and caused billions of dollars in damage.

The city of San Antonio already had a storm water utility fee in place since 1993, generating money that officials say goes toward drainage services as well as the installation, operation and maintenance of drainage infrastructure.

Across Bexar County, SARA operates 28 dams. The most visible is the Olmos Dam north of downtown. Another is the San Antonio River flood tunnel to protect downtown. A few miles northeast is the McAllister Dam near the airport, which can hold three times as much water as Olmos.  

Recently, the Bexar County Regional Watershed Management partnership was formed. It now encompasses nearly all the suburban cities in Bexar County, including the city of San Antonio, and the River Authority.

See if your home is in a floodplain with this map

By the end of this year, BRWN will wrap up its 10-year, $500 million program to improve public safety and keep rainwater from overwhelming roads and property. The majority of the projects have been completed, while six remain under construction.

"You're never going to stop rain," County Public Works Director Renee Green said during an April 2016 interview with KSAT. "You're never going to stop water draining into the area. But these flood control projects have made it much more safe for the public."

Another issue is that when the federal flood boundaries were drawn in 1975, much of San Antonio had already been built. In the last decade, 3,000 properties have been removed from the flood plain, but another 11,000 remain, a number the river authority said is too high.

“So the moment that standard was developed, immediately, there were homes that were considered at risk of flooding,” said Nefi Garza, with San Antonio’s Transportation and Capital Improvements.

Garza’s sole focus is how flooding impacts the city and how the TCI department projects can help mitigate the risk.

30 years later: When the Guadalupe River turned deadly

San Antonio voters approved the city to spend $152 million in 2007, $128 million in 2012 and nearly $139 million this year in bond money for drainage and flood control issues across the city. 

“Part of our responsibility is to go into these older neighborhoods and retrofit or reconstruct some of the work that is being done in that area to reduce the risk on those homes,” Garza said.

But San Antonio River Authority assistant general manager Steve Graham said more needs to be done.

“There is still quite a bit more we can do in investment. I have heard numbers between $1 (billion) and $2 billion, probably in additional investment," Graham said.

How bad could it get?

Listening to Graham speak, it becomes clear he has poured over the information the models have spit out and he knows, no matter what, that 50 inches of rain in the span of a few days would not bode well for San Antonio.

Apache Creek at Lake Elmendorf on the West Side

Flooding would cause the San Antonio River flood a large portion of downtown.

“So this is (Highway) 281,” Graham said as he showed the newest Nexrad data of potential flooding. “There is the (Olmos) Dam, and what happens is our dam would fill up with water. In fact, it would have more water than it can hold, and you have 4 foot of water over the top of the dam. Highway 281 would be impassable for about 13 days.”

Flood control still a major priority across San Antonio

The River Authority has spent the weeks since Harvey hit the Texas coast analyzing how well San Antonio waterways would hold up in the event of a similar storm.

At its board meeting on Wednesday, the organization showed the extent of damage across the San Antonio River basin: flooding along and east of Broadway Street, into the University of Incarnate Word and water overrunning the redeveloped Pearl.

“It is a good exercise to go through our own vulnerabilities,” Graham said. “Are we prepared for something severe like this as well?”

The River Authority also has a tool on its website that allows people to see the odds of a flood occurring at their home. 

San Antonio is not Houston

San Antonio's floods in 1998 and 2002 and Harvey's effect on Houston were very different — so, too, are the Alamo and Bayou cities.

The rains of ‘98 still hold many records in San Antonio, including the 24-hour rainfall record of 11.26 inches – the majority of which fell in the span of a few hours.

It highlights the type of rain that worries Graham the most.

“We have learned that the biggest risk here is flash-flooding. Quick, intense rains that come and go and sweep people off the roads. Where Harvey had 51 inches in five days, I would be more concerned (about) 10, 12, 13 inches in six or nine hours,” he said.

The flood of 2002 came over the course of several days, culminating with almost three feet of rain falling near Sisterdale, in Kendall County.

Flood of '78: The other storm that dropped at least 4 feet of rain

There is another difference that separates the two largest cities in the state: elevation.

“(A flood) will come through in hours, but it will be very treacherous. All of our streets would be very impassable. The river would get very high, but we would not have people stranded for days like in Harris County," Graham said.

While that elevation will spare Bexar County days of floodwaters festering, it is also why flooding here is so dangerous.

Courtesy: SARA

“Intensity is much more important in this area than the volume,” Graham said.

Future plans

Unlike in years past, the cities in Bexar County are now working together. Planners realized that while they knew where the city lines are drawn, flood waters did not.

“I believe what is more extreme for San Antonio is something like 13 inches in six hours,” Graham said. “That is a much worse event than 51 inches over five days.”

Either way, Graham said it might be more feasible to look at the area's critical infrastructure and make sure they are well-above the 100-year flood plain.

“All of these things might, say with certain criticality, we add freeboard of a certain amount, based on whether it be a home, highway, hospital or important infrastructure,” he said.

Another debate happening nationwide, Graham said, is whether or not the FEMA should expand flood regulations beyond streams and rivers. 

As the city continues to grow, so, too, does the need to keep new development out of the flood zone.

As part of SA Tomorrow, the City Council voted in 2016 to include the city evaluate and update if necessary impervious surface standards. The plan includes language about limiting impervious cover, adding low impact development and "if deemed necessary to update the standards, working with stakeholders, new impervious standards would be identified to reduce flooding, improve water quality, and reduce urban heat islands."

“We have a team of engineers that focuses on reviewing their (developers') plans to make sure they keep with the city of San Antonio Unified Development Code and Standards,” Garza said.

However, Graham said the river authorities research shows additional development leads to more flooding. 

"There is a direct correlation between impervious cover, i.e., development and peak flooding," he said.

Both Graham and Garza said the 100-year flood plain is a good standard, one that Garza said also makes financial sense.

Garza used the building of a new bridge over Salado Creek as an example. It cost the city about $8 million, but would have cost more than four times that amount if the city had built it to Harvey standards -- a standard that would have left the bridge dry during a flood but not the surrounding land, making it impassable.

Garza also highlighted the need for how the area would recover.

“We need to start asking about our ability to bounce back. No city in the world is prepared for that kind of event,” he said.

SARA Harvey Simulation

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