The East Basse Road exit is flooded after heavy weekend rains on Oct. 24, 2015. Photo by Iris Dimmick.
San Antonio residents watch the rising waters at the East Basse Road exit off of Highway 281 during fall flooding in 2015. Credit: Iris Dimmick / San Antonio Report

This September, the $500 million Bexar County Flood Control Plan will come to a close. The 10-year capital improvements program was established in 2007 by Bexar County Commissioners in response to a 100-year flood that claimed nine lives in 2002 and earned San Antonio and New Braunfels the nickname “Flash Flood Alley.”

The plan’s expiration comes at a time when San Antonio is poised for unprecedented growth that threatens to aggravate flooding conditions as increasing urban density results in more water runoff. Rapid development contributed to disastrous flooding conditions in Houston and surrounding areas, where Hurricane Harvey dumped more than 50 inches of rain and displaced more than 30,000 residents over the past two weeks. The storm’s death toll stands at 47, according to the latest media reports, but is expected to rise as floodwaters recede.

With the lessons of Harvey fresh in the minds of local leaders, Bexar County officials are taking a renewed look at the area’s flood preparedness. Bexar County Department of Management and Finance Director Seth McCabe last week requested that the Commissioners Court wait to determine whether the program merited further funding, hinting that building more heavy infrastructure in the form of bridges, tunnels or dams was not the best solution for mitigating the effects of a catastrophic storm.

“If we had gotten the forecasted amount of rain [20-plus inches], it would have been as bad or worse than [floods in] 1998,” McCabe said at the Commissioners Court meeting. “Simply put, depending on how much rain falls, where it falls, and for how long, there’s probably no way you can ever 100% ever build your way … out of danger for an event of that magnitude.”

San Antonio may not be able to build its way out of a flood, but it can easily build its way into one. Surfaces such as parking lots, roofs, driveways, and streets that accompany increased development create more impervious cover – areas that water cannot penetrate.

“Increased development will increase the flow, velocity, and amount of water that is going to our creeks and rivers,” said Suzanne Scott, general manager of the San Antonio River Authority (SARA). “We have to balance the growth of our city with protecting our community from flooding.”

Currently, about 15,000 structures in San Antonio lie within a 100-year floodplain, Scott said. That figure is 3,000 fewer than when the City of San Antonio announced in 2010 stricter regulations on developments occurring in at-risk areas. As storm water channels are widened to accommodate more surface run off, the boundaries of a projected 100-year floodplain recede, reducing the number of homes contained within them.

However, as new residents flock to the region the likely surge in development will pose a significant challenge to the city’s flood infrastructure. San Antonio anticipates adding over half a million new residents by 2030, according to the Urban Institute.

To date, the Bexar County Flood Control Plan has identified and initiated approximately 50 flood-control projects in the San Antonio region reflecting areas of increased residential population. The projects, set for completion within the next 12 months, range from building new bridges to raising roads at low-water crossings. This interactive map provided by Bexar County Flood Control displays the locations and details of each project.

The City of San Antonio works with the River Authority and Bexar County to identify 100-year flood plain areas that are constantly changing as development changes the city. Local drainage projects are managed by the City as capital improvement programs, while the Bexar County Flood Control Plan leverages the Bexar County flood-control tax to fund watershed and flood-control projects at the regional level. Projects are prioritized based on criteria such as safety, impact, and cost.

As rural areas around San Antonio are consumed by subdivisions, flood control is a growing concern to the county, which alternates between big spending on piecemeal infrastructure projects and budget-conscious preventative measures.

“A rural area today in five years could be developed into a subdivision that needs more than a flashing warning,” Commissioner Paul Elizondo said, “A bridge will use up $27 million. With that you can fund a lot of low-water crossing safety measures, which occur more frequently than the larger projects.”

River Authority Lead Engineer and Assistant General Manager Stephen Graham insists that infrastructure remains a priority for the City.

“We need more infrastructure,” he said in a televised appearance on “Texas Week with Rick Casey” last Friday. “But we also need to do more avoidance and smart development going forward.”

Mike Frisbie, director of transportation and capital improvements for the City of San Antonio, said low-water crossings are one of the city’s greatest vulnerabilities.

“Where we are vulnerable, and most cities are, is street flooding and drivers taking risks by driving through low water crossings,” he said.

There are 145 low water crossings in San Antonio, Frisbie said. Some of the areas most prone to flooding are on the Westside along Leon Creek and Elmendorf Lake. Currently, four drainage projects funded by the 2017 Capital Improvements bond program are in the pre-design phase in these areas, amounting to a total of $67.3 million.

Do you live near an at-risk flood area? Type an address into the search bar in the interactive map above to see if it lies in a floodplain. Compare at-risk areas to where the City is investing in flood preparedness by clicking on a bond project to learn more about its status, budget and scope.

The city has invested over $400 million in drainage and flood projects since the 2007 bond. Currently, 96% of the city’s drainage projects from the 2012 bond are either complete or under construction. On the Northside, 71% or five of the seven projects from the 2012 bond have been completed. Four of the remaining 11 projects, or 36%, on the City’s central, Southside, Eastside and Westside are complete, according to the City of San Antonio’s GIS data on Capital Improvements. Flood risk is notably higher in these parts of town as elevation levels are lower than in other parts of the city.

Given the city’s dramatic history of flood disasters, it is inevitable that San Antonio will experience another flood. Spanish records tell of periodic flooding as early as 1724. Catastrophic flood events put downtown San Antonio under several feet of water in 1913 and later in 1921. The 1921 flood brought a recorded 23.11? of rain and led to the construction of the Olmos Dam from 1925-27.

After the devastating flood of 1946, Bexar County and the San Antonio River Authority partnered with the U.S. Army Corps of Engineers to build one of the first flood control projects in San Antonio, covering 31 miles of the San Antonio River and its tributaries.

In 1991 and 1997, the San Pedro Creek and San Antonio River Tunnels were completed. Together these tunnels divert 100-year floodwaters 150 feet below downtown to avoid urban areas, releasing water further downstream at Lone Star Boulevard and Mission Road near Roosevelt Park. Construction of the two tunnels was completed just in time for the 1998 flood that destroyed 1,100 homes and ended 31 lives.

The 1998 flood triggered a renaissance of flood preparedness in San Antonio. In 2004, the River Authority, in partnership with FEMA, launched a $14 million dollar project to update all the hydrology models and maps of Bexar County watersheds. The maps, which were released in 2010, provide a guide for developers to estimate flood risk and plan for surface runoff. Today, this data is regularly updated and re-transmitted to FEMA.

“That is the foundation now of how decisions are made,” Scott said. “Those maps and models are already being redeveloped to reflect capital investments and also emerging development.”

Meanwhile, whether or not the Bexar County Flood Control Plan will receive an extension beyond 2017 remains unclear, as McCabe asked County Commissioners for more time to review the County’s High Water Alert Lifesaving Technology (HALT) program before approving future funding for the plan. The HALT program is a network of low-water crossings outfitted with sensors that detect rising water and warn drivers of dangerous crossings – in some cases triggering automated gates that block crossings altogether.

Attitudes among county and city officials after Hurricane Harvey are markedly different from those after the 1998 flood that galvanized civic action leading up to the development and funding of the Bexar County Flood Control Program.

“We were very much prepared for the aftereffects of Hurricane Harvey,” Frisbie said. “But obviously if you’re going to get 50 inches of rain, no system can handle that.”

Several data tools are available to learn more about San Antonio’s flood preparedness:

FEMA Flood Zones Explained

FEMA Flood Dataset for Bexar County

River Authority Floodmap Viewer

River Authority Data Viewer

Emily Royall is the Rivard Report's former data director.