Be River Proud

Flood Risk

The River Authority uses comprehensive planning, precision protection, strategic partnership, and community preparedness to help communities throughout the San Antonio River Basin reduce the devastating effects of flooding.

Why does it flood?

We live in a region known as Flash Flood Alley. It stretches from Del Rio in southwest Texas, east to San Antonio and follows the IH-35 corridor north through the Dallas-Fort Worth metroplex. Heavy rainfall and drainage off this landscape, also known as the Balcones Escarpment, combine to make this part of Texas one of the most flood-prone regions in North America.

Flooding history in San Antonio
San Antonio River Walk Association - image of historical flooding in San Antonio

1790: The de la Garza House constructed near San Pedro Creek. The structure is believed to have been one of the oldest residences left standing in the city and is listed on the NRHP.

A flooded river

1845: San Antonio River and area creeks flood. Following the flood, the first proposal was made to build a dam near the headwaters of the San Antonio River at the end of Olmos Creek.

1851 flood of San Antonio

1851: City Council takes official action to reserve a clearly defined area for San Pedro Springs Park. The San Antonio Daily Ledger reported: A public square embracing an extent of fifty acres, has been set apart, above our town. From the heart of this square, leap forth, from God’s alembic, the clear waters of San Pedro.

Firemen helping two children during a flood

1899: The San Antonio River and area creeks flood. 

A flooded road in 1913

October 1, 1913: A record rainfall of over 7 inches in 24-hours caused major flooding along the San Antonio River, San Pedro Creek and Alazán creeks. Four lives were lost and significant damage occurred in downtown San Antonio estimated at $250,000 (almost $6.2 million in 2017 dollars).

1921 flood in San Antonio

September 9, 1921: San Antonio historic flood kills 51 people and causes $3.7 million dollars in damages (over $52.1 million in 2017 dollars). The 7.38 inches officially recorded in San Antonio combined with amounts twice as heavy from higher ground to the north, sent a massive surge of water down the San Antonio River. All but four of the deaths occurred along the San Pedro and Alazán creeks.

Building a dam

1926: June 28, 1929: Young architect, Robert H. H. Hugman, presents his plan for “The Shops of Romula and Aragon” to Mayor Chambers, two City Commissioners, property owners and civic leaders. The proposal endorses the bypass channel and recommends floodgates at the north end, a small dam at the south end and a tainter gate in the channel to check the flow and create pools of water. The Depression prevents any construction other than the bypass channel that was begun in 1926 and completed in 1930.

The Olmas Dam

1935: Following a storm, the Olmos Dam proved its worth by holding back 20 feet of water.

1946 flood in San Antonio

1946: The San Antonio River and area creeks flood resulting in the loss of four lives. 

Opening of the San Antonio River Channel Improvement Project in 1954.

1954: As a result of the flood of 1946, the U.S. Congress authorized the San Antonio River Channel Improvements Project (SACIP) allowing Bexar County and the San Antonio River Authority (SARA) to enter into a partnership with the U.S. Army Corps of Engineers to improve flood control along 31 miles of the San Antonio River and its tributaries. This involved realignment and channelization of the river system to move flood waters quickly away from urbanized areas. Construction began on the SACIP in 1958.

A map of San Antonio River Authority Dams

1959: Nine dams along Calaveras Creek (Bexar County) and eleven along Escondido Creek (Karnes County) were completed and plans were underway for additional dams along Martinez Creek and Salado Creek (both in Bexar County).

Construction of the tunnel under San Antonio

1997: Completion of the San Antonio River Flood Tunnel designed to work with the Olmos Dam to protect downtown San Antonio from damage.  The project includes an inlet facility located at Josephine Street and the San Antonio River, a 24-foot diameter, 3-mile long tunnel and an outlet site at Lone Star Boulevard.  Ten months after completion of the tunnel, on October 17-18, 1998, south central Texas experienced record-breaking rainfall, and both the San Pedro Creek and the San Antonio River tunnels performed as designed, sparing downtown San Antonio from a devastating flood. In 1999, the tunnel project won the State of Texas Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers; it also received a national-level Award of Merit. A year later, it was one of four projects to receive the Federal Design Achievement Award from the National Endowment for the Arts (NEA), as well as an achievement award from the American Society of Civil Engineers in recognition of the San Antonio River Tunnel Inlet Site.

Flooded Road

1998: San Antonio suffers 100-year flood disaster.

A flooded Highway in 2002

July 2002: Devastating floods hit the San Antonio River and area creeks.

Flash Flood Alley

In the San Antonio River Basin of South Texas, steep terrain, shallow soils, and narrow river channels send runoff quickly downhill. The result is deep, fast, and erosive flood waters. These destructive forces have the potential to penetrate communities downstream, threatening lives and property throughout the basin.

The San Antonio River Authority is meeting the challenge head-on with a multi-level approach to flood risk management.

Hover or touch the map below to view the counties in Texas that are part of "Flash Flood Alley."

Texas Flood Alley Map
Texas Flood Alley Map Zoomed
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