Major investments in flood control infrastructure on the San Antonio River over the past 100 years has saved downtown San Antonio in terms of life and property, and has opened opportunity for a growing city center to overcome many of the hurdles imposed by being in the heart of Flash Flood Alley.  

Olmos Dam: The First Line of Defense

Four miles north of downtown, a concrete wall stretches across the open space between Highway 281 and the edge of Alamo Heights.  Olmos Dam was built to prevent destruction of downtown from flooding.  In 1921, lethal amounts of rain caused massive flood waters to engulf downtown San Antonio, killing 51 people.  

The completion of Olmos Dam in 1926 marked the beginning of a comprehensive flood control system to protect downtown.  Following a storm a 1935, the Olmos Dam proved its worth by holding back 20 feet of water, and, for over 90 years now, the Dam has stood guard over downtown.  Since its completion, Olmos Dam has undergone two major upgrades to ensure its continued reliability: once in the 1982 and again in 2010. 

Origins of the San Antonio River Walk

In 1929, just prior to completion of a flood control bypass channel in downtown San Antonio, a young architect named Robert H. H. Hugman presented his proposal endorsing the bypass channel and offering a plan to protect and utilize the “river loop.”  The idea of the modern River Walk was born. 

Funds became available to build the River Walk in 1938 from the Works Projects Administration (WPA) and from a bond assessment of local property owners.  The River Walk was completed in 1941 including the expansion of the pilot channel, the installation of several dams, construction of underground drains, and the installation of flood gates at both ends of the river loop.  Today, there are also flood gates at Nueva and S. Alamo Streets. 

Another major flood in 1946 led to a partnership between Bexar County, the San Antonio River Authority (SARA), and the U.S. Army Corps of Engineers (USACE).  In 1954, Congress authorized the USACE to work with Bexar County and SARA to channelize 31 miles of the San Antonio River and its tributaries for flood control.  In addition to channelization, which began in 1958, the San Antonio River Channel Improvement Project eventually included construction of the San Antonio River and San Pedro Creek tunnels.  

A Tale of Two Tunnels

Running three miles from Josephine Street to Lone Star Boulevard, the San Antonio River Tunnel carries flood waters, which would otherwise decimate downtown San Antonio, 150 feet underground, bypassing downtown lives, businesses and property.  SARA was the local construction project manager, and the tunnel operation was turned over to the City upon the project’s completion. 

Completed in 1997 for a cost of $111 million in federal and local funds, this engineering marvel experienced its first major test in 1998 when flood waters were diverted from downtown, saving hundreds of millions of dollars of property from flood damage, effectively paying for itself in one flood event.  Its subterranean route follows Alamo Street beneath Alamo Plaza, Hilton Palacio del Rio, La Villita and Beethoven Hall.  Augmented by the comprehensive flood control system of dams, flood gates and drainage features, the San Antonio River Tunnel is credited with averting significant property damage during major flood events in 1998, 2002, 2013 and 2015.  

The second tunnel running under San Pedro Creek, which became operational in 1991, begins at W. Quincy Street and emerges at Guadalupe Street.  Both tunnels transport 80% of the 1% Annual Chance Storm (aka 100-year flood) beneath downtown San Antonio and release it downstream, moving up to three million gallons of water per minute.  The remaining flows travel via the main channel.

The story of San Antonio is one of disaster met with resilience.  Today, downtown San Antonio is immensely safer than it was a century ago.  The flood control improvements have created space for city center growth, investment, and vibrancy.  Thanks to smart planning and a communal willingness to invest in our community, future generations will have greater opportunity to recreate, work and flourish in our city center.  Resilience runs deep in the heart of San Antonio. 

- Steven Schauer 
SARA Director of Government and Public Affairs