ASDSO Conferences and Seminars

FIELD TRIP to City of San Antonio Flood Control Tunnel and Olmos Dam

When: Friday, September 15, 8:00 am – 12:30 pm

Description: The San Antonio River Tunnel project (SART) - completed in 1998 - was designed to work with Olmos Dam Floodwater Detention to protect downtown San Antonio from damage. The project includes an inlet facility located at St. Josephine Street and the San Antonio River, a 24-foot diameter tunnel, and an outlet site at Lone Star Boulevard. The inlet and outlet sites were designed and landscaped to create a park-like setting, in keeping with the character of the adjacent neighborhoods and the city’s popular tourist attraction the River Walk. The tunnel, capable of funneling over three million gallons of water per minute, was bored over ten years and one month and runs three miles long. Soon after it was constructed, SART protected life and untold millions of dollars of property from flood damage when it passed the “flood of record” for the area in October 1998. An innovative alternative to river channelization, the project’s tunnel concept minimizes disruption. Additionally, SART is beneficial in its reduction of environmental impact. One advantageous feature of the project, the recirculation of tunnel water, creates both higher water quality and conserves water, which had historically been pumped from the Edwards Aquifer to supplement river flow. 

The San Antonio Water System (SAWS) also implemented a treated effluent water recycling program so that the flow would be supplemented by recycled water at the tunnel inlet and in Brackenridge Park. This allowed the pumps, which had previously drawn water from the aquifer to supplement the base flow of the river, to be turned off. This project represents innovative and functional design and is a classic example of outstanding cooperative effort between local and federal government agencies. (Source: San Antonio River Flood Control Tunnel, 1998 OCEA ASCE Texas Section 3/15/2017)

Olmos Reservoir is located four miles north of San Antonio in Bexar County, on Olmos Creek, a tributary of the San Antonio River. The reservoir was constructed after the record flood of September 1921, which extensively damaged the San Antonio business district. Construction of the dam started in 1925 and was completed in 1926. In March 1979, improvement was made to strengthen and anchor the dam, and modification to the gate operations to provide an emergency spillway. The dam is gravity concrete structure of 1,941 feet long with a maximum height of 60 feet. The reservoir has a capacity of 12,600 acre-feet and a surface area of 889 acres at the top of flood control pool of 725 feet above mean sea level. The drainage area above the dam is 32 square miles. (Source: 

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Registration: $65 per person includes motorcoach transportation, guided facility tours, light snack and beverages.

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