Flood Control > San Antonio Channel Improvements Project (SACIP) > SACIP

SACIP

SAN ANTONIO RIVER AND SAN PEDRO CREEK TUNNELS
(SAN ANTONIO CHANNEL IMPROVEMENT PROJECT)

AUTHORIZATION OF THE SAN ANTONIO CHANNEL IMPROVEMENT PROJECT:

The 1921 flood in Bexar County was a major reason for the adoption of a flood control plan by the City of San Antonio, Texas. The plan included the construction of Olmos Dam at the headwaters of the San Antonio River and widening and deepening of specific sections of the San Antonio River and its four tributary creeks to prevent flooding in the City of San Antonio. After the flood of 1946 the U.S. Army Corps of Engineers completed a flood control examination and survey of the earlier plan and submitted their report (entitled the San Antonio Channel Improvement Project) to Congress for approval and authorization. The San Antonio Channel Improvement Project (SACIP) was authorized in 1954 and the San Antonio River Authority was designated as the "local interest" sponsor.

THE PARTICIPANTS:

The River Authority's responsibility as "local interest" sponsor in the SACIP includes right-of-way acquisition, utility relocations and construction of bridges and in-channel dams mainly financed by the Bexar County Flood Control Tax. The Corps of Engineers designs and constructs the channel project. The City of San Antonio finances segments not covered by the County Tax and operates and maintains the completed segments of the flood control channel.

THE SACIP:

The SACIP has been divided into construction segments, part of which have been completed. Design and construction of these segments by the Corps of Engineers depends on the availability of Federal funding.

One segment of the SACIP authorized for construction included the San Antonio River, extending from U.S. Highway 281 at Brackenridge Park to Lone Star Boulevard. The conventional methods of widening and deepening the existing river bed and channel proved to be too disruptive, expensive, and too complex hydraulically and geometrically. The Corps of Engineers selected the construction of an inverted siphon tunnel as the most feasible, economical and least disruptive solution to the problem of flood control on the San Antonio River from U.S. Highway 281 to Lone Star Boulevard. Flood control by inverted siphon tunnel for the San Pedro Creek, from Quincy to Guadalupe Streets, was selected as the cost effective alternate because of the opportunity to construct at the same time as the San Antonio River Tunnel.

THE TUNNELS:

Both the San Antonio River and San Pedro Creek tunnels are designed to divert a major portion of the 100 year storm floodwaters beneath downtown San Antonio and release it safely into the San Antonio River/San Pedro Creek downstream. The tunnels are 24 feet, 4 inches diameter inverted siphons located approximately 140 feet below ground level and for the most part are located under existing public right-of-way.

Each tunnel consists of an intake structure, outlet structure, maintenance and ventilation shafts as well as the tunnel itself. Figure 1 shows graphically how the tunnels work. The inlet and outlet structures and maintenance shafts are constructed by conventional methods. The tunnels are constructed using a tunnel boring machine (TBM). The TBM is assembled underground after excavation of the outlet structure shaft and an assembly chamber. Excavated materials are removed through the outlet structure and transported to a disposal site. The Ohbayashi Corporation, the tunnel Contractor, used pre-cast concrete segments for the tunnel lining. See Attachment No. 3 for additional tunnel statistics.

PLANS AND SPECIFICATIONS:

Plans and specifications for the San Antonio River and San Pedro Creek tunnels were prepared by the U.S. Army Corps of Engineers' Architectural/Engineering Consultants - Parsons, Brinckerhoff, Quade and Douglas in Chicago, Illinois. The construction is administered by the U.S. Army Corps of Engineers, Fort Worth District, with the River Authority acting as liaison and local interest sponsor for the project. Landscaping and water quality enhancing aeration/recirculation systems were designed by the River Authority.

FUNDING:

Construction of the project is funded by the Corps of Engineers with the local interest portion and right-of-way acquisition for the San Antonio River Tunnel funded by the River Authority through the Bexar County Flood Control Tax and the San Pedro Creek Tunnel funded by the City of San Antonio.

PROJECT DESCRIPTION:

The San Antonio River and San Pedro Creek are of inadequate capacity to prevent excessive flooding within the heart of San Antonio, Texas. The U.S. Army Corps of Engineers, Fort Worth District together with the San Antonio River Authority have embarked on a program of alleviating these flooding problems for storms up to a 100 year frequency of recurrence by use of inverted siphon tunnels. A summary of the detailed project descriptions that follow are contained in Attachments No. 1 and No. 2.

ENVIRONMENTAL ASSESSMENT:

An environmental assessment prepared for the tunnels project determined that the recommended plan was not controversial and would not have a significant adverse impact on the natural or manmade environment and therefore did not require preparation of an environmental impact statement.

CONCLUSION:

The inverted siphon plan for Corps' Units 8-4, 8-5-1 and 7-3-1 recognizes the highly urbanized setting and sensitivity of resources in San Antonio and is considered the most cost-effective and least environmentally damaging alternative solution to flood problems within these areas of San Antonio.

ABSTRACT

FLOOD CONTROL IN SAN ANTONIO

Both the San Antonio River and San Pedro Creek Tunnels are designed to divert a major portion of the 100 year storm floodwaters beneath downtown San Antonio and release it safely into the San Antonio River/San Pedro Creek downstream. The tunnels are 24 feet 4 inch diameter inverted siphons located approximately 140 feet below ground level and for the most part located under existing public right-of-way.

Each tunnel consists of the horizontal bore, intake structure, outlet structure, maintenance and ventilation shafts. The inlet and outlet structures and maintenance shafts were constructed by conventional excavation and shoring methods. The tunnel is being constructed using a tunnel boring machine (TBM). The TBM was assembled underground after excavation of the outlet structure shaft and an assembly chamber. Excavated materials are removed through the outlet structure and transported to a disposal site. The tunnel contractor is using pre-cast concrete segments for the tunnel lining.

The San Pedro Creek Tunnel bore (6,060 feet long) was completed in July 1989 and its inlet and outlet structures are scheduled for completion mid 1991. The San Antonio River Tunnel (16,330 feet long) is currently experiencing some construction difficulties and completion of the bore is currently scheduled for late 1992.

Plans and specifications for the San Antonio River and San Pedro Creek Tunnels were prepared by the U.S. Army Corps of Engineers' Architectural/Engineering Consultants—Parsons, Brinckerhoff, Quade and Douglas in Chicago, Illinois. The construction is administered by the U.S. Army Corps of Engineers, Fort Worth District, with the San Antonio River Authority acting as liaison and local interest sponsor for the project. Landscaping and water quality enhancing aeration/recirculation systems are being designed by the San Antonio River Authority.