San Pedro Creek Tunnel

The San Pedro Creek flood diversion tunnel is approximately 6,000 feet long with a finished inside diameter of 24 feet, 4 inches lined with precast concrete segments. It commences near the Interstate 35-Interstate 10 interchange, between N. Santa Rosa Street on the west and Camaron Street on the east, where an intake approach channel is constructed (See Figure 2 for route). The tunnel inlet shaft is constructed downstream of the approach channel and is 24 feet by 4 inches in diameter dropping approximately 119 feet to the tunnel invert. The tunnel outlet shaft is 35 feet in diameter and contains embedded piping for dewatering facilities.

The tunnel inlet, outlet and maintenance shafts were constructed by conventional methods. The tunnel was constructed using a tunnel boring machine (TBM). The TBM was lowered through the outlet shaft in sections and assembled underground. The TBM bored the tunnel going upstream and in August 1989, the TBM was removed in sections through the tunnel inlet shaft. Excavated materials were removed through the tunnel outlet structure and transported to a disposal site. The tunnel became operational in June 1991.

A subsequent San Antonio River Authority contract added additional pumping capacity for tunnel recirculation. Construction of this phase was completed in June 1997.

San Pedro Creek Tunnel
San Pedro Creek Tunnel
Scheduled

Start of Project: (Shafts and Tunnel) November 1987
Became Operational: June 1991
Recirculation Facilities Complete: June 1997

Size

Approximately 6,060 feet of 24 feet, 4 inches diameter inverted siphon at a depth of approximately 140 feet.

Estimated Total Project Cost (Tunnel, Inlet and Outlet)

Federal Cost (approximate) $34,600,000
Local-City of San Antonio & San Antonio River Authority (approximate) $4,200,000  
Total Project Cost: $38,800,000

Location

Inlet downstream of Quincy Street: in the center of San Pedro Creek. Tunnel built beneath San Pedro Creek. Outlet upstream of Guadalupe Street at San Pedro Creek: west bank of San Pedro Creek.

Designed

To carry the 100-year flood flow of 4,600 cfs and allow 550 cfs down the existing channel at peak.

Inlet Structure

Connects the tunnel intake structure to the proposed San Pedro Creek Channel east of IH-35 at San Pedro Creek. The inlet structure contains a 90-foot wide intake ogee weir and apron structure with 70-feet long grated roof and trash racks. Pumps downstream of the tunnel inlet bypass water from the tunnel intake and release it downstream for base flow diversion and to the outlet recirculation structure for recirculation of the tunnel water.

Outlet Structure

Directs discharge from the tunnel outlet shaft to the existing San Pedro Creek Channel. Measures 207 feet across the front; 98 feet across the rear and 80 feet from front to rear. Consists of cantilevered retaining walls, trash racks and grated roof. A maintenance access ramp is located on the upstream side of the tunnel outlet at Guadalupe Street to provide vehicular access to the existing channel bottom and to maintain the trash racks. A maintenance access structure is built on top of outlet structure.

Tunnel

The Ohbayashi Corporation excavated the tunnel by tunnel boring machine. The diameter of tunnel is 24 feet, 4 inches using pre-cast concrete segmented lining.

TUNNEL STATISTICS
  SAN PEDRO CREEK TUNNEL SAN ANTONIO RIVER TUNNEL
Inlet Shaft:    

Size (diameter)

24 feet 24 feet

Depth from surface to invert of tunnel

119 feet 118 feet
     
Outlet Shaft:    

Size (diameter)

35 feet 35 feet

Depth from surface to invert of tunnel

144 feet 144 feet
     
Tunnel:    

Size (diameter)

24 feet by 4 inches 24 feet by 4 inches

Length to centerline of shafts

5,985.05 feet 16,224.37 feet

Average depth from surface to invert

142 feet 151 feet
     
Capacity Flow of Tunnel 4,600 cfs+ 6,700 cfs+
Water Flow Velocity 10 ft/sec+ 15 ft/sec+