Deep-Water Intake and Tunnel System Aims to Reduce Drought Vulnerability
Freese and Nichols’ joint venture with Walker Partners to meet water needs for the Central Texas cities of Cedar Park, Round Rock and Leander received international attention in the North American edition of Tunnelling Journal, a United Kingdom-based magazine. (The British spelling is Tunnelling.)
The JV is assisting the Brushy Creek Regional Utility Authority on Phase 2 of its Raw Water Delivery System, which involves a deep-water intake and conveyance system to draw water from Lake Travis to a new high-capacity pump station adjacent to the Cedar Park Water Treatment Plant. Schnabel Engineering serves as a subconsultant for geotechnical and tunnel engineering on the project.
The new $174 million system aims to reduce drought vulnerability for the three BCRUA member cities in a rapidly growing area north of Austin.
The article, “Lake Travis on Tap,” provides a detailed description of the project’s tunneling components and includes quotes from Freese and Nichols’ Rusty Gibson, Lead Technical Professional for the Transmission and Utilities Practice, and Erin Flanagan, JV Project Manager.
While Lake Travis is the area’s main water source, it’s also highly popular for recreation. The project site also includes dedicated nature preserves, and design had to take into consideration environmental concerns and requirements set by the Lower Colorado River Authority, which controls the lake, and the U.S. Army Corps of Engineers.
The intake system will have an ultimate capacity of 144.7 million gallons per day (MGD). Elements include an intake assembly, maintenance building for zebra mussel control chemicals, gravity flow tunnel, pump station, transmission tunnel, roadway impact evaluation, geotechnical, and off-site improvements at the Cedar Park, Leander and BCRUA WTPs. In addition to final design, the team is handling stakeholder coordination, permitting and public outreach.
For the intake, two lake taps, or vertical shafts, will be drilled from a barge on Lake Travis and connect to an intake tunnel below the lakebed. The intake tunnel, about 9,000 feet long and 12 feet in diameter, extends from the lake tap to the pump station. A second tunnel, 2,600 feet long and 12 feet in diameter, will accommodate the transmission pipeline.
Construction safety and the lake environment were among important concerns during design.
Divers will be needed to perform some of the intake shaft construction in the lake, but the design team tried to minimize underwater work to increase safety.
Protecting the lake’s water quality also was imperative. Because material from the intake construction cannot be left in the lake, the design uses reverse circulation drilling to excavate the two lake taps, with the cuttings then taken by barge to a filter system on the shore.