Waller Creek Flood-Management and Water Quality Improvements

Original Project

The Waller Creek Tunnel project was included in the November 1998 bond election. An amount of $25,000,000 was approved for the project. This amount was derived from a January 1996 consultant study conducted for the City of Austin. The purpose of the project was to divert 100-year storm event flows from the lower Waller Creek channel. This would provide flood protection to 42 existing buildings, prevent the flooding of 12 roadway crossings, and reduce the width of the floodplain from up to 800 feet to the width of the channel. The reduction in floodplain produced by the project would significantly increase the amount of developable land area in the lower Waller Creek watershed.

After the 1998 bond election, the Brown & Root / Espey Padden Joint Venture was selected to review the project described in the January 1996 study and prepared recommendations to meet the original design goals. The recommended project provides 100-year storm event flood protection with no out-of-bank or roadway flooding. The tunnel would be 22 ft. in diameter and approximately 5000 ft. in length. The project originates in Waterloo Park with discharge to Town Lake. A Sabine Street route was recommended. Significant inlet and outlet structures are required and because the structures are in parkland, aesthetics of the structures are a major consideration. The inlet structure would include a pond, a cone or morning-glory shaped inlet structure, small dam, access bridge, pump building and significant landscaping enhancements. The inlet also includes mechanical screens to ensure operational reliability and a system to pump small quantities of water from the tunnel to the creek. This pumped water will augment the base flow in the creek and by so doing enhance its aesthetic appeal and water quality. The outlet structure includes a pond, an outlet shaft, and a de-watering pump system. A floating stage will be located on the outlet shaft. An outdoor amphitheater will be built on the slopes surrounding the outlet pond.

The revised cost of the original project is estimated at $52.8 million. An additional $9.5 million is required to reduce the maximum depth of flow in the lower channel to four feet.

Project Cost Reduction Analysis

Because the estimated cost of the of the original project significantly exceeded the cost of the project as estimated in the January 1996 study and the funds available, additional studies were commissioned to study means of reducing the cost of the project while achieving as many of the original project goals as possible. The hydraulics of the lower Waller Creek were studied in detail. Significant cost savings could be realized by diverting 55% of the 100-year stormwater flows. This diversion would require a 15.5-ft. diameter tunnel. The 100-year stormwater flows would remain in the channel with the 15.5-ft. diameter tunnel except for a small area between 8th and 10th Streets. A Red River Street route is recommended. This project would reduce the size of the lower floodplain by 98% and make 1.225-million sq. ft. of land area available for development.

The estimated cost of the reduced scope project is $45.9 million. This project is recommended for construction. The design of the project would require 19 months. The construction of the project would be completed in 3 years 9 months.

Benefit-Cost Analysis

A benefit-cost analysis was completed for the project. The study considered the cost of the project (original and reduced scope), flood damage costs, roadway upgrade costs and tax revenues benefits. Development scenarios were prepared with and without the construction of the tunnel and for various building types and densities. The development scenarios were developed considering zoning requirements, Capital view corridors, and developments planned or underway. Payback for 15.5-ft. diameter tunnel project considering construction cost and all revenues to the City of Austin (only) is 7 to 12 years. The range in payback period is due to alternate development density scenarios for the creek corridor.

Coordination with TxDOT and Recommendation

The TxDOT is planning to reconstruct IH-35 below ground elevation between 15th Street and Riverside Drive. Studies are underway to determine the feasibility of a joint drainage project with TxDOT. The joint project, if feasible, would allow TxDOT use of the Waller Creek Tunnel to convey stormwater from the IH-35 project. If joint project is feasibility is proven, the size of the tunnel would be increased and cost-sharing discussions with TxDOT would be conducted. Initial studies indicate that TxDOT will probably develop a drainage system for the roadway independent of the City's Waller tunnel project.

Funding

The recommended project cost estimate is $45.9 million (in year 2000 dollars). This amount significantly exceeds the funds available from the November 1998 bond authorization. The preliminary engineering report is under final revision by the City's consultant team. The project will be on hold, pending additional funding, at the completion of the preliminary engineering report.

Basic Data

• Project Contact: Gary M. Kosut, P.E., Watershed Protection and Development Review Department, 974-3374
• Estimated Project Cost: $45,900,000

Back to the July 2001 Downtown Report