Waller Creek Tunnel Project Conceptual and Preliminary Engineering Report

EXECUTIVE SUMMARY: This report summarizes the findings and recommendations of the conceptual design and preliminary engineering phase study, undertaken by the Brown & Root / Espey-Padden Joint Venture, for the Waller Creek Tunnel Project. The purpose of this project is to provide flood control and water quality enhancements to the lower Waller Creek watershed through the construction and operation of appropriate stormwater facilities and to allow a subsequent increase in urban development within the reclaimed floodplain area within the lower Waller Creek corridor. This study compared alternative designs for the diversion of the 100-year event flow from the lower reach of Waller Creek. The recommended facilities to accomplish this objective, based on diversion of the 100-year event, require the following major components: 1) The inlet design is the “100-year Morning Glory with Mechanical Screens and Water Features” located immediately north of 12th Street in Waterloo Park. The inlet design includes an in-channel diversion structure, trash screening equipment, inlet shaft, recirculation pumping system and associated structures, control building and landscaping. 2) The tunnel alignment of approximately 5,400 feet in length with 22-foot inside diameter is generally located under Sabine Street with right-of-way approximately 50 feet below the ground surface. The diversion of stormwater flows from the lower reach of Waller Creek is feasible through the use of a series of side overflow weirs. While diversion weirs located 10th and 9th Streets could be connected directly into the main tunnel, hydraulic analysis indicates that diversion weirs located at 6th and 3rd Streets would require an independent diversion lateral connected directly to the outlet structure. 3) The outlet facilities located in an excavated “lagoon” immediately west of Waller Creek’s outfall to Town Lake (West Creek site) consist of an outlet shaft, control weir, recirculation screens, tunnel dewatering pump station, control building and appropriate landscaping and recreational amenities. The recommended facilities necessary to meet the original project goal of keeping the 100-year flood flow within the existing channel of the lower Waller Creek have a project cost of $52.8 million, based on January 2000 prices. $40.8 million of this cost is construction cost. The remaining $12.0 million is right-of-way, engineering, testing and construction management. The project costs are significantly beyond the $25 million approved in the May 1998 bond elections. Based on these findings, in March 2000 the city authorized additional analysis to develop alternative flood protection goals and design recommendations to reduce the project cost. The results of this analysis are represented under separate report titled “Waller Creek Tunnel Project, Scope Reduction Cost and Benefit-Cost Analysis”, Brown & Root /Espey Padden, A Joint Venture.