A Tale in the Lake: Marine Construction of the 300 MGD Raw Water Intake for City of Austin’s Water Treatment Plant No. 4

摘要

The recently built Raw Water Intake is responsible for reliably supplying up to 300 millionrngallons of high quality fresh water daily to the newest pearl on the crown of City of Austin’srnpublic water system ------ Water Treatment Plant No. 4. The massive intake structure, which isrnnearly made exclusively of metal components, consists of three large custom designed screensrnweighing 45 tons each situated at varying depths, steel piping of 9-foot diameter in variousrnconfigurations and sophisticated support mechanisms. The entire intake structure sprawls morernthan 200 ft in length and extends 150 ft in depth. Founded at one of the deepest spots at thernbottom of Lake Travis, the intake structure would be completely submerged when the lake is atrnits normal conservation pool level.rnThe majority of the construction work for the Raw Water Intake was conducted in Lake Travisrnby a marine contractor. This paper focuses on the specialized equipment, construction techniquesrnand procedures demanded by the project needs, which are rarely encountered in typical waterrnprojects. The specialized equipment included fleets of floatable barges, heavy drilling rigs,rncrawler cranes and sophisticated underwater positioning devices. In addition, diver’s assistancernand video recording were employed throughout the project. The most vital construction stepsrnincluded the following: 1) Bathymetry survey in the vicinity of intake structure to obtain andrnverify a more thorough understanding of site condition, in addition to the site informationrnprovided in the bid documents; 2) Construction of the 12.5-foot diameter, 80-ft deep drilled shaftrnand grouting of the riser pipe that serves as the foundation of the lower intake screen; 3)rnConstruction of the steel pile foundations that support the middle and upper intake screens; 4)rnInstallation of three intake screens underwater; 5) Connection of the intake structure to the rest ofrnthe raw water system and commission of the intake, i.e., the “lake tap” operation, which wasrnperhaps the most exciting yet risky portion of the entire project.