Padre Island Water Supply Project Minimizes Environmental Impact Using HDD Technology

Abstract

Padre Island is part of a barrier island complex that runs along the Texas coastline, from Galveston to Brownsville, Texas. It is bounded on the east by the Gulf of Mexico and by Laguna Madre on the west. A portion of the island is located within the limits of the City of Corpus Christi (City) and the water supply to the island is operated and maintained by the City. Prior to this project, the island was served by a 650 mm (24-inch) steel water transmission main that was constructed across the Laguna Madre in 1968. Survey and assessment of the existing pipeline indicated that it was nearing the end of its useful life. In order to increase the reliability of their water distribution system the City decided to pursue the design of a redundant water transmission main. To minimize impact to the natural resources in the area it was decided to locate the alignment on the south side of the John F. Kennedy Memorial (JFK) Causeway and to construct the pipe line using horizontal directional drilling (HDD) and conventional trenching methods. HDD was used to span the two major water crossings and conventional trenching was used to install the pipe through the dredged materials. During the design phase the City also decided to construct a 200 mm (8-inch) gas line and a 120 mm (4-inch) communications conduit along the same alignment as the water transmission main, allowing them to extend gas and communication service to the island. The final project consisted of 3,290 m (10,800 feet) of conventional trenching installation and 1,905 m (6,250 feet) of HDD installation for a 495 mm (18-inch) water transmission main, a 200 mm (8-inch) gas main and a 120 mm (4-inch) communications conduit. The first and most difficult HDD segment extended approximately 1,645 m (5,400 feet) from the mainland to the eastern side of the Humble Channel. A second 260 m (850 feet) HDD segment was constructed under the Gulf Intracoastal Waterway. This paper will discuss the design and construction of the Padre Island Water Supply project, focusing on the unique project challenges presented by the close proximity to the coast and important natural resources, as well as the very long and challenging HDD sections utilized.