Sr Structural Engineer - Transportation LJA Engineering, United States
Abstract: TxDOT has operated the Port Aransas Ferry facility located in Nueces County since 1968, connecting State Highway 361 from Harbor Island to Mustang Island, across the Corpus Christi Ship Channel (CCSC). The ferry is essential for providing access to the mainland for the residents of Port Aransas and operates 365 days a year, 24 hours a day. The ferry crossing is considered a hurricane evacuation route and is only shut down 24 hours prior to hurricane landfall or high winds exceeding 55 mph. The only other vehicular access to Mustang Island is the John F Kennedy Memorial Causeway bridge, approximately 18 miles to the South.
The Harbor Island landing has five ferry slips and the Mustang Island landing has six ferry slips, one of which is for maintenance. The facility has been expanded, modified, and repaired many times over the years of its operation resulting in an amalgam of various infrastructure components. There are two different ferry configurations currently in operation: four 20-car vessels and five 28-car vessels. TxDOT plans to phase out the 20-car configuration.
Over the last decade, maritime traffic through the CCSC has significantly increased, both in tonnage per vessel and frequency, due to increased import/export activity through the Port of Corpus Christi. Currently, the CCSC at the ferry landings is not deep enough to allow for fully laden vessels to transit and is planned to be deepened to allow transit of loaded Very Large Crude Carrier class vessels.
The ferry landing is subject to several issues, both periodic and permanent, such as no severe weather mooring, outdated electrical system subject to storm surge, bulkhead presenting signs of failure, lifting cable for the transfer ramps occasionally off track, and ferry fueling limited to a single slip.
The infrastructure is in dire need of repair and modernization to address impacts from increasing marine traffic, increase resilience to major storm events, and accommodate the increasing vehicular traffic.
The project scope was to evaluate the existing infrastructure of the ferry facility and make recommendations on how to effectively update the facility and to mitigate the impacts of channel deepening to the operation of the facility. The project scope included a hydrodynamic study of passing vessels as well as an in-depth study to evaluate options.
The study resulted in design of new mooring and berthing system to allow ferries to be moored in slip during a hurricane, design of a new anchored bulkhead, rehabilitation of the ramp counterweight towers, design of new transfer ramp, elevated steel truss utility rack, elevated electrical power and supply, increased fueling capacity, removal of buried fuel tanks, new electrical system, conversion of ramp operations from winch and cable to a hydraulic system, and construction sequencing to maintain round-the-clock operation of the ferry.
Construction of the project was split into three phases, one for Mustang Island and two for Harbor Island, first for landside improvements and second for mooring and berthing structures. Design was completed for Mustang Island in April of 2023 and construction is underway.
How does this project / topic contribute to the advancement of the industry and profession?: This project exhibits features that may be implemented to increase resistance to severe weather events, including storm surges and hurricanes, to allow ferry facilities to reopen more quickly after the passage of such events and better serve impacted citizens more efficiently. Features which support this increase in service include the elevated utility system, above ground fuel tank, hydraulic system operated with environmentally friendly hydraulic fluid, severe weather mooring system, elevated redundant back up power, and improved breakwater. As operations were able to be maintained during construction, the techniques used showcase how owners can upgrade their facilities without significantly impacting revenues.
Does the project / topic implement new and innovative techniques, materials, technologies, and delivery methods?: This project featured extensive use of Thermal Sprayed Aluminum (TSA) coating on steel components which were exposed to direct saltwater contact as well as aerial contact. Floating dolphins on steel monopiles were used to allow the Owner to be able to moor their vessels withing their limited right-of-way during severe weather storm events. A unique spring compression/compression bearing system, constructed out stainless steel, was developed to allow for a flexible connection between the abutment and the transfer ramp.
What was the most challenging aspect of your project / topic and how did you handle it to ensure success?: Impacts to berthed ferries from the wake generated by passing vessels posed the largest challenge. Results from the passing vessel model and supported by online video evidence produced significant drawdown on the order of 6 plus feet as well as increased currents from returning water on the order of 5 ft/s to 12 ft/s depending on vessel. Upon review of several options, an operational procedure was discussed with ferry terminal operations and adopted that would cease loading operations during passage of a large vessel.
Who is the target audience for this paper?: With this project being multi-discipline with significant scopes it would be of interest to a wide audience such as: Ferry and Marine Terminal Operators, Transportation Engineers, Structural / Marine and Coastal Engineers, Electrical Engineers, Utility and Mechanical Engineers.
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