In April 2015 the Jacksonville District awarded Manson Construction Company a $39520500 contract for dredging and construction work along the St. Johns River at Mile Point. This project will correct a navigation issue where the river and Intracoastal Waterway (IWW) meet in anticipation of the larger port deepening project which will complete the design and engineering phase in November.
The Port Authority of Jacksonville has advanced the federal share of the funding for the Mile Point project under an agreement that it will be reimbursed. The project funding is split 75/25 percent between the Corps and the port. A Project Partnership Agreement covering the funding agreement between the two for the Mile Point project was signed on January 30 2015. The port will invest $43.5 million total $39 million for construction including the port’s share and funds for design.
Manson is working on-site at Mile Point mobilizing equipment to start construction in early November.
Five thousand feet of shoreline make up Mile Point located along the north shore of the St. Johns River and east of the IWW. The confluence of the St. Johns River with the IWW is known as Mile Point an area that experiences difficult crosscurrents on the ebb tide. All vessels with a transit draft greater than 33 feet inbound and 36 feet outbound must adhere to navigational restrictions on the ebb tide.
To correct the problem work will begin on removing an existing 3100-foot training wall and building a new 4250-foot western training wall which will help guide river currents where they pose an issue for vessels. The design was developed in the Corps modeling center in Vicksburg Mississippi to find the right placement for the wall to better serve navigation and correct the currents that affect navigation at Mile Point. The new training wall will also border and protect Great Marsh Island a marsh wetland area to be created with the dredged material from the project.
Manson will dredge a flow improvement channel to allow recreational vessels to get through the channel to the IWW while work continues on the new training wall. Dredges will remove 43000 cubic yards for the new channel. That work will begin in early 2016 and will be completed by March.
Geotextile tubes will form the framework for the new saltwater marsh approximately 3800 linear feet of tubes. The reconfiguration of the training wall would result in the loss of approximately 8.15 acres of salt marsh and approximately 0.75 acres of oyster habitat. The restoration will add 53 acres of salt marsh at Great Marsh Island and approximately 2.77 acres of oyster habitat at the island and along the reconfigured wall.
The material dredged from the flow improvement channel will form the new salt marsh. The sediment will remain in place for one year after which time Corps biologists will return to plant native species.
As the final leg of the Mile Point project the contractor will relocate the eastern leg training wall about 2050 feet from May 2016 to August. With final inspections the Corps said the project should be complete by October 2016.
While the Port of Jacksonville deepening project failed to receive federal funding from Congress in the FY2016 budget Jacksonville District spokesperson and project manager for the Mile Point and deepening projects Jason Harrah said the port has again agreed to advance the funding so the project can continue forward to construction ahead of the congressional authorization of federal funds for the project. Lieutenant General Thomas Bostick signed the Chief’s Report for the project on April 16 2014 and the project will complete the preconstruction design and engineering phase in November.
The $710 million project will deepen the federal navigation channel from 40 to 47 feet from river mile 0 to river mile 13. Widening of the channel in several places and two new turning basins – at Blount Island and Brills Cut – will accommodate two-way traffic for post-Panamax vessels.
While the St. Johns Riverkeeper organization filed a lawsuit notifying of its intent to sue the Corps of Engineers over the dredging project Harrah said the project will continue as scheduled pending any legal action.
“This congressionally authorized project was extensively studied and modeled and rigorously peer-reviewed by internal and external experts. Based on certified Corps of Engineers models and other relevant information deepening the St. Johns River is projected to have a positive economic benefit and only minor environmental effects” Harrah said.
One of the models used the EFDC (Environmental Fluid Dynamics Code) hydrodynamic model could using the established science of the model break ground on modeling the environmental impacts of deepening projects.
The EFDC originally developed by the Environmental Protection Agency (EPA) and the St. Johns River Management District has been used extensively as a hydrodynamic model to simulate aquatic systems. With support from EPA the model is maintained by Tetra Tech. It contains dynamically linked hydrodynamic sediment transport contaminant and water quality modules. Although the tool has only been recently modified for deepening projects the model is highly used and widely respected Harrah said. Although no examples of post construction monitoring of a deepening project can be applied to the ERDC performance yet the Corps is confident that this model can accurately predict the influence of depth and geometry on hydrodynamics and transport in an estuary.
For the Jacksonville port deepening project that original model was adapted by Taylor Engineering to model the effects of deeper water on salinity. Once completed the model predicted very minimal impacts with minor increases in upstream salinity Harrah said. For example the model predicts that the deepening will cause salinity to increase 0.2 parts per thousand at Acosta Bridge. “This increase is minor” Harrah said. “The salinity at this location naturally ranged between 1.4 to 14.4 parts per thousand during our six-year model simulation period.” He said the range is linked to rainfall variability and periods of drought and sea level rise can increase salinity levels more than the model’s predictions for the effects of the deepening project.
“The key is it’s never really been done” Harrah said. With the help of the U.S. Coast Guard the Corps will place salinity cages in the water to monitor flow and salinity data before during and after the project up to 10 years. If the monitors detect a spike in the readings the model can accurately detect if it occurred as a result of the deepening or other natural occurrences.
The Jacksonville port deepening project will be broken into four contracts – A B C and D. The initial contract will be awarded in January 2016 with a Project Partnership Agreement between the port and the Corps anticipated to be in place by March 2016.