US Army Corps Makes Good Progress on Miami Harbor Project
Progress is on schedule with the Miami Harbor deepening and widening project, including the successful construction of artificial reefs and relocation of about a thousand healthy corals.
The U.S. Army Corps of Engineers, Jacksonville District and its contractors are at the 35 percent completion mark, with more than one million cubic yards of material safely removed from the federal channel and the majority of mitigation construction completed.
Operations in the outer channel, which began in November 2013, calls for dredging approximately 2.1 million cubic yards of material from the harbor entrance channel, relocating coral, creating artificial reef, and constructing seagrass mitigation sites. The Corps estimates completing the outer channel construction by November 2014. This work will bring the entrance channel depth to 52 feet, plus one foot allowable over-depth, and widen the outermost portion of the entrance channel to 800 feet. Additionally, the project includes deepening and widening the inner channel, with full project completion scheduled for July 2015.
The Corps' contractor, Great Lakes Dredge & Dock Company, are constructing approximately ten acres of artificial reefs and divers and scientists have already transplanted healthy corals greater than 25 centimeters and more than 700 healthy corals more than 10 centimeters in size from the project area to adjacent natural reef tracts and onto a portion of the newly created artificial reefs. Divers carefully harvested the corals from the channel's edges, as collecting from the channel bottom was too dangerous in the busy port.
Thirty-eight staghorn coral (photo) (Acropora cervicornis) colonies, a branching coral species that's listed as "threatened" and protected under the Endangered Species Act, were relocated from the channel's edges to outside the project area to avoid potential impacts. A fragment from each coral was also collected and transported to a permitted Acropora nursery at the University of Miami's Rosenstiel School of Marine and Atmospheric Science. The National Marine Fisheries Service's 2011 Biological Opinion included these and additional measures to minimize impacts to the coral colonies and preserve genetic material to aid in the recovery of the species.
As part of the Corps' two-year coral relocation monitoring program, scientists assessed the staghorn colonies about 40 days post-relocation to evaluate survivorship, health, security of the reattachment bond, and any breakage of branches.
"After 40 days, all of the 38 relocated staghorn colonies were alive and in good health, with only minor bleaching and partial mortality," according to scientist Anne McCarthy from CSA Ocean Sciences Inc. "Encouragingly, several colonies were also observed as having new tissue growth over the epoxy base, demonstrating the coral's ability to rapidly adapt to its new environment," she said.
McCarthy and her team conducted a comprehensive survey of corals using a diver-operated underwater navigation system that allowed for the precise location of candidate corals for relocation. Scientific divers also conducted a visual health assessment of each coral colony to document any signs of disease, bleaching, or recent tissue mortality to provide a baseline for later comparison during monitoring.
"I'm very pleased with the overall progress," said Corps Project Manager Laurel Reichold. "The mitigation construction and relocations went exceptionally well, and we anticipate a very good survival and growth rate for the relocated corals."
Once reef construction and the coral relocation work was completed, the Corps opened the project area to the Florida Fish and Wildlife Conservation Commission for a limited time so permit holders could also collect additional marine resources prior to dredging.
Corps Biologist Terri Jordan-Sellers, who works closely with environmental and wildlife agencies and similar parties, said she was pleased the Corps was able to provide a twelve-day access window. "Staying on schedule with construction work is extremely important, and I'm very glad we were able to provide an opportunity for recovery of some corals that would have otherwise been lost."
Putting a dredge on standby is not a fiscally responsible option as it can cost taxpayers $50,000 to $100,000 per day. The construction site will close Saturday, when excavation work starts.
Excavation – or stripping off loose materials – construction will last several weeks and then be followed by cutter-suction operations - or digging out the rock, which Reichold anticipates will take a few months in the outer channel area. After this occurs, the Corps will have a good idea of areas that might require underwater confined blasting.
"So far, Great Lakes has made significant progress dredging the outer channel without the need for blasting," Reichold said. "Confined underwater blasting may occur in the October or Fall timeframe if conventional dredging methodologies can't excavate the material, but we won't know where or how much may be required until then."
Used successfully in Miami Harbor in 2005, confined underwater blasting is a method that pre-treats or fractures the top of bedrock prior to dredging. The majority of blast energy is confined in the rock and studies have shown that by using this technique there's up to a 90% decrease in the strength of the pressure wave, which helps protect the ecosystem. The Corps' detailed plan includes extensive monitoring and protocols to ensure protection of wildlife. These protocols were shown effective during the 2005 job, as there were no reported injuries or deaths of mammals, sea turtles or any other sustained habitat impacts.
Go to http://www.youtube.com/watch?v=6hrkttPANMM to watch a 35-minute video in which Jordan-Sellers explains underwater confined blasting using examples from operations conducted in Miami Harbor in 2005. Jordan-Sellers teaches environmental courses at Jacksonville University and requires students to view this video.
Dr. Mark Fonnesca, CSA scientist and world renowned expert on seagrass restoration, is the senior ecologist implementing the harbor project's ongoing seagrass mitigation plan. Fonnesca literally wrote the seagrass restoration book during his 30 years with the National Oceanic and Atmospheric Administration as a research scientist and research branch chief.