Dredge Essayons helps safeguard sea turtles during Hawaii dredging

Dredge Essayons helps safeguard sea turtles during Hawaii dredging
Corps partnership demonstrates new approach for species protection

Patrice Creel
Public Affairs Office, Engineer Research and Development Center

A multi-agency field testing team conducted evaluations of new species protection equipment aboard the Essayons at Barber’s Point in Oahu, Hawaii in March 2016.

A multi-agency field testing team conducted evaluations of new species protection equipment aboard the Essayons at Barber’s Point in Oahu, Hawaii in March 2016.

The U.S. Army Engineer Research and Development Center (ERDC) has been leading research and technology development for 30 years to minimize the risk of entraining sea turtles and other protected species during dredging projects.

Researchers from two ERDC labs collaborated with several districts, a dredge company and federal agency teams this spring in Hawaii to add to the list of protective technology. Field testing of this new equipment was held aboard the Portland District dredge Essayons at Barber’s Point, Oahu.

Developing effective protection systems for the seven species of sea turtles, which have existed since the time of the dinosaurs, is an ERDC research priority. With a streamlined shell ideal for swimming, these turtles cannot retract heads and legs into their shells, unlike their land cousins.

Land and sea turtle expert Dena Dickerson of the Engineer Research and Development Center's Environmental Laboratory with her African spur tortoise pet of 20 years.

Land and sea turtle expert Dena Dickerson of the Engineer Research and Development Center’s Environmental Laboratory with her African spur tortoise pet of 20 years.

Research Biologist Dena Dickerson is the lead researcher and ERDC’s foremost turtle expert. She teamed up with other ERDC specialty labs, the Corps’ Dredging Operations Environmental Research program, the Honolulu and Portland districts and the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service to evaluate a new technique to protect sea turtles during hopper dredging. The field testing team also included staff from San Francisco District and Great Lakes Dredge and Dock Co.

Dickerson credits the partnerships with providing a valuable opportunity to test innovative equipment designed to provide additional protection to sea turtles and improve dredging efficiency.

Curtain of chains

The sea turtle protection equipment was an array of chains forming a curtain that extends from the dredging drag arm approximately 25 feet ahead of the draghead. These “tickler” chains were designed after similar chain equipment used by the fishing industry and for aquatic biological sampling, where chains are hung from fishing nets and dragged along the sediment to induce organisms to move up off the sediment and into the nets.

The tickler chains are designed to keep turtles out of the way of dredging activities.

The tickler chains are designed to keep turtles out of the way of dredging activities.

“We hung the tickler chains off the dredge Essayons’ drag arm and dragged them along the seafloor ahead of the draghead to stimulate any turtles on or near the seafloor to move away from the draghead and prevent entrainment,” Dickerson said.

If effective in sea turtle protection, these lighter-weight tickler chains could be used during some dredging where the currently used protection equipment, such as draghead deflectors, cannot be used. They might also be used in tandem with draghead deflectors to provide increased protection and allow for expanded dredging windows or used in lieu of draghead deflectors.

New sea turtle requirements

“Beginning in March, hopper dredging projects in Hawaii were required to implement the same sea turtle management and mitigation techniques required on Atlantic and Gulf of Mexico dredging projects,” Dickerson said.
She added that the new approach to sea turtle protection required that field validation was performed in Hawaii, since these mitigation techniques would be directly applicable to all U.S. coastal hopper dredging projects as well as international hopper dredging within sea turtle habitat.

Cameras go deep to evaluate equipment

Research Hydraulic Engineer Tim Welp with the Coastal Hydraulics Laboratory explained that the study evaluated the chains’ performance of fouling and entanglement during actual dredging activities by using three types of underwater camera systems. Monitoring equipment included a high-frequency acoustic camera (3.0 MHz high resolution/high definition imaging sonar) mounted on a pan/tilt rotator assembly, a high definition camera with lights and GoPro cameras in underwater housings. The study also evaluated the ability to use underwater camera systems to monitor dredging equipment during real-time dredging operations. The cameras were mounted on the dragpipe near the draghead of the dredge.

“While water turbidity really limited data quality of the high definition and GoPro camera systems, images collected with the acoustic camera were so good that we were able to discriminate individual links in the ½-inch diameter chain and ‘see’ sediment interactions with the draghead and chains that, to my knowledge, had not been done before,” Welp said.

Dredge movement unrestricted

“This study demonstrated that the chains could be deployed as designed on an operating dredge without entanglement or restriction to dredging activities,” Dickerson said.

The effectiveness of the chains in reducing entrainment of sea turtles is still being evaluated, but the study demonstrated for the first time that high-frequency acoustic cameras could be successfully used to monitor dredging equipment and dredging operations, as well as sea life, during ongoing dredging activities.

Dickerson emphasized that the results of this study will have direct application for all hopper dredging projects with potential entrainment issues of protected resources. Over the past 30 years, significant resources have been invested in developing methods to minimize impacts to protected resources, such as sea turtles, during dredging.

This new tool provides the U.S. dredging industry more flexibility in the management options for sea turtle protection – and potentially other species – since issues related to potential entrainment of sea turtles and other sea life during dredging projects is a primary concern for USACE, the dredging industry and regulatory agencies.

“This is a prime example of how our researchers can develop scientifically sound, innovative solutions to environmental challenges from dredging projects. We understand the value of teamwork and technical excellence to provide exceptional products for our customers,” Dickerson said.