By Patrice CreelAugust 18, 2016
For more than 30 years the U.S. Army Engineer Research and Development Center (ERDC) has been leading research and technology development to minimize the risk of entrainment of sea turtles (and other protected species) during dredging projects.
"Entrainment of sea turtles (direct uptake by the suction field generated at the draghead) during hopper dredging has been a potential issue during hopper dredging projects in the Southeastern U.S. since 1980," said Environmental Laboratory Research Biologist Dena Dickerson, who is a leading researcher in these efforts as ERDC's foremost turtle expert.
Developing efficient and effective protection systems for the seven species of sea turtles, which have existed since the time of the dinosaurs, continues as an ERDC research priority. With a streamlined shell design for swimming, these turtles differ from their land cousins, having no ability to retract heads and legs into their shells.
Dickerson and Research Hydraulic Engineer Tim Welp with the Coastal Hydraulics Laboratory have teamed up within the USACE Dredging Operations Environmental Research (DOER) Program to evaluate a new technique to protect sea turtles during hopper dredging. The field testing team also included Biological Science Environmental Manager Stephen Willis, San Francisco District, and Doug Novy, Great Lakes Dredge and Dock Inc.
The sea turtle protection equipment tested 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.
For these applications, tickler chains are hung from fishing nets and dragged along the sediment to induce organisms to move up off the sediment and into the nets.
"We hung the tickler chains off the [Portland District 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 to prevent entrainment," Dickerson said.
If shown to be effective in sea turtle protection, these tickler chains could potentially be used during some hopper dredging projects where the currently used protection equipment, such as draghead deflectors, cannot be used; in tandem with draghead deflectors to provide increased protection and allow for expanded dredging windows; or in lieu of draghead deflectors.
"The lighter-weight tickler chains would potentially provide more efficient, safer and productive dredging than the currently used draghead deflector," Dickerson said.
The field testing team conducted evaluations of this new equipment March 24-25 aboard the Essayons at Barber's Point in Oahu, Hawaii.
"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.
"ERDC assisted Honolulu District and Pacific Islands National Marine Fisheries Service in five channels throughout Hawaii, establishing appropriate sea turtle and marine mammal protection equipment and protocols there.
We are now monitoring programs for hopper dredging done during March and April."
The Honolulu District contacted ERDC for assistance through the Dredging Operations Technical Support program, known as DOTS, because of its prior assistance to the district for protected species consultation work with NOAA related to the Hawaii dredging projects.
"The new approach to sea turtle protection required field validation, performed in Hawaii through the DOER program, 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," Dickerson said.
The partnership between ERDC, the Honolulu and Portland districts, and the National Marine Fisheries Service (NMFS) provided a valuable opportunity to test innovative equipment designed to provide additional protection to sea turtles and improve dredging efficiency.
"The DOER study evaluated the chains' performance (fouling, entanglement) during actual dredging activities using three types of underwater camera systems for equipment monitoring, including 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.
"All were mounted on the dragpipe near the draghead of the dredge. The study also evaluated the ability to utilize underwater camera systems to monitor dredging equipment during real-time dredging operations.
"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 half-inch diameter chain and also 'see' sediment interactions with the draghead and chains that, to my knowledge, has not been done before," Welp said.
"This study demonstrated that the chains could be deployed as designed on an operating dredge without entanglement or restriction to dredging activities," Dickerson added.
The chains' effectiveness in reducing entrainment of sea turtles is still being evaluated through data collected by endangered species monitors on the dredge. The study also demonstrated for the first time that high-frequency acoustic cameras could be successfully used to monitor dredging equipment and operations, as well as sea life.
Dickerson emphasized that study results will have direct application for all hopper dredging projects with potential entrainment issues of protected resources.
"This is a new tool for the U.S. dredging industry to provide more flexibility in the management options for sea turtle protection and potentially other species.
"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.
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 research is a prime example of how ERDC's researchers can develop scientifically sound, innovative solutions to environmental challenges from dredging projects.
"One of ERDC's key talents is that we are a multi-discipline organization. That allows for across-laboratory and across-USACE teamwork — and, in this study, additional partnering with NMFS and the dredging industry — to address complex problems facing our nation," Dickerson said.