www.dredgemag.com IDR June/July 2019 7
Planning began in 2016 with a visit to the site by the Corps' South Atlantic Division com- mander. In subsequent months, the Corps held stakeholder meetings and public hearings while coordinating with the state Coastal Resource Division and Jekyll Island Authority (JIA). Other agencies brought in for assistance in- cluded The Nature Conservancy, the National Oceanographic and Atmospheric Administra- tion, the U.S. Fish and Wildlife Service and the U.S. Environmental Protection Agency. In 2017, the Coastal Resource Division con- ducted side-scan sonar and water quality surveys of the deep hole site and followed with addi- tional surveys of the potential upland material placement sites that included collecting imagery and elevation data. "We gathered background data to help the Corps come up with parameters on the place- ment of material and to help with their engi- neering. We used a tow behind side scan to get depth measurements, and we did a two-year study to measure the biological parameters like marsh grass stem density and height, and micro benthos, like mussels, density and habitat distri- bution," Moore said. Following the research, two placement op- tions were chosen for the pilot program-in- water placement in the "Deep Hole" and upland spraying of material on marshland. Work on Jekyll Creek includes removing approximately 200,000 cubic yards of sediment from the east- ern 75 feet of the channel bringing the channel to a depth of 10 feet. "The removed material is being placed at two locations using methods that have never been used in Georgia to help keep sediment in the coastal system and maintain the health of ad- jacent marshlands. The goal of the pilot project is to explore whether these techniques can be used in the future to build coastal resiliency in the state," Moore said. DEEP HOLE PLACEMENT The first sediment-placement location is north of Jekyll Creek in the St. Simons Sound. This location is known as the "Deep Hole," since at 60 to 80 feet deep it is naturally deeper than surrounding areas in the sound that are dredged to just 38 feet deep. About 97 percent of the dredged sediment is being placed in the Deep Hole, where tides naturally spread materials. This sediment is being deposited by pipe near the bottom of the Deep Hole, about five feet from the sea floor. Tracers are being placed on the river bottom with the dredged materials, so scientists with Jacksonville, Florida-based LG2 Environ- mental Solutions can monitor the movement of the placed sediment for up to two years. Cottrell has previously placed materials in deep channels along the James River in Virginia, but the hole for this project is deeper and more challenging since it sits in open water instead of in a protected river. Weather is a bigger factor as is safety. "We're working near the center of the in- let, so our main concern is safety of the crew. We're monitoring the barges that run through here constantly, mostly car carriers heading into Brunswick. We want to make sure they see us and we see them," Carlock said. The remaining dredged sediment is being placed on nearby marsh using a spray technique called "rainbowing." Cottrell is using a small dredge pump equipped with a special nozzle to spray the material in an arc, so that it leaves a thin layer over five acres of marsh. About 5,000 cubic yards of sediment is scheduled to be pumped onto the marsh north of the Jekyll Island Airport. This area of marsh has a lower el- evation, which makes it susceptible to saltwater inundation as sea level rises. The goal of spray- ing dredged sediment into this area is to raise the elevation one to two inches in some places and up to one foot in others, allowing new marsh grass to grow atop it at higher elevations. "We're learning that the more you traverse on the material on the marsh the deeper it gets so we're trying to minimize the impact on the marsh itself by not using heavy equipment but still filling the site effectively. We pump for a set amount of time, stop, let the material settle in place and then start back up," Carlock said. Carlock also said the work has to be done at low tide otherwise the water can come in higher than the coir logs. This placement is unique for Cottrell, which has not used coir logs before. SEDIMENT CONTAINMENT Coconut-fiber containment logs or coir logs were put in place by Nichols Construction Inc. from Hortense, Georgia, to prevent the material from running into the waterway. According to
Cottrell Contracting had to minimize the use of heavy equipment as they laid pipe in the wetland disposal area. Dredging of Jekyll Creek is part of a pilot program where material will be sent via pipe to both a deep hole in the channel and onto nearby wetlands.
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