Dredging Projects on the Coast Affected by Hurricane Florence: Beach Nourishment Projects Prove to Be Important Factor in Mitigating Damage
Hurricane Florence came ashore in North Carolina on September 15 disrupting lives and turning parts of the Carolinas into inaccessible islands. With dredging projects underway in areas from South Carolina to New York, contractors had to make decisions on if and when to pack it up and head to safety.
Once the storm passed, beach nourishments that were underway had to be resurveyed to determine if more sand was needed and contracts had to be adjusted, and then contractors had to remobilize and start again.
Great Lakes Dredge and Dock was working in Myrtle Beach when Hurricane Florence hit and had to move about 25,000 feet of pipe, five loaders and two dredges to safe locations. Marinex was further south in Folly Beach and removed approximately 15,000 linear feet of pipe along with front loaders, back hoes and dredges. That demobilization took about two days and getting back up after the storm took about a week. Despite the delays, though, both projects remain on schedule, largely attributable to sound planning.
Severe Weather Plans
When a dredge company contracts for a nourishment job it typically includes a “marine severe weather contingency plan,” as a component of the contract submittals. Whether from a tropical storm, hurricane or winter storm, dredge companies working on the coast will need to have contingency plans for work disruption.
“All projects that can be impacted by severe weather have marine severe weather contingency plans,” said Tim Weckwerth, vice president at Weeks Marine Inc. “The plans are relatively boiler plate until we show up on a project and determine where the safe harbor is, where there’s enough high ground for the land-based equipment and what the U.S. Coast Guard rules are for the given area.”
The details are scoped out before there’s any chance of a storm as part of the dredging project preparation. The dredge contractors work with local governments to find accessible areas on high ground that can store upland equipment like bulldozers, and pipe far enough away to avoid storm surges and wind impacts. Such locations could be a mile away or several miles away so transport time has to be factored into the evacuation plan. The dredge company will contract with local brokered trucks to move the equipment, so those companies also must be identified as part of preconstruction plans.
Water-based equipment stays in the water but usually must be relocated to a safe harbor.
“We disconnect anything in the water that floats from anything that does not. Floating hoses are disconnected from the submerged pipelines, and we move them with towing vessels. The Coast Guard rules tell us where most equipment, like our large towing vessels, and barges can go; where we are allowed to put the equipment whether secured at a dock, or anchored or spudded in protected bays or a nearby inland river system,” Weckwerth said.
The Coast Guard rules depend on whether the vessels are self-propelled or not. “If you can leave under your own power, you typically are directed to leave,” Weckwerth said.
Since many dredges now have onboard accommodations for a crew, the crews generally stay with the dredge moving into a safe harbor. Land-based crews are evacuated from the job site either locally if it appears the storm will be short-lived and not too destructive, or they are sent home. Any crews staying locally will often spend time after the storm has passed performing maintenance on equipment that was moved upland until it is mobilized back to the project.
Knowing when to begin evacuating is also part of the plan. Most governments and private owners that hire dredging contractors require a hurricane preparedness plan, which stipulates when actions will occur.
“Depending on the size and scope of the storm, a countdown clock begins. The clock is based on how much stuff there is on a job, and the mobility efforts needed to move each of the pieces of equipment, but at a minimum they monitor and move starting at a minimum of 72 hours before initial impact,” Weckwerth said. The hurricane plans stipulate what actions will occur at 48 hours, 24 to 36 hours and then when the impact is imminent.
Once the storm has passed everything has to be remobilized, but when that can occur varies.
“Getting back in is based on when local municipalities will let you in. It could be a very long time,” Weckwerth said.
Local authorities assure an area is safe before they let anyone back in and after a major storm, getting beach nourishment back up and running is often a low priority. During Hurricane Florence, Weeks had crews working on beaches in New York and New Jersey. While that area was not in the path of the storm, the sea conditions were bad enough that crews had to stop work two to three days before the storm hit. Because they were not facing tidal surge issues, they left landside equipment onshore, but secured. The vessels were all relocated. Area projects were able to start again about a week after the storm had come ashore.
Outside of the planning and work that dredge contractors have to face in a storm, there’s a cost to evacuations that goes beyond lost work time. Upland storage areas can charge rent, broker trucks have fees, any equipment repairs cost extra. Dredge companies try to factor some of that into contracts, but its not unusual for a company to have to absorb the extra costs.
After the Storm
Once Hurricane Florence passed, the U.S. Army Corps of Engineers, working with state and local partners, hit the beach to analyze how much sand was lost, if ongoing nourishment projects needed to be expanded and to see how well past nourishment projects performed.
Wes Wilson, project manager with the Corps Charleston District for the Myrtle Beach and Folly Beach projects explained, “We look at pre-storm surveys for a good baseline and compare those to sand lost during the event. We then figure out what quantities of sand it will take to reconstruct to the full template.”
In South Carolina, the Corps Charleston District undertook a post-hurricane assessment of the Myrtle Beach Storm Damage Reduction project using Rapid Assessment Mobile LiDar (RAMbLr) – an all-terrain vehicle equipped with a Light Detection and Ranging (LiDAR) system – to survey the beach. RAMbLr creates topographic maps that are compared to the survey maps created prior to the storm. Wilson said LiDar technology has only been around since 2015, but it has increased the simplicity and accuracy of conducting beach profiles.
The Corps takes the survey data, determines a cost ratio and puts that together into a Project Information Report, which is sent first to the regional office, in this case the South Atlantic Region in Atlanta, and then to headquarters in Washington, D.C. for approval. For the Myrtle Beach project, in what Wilson described as “a first,” this process happened in record time. With GLDD working on the Reach 2 portion of the overall project, the Corps received approval to add 300,000 cubic yards of sand to the existing 800,000 cubic yards to replace what was lost in Reach 2 during Hurricane Florence. No new contracts were needed. The Corps is still working on the data analysis for Reach 1 section, which had already been nourished, to see if GLDD will need to go back to move additional sand in those locations as well.
The Corps is also working on surveys for Folly Beach. When Florence hit, the Folly Beach project had placed about 75 percent of the contract volume.
Wilson said the Corps is close to awarding another modification for Florence sand loss. “We’re trying to stay out in front with Hurricane Florence to incorporate losses so we don’t have to come back with additional nourishment,” Wilson said.
“If we didn’t have sand in place we would have had overwash, public access area damage, walkover damage, but by putting the project in place it protected and reduced the risk,” Wilson said. “At the end of the day our goal for emergency projects is to put majority of structure in place before storm events. That just doesn’t always happen.”
Wilson continued to explain that dunes play a significant role in how well areas fare during storms. Dune height has grown over the years and the Corps has an efficient and effective fencing and grass planting program to reduce risk. In addition, the pre-storm surveys help identify areas that erode more quickly than others meaning more sand will be placed on those stretches of beach.
Surveys conducted in North Carolina post-Florence indicated that nourished beaches did a better job of protecting upland infrastructure than beaches that had not been nourished.
The week of September 17, Geodynamics, LLC surveyed 122 profile locations along Bogue Banks in North Carolina just north of where the storm came ashore. The company had last conducted a survey in the spring of 2018, which served as the pre-hurricane survey for comparison. The surveys are used to calculate spatial changes of the dunes over time, mean high and low water lines and mean sea level. The data shows rates of erosion and accretion, showing sediment volumes and movement before and after nourishment projects.
The additional sands and dune construction that has been done over the years appeared, upon an assessment by Carteret County, to have worked as there was no flood damage to oceanfront structures and no breaches of the frontal dunes. The areas of Bogue Banks where sand has been placed three times since 2011, fared far better in terms of erosion and escarpment than other stretches of beach.
Compared to the last hurricane to hit this area, Hurricane Floyd in 1999, damage was greatly minimized. This was particularly good news as tide gauges indicated Florence exceeded the highest water level ever recorded at 3.75 feet.
The annual surveys on Bogue Banks have concluded that since 1999, Bogue Banks has gained approximately 9.6 million cubic yards of sand, mostly due to beach nourishment projects. Approximately 14.5 million cubic yards of sand has been placed directly on Bogue Banks, while 4.9 million cubic yards have eroded. Measured across the 24.3 miles of oceanfront, the island has lost sand at a rate of -2.0 cubic yards per linear foot each year.
The number of storms to hit in a given year can drastically change that amount, but overall beach nourishment projects have shown to be a crucial part of reducing upland damage and destruction.