Sand Resources for Shore Protection Projects in New Jersey
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New Jersey Geological Survey Information Circular Sand Resources for Shore Protection Projects in New Jersey New Jersey’s active and successful shore protection program requires large and readily available offshore sources of sand for beach nourish- ment projects. Through cooperation of the New Jersey Geological Survey and other State and Federal agencies, potential sources of sand are located for these projects. This work helps to ensure long range plans that protect the safety and property of New Jersey’s citizens. Introduction Coastal engineers from the State’s A beach is a flexible and effective coastal Department of Environmental Protection’s structure offering storm wave and flood pro- (NJDEP) Engineering and Construction Sec- tection. When erosion of New Jersey’s shore tion and the US Army Corps of Engineers necessitates action, beach nourishment collect data, evaluate impacts, and create projects have become the primary method computer-generated beach profile models to to develop a protective beach. Identifying determine an appropriate beach shape for a sand sources is a critical part of these proj- particular location. Scientists from the US ects. Minerals Management Service gather eco- A beach’s profile is a cross-section of the nomic mineral resource and biologic data in surface of a beach from land to ocean. Its federal waters. In this way, engineers and shape varies with the changing seasons. scientists determine the method and scope During summer months, the beach profile is of a beach nourishment project. broad and flat. In winter, the profile steep- The most efficient way to deliver large ens in response to increased wave energy. amounts of sand is to dredge and pump During storms, strong winds drive steep a sand-water slurry onto the beach (fig. 2) Figure 2. Bulldozer building a protective waves toward the shore that may exceed through a pipeline. This method of shore beach using sands pumped from an offshore the seasonal equilibrium of the beach. In protection requires large quantities of sand. sand source. The hydraulic dredge is on the a prolonged, severe storm, winds push the A rule of thumb is that for every foot of horizon. sea to higher levels along the coast, caus- protective beach, one cubic yard of sand is ing inland flooding, particularly during high required. For example, if the State needs to less stable and erode more quickly. As a tide. extend 1,000 feet of shoreline 200 feet far- result, more frequent nourishment would The sand on a beach acts to absorb wave ther offshore, it will require 200,000 cubic be required. energy through the movement of countless yards of sand -- nearly 20,000 truckloads! Geologists map areas offshore where grains of sand. In so doing the beach and An offshore sand source pumped directly coastal engineers project a need for sources its dunes become the first line of defense onto the beach is more efficient and less of nourishment sand. The geologic maps against storm-driven coastal flooding. The costly than trucks. When smaller volumes produced are the most efficient way to pre- cost of that protection is measured as of sand are needed, Hopper or Dustpan dict, locate and estimate the quality and beach erosion. A season of strong winter dredges can be used to pick up material size of a beach sand resource. The area of storms, a northeaster, or hurricane, may from a source and deliver it to the beach in investigation generally extends approxi- erode a beach and its dunes to an extent need of nourishment. mately seven miles offshore, the economi- that it can not recover to a suitable profile cally feasible distance for obtaining beach within an acceptable time frame (fig. 1). The Geologic Mapping of Beach Sand replenishment sand. goal of beach nourishment is to add sand Resources to the system so that the beach will have Beach Sand and the Ice Age the quantity of sand needed at that location Geologists from the New Jersey Geologi- to absorb wave energy, and reduce coastal cal Survey (NJGS) study the ocean bottom The sediments offshore New Jersey are flooding. The most effective protective sediments off the coast of New Jersey to largely composed of sand, silt, clay and beaches include dunes, vegetation, habitat- locate potential sources of suitable beach organic material that has been deposited, protection areas, and a beach profile that sand. This would be an easy job if the eroded and reworked over the past 125,000 is appropriate for wave conditions at that entire ocean bottom were covered with years. The most influential geologic event location. sand, but fine-grained silts and clays are in New Jersey during this period was the also common bottom sediments. lowering and subsequent rise of sea level Sand is not all the same. Grain size during the last glacial period beginning variation within the sediment is a criti- about 25,000 years ago. At the time of the cal factor in designing a stable beach. last glacial maximum when an enormous The energy and direction of waves along a volume of Earth’s water was stored as ice, beach is what actually controls the range sea level dropped more than 300 feet below of grain size along the shore. These factors what it is now, and the New Jersey shoreline vary with every mile of coastline, and must was located tens of miles beyond the pres- be modeled for every beach. The beaches ent coastline. As sea level rose at the end of of Cape May, for example, are composed the last ice age, the same dynamic coastal of finer-grained sand than the beaches features that we see today (barrier islands, located farther north at Sandy Hook. If spits, inlets, back bays, and marshes) Cape May sand were placed on a Sandy moved landward. The remnants of these Figure 1. View of a beach profile after a Hook beach, it would be unsuitable for features serve as the sand resources now winter storm event. local wave conditions. The beach would be used for beach nourishment. NW ocean surface SE 40 Line 25b 15 T w o - w 50 ocean floor 20 a Core 17a y t t r a e v e 25 f e l n i t 15 i m s t 30 e n e f r o m 30 i m d 35 e o s c e d 45 a n n a 40 r s e u t 60 r a f a w 45 c e n i 75 i n h t m p 50 e i l l D i 90 s e c o n d s ~ 700 feet Figure 3. Seismic profile of ocean bottom sediments. Colored lines have been added to enhance the readability of the figure. Thick-colored lines are drawn at the boundary between geologic units and thin-colored lines highlight layering within the different units. Vibracore data is used to determine the composition of the ocean bottom sediments. Sea Floor Mapping and Sampling Once geologists map and evaluate a Geologists use both direct and indirect suitable sand resource, the volume of sand sampling methods to collect information is calculated. This information is passed about deposits offshore. Direct sampling on to State and Federal coastal engineers Figure 5. Geologist noting geologic char- of the actual sea floor sediments is accom- and scientists who investigate the potential acteristics of an extracted Vibracore (split plished by drilling or vibracoring. Indirect physical and biological impact of extract- and placed in black tray). After complet- methods measure the differences in the ing the undersea resource. After a sand ing a geologic description of the core it is physical properties of sea floor sediments source is chosen, the engineers design and photographed and sampled for laboratory by using acoustic (sound) or electrical implement a comprehensive plan for the analysis. instruments. new protective beach. The entire beach Geophysical acoustic methods, includ- nourishment process, from mapping the This coordinated effort is a successful ing bathymetric sonar, sidescan sonar, and resource to nourishing a beach, can take strategy that protects people, property, seismic profiling, are highly effective for several years. and coastal wildlife habitat while pre- marine subsurface mapping. A significant serving the beauty of New Jersey’s scenic advantage of these systems is that data is coastline. collected from a moving boat that yields a two- or three-dimensional representation. Seismic profiling uses a pulse of sound STATE OF NEW JERSEY that is transmitted through the seawater and into the bottom sediments. The energy Richard J. Codey, Acting Governor of this signal reflects (echoes) off sediment Department of Environmental Protection layers, and is recorded when it returns to Bradley M. Campbell, Commissioner the surface. A seismic cross-section of the Land Use Management sediment layers about 150 feet thick is gen- erated for analysis (fig. 3). In each area of Ernest P. Hahn, Assistant Commissioner investigation, a grid with tens to hundreds New Jersey Geological Survey of miles of seismic data is collected. Karl Muessig, State Geologist NJGS geologists use the seismic data NJ DE P L to determine the shape and location of off- GEO OGI Y C E A S L shore deposits and pinpoint the best places R S E U J R V W to sample the ocean bottom. At these loca- E E Y tions a core sample, used to determine the Figure 4. Vibracore rig being deployed off N composition of the sediment layers, is taken the side of a boat. The four-legged base using a vibracore drill rig. (foreground) is rotated to sit on the ocean 18 3 5 Vibracore equipment is lowered from an bottom.