Coastal Geology in our National Parks

Engineering Impacts on the Coastal Environment

The anthropogenic (human-influenced) alteration of our coastal environments may take many forms including, but not limited to: the creation and/or stabilization of inlets, beach nourishment and sediment bypassing, the creation of dunes for property protection, the dredging of waterways for shipping and commerce, and the introduction of hard structures such as jetties, groins, and sea walls. These alterations change coastal dynamics and have far-reaching effects on coastal ecosystems, hydrodynamic and tidal regimes, and sediment transport rates.

This site describes the impact of vairous types of coastal modifications including the soft engineering activities of dredging, beach nourishment, and beach scraping. In addition several types of structures, including groins, jetties, seawalls, and bulkheads, and their impacts are described.

USGS photo	NPS photo	USGS photo, Jim Allen

According to NPS management policies natural coastal processes will be allowed to continue without interference. However, there are times when "natural" processes may interfere with the preservation of cultural resources and/or park infrastructure. When severe coastal erosion and storm events have detrimental effects on park resources, modifications to coastal dynamics may be necessary. Effects of coastal modifications on natural park resources (biological and physical) must be thoroughly investigated for informed decision making. Coastal park managers must often achieve a balance between the preservation of historic landmarks (forts, lighthouses, etc.) and the protection of natural ecosystems. In addition, a history of long-term human alteration, combined with a lack of historic documentation, makes it difficult to define a "natural" coastal system. An understanding of how anthropogenic modifications will alter shoreline environments and park resources is vital for effective coastal management.

Soft Engineering

Dredging

Dredging, the removal of material, including sand, silt, gravel and other subaqueous materials from our coastal waterways is a widely debated topic in coastal management. The effects of dredging waterways and ports to benefit shipping, transport and recreation are not fully understood. Opponents claim that coastal dredging may have detrimental environmental impacts, and may interfere with sediment transport and flow dynamics in coastal and marine systems. Dredged sediments may include harmful contaminants and pollutants. After dredging, these sediments are often redeposited offshore or used for the creation of dredge spoil islands adjacent to the scoured waterways. In addition, dredged sediment may be incorporated into beach nourishment projects. The grain size of dredged materials may not be compatible with native beach sediment. Grain size alterations and contaminant loading may exceed flora and fauna tolerances, negatively impacting native ecosystem functions. Proponents of dredging cite that this method of material removal is necessary for commerce, recreation and national defense. Interagency partnerships, such as the Nature Conservancy and the Army Corps of Engineers http://www.sandandgravel.com/news/welcome.html, have been established to promote a better understanding of how dredging will impact coastal environments.

Army Corps of Engineers photo	NOAA photo

See the following sites for detailed information on the methods and impacts of coastal dredging:

http://www.wes.army.mil/el/dots/ - Dredging Operations Technical Support (DOTS) provides direct environmental and engineering support to the Army Corps of Engineers Operations and Maintenance (O&M) Dredging Missions. This site provides information on dredging research, benefits, and resources.

http://bonita.mbnms.nos.noaa.gov/resourcepro/
resmanissues/dredge.html - Overview of dredging by the Monterey Bay National Marine Sanctuary (NOAA).

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Beach Nourishment

Beach nourishment is the process of placing additional sediment on a beach. This material is obtained from a source that lies either inland or is dredged offshore. Nourishment entails the removal of sediment from borrow sites (inland or offshore), and the subsequent transport of the sediment to the beach area. Borrow sites may alter sediment transport, hydrodynamic patterns, and marine ecosystem functions at the borrow site. These changes may change borrow pit biota, or create erosional "hot spots" on the adjacent shoreline. Subaqueous nourishment is an alternative form of replenishment. The creation of offshore berms (mounds) may be utilized for the subsequent landward migration of sediments, often leading to sediment accretion on adjacent beaches. Although still a fairly new replenishment method, and not documented as fully effective, subaqueous nourishment may be substituted due to cost limitations or biotic complications (such as endangered species or migration) resulting from direct beach nourishment.

Often, beach nourishment is needed to mitigate the effects of the hard structure stabilization of our coastline. These structures (jetties, groins, seawalls, etc.) may increase downdrift erosion rates, promoting a need for continued coastal modifications through nourishment. The need for beach nourishment after human alteration is quite evident at Assateague Island National Seashore (ASIS). In the mid-1930's, a jetty system was established to stabilize the Ocean City Inlet by the Army Corps of Engineers. While sediment transported by north-to-south longshore currents increased sediment accretion updrift of the jetties at Ocean City, erosion and barrier island rollback (Assateague has migrated westward more than 350 meters since 1933!) have occurred on ASIS to the south of the jetties. The deterrence of longshore sediment transport to ASIS has had numerous detrimental impacts on the island's biological, geological and cultural resources. Both short-term and long-term beach nourishment plans are in place to mitigate the destructive effects of jetty placement.

For more information concerning Assateague Island National Seashore please see the following Web sites:

http://bigfoot.wes.army.mil/6718.html - Ocean City/Assateague Island, Maryland Studies by Gregory Bass of the USACE.

http://pubs.usgs.gov/circular/c1075/conflicts.html - USGS report on coastal conflicts that highlights Ocean City jetty construction and ASIS migration.

http://www.newsline.umd.edu/etcetera/specialreports/
reachbeach/assateague041301.htm - Very interesting article in Maryland Newsline describing USACE nourishment efforts on ASIS.

For more information concerning the methods, environmental impacts and costs of dredging please visit the following web sites:

http://www.csc.noaa.gov/opis/html/descrip.htm - This informative site provides an overview of NOAA dredging activities, including legal and political constraints, sand resources for beach nourishment and potential impacts of nourishment projects.

http://www.ocrm.nos.noaa.gov/pdf/finalbeach.pdf - NOAA web site containing a National Overview of State, Territory, and Commonwealth Beach Nourishment Programs.

http://www.usace.army.mil/inet/functions/cw/hot_topics
/beachnourishment.htm - USACE review of beach nourishing projects on environment.

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Beach Scraping

Beach scraping (grading, bulldozing) is the process of reshaping beach and dune landforms with heavy machinery. Usually a layer of sand from the lower beach is moved to the upper beach. The creation of dunes is used to give property owners a sense of security from beach erosion, severe storms and winter wash over events. During the summers, the created sandbanks may be bulldozed flat, providing water views to property owners, while increasing harm to coastal biota and habitat. The effects of beach scraping on coastal environments are little known. Proponents claim that beach scraping is a time and cost effective method to ensure shoreline protection, while opponents state that this method may be the most ecologically destructive form of coastal manipulation to date.

Please see the following site for more information on beach scraping.

http://www.ncsu.edu/seagrant/FRG/98ep-05.html - Sea Grant briefly summarizes how beach scraping effects biology and turbidity in North Carolina.

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Hard Structures

Hard structures are often placed in marine environments to counteract erosion in sediment-deficient areas, or to deter accretion in dynamic areas such as inlets. Unfortunately, these anthropogenic modifications usually increase erosion in adjacent downdrift areas, increasing the necessity for additional shoreline stabilization efforts. The creation of new hard structures is currently banned in many states, or strongly discouraged in coastal management practices. Groins are shore perpendicular structures, used to maintain updrift beaches or to restrict longshore sediment transport. Permeable groins are becoming popular, and may negate some of the negative effects of impermeable groins. Jetties are another type of shore perpendicular hard structure. Jetties are normally placed adjacent to tidal inlets to control inlet migration, and to minimize sediment deposition within the inlet.

Sand is trapped on the south side of the jetty (left side of photo). Longshore transport moves in a northerly direction at this location in New Jersey. Scott Douglas photo from Saving America's Beaches

Shore parallel structures include seawalls, bulkheads and revetments. These structures are designed to protect coastal property not the beach fronting the property. Development permits are relatively easy to obtain in many states because seawalls may be built above the high water mark, and they are relatively inexpensive (when compared to beach nourishment). However, seawalls may accelerate erosion on the beaches fronting properties they are intending to protect. Wave energy is reflected off of the seawall rather than absorbed by a soft sediment shoreline. The increased wave energy and sediment source trapped behind the sea wall often decrease the sediment supply near the seawall, increasing erosion on adjacent beaches. Therefore, alternatives to these hard structures are strongly encouraged and actively sought by the NPS.

A seawall at Golden Gate National Recreation Area, California, NPS photo	A wooden bulkhead protects the end of an oil and gas pipeline on the Gulf of Mexico. A restoration project was conducted to fortify this area as it filled repeatedly with water. NOAA photo

Other anthropogenic structures that are used to stop or alter natural coastal changes include breakwaters, headlands, sills and reefs. These structures are composed of either natural or artificial materials, and are designed to alter the effects of waves and slow coastline erosion and change. Submerged reefs and sills dampen wave energy and may increase local fisheries due the creation of new habitat. However, the long-term effects of these structures, on both physical and biological processes, must be more thoroughly examined.

For more information concerning these and other anthropogenic modifications, please see the following Web sites:

http://www.beachbrowser.com/Archives/Environment/August-99
/BEACHES-OR-BEDROOMS.htm - Wilmington Morning Star newspaper article concerning the construction of hard structures on North Carolina shores. Site contains links to other articles discussing coastal management issues, Dr. Orrin Pilkey, and barrier island geomorphology.

http://www.crcwater.org/issues4/19980412coastalerosion.html - Associated Press article entitled "Development-protecting seawalls debated."

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