Mitigating Shore Erosion Along Sheltered Coasts (2007) / Chapter Skim
Currently Skimming:
1 Introduction
1 Introduction
Pages 11-24
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 11... ...
This report reviews options available to address and mitigate1 erosion of sheltered coasts and explores why certain decisions are made regarding the choice of erosion mitigation options; provides critical information about the consequences of altering sheltered shorelines; and, provides recommendations about how to better inform decisions in the future. STUDY HISTORY Before decisions can be made concerning appropriate shoreline management strategies on sheltered coasts, several topics must be understood.
|
From page 12... ...
Sheltered shorelines, though often contiguous with the open coast, border smaller, contained, bodies of water separated from the open ocean by islands, peninsulas, reefs, or other geomorphic features. Many of the processes that govern erosion and deposition on the open coast also apply to sheltered coasts, but generally the scale at which these processes function is significantly reduced within sheltered coastal areas.
|
From page 13... ...
that often characterize habitats on sheltered coasts and are generally not found along open coasts.4 Many of these sheltered areas are river valleys that have been drowned by rising sea-level, or drainage features that are protected by headlands or islands. Many of these semiprotected sheltered shorelines border estuaries.
|
From page 14... ...
Such efforts may or may not be successful at preventing erosion, but most interrupt natural processes, frequently causing erosion in other areas and loss of the original habitats and other natural shoreline features. The following case studies illustrate two examples of the growing problem of eroding sheltered shorelines and the severity of how human responses have altered the function of sheltered shorelines.
|
From page 15... ...
Raritan Bay, New Jersey Raritan Bay extends from the mouth of New Jersey's Raritan River to the entrance to the Atlantic Ocean, between the Verrazano Narrows to the north and Sandy Hook to the south. It measures about 22 kilometers (approx.
|
From page 16... ...
In a simple situation forced only by tides and waves on beaches with a rapid equilibrium response, this definition could be sensibly enforced. However, delineation of this boundary is complicated by the wide range of time scales over which sea level varies (from millennial glacial and interglacial climate periods to decadal climate fluctuations including El Niño to annual or seasonal storm surge signals)
|
From page 17... ...
For shores backed by sea cliffs or bluffs, the location most relevant to defining erosion may not be that of a specific elevation contour, but may instead be the location of the bluff top. To describe the physics of coastal processes requires consideration of the "shore zone," defined as the active volume of sediment affected by wave action.
|
From page 18... ...
Thus, a landward shoreline movement that recovers prior to the next storm would not usually be considered erosion, despite the potential loss of property associated with that variation. Inundation refers to the temporary submergence of typically dry lands when there is an exceptional rise of the sea surface, and floodwaters cover the adjacent low-lying land.
|
From page 19... ...
This quantity integrates detailed profile fluctuations that would otherwise confuse estimation based on a more traditional shoreline location. NOTE: H = Height between dune foot and mean low water [m]
|
From page 20... ...
0 MITIGATING SHORE EROSION ALONG SHELTERED COASTS 1 Lo 3 we rM ac ho do cC ree 6 k 2 4 5 FIGURE 1-3 Aerial image of Lower Machodoc Creek on the Potomac River in Westmoreland County, Virginia, showing the irregularity and diversity of shore types. The insets are six typical shoreline profiles around sheltered coasts.
|
From page 21... ...
The location and extent of any of these features is dependent on site-specific conditions. While some sheltered shorelines include hard rock outcrops, the erosion of features such as rock cliffs or shore platforms on sheltered coasts is considered a slow process and one unlikely to result in the need for the protective shoreline measures that are the focus of this study.
|
From page 22... ...
As sea level rises, waves will attack the bluff face and toe of the slope, gradually undercutting the bluff and causing sections of it to fall away. The erosion rate is dependent upon the degree of consolidation; rocky bluffs are not readily eroded by the forces that characterize sheltered coasts.
|
From page 23... ...
These plant communities as well as the mudflats support a highly diverse and productive number of associated animals. Therefore, techniques to mitigate shoreline erosion that change the substrate characteristics will lead to changes in the associated plant and animal communities.
|
From page 24... ...
Chapter 4 covers ecosystem services and values and how they are affected by shore erosion and mitigation measures, including living and nonliving components of the coastal habitats and the impacts of the most common structures installed to prevent erosion (revetments, breakwaters, seawalls, groins, and pilings)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.