Coastal Construction Manual - National Ready Mixed Concrete ...
Coastal Construction Manual - National Ready Mixed Concrete ...
Coastal Construction Manual - National Ready Mixed Concrete ...
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IDENTIFYING HAZARDS 3<br />
3.5.2.3 Erosion Due to Manmade Structures and Human Activities<br />
Human actions along the shoreline can both reduce and increase<br />
flood hazards. In some instances, structures built or actions taken<br />
to facilitate navigation cause erosion elsewhere. In other cases,<br />
structures built or actions taken to halt erosion and reduce flood<br />
hazards at one site increase erosion and flood hazards at nearby sites.<br />
For this reason, evaluation of a potential coastal building site requires<br />
consideration of natural and human-caused shoreline changes.<br />
NOTE<br />
More information on beach<br />
nourishment is provided at<br />
http://www.csc.noaa.gov/<br />
beachnourishment.<br />
Effects of Shore Protection Structures<br />
In performing their intended function, shore protection structures<br />
can lead to or increase erosion on nearby properties. This statement<br />
should not be taken as an indictment of all erosion control structures,<br />
because many provide protection against erosion and flood<br />
hazards. Rather, this <strong>Manual</strong> simply recognizes the potential for<br />
adverse impacts of these structures on nearby properties and offers<br />
some siting guidance for residential buildings relative to erosion<br />
control structures (see Section 4.6), where permitted by States and<br />
communities. These potential impacts vary from site to site and<br />
CROSS REFERENCE<br />
Adverse impacts of erosion<br />
control structures can<br />
sometimes be mitigated<br />
through beach nourishment.<br />
See Section 4.7.<br />
structure to structure and can sometimes be mitigated by beach nourishment—the placement of additional<br />
sediment on the beach—in the vicinity of the erosion control structure.<br />
Groins (such as those shown in Figure 2-12, in Chapter 2) are short, shore-perpendicular structures designed<br />
to trap available littoral sediments. They can cause erosion to downdrift beaches if the groin compartments<br />
are not filled with sand and maintained in a full condition.<br />
Likewise, offshore breakwaters (see Figure 3-44) can trap available littoral sediments and reduce the sediment<br />
supply to nearby beaches. This adverse effect should be mitigated by combining breakwater construction<br />
with beach nourishment—design guidance for offshore breakwater projects typically calls for the inclusion<br />
of beach nourishment (Chasten et al. 1993).<br />
Figure 3‐44.<br />
Example of littoral<br />
sediments being<br />
trapped behind offshore<br />
breakwaters on Lake<br />
Erie, Presque Isle, PA<br />
SOURCE: USACE<br />
COASTAL CONSTRUCTION MANUAL<br />
3-47
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