bulkheads that extend into water areas often adversely alter water 

 circulation, increase scouring of the bottom, reduce the surface area of 

 the estuary, and preempt such vital habitat areas as tideflats and 

 shellfish beds, in addition to marshes. 



An exception to the requirement of building bulkheads behind the 

 annual flood line may be justified for bare shorelines, ones that have not 

 supported vegetation and cannot do so in the future. Erosion is typically 

 severe on such shorelines, and stabilization is often clearly needed. 



Once a bulkhead is in place there is very little that can be 

 accomplished toward minimizing its impacts with the exception of placing 

 stone riprap in front of the structure. Therefore details of design and 

 placement must be worked out suitably before construction starts. In the 

 case of major facilities associated with OCS operation the choice of 

 allowing bulkheads to extend into shallow waters must be weighed against 

 possible dredging required to get navigation up to the bulkhead at a more 

 landward location. These should be reviewed on a case-by-case basis. 



4.3.3 Design 



Bulkheads vary greatly in detail of construction and the variety of 

 design and location. These structures may be constructed of wooden piles 

 and planks (Figure 13), interlocking sheet steel (Figure 14), or concrete 

 slabs. Rock riprap structures are also included in this discussion of 

 bulkheads, intertidal shoreline protection devices. 



A design feature of value is perforation ("weepholes") of the bulkhead 

 to permit the natural flow of groundwater and runoff to pass through the 

 structure. This release of fresh water provides wetlands with waterborne 

 nutrients and allows the land above the bulkhead to drain. This design 

 also releases hydrostatic pressure from the groundwater head which if 

 allowed to accumulate will cause structural collapse. When an area is 

 exposed to moderate wave energies, riprap with a filter-cloth backing 

 is ecologically more desirable because of its permeability than a verti- 

 cal bulkhead. The submerged section provides a greater surface area for 

 the attachment of algae, barnacles, and other animals than found on the 

 less biologically productive smooth, flat surface of a vertical bulkhead. 

 Riprap can easily be built to conform to the natural configuration of the 

 shoreline. Riprap structures are less expensive than concrete and are 

 often comparable in price to wooden bulkheads. Riprap structures are 

 usually built on a 2:1 slope and have extended lifetimes. They are 

 constructed with the toe below the mean low-water line (Figure 15). 



4.3.4 Construction 



In large-scale construction, driven pilings are preferred to jetted 

 pilings as bulkhead supports. Jetting tends to force greater volumes of 

 silt into the water that may lead to turbidity, lowered dissolved oxygen. 



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