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Coastal zone
Published in Arved J. Raudkivi, Loose Boundary Hydraulics, 2020
A seawall can protect an erosion escarpment on a beach but if the underwater profile is steadily retreating, the wall would have to extend down to a depth in which the bed material movement ceases. Various types of protective walls can be effective in limiting or minimizing erosion during extreme storm effects, provided the long term sand requirements of the shoreline are satisfied. Walls that regularly face wave action reflect wave energy. This leads to a complex three-dimensional wave pattern near the wall by all but normally incident waves. This increases the level of turbulence, the amount of sediment mobilized in front of the wall and leads to flattening of the bed profile (lowering) for about two wavelengths from the wall. Seawalls have been built predominantly as concrete or stone structures but timber and loose rock have also been used. Loose rock protection in many locations has a cost advantage and is very flexible.
The Hard Habitats of Coastal Armoring
Published in Elizabeth Mossop, Sustainable Coastal Design and Planning, 2018
Seawalls refer to shore-parallel structures designed to stop erosion and retreat of the shoreline, limit inundation, and ameliorate wave action (Kraus, 1988) (Figure 23.3a). Seawalls are often vertical walls or steep revetments (embankments), primarily made of concrete, natural stone, riprap, steel, and even treated timbers. They are located at the intertidal zone between marine and terrestrial environments, and many are configured to allow other functions such as boat docking (i.e., as found with bulkhead walls). Breakwaters are coastal structures that protect beaches, harbors, urban shorelines from waves and strong currents (Figure 23.3b) (Nichols and Williams, 2009). They are often linear structures constructed of stone or concrete and can be arranged perpendicular to the shore, or parallel offshore, depending on the criteria of the specific site. Two main classifications of breakwaters exist, those that are vertical in section and those that are mounded or sloped in section. They may also be low-crested (slightly subsurface, or near the surface) or intertidal with parts of the structure exposed during high and low tide. (Note: Sometimes the terms jetty and groin are used interchangeably with breakwater.) Although seawalls and breakwaters are functionally and typologically distinct, both may be similarly modified to improve habitat value utilizing similar principles.
Coastal engineering and management
Published in David R. Green, Jeffrey L. Payne, Marine and Coastal Resource Management, 2017
Seawalls are vertical or near vertical structures constructed from concrete, steel or masonry. They are typically used to protect land, infrastructure and other built assets from erosion, flooding and overtopping due to storm surges and waves. Such structures prevent the recession of the high water mark, however by introducing them into a system they may remove local sediment supplies to the fronting and down-drift beaches. Additionally, seawalls can increase wave reflection and lead to increased lowering of beach levels in front of them.
Long-term deformation and damage analysis of marine clay around seawalls under coupled dynamic-seepage loading
Published in Marine Georesources & Geotechnology, 2022
Huayang Lei, Ziyang Qi, Shuangxi Feng
The seawall is an important structure in coastal areas to guard against storm surges and seawater intrusion. The operation of seawalls directly impacts people’s life safety and urban construction (Balaji, Sathish, and Misra 2017; Zhang et al. 2020). However, seawalls are often built on deep marine and coastal soft soil ground of silt and mud (called marine-deposited clay ground), which has high compressibility, low strength and low permeability (Ng, Liu, and Li 2013; Yin, Yin, and Huang 2015; Lei, Feng, and Jiang 2018; Feng and Lei 2021). During service, the soft soil ground will often bear stresses due to seawater, including rising and falling tides; i.e., the soil element of marine-deposited clay ground will bear dynamic loading induced by sea wave impacts and seepage loading caused by tides. A large amount of evidence from engineering practice demonstrates that the postconstruction settlement of seawalls built on deep soft soil ground can reach several metres, which causes great difficulties in the calculation of construction quantities and elevation design of seawalls (Dou and Swann 2017; Ahmad et al. 2019). Moreover, when the postconstruction settlement caused by the time-dependent deformation of soft soil exceeds the designed settlement value, the fortification standard of the seawall will be lowered, and uneven settlement may cause the seawall to tilt or slide (Peng and Cheng 2017).
Game-theoretic modeling of pre-disaster relocation
Published in The Engineering Economist, 2020
Vicki M. Bier, Yuqun Zhou, Hongru Du
Not surprisingly, Kirshen et al. (2008) finds retreat to be cost-effective in less densely developed areas, with options such as seawalls more desirable in highly populated areas (since the cost of the seawall can be amortized over a larger amount of property to be protected). However, seawalls can be expected to provide only temporary protection in the face of continued increases in sea levels, and are not effective in places with porous geology, such as Florida. In addition, the apparent safety provided by seawalls tends to attract more development to flood-prone areas, thus increasing long-term vulnerability while decreasing short-term damage (Hino, Field, & Mach, 2017). Not surprisingly, Turner, Burgess, Hadley, Coombes, and Jackson (2007) find that the optimal choice of strategies is crucially dependent on the time horizon and discount rate assumed in the analysis, with managed retreat viewed more favorably over longer time horizons. Thus, engineering strategies focused on keeping water out of populated areas may be ineffective against long-term continuing sea-level rise.
Reliability-based assessment and design of stone-filled crib seawalls for shoreline protection
Published in Marine Georesources & Geotechnology, 2018
Seawalls are commonly designed and constructed along the shoreline as a form of coastal defense. They prevent areas of human habitation, conservation, and leisure activities from the progressive damages due to tides and waves and the destructive impacts of tsunamis (e.g., Kamphuis 2010). In terms of the types of wall face, the seawalls can be categorized into vertical walls, curved walls, and mounds. Many kinds of materials can be used in the seawall construction, including, but not limited to the cast-in-place concrete, steel sheet pile, precast block, and rock-filled cribs (OCM 2011). Since the primary function of seawalls is to resist wave action along the coastal property of high value, their performance deterioration and failure under an extreme event always result in considerable economic loss. For example, in Netherlands, the 3,700-km-long seawalls protect assets with value of USD $280 billion from the floods; the initial construction of those seawalls cost USD $14.6 billion, while the annual repair and maintenance cost is approximately USD $1,700 million (Lu, He, and Liu 2005).