Storm Hazard
653
Part C | 30
30. Storm Hazard Mitigation Structures
David R. Basco
Hard structures have long been the method of
shore protection from coastal storms. In this chapter, we first introduce the design criteria, design
philosophy, and design constraints. Both armored shorelines (seawalls, dikes, revetments,
etc.) and stabilized shorelines (headland breakwaters, near-shore breakwaters, groins, etc.), are
possible alternatives. However, stabilized shorelines coupled with beach nourishment (Chap. 29)
have become the preferred choice for many reasons at many locations. Rubble-mound (rock)
structures and monolithic (concrete) structures
are the most common types. Their functional design (wave run-up, overtopping, plan form layout,
etc.) and structural stability (armor layer, sliding,
overturning, etc.) are the focus of this chapter
summarizing the latest and most trusted probabilistic design methods employed in the United
States, Europe, and Japan. There exists a very large
literature on these topics. Design practice details
are quite extensive; we include website links to
major reference sites, and a responsible engineer
must consult these references for all the details.
In the future, the potential for the accelerated,
relative sea level rise (including local subsidence)
will increase the risk for more damage and reduce
the resilience of existing shore protection systems.
The design of hard structures for shore protection
30.1 Design Criteria, Philosophy,
and Constraints ................................... 655
30.1.1 Water Levels.............................. 655
30.1.2 Wave Conditions........................ 656
30.1.3 Surf Conditions on the Structure . 656
30.1.4 Probabilistic Design ................... 657
30.1.5 Coastal Risk............................... 657
30.1.6 A Coastal Storm Severity Index .... 657
30.1.7 Design Constraints ..................... 657
30.2 Coastal Armoring Structures ................. 658
30.2.1 Types and Purpose..................... 658
30.2.2 Functional Design...................... 658
30.2.3 Structural Design ....................... 663
30.3 Shoreline Stabilization Structures ......... 674
30.3.1 Types and Purposes ................... 674
30.3.2 Functional Design...................... 675
30.3.3 Structural Design ....................... 681
30.4 Websites and Sea Level Rise Trends....... 681
30.4.1 Websites................................... 681
30.4.2 Sea Level Rise Trends ................. 681
References................................................... 681
continues to evolve over time. As sea levels rise
more quickly, the need for more basic research
and more knowledgeable coastal engineers will
also increase.
Armoring the shoreline with a hard structure has long
been a traditional way of coastal shore protection from
the excessive forces of the sea. Since about 1950,
coastal population increases, tourism, and concerns
for the environment have caused a shift away from
the traditional armoring solution. Shoreline stabilization structures and the addition of natural sediments
(Chap. 29) have often become the preferred choice
for shore protection. In this chapter, hard structures
refers to both (1) coastal armoring structures (seawalls,
dikes, revetments, etc.) and (2) shoreline stabilization
structures (head lands, breakwaters, groins, reefs, sills,
etc.). These structural alternatives are changes to the
natural, physical system for shore protection. Nonstructural alternatives (flood proofing, zoning, retreat, etc.)
are changes to the built environment by adaptation
and accommodation. There are many alternatives for
shore protection as illustrated in Fig. 30.1. The correct
choice depends on the design constraints for the particular site and is the responsibility of the design coastal
engineer.
The excessive forces are the result of:
1. Coastal storms that produce elevated water levels,
high waves, and strong currents over the storm duration, and
653
Part C | 30
30. Storm Hazard Mitigation Structures
David R. Basco
Hard structures have long been the method of
shore protection from coastal storms. In this chapter, we first introduce the design criteria, design
philosophy, and design constraints. Both armored shorelines (seawalls, dikes, revetments,
etc.) and stabilized shorelines (headland breakwaters, near-shore breakwaters, groins, etc.), are
possible alternatives. However, stabilized shorelines coupled with beach nourishment (Chap. 29)
have become the preferred choice for many reasons at many locations. Rubble-mound (rock)
structures and monolithic (concrete) structures
are the most common types. Their functional design (wave run-up, overtopping, plan form layout,
etc.) and structural stability (armor layer, sliding,
overturning, etc.) are the focus of this chapter
summarizing the latest and most trusted probabilistic design methods employed in the United
States, Europe, and Japan. There exists a very large
literature on these topics. Design practice details
are quite extensive; we include website links to
major reference sites, and a responsible engineer
must consult these references for all the details.
In the future, the potential for the accelerated,
relative sea level rise (including local subsidence)
will increase the risk for more damage and reduce
the resilience of existing shore protection systems.
The design of hard structures for shore protection
30.1 Design Criteria, Philosophy,
and Constraints ................................... 655
30.1.1 Water Levels.............................. 655
30.1.2 Wave Conditions........................ 656
30.1.3 Surf Conditions on the Structure . 656
30.1.4 Probabilistic Design ................... 657
30.1.5 Coastal Risk............................... 657
30.1.6 A Coastal Storm Severity Index .... 657
30.1.7 Design Constraints ..................... 657
30.2 Coastal Armoring Structures ................. 658
30.2.1 Types and Purpose..................... 658
30.2.2 Functional Design...................... 658
30.2.3 Structural Design ....................... 663
30.3 Shoreline Stabilization Structures ......... 674
30.3.1 Types and Purposes ................... 674
30.3.2 Functional Design...................... 675
30.3.3 Structural Design ....................... 681
30.4 Websites and Sea Level Rise Trends....... 681
30.4.1 Websites................................... 681
30.4.2 Sea Level Rise Trends ................. 681
References................................................... 681
continues to evolve over time. As sea levels rise
more quickly, the need for more basic research
and more knowledgeable coastal engineers will
also increase.
Armoring the shoreline with a hard structure has long
been a traditional way of coastal shore protection from
the excessive forces of the sea. Since about 1950,
coastal population increases, tourism, and concerns
for the environment have caused a shift away from
the traditional armoring solution. Shoreline stabilization structures and the addition of natural sediments
(Chap. 29) have often become the preferred choice
for shore protection. In this chapter, hard structures
refers to both (1) coastal armoring structures (seawalls,
dikes, revetments, etc.) and (2) shoreline stabilization
structures (head lands, breakwaters, groins, reefs, sills,
etc.). These structural alternatives are changes to the
natural, physical system for shore protection. Nonstructural alternatives (flood proofing, zoning, retreat, etc.)
are changes to the built environment by adaptation
and accommodation. There are many alternatives for
shore protection as illustrated in Fig. 30.1. The correct
choice depends on the design constraints for the particular site and is the responsibility of the design coastal
engineer.
The excessive forces are the result of:
1. Coastal storms that produce elevated water levels,
high waves, and strong currents over the storm duration, and