Types of Coastal Protection Structures
There are various structures that considered or used as coastal protection structures for example groins, seawalls, bulkheads, break waters, and jetties. Description and advantages of these structures will be discussed in this article.1. Seawalls
This large coastal protection structures can be built using different types of construction materials such as rubble mound, granite masonry, or reinforced concrete. Seawalls are commonly built and run along shoreline to prevent coastal structures and areas from the detrimental influence of ocean wave actions and flooding which are driven by storms. There are various arrangements or configurations that might be employed includes curved face seawall, stepped face seawall, rubble mound seawall. These forms will be explained in the following sections:a- Curved face seawall
Curved face seawall is designed to withstand high wave action effects. Foundation materials loss, which might be caused by scouring waves and/or leaching from over topping water or storm drainage underneath the wall, is avoided by employing sheet pile cut off wall. Moreover, the toe of the curved face seawall is built from large stones to decrease scouring. Figure-1 show curved face sea wall with its components.
Figure-1: Seawall with Curved Face Configuration
b- Stepped face seawall
Stepped face seawall is used to oppose or resist moderate wave actions. Reinforced concrete sheet piles with tongue- and- groove joints are employed to construction this type of seawall. The spaces which is created between piles is either filled with grout in order make sand proof cut off wall or install geotextile fiber at the back of the sheet pile to form sand tight barrier. Applying geotextile is beneficial because it allows seeping water through and consequently prevents accumulating hydrostatic pressure. Figure 2 shows stepped face seawall with the components and details.
Figure-2: Stepped Face Seawall and its Components
c- Rubble Mound Seawalls
Design and construction this type of seawall configuration might be easier and cheaper. It can resist substantially strong wave actions. Despite scouring of the front beach, quarry stone comprising the seawall could be readjusted and settled without causing structural failure. Figure 3 provide components of rubble bound seawall. The rubble bound seawall dimensions are determined based on site conditions.
Figure-3: Rubble Mound Seawall
2. Bulkheads
Bulkheads can be constructed by concrete, steel, or timber. There two major types which are gravity structures and anchored sheet pile walls. The bulkheads might not have exposed to substantially strong wave actions and its main purpose is to retain earth but scouring at the base of the structure should be considered by the designer. Cellular sheet pile bulkheads are employed for situations where rock is close to the surface and enough penetration cannot be achieved for the anchored bulkhead type. Moreover, sheet pile should be sufficiently reinforced for bending moment, soil conditions, hydrostatic pressures, and support points. Both Figure 4 & Figure 5 show gravity and anchored sheet pile bulkhead seawall.
Figure-4: Gravity Bulkhead Seawall
Figure-5: Anchored Vertical Sheet Pile Bulkhead
3. Groins
Groins are shore protection structures that decrease erosion affects to the shoreline by changing offshore current and wave patterns. Groins can be built by materials such as concrete, stone, steel, or timber and are categorized depend on length, height, and permeability. Furthermore, groins are commonly constructed vertically to the shoreline and it can either impermeable or permeable. Figure 6 show prestressed sheet pile groin seawall.
Figure-6: Prestressed Concrete Sheet Pile Groin
4. Jetties
Jetties are usually built of materials such as concrete, steel, stone, timber, and occasionally asphalt used as binder. This structure is constructed at river estuary or harbor entrance and extended into deeper water to oppose forming of sandbars and limit currents. Both Figure 7 and Figure 8 show jetty component details and constructed jetty at site respectively.
Figure-7: Quadripod and Rubble Mound Jetty Details
Figure-8: Jetty Construction for Coastal Protection
5. Breakwaters
There are three major types of breakwaters namely: offshore, shore-connected, and rubble mound. Not only are they used to protect shore area, anchorage, harbor from wave actions but also to create secure environment for mooring, operating, and handling ships. Details and application of breakwater are provided in Figure 9 and Figure 10.
Figure-9: Rubble Mound Breakwater
Figure-10: Breakwater Application