Coastal structures are anything man-made located in the coastal zones and are constructed for erosion management, routing, beach nourishment, and some allow access to the seawaters. These structures are able to protect mooring basins and entries from the waves and stabilize the navigation stations at inlets and are targeted at averting coastal erosion and flooding of the surrounding areas and can be utilized in coastal protection schemes.
Types of coastal protection structures
1- Shore protection structures,
2- Berthing and mooring ships structures, and
3- Marine and offshore industry structures.
1. Shore Protection Structures
Shore protection structures like seawalls, revetments, groins, ripraps are constructed to endure waves, scour, and overtopping. The waves may lead to the failure of these structures.
1.1. Seawalls
Seawalls are commonly built and run along shorelines 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 can be built using different types of construction materials such as rubble mound, granite masonry, or reinforced concrete.
Curved face seawall is designed to withstand high wave action effects like foundation materials loss or leaching from overtopping water or storm drainage underneath th e wall. The toe of the curved face seawall is built from large stones to decrease scouring.
Stepped face seawall is used to oppose or resist moderate wave actions. Reinforced concrete sheet piles with tongue- and- groove joints are employed to construct this type of seawall. The spaces which are created between piles are either filled with grout in order to make sand proof cut off the wall or install geotextile fiber at the back of the sheet pile to form a sand tight barrier. Applying geotextile is beneficial because it allows seeping water through and consequently prevents accumulating hydrostatic pressure.
Rubble Mound Seawalls is designed to resist substantially strong wave actions. Design and construction this type of seawall configuration might be easier and cheaper. It can . Despite scouring of the front beach, quarry stone comprising the seawall could be readjusted and settled without causing structural failure. The rubble bound seawall dimensions are determined based on site conditions.
1.2. Revetments
Revetments are the structures constructed parallel to the shoreline for protecting the coastline from erosions. These structures are capable to absorb and reduce the energy of the waves before they reach the banks. Revetments are made using materials composed of stone, precast concrete block or asphalt as to armor the natural sloping of shoreline contours. These slopes can either be smooth or rough depending on the structure's design. Revetments are composed of three major elements-armor layer, filter zone, and toe coating. An armor layer is an essential foundation which shelters against the wave action. The filter layer, in turn, sustains the armor permitting the water to pass through the revetment restricting any sediment to be washed through the armor. The toe layer protects the structure and avoids dislodgment of the seaward edge of the structure, as well as offering the necessary support for all the layer components. Generally, the revetment covers the shore area and the shallow nearshore, which usually is the same area where beach building is possible. The revetment requires continuous supervision which may involve substituting or relocating the armor units.
1.3. Groins
Groins are constructed verrtically to the shoreline, either impermeable or permeable, to 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.
- Long/short groins
- High/low groins
- Permeable groins
1.4. Riprap
Ripraps are implemented in regions that experience continuous exposure to coastal corrosions. These are capable of resisting erosions dependent upon the size of the boulder’s used, its density, endurance, as well as the calibration and compactness of the edifices layer. The riprap retaining wall is constructed depending on the essentiality of both the waterfront and pneumatic attributes of the design flood for the stream.
2. Berthing and mooring ships structures
These structures are constructed to retain highland sediment and defer alongshore haulage.
2.1 Breakwaters
Breakwaters are structures built of concrete block or rocks or in some conditions a combination of both rock and concrete, designed to minimize wave activity and also to provide the harbors with an appropriate tranquil environment. These structures can be fixed or floating and impermeable or permeable as to permit the transfer of sediment towards the coast of the structures, where the selection of the structure mainly relies on the water depth and tidal range. 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. Breakwaters can be categorized into many groups like sloping-front, vertical-front, floating, rubble-mound, and caisson breakwaters.
2.2 Jetties
Jetties are built at river estuary or harbor entrance and extended into deeper water to oppose forming of sandbars and limit currents, using concrete, steel, stone, timber, and occasionally asphalt used as binder. Jetties are designed on both sides of the bay to connect the shores and are built parallel to the navigation channel, which can be found perpendicular to the shore. Jetties maintain canals by the river bays as well as tidal coves. Jetties stabilizes the channels and restrict the accumulation of deposit within the channel.
3. Marine and Offshore Industry Structures
Offshore construction is the installation of structures and facilities in a marine environment
3.1 Drydock
A drydock is for constructing, sustaining and renovating various water vessels such as boats, ships, and other crafts. When a vessel is to be berthed, the structure operates by flooding the dock and detaching the gateway. Once the vessel enters the bateau, it is appropriately situated and stabilized, the impermeable gateway is situated in its position and the dock is drained until it is dry, allowing the vessels progressively to lay onto the founding blocks harbored to the ground. Along with is a detachable impermeable gateway, a dry dock gateway can be found in various types and compositions.
3.2 Slipways
Slipways utilize lubricated lumber skids for techniques in redeeming and propelling vessels and lack mechanistic components as well as sustainment, and the craft inhabits the slipway pending its re-launch following maintenance operations. Normally, the structure is capable of withstanding vessels that weigh up to 5 tons. The vessel typically falls within the dockside. Standardly, the slipway should have a width of 5 meters at least, as well as a water depth no less than 1.5 meters at the foundation. Facilities operating mechanical drifts that dislodge crafts weigh at most 500 tons, can be categorized into three methods
Automated Slipway
Portable Platform / Mobile Lift
Synchro Lift / Ship Lift
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**The content of this article is taken from web open source. The blogs are intended only to give technical knowledge to young engineers. Any engineering calculators, technical equations and write ups are only for reference and educational purpose.
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