A breakwater is infrastructure built to break waves or waves by absorbing some of the wave energy. Breakwaters are used to control abrasion which can erode the shoreline and also to calm the waves at port so that ships can dock at port more easily and quickly.
The breakwater can be divided into two types, namely “onshore” and “offshore” breakwaters. The first type is widely used in protecting port waters, while the second type is for coastal protection against erosion. In general, the planning conditions for the two types are the same; only in the first type it is necessary to examine the characteristics of the waves at several locations along the breakwater, such as in jetty planning.
Breakwater or in this case an offshore breakwater is a building made parallel to the coast and located at a certain distance from the coastline. The breakwater is built as a form of coastal protection against erosion by destroying the wave energy before it reaches the beach, causing sediment to occur behind the building. This sediment can obstruct the transport of sediment along the coast, therefore the breakwater must be designed properly so that ocean currents do not cause silting because the sand that is involved in the flow settles in the harbor pool. When this happens, the port needs to be dredged regularly.
A. BREAKWATER FUNCTIONS
- The breakwater functions as a protection for the water pool from waves that can disrupt activities in the water during high tides, storms or other natural events.
- The breakwater functions to reduce wave energy and reduce sediment deposits that enter the protected area. Sediment delivery along the coast originating from the surrounding area will be deposited behind the building. The coast behind the structure will be stable with the formation of these sediment deposits.
- A wave that spreads about a wave- absorbing building is partially reflected (reflection), partially forwarded (transmission) and partially destroyed (dissipation) through the breaking of the wave, fluid viscosity, basic friction and others.
- The distribution of the amount of reflected wave energy, destroyed and transmitted depends on the characteristics of the incoming waves (period, height, and water depth), the building type of the wave damper and the geometry of the damping building (slope, elevation and top of the building).
B. Types of Breakwater
1. Slant Side Breakwater
The sloping breakwater is made of piles of natural stone which is protected by a protective layer in the form of concrete or large rocks of a certain shape. This type of breakwater is more suitable for use in soft soil conditions and is not too deep. The sloping breakwater is more flexible so that if it is hit by a strong wave attack, the damage will not occur suddenly. The granular arrangement of the breakwater consists of several layers, namely on the outside it consists of large stones and the smaller the size goes inside. The shape of the grains used will also affect the bonds between the grains so that the grain forms used generally have sharp edges because the bonds between the grains will be better and more stable.
The protective stone grains can be in the form of natural stones weighing up to tons and it can also be made of artificial stone made of concrete in the form of cubes or other forms. Artificial protective items from concrete can be: Tetrapod, Cube, Tribar, Quadripod, Dolos, Core-loc Accropod.
2. Upright Side Breakwater
This type of breakwater is usually placed in the sea at a deeper depth with hard subgrade. Because the breakwater wall is upright, there will be a clapotid wave, which is a superposition between the incident wave and the reflected wave.
The height of the klapotid wave is 2 times the height of the incident wave. Some things to note are:
- For depths greater than 20 meters, upright side breakwaters are constructed above the sloping breakwater.
- The maximum depth of water is 15 – 20 meters.
- The width of the breakwater is at least 3/4 high.
- The depth below the lowest water level to the base of the building is not less than 1 ¼ -1 ½ times or better 2 times the height of the incoming waves.
- The height of the breaker above the surface of the highest tide should not be less than 1 1/3 -1 ½ times the height of the wave coming.
Types of Construction Breakwater Upright.
A. Blok Beton
Made of mass concrete blocks arranged vertically. Each block is locked with reinforced concrete which is cast in place after the blocks are assembled. The top of the breakwater is made of a concrete wall that is cast in place. The foundation is made of piles of stones covered with a protective layer of concrete blocks.
B. Cell Board Stake (Sheet Pile Cells)
This breakwater consists of a concrete sheet pile and a concrete pillar that is poked through the soft soil until it reaches the hard ground. The top of the sheet pile and the pillar is made of concrete blocks. This breakwater is made when the seabed consists of very thick soft soil, making replacement of soft soil with sand expensive.
C. Kaison (Caisson)
The breakwater is made on land and then brought down to a predetermined location by being towed by the ship. Transport to the site is carried out when the water is calm. After arriving at the location the emperor was drowned to the seabed by filling it with water and then filled with sand. The upper part is then made of concrete floors and walls. Caesons are made like a box with the underside closed and with the walls of the diaphragm dividing the box.
3. Combined Breakwater
Combined breakwater is a combination of upright and slanted side breakwater, wherein the upright wave breaker is built on top of the beveled breakwater. This combined breakwater is used at very deep water depths and the subgrade is unable to withstand the load of the upright breakwater. What is unique is that at low tide the function is the slanted side breakwater, while if the tide is high, the one that functions is the upside breakwater. As for further considerations regarding the comparison of the vertical side to the pile of stones. Basically there are three kinds, namely:
- The stone pile is made to be as high as the water during the highest tide, while the side building is upright only as a cover for the top.
- The stone pile is as high as the lowest water while the upright side of the building must hold the highest water
- The stone pile is only an addition to the foundation of the upright side building.
C. BREAKWATER PLANNING CONSIDERATIONS
In planning a breakwater, of course there are important factors that need to be considered. Among them are:
- Port Size and Layout
- Breakwater Materials
- Depth of Water
- Seabed Soil Conditions
- Wave size and wave direction
- Tide out the sea water