User:Kkings3/sandbox/Kenny's Sandbox

Detached breakwaters are structures built parallel to the shoreline of a beach that aid in reducing wave energy and encourage sediment deposition to help prevent beach erosion. They are usually made out of armor stone or precast concrete blocks. The deposition of sediment can either result in a salient or a tombolo. A salient is a U-shaped accumulation of sediment that extends from the shoreline towards the breakwater and is preferred over tombolos. A tombolo forms when the accumulation of sediment causes the beach to connect with the breakwater. Typically, tombolos form when the length of the breakwater is greater than or equal to 0.8 times the distance from the shore. Salients are preferred over tombolos because tombolos can result in a loss of sand downdrift, which can lead to further eosion. When many detached breakwaters are built in succession the group is called a segmented breakwater. Segmented breakwaters are used to guard large sections of coast .

Coastal Erosion

Coastal erosion is a major problem facing the United States. Coastal erosion has been estimated to annually cost billions of dollars in property damage in the United States. The effects of coastal erosion are taking a large toll on the city of New Orleans, costing millions of dollars in pumping and dike maintenance . In the past 80 years, Louisiana has lost 1,900 miles² of wetlands. Almost 25 to 35 miles² of wetlands disappear every year . If the current rate of coastal erosion goes unchecked, Louisiana's land loss will be close to 640,000 acres, about the size of Rhode Island, by 2050 . By 2050:

• $550 million will be lost from Louisiana commercial fisheries each year

• $200 million will be lost from Louisiana recreational fisheries each year

• More than 155 miles of ports and additional waterways will be gone, including New Orleans

Detached breakwaters provide a way to reduce beach erosion while also protecting from strong storms such as hurricanes. The salients and tombolos that form because of the detached breakwaters contribute to shoreline restoration and expansion. By using detached breakwaters along the coast of Louisiana and other states, coastal erosion can be reduced.

Types of Breakwaters

Because of the many different variables associated with the construction of breakwaters, such as length of the breakwater, type of beach the breakwater is protecting, and distance from the breakwater to the shore, there are different types of breakwaters that can be implemented to protect coastlines .

Submerged breakwaters

Submerged breakwaters, also called low-crested breakwaters, are rock or concrete structures built to reduce wave energy, but the reduction in wave energy is not as high as it would be with an emerged breakwater. The deposition of sediments is also lower with a submerged breakwater than it is with an emerged breakwater. However, submerged breakwaters have many redeeming qualities that sometimes make them more suitable for a beach than emerged breakwaters. Detached breakwaters can be considered visually unappealing and may take away from the view of the water. Submerged breakwaters leave the panoramic view of the water unobstructed while still contributing to beach rejuvenation. Because they are underwater rock-like structures, the submerged breakwaters provide good habitat for fish and other aquatic life. Submerged breakwaters provide a sound economic alternative to the slightly more expensive emerged breakwaters. Because waves move over the top of the submerged breakwaters, the water causes a smoother sand accumulation to form when compared to the traditional detached breakwaters.

Submerged breakwaters do have negative aspects over other types of breakwaters. For example, because they are located under the water, it is possible for boats to either wreck or get damaged because they are harder to see. It is also possible that because of storm surge and tides, a submerged breakwater can be high in relative terms to the surrounding water at a normal level. This takes away the benefit of having a breakwater that does not obstruct the view of the water. Submerged breakwaters can cause dangerous currents for swimmers who get too close to them due to the water rushing over the top of the breakwater. Finally, submerged breakwaters do not provide as great of shoreline protection or sediment accumulation as emerged breakwaters.

Floating breakwaters

Floating breakwaters are used to reduce waves caused by storms or boats that contribute to shoreline erosion and property damage. Floating breakwaters are buoyant barriers that are used in marinas as piers while still having some protective qualities. Floating breakwaters are able to stay above the water level and are therefore useful in areas with varying tidal levels. They are used primarily in marinas because they are not viable in open sea locations.

Floating breakwaters are also used when the view of the beach needs to remain unobstructed. They are not considered to be visually unappealing, and are used when it is important for the beach to look its best. Floating breakwaters do not inhibit the movement of fish or the circulation of water. They can be easily towed or relocated out of the water if there is a possibility ice formation will be a problem. For water exceeding more than 6 m, floating breakwaters can provide a cheaper alternative than bottom connected breakwaters. Due to their buoyancy, floating breakwaters offer the ability to be relocated or rearranged with the greatest amount of ease when compared to the breakwaters built from concrete and armor stone .

Applicability of detached breakwaters

The ability for a breakwater to function properly depends on the type of coast it is protecting. Coasts are divided into one of five groups based on the angle of incidence of the prevailing waves. The five types of coast are:

1. Type 1: Perpendicular wave approach, where the angle of incidence is close to 0°
2. Type 2: Nearly perpendicular wave approach, where the angle of incidence is 1°-10° and net transport of sediment is small to moderate
3. Type 3: Moderate oblique wave approach, where the angle of incidence is 10°-50° and where there is a large net transport of sediment
4. Type 4: Very oblique wave approach, where the angle of incidence is 50°-85° and where there is a large net transport of sediment
5. Type 5: Nearly coast-parallel wave approach, where the angle of incidence is >85° and net transport of sediment is close to zero

Type 1 coasts

Building detached breakwaters to aid in the prevention of beach erosion on Type 1 coasts requires extra effort in order to function properly. Local erosion will occur on both sides of the breakwater because sand will be trapped in its lee areas. In order for the detached breakwaters to perform properly, the sheltered areas located behind the breakwater must be filled in with sand. When combined with the sand filling of the sheltered areas, detached breakwaters can be used to preserve and protect Type 1 coasts.

Type 2 and perpendicular parts of Type 3 coasts

Detached breakwaters seem to be very effective on Type 2 and the perpendicular parts of Type 3 coasts. Sediment is deposited on the upstream side of the breakwater, as well as the sheltered areas behind it. While the accumulation of the sediment occurs on the upstream side and in the sheltered zone, downstream erosion can occur in small increments. If the detached breakwater is too long, a tombolo will form connecting the beach to the breakwater. If the breakwater is not long enough to form a tombolo, a salient will form slightly upstream from the breakwater .

An issue with building breakwaters on Type 2 and certain Type 3 coasts is that if the breakwater is too close to the beach, it can collapse because of the erosion of its seabed. It is very important to strengthen and rejuvenate the seabed surrounding the sea side area of a detached breakwater that is too close to the beach .

The initial planning and design of the detached breakwaters is the most important part of the whole process of preventing beach erosion. The dimensions of the breakwater must perfectly fit the location where the breakwater will be placed or it will actually cause more erosion than before. While beach nourishment is a way to make sure the breakwater continues to do its job, it is much easier to design the breakwater in a way that optimizes the amount of deposition of sediment while minimizing the amount of downstream erosion. Many smaller breakwaters are considered to be obsolete when compared to the results of a few larger breakwaters .

Type 4, 5 and oblique parts of Type 3 coasts

Segmented breakwaters are most ideal for Type 4,5 and oblique parts of Type 3 coasts because the effective length of the structure perpendicular to the wave direction is relatively small. Single detached breakwaters are not ideal because they do not offer enough length in relation to the waves hitting them in a perpendicular manner to actually protect the shore and create an ideal accumulation formation .

Segmented breakwaters with small breaks in between each breakwater provide the best results for these types of coasts because the small breaks allow wave direction to not play a factor in the formation of pocket beaches. Because of this, segmented breakwaters with short interspersed gaps can be used on all types of coasts .