Bulkhead (barrier) - AbsoluteAstronomy.com

Retaining wall

Retaining walls are built in order to hold back earth which would otherwise move downwards. Their purpose is to stabilize slopes and provide useful areas at different elevations, e.g...

, such as a bulkhead within a ship

Bulkhead (partition)

A bulkhead is an upright wall within the hull of a ship or within the fuselage of an airplane. Other kinds of partition elements within a ship are decks and deckheads.-Etymology:...

or a watershed

Drainage basin

A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...

retaining wall. It may also be used in mine

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

s, to contain flooding.

Certain bulkheads, e.g., at the Hudson River

Hudson River

The Hudson is a river that flows from north to south through eastern New York. The highest official source is at Lake Tear of the Clouds, on the slopes of Mount Marcy in the Adirondack Mountains. The river itself officially begins in Henderson Lake in Newcomb, New York...

are of historical and architectural value.

Coastal bulkheads are most often referred to as seawall

Seawall

A seawall is a form of coastal defence constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation and leisure activities from the action of tides and waves...

s, bulkheading, or riprap

Riprap

Riprap — also known as rip rap, rubble, shot rock or rock armour or "Rip-rap" — is rock or other material used to armor shorelines, streambeds, bridge abutments, pilings and other shoreline structures against scour, water or ice erosion.It is made from a variety of rock types, commonly granite or...

revetments. These manmade structures are constructed along shorelines with the purpose of controlling beach

Beach

A beach is a geological landform along the shoreline of an ocean, sea, lake or river. It usually consists of loose particles which are often composed of rock, such as sand, gravel, shingle, pebbles or cobblestones...

erosion

Erosion

Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...

. Construction materials commonly used include wood pilings, commercially developed vinyl products, large boulder

Boulder

In geology, a boulder is a rock with grain size of usually no less than 256 mm diameter. While a boulder may be small enough to move or roll manually, others are extremely massive....

s stacked to form a wall, or a seawall

Seawall

built of concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

or another hard substance.

Coastal property owners typically seek to develop bulkheads in an attempt to slow large landslide

Landslide

A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...

erosion caused by wave

Ocean surface wave

In fluid dynamics, wind waves or, more precisely, wind-generated waves are surface waves that occur on the free surface of oceans, seas, lakes, rivers, and canals or even on small puddles and ponds. They usually result from the wind blowing over a vast enough stretch of fluid surface. Waves in the...

action.

Studies over recent decades have resulted in public awareness as to potential negative effects that bulkheads may bring to beaches and the interconnected habitat

Habitat (ecology)

A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...

areas of fish, plants, and birds. Many states have enacted laws to protect beaches to allow for future use of the beaches, as well as protect these natural habitats. As of 1971, Washington State property owners are required to obtain a permit for the construction of bulkheads that adhere to the strict regulations of the Shoreline Management Act (SMA), enacted by the state legislature.

Effects

While bulkheads may serve their purpose to slow erosion at a bluff

Cliff

In geography and geology, a cliff is a significant vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually...

or beach

Beach

front, they commonly cause a domino effect

Domino effect

The domino effect is a chain reaction that occurs when a small change causes a similar change nearby, which then will cause another similar change, and so on in linear sequence. The term is best known as a mechanical effect, and is used as an analogy to a falling row of dominoes...

of change to the beach profile. The increased wave

Ocean surface wave

reflection

Reflection (physics)

Reflection is the change in direction of a wavefront at an interface between two differentmedia so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves...

caused by their presence can result in an increased re-suspension of sand

Sand

Sand is a naturally occurring granular material composed of finely divided rock and mineral particles.The composition of sand is highly variable, depending on the local rock sources and conditions, but the most common constituent of sand in inland continental settings and non-tropical coastal...

in the water in front of the bulkhead. This can lead to more sand being distributed in the alongshore direction, away from the beach profile. Due to coastal littoral drift, the sand would then instead be distributed toward the ends of the bulkheads, leaving larger gravel

Gravel

Gravel is composed of unconsolidated rock fragments that have a general particle size range and include size classes from granule- to boulder-sized fragments. Gravel can be sub-categorized into granule and cobble...

and sometimes bedrock

Bedrock

In stratigraphy, bedrock is the native consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil...

in place of the once sandy beach.

Since sand is a natural habitat for several species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

of fish to lay their eggs and is also the only surface in which eelgrass

Zostera

Zostera is a small genus of widely distributed seagrass, commonly called marine eelgrass or simply eelgrass . The genus Zostera contains sixteen species.-Ecology:Zostera is found on sandy substrates or in estuaries submerged or partially floating...

can take root, these natural processes can no longer take place in this now sand-stripped location. The absence of eelgrass means that the spawning

Spawn (biology)

Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...

habitat for herring

Herring

Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...

and the protection for juvenile salmon

Salmon

Salmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...

would no longer be present. This new sand-stripped habitat also encourages other species, such as kelp

Kelp

Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....

, to move in.

External links

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.