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Wilmington, North Carolina once had a thriving Black middle class and an elected interracial government. In 1898 white supremacists used violence to overthrow that government, kill Black residents and drive many others from the city.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
A groyne (British English) or groin (American English; see spelling differences) is a rigid aquatic structure built perpendicularly from an ocean shore (in coastal engineering) or a river bank, interrupting water flow and limiting the movement of sediment. It is usually made out of wood, concrete, or stone. In the ocean, groynes create beaches, prevent beach erosion caused by longshore drift where this is the dominant process and facilitate beach nourishment. There is also often cross-shore movement which if longer than the groyne will limit its effectiveness. In a river, groynes slow down the process of erosion and prevent ice-jamming, which in turn aids navigation.
All of a groyne may be underwater, in which case it is a submerged groyne. They are often used in tandem with seawalls and other coastal engineering features. Groynes, however, may cause a shoreline to be perceived as unnatural. Groynes are generally straight but could be of various plan view shapes, permeable or impermeable, built from various materials such as wood, sand, stone rubble, or gabion, etc.
The term groyne is derived from the Old French groign, from Late Latin grunium, "snout".[1]
A large number of groynes were found along a 1,000-kilometre stretch of the river Nile, between the first and the fourth cataract.[2] The earliest ones dated so far were found to be over 3,000 years old, but researchers are hypothesising that the technique might already have been understood in the fourth millennium BCE.[2] The newly discovered groynes are located in what are now Egypt (Aswan), but mainly in Sudan, in areas of ancient Nubia, some of them built by the Egyptian overlords and some possibly the work of local Nubians.[2]
One of the earliest mentions of groynes is in connection with the planned improvements to the silted-up Dover harbour, by one Fernando Poyntz in 1582.[3][4][5]
In 1713 the first wooden groyne to protect Brighton's seafront and coastline was built, which had been heavily damaged in the Great storm of 1703, and again in 1705.[6] In 1867, the first concrete groyne was built near East Street, Brighton as a promenade 195 feet (59 m) long.[7]
A groyne gradually creates and maintains a wide area of beach on its updrift side by trapping the sediments suspended in the ocean current. This process is called accretion of sand and gravel or beach evolution. It reduces erosion on the other, i.e. downdrift, side by reducing the speed and power of the waves striking the shore. It is a physical barrier to stop sediment transport in the direction of longshore drift (also called longshore transport). If a groyne is correctly designed, then the amount of material it can hold will be limited, and excess sediment will be free to move on through the system. However, if a groyne is too large it may trap too much sediment, which can cause severe beach erosion on the down-drift side.
Groynes are generally placed in series, generally all perpendicular to the shore. The areas between groups of groynes are groyne fields.
A poorly designed groyne (too long and not suited to the unique features of the coast) can also accelerate the erosion of the downdrift beach, which receives little or no sand from longshore drift. This process is known as terminal groyne syndrome, because in a series of groynes it occurs after the terminal groyne (last groyne on the downdrift side of the beach or coastline).
A breakwater is an artificial offshore structure built parallel to the shore -- similar to naturally formed barrier islands -- that normally remains unattached to the shore. When a groyne is built to attach the breakwater to the shore, it is called a "headland groyne", also known as "bulkhead groyne", "headland breakwater", "T-head groyne", or "T-shaped groyne".
A groyne's length and elevation, and the spacing between groynes is determined according to local wave energy and beach slope. Groynes that are too long or too high tend to accelerate downdrift erosion, and are ineffective because they trap too much sediment. Groynes that are too short, too low, or too permeable are ineffective because they trap too little sediment. If a groyne does not extend far enough landward, water (for example at a high tide combined with a storm surge) may flow past the landward end and erode a channel bypassing the groyne, a process known as flanking.
River groynes (spur dykes, wing dykes, or wing dams) are often constructed nearly perpendicular to the riverbanks, beginning at a riverbank with a root and ending at the regulation line with a head. They maintain a channel to prevent ice jamming, and more generally improve navigation and control over lateral erosion, that would form from meanders. Groynes have a major impact on the river morphology: they cause autonomous degradation of the river.[8]
They are also used around bridges to prevent bridge scour.
Groynes can be distinguished by how they are constructed, whether they are submerged, their effect on stream flow or by shape.[9]
Groynes can be built with different planview shapes. Some examples include straight groynes, hockey stick or curved, inverted hockey stick groynes, tail or checkmark shaped groynes, L head, straight groynes with pier head (seaward end raised on the stilts, since the pier head is raised on the stilts it does not act as the breakwater), T-head (headland groyne, breakwater attached to the shore with straight groyne, the head/breakwater itself could be shaped straight, Y-shaped, arrow or wing shaped head).
Wooden groynes, sheetpile groynes, sandbag groynes, rubble mound or gabion groynes, etc.
Groynes can be permeable, allowing the water to flow through at reduced velocities, or impermeable, blocking and deflecting the current.
Groynes can be submerged or not under normal conditions. Usually impermeable groynes are non-submerged, since flow over the top of solid groynes may cause severe erosion along the shanks. Submerged groynes, on the other hand, may be permeable depending on the degree of flow disturbance needed.
Groynes can be attracting, deflecting or repelling.
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A groyne (British English) or groin (American English; see spelling differences) is a rigid aquatic structure built perpendicularly from an ocean shore (in coastal engineering) or a river bank, interrupting water flow and limiting the movement of sediment. It is usually made out of wood, concrete, or stone. In the ocean, groynes create beaches, prevent beach erosion caused by longshore drift where this is the dominant process and facilitate beach nourishment. There is also often cross-shore movement which if longer than the groyne will limit its effectiveness. In a river, groynes slow down the process of erosion and prevent ice-jamming, which in turn aids navigation. All of a groyne may be underwater, in which case it is a submerged groyne. They are often used in tandem with seawalls and other coastal engineering features. Groynes, however, may cause a shoreline to be perceived as unnatural. Groynes are generally straight but could be of various plan view shapes, permeable or impermeable, built from various materials such as wood, sand, stone rubble, or gabion, etc.
Bincleaves Groyne is a breakwater located off the southern area of Weymouth, England. It is the second largest of four breakwaters which create Portland Harbour. It is separated from the Northeastern Breakwater by the North Ship Channel. A landing stage is situated on the southern side of the breakwater near the Western Ledges. Bincleaves Groyne features the C Pier Head Battery on the southern tip. The arm is an Admiralty extension to the earlier breakwater built by the Great Western Railway and known as the Bincleaves Groyne. The head is 100 ft in diameter. The battery was opened in 1901 and was armed with two 12-pounder quick-firing (QF) guns for anti-torpedo craft defence. By the First World War the 12-pounder guns had been removed and replaced with a 6-inch breech-loading (BL) Mk. VII gun. The 6-inch gun was removed in 1924 and in 1934 two 12-pounder guns were transferred across from the recently decommissioned B Pier Head. In 1944 emplacements were constructed for two 6-pounder guns, but the guns were not mounted for a number of years. During the Second World War the battery was manned by 107 Battery of 522 Coast Regiment. A field visit in 1983 found the structure to be extant. At the C Pier Head Battery a World War II petroleum warfare site was constructed in 1940–41, and comprised a flame thrower. However the field visit in 1983 had found the site had been demolished. On site is a World War II 29 millimetre spigot mortar emplacement (pedestal). It was constructed after May 1941 and is built of concrete and steel. The field visit in 1983 found the structure to be in a good condition. Almost within the centre of the arm another 29 millimetre spigot mortar emplacement is located near Military Pier. Again it was constructed after May 1941, of concrete and steel, and remains in good condition. The A Pier Head Battery is located on the outer breakwater where the Portland Breakwater Lighthouse is situated, and B Pier Head Battery is located on side of this arm.
The River Clyde ( ; Scottish Gaelic: Abhainn Chluaidh, pronounced [ˈavɪɲ ˈxl̪ˠuəj]) is a major river of western Scotland and the third-longest in the country at about 170 kilometres (110 mi) in length. Its river network extends to 4,244 km and drains a basin of 1,903 km2, expanding to 3,854 km2 when the Clyde estuary system with the Kelvin, White Cart, Black Cart and Leven is included. Around 1.79 million people, 33.8% of Scotland's population, live within this catchment. The river rises in the Lowther Hills and flows north-west through South Lanarkshire and Glasgow before deepening into the Firth of Clyde past the Tail of the Bank off Greenock. Shoals and shallows meant only small vessels could use the river, and in 1688 Glasgow merchants built Port Glasgow 5.4 kilometres (3.4 mi) upriver for seagoing ships. From the late 18th century the upper estuary and river through Glasgow were systematically engineered using groynes, longitudinal training walls and continuous dredging, and by removing rocky obstructions such as a large part of the Elderslie Rock. This enabled ocean-going access and supported Glasgow's rise as a world centre of shipbuilding and marine engineering in the 19th and 20th centuries. Greenock Ocean Terminal brought container shipping to the Clyde in 1969, and most commercial deep-water functions migrated down the estuary, while the upper river corridor has seen major regeneration in Glasgow. Environmental quality has improved from historic industrial lows, though legacy contaminants and periodic low-oxygen episodes in the outer firth have been reported.
A Coruña (Galician pronunciation: [ɐ koˈɾuɲɐ] ; in Spanish: La Coruña [la koˈɾuɲa] ; also informally called Coruña; historical English: Corunna or The Groyne) is a city and municipality in Galicia, Spain. With a population of 249,255, it is the 2nd-largest city in Galicia behind Vigo. The city is the capital of the Province of A Coruña, having also been the political capital of the Kingdom of Galicia from the 16th to the 19th centuries, and as a regional administrative centre between 1833 and 1982. A Coruña is located on a promontory in the Golfo Ártabro, a large gulf on the Atlantic Ocean. It is the main industrial and financial centre of northern Galicia, and holds the headquarters of the Universidade da Coruña. A Coruña is the city with the tallest mean-height of buildings in Spain, also featuring a population density of 21,972 inhabitants per square kilometre (56,910/sq mi) of built land area.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Mae Jemison, aboard Space Shuttle Endeavour in 1992.
