The technical meaning of maintenance involves functional checks, repairing or replacing of necessary devices, machinery, building infrastructure, supporting utilities in industrial, business and residential installations. Over time, this has come to include multiple wordings that describe various cost-effective practices to keep equipment operational. Together, these functions are referred to as Maintenance and overhaul. MRO is used for Maintenance and operations. Over time, the terminology of maintenance and MRO has begun to become standardized; the United States Department of Defense uses the following definitions: Any activity—such as tests, replacements and repairs—intended to retain or restore a functional unit in or to a specified state in which the unit can perform its required functions. All action taken to restore it to serviceability, it includes inspections, servicing, classification as to serviceability, repair and reclamation. All repair action taken to keep a force in condition to carry out its mission.
The routine recurring work required to keep a facility in such condition that it may be continuously used, at its original or designed capacity and efficiency for its intended purpose. Maintenance is connected to the utilization stage of the product or technical system, in which the concept of maintainability must be included. In this scenario, maintainability is considered as the ability of an item, under stated conditions of use, to be retained in or restored to a state in which it can perform its required functions, using prescribed procedures and resources. In some domains like aircraft maintenance, terms maintenance and overhaul include inspection, rebuilding and the supply of spare parts, raw materials, sealants and consumables for aircraft maintenance at the utilization stage. In international civil aviation maintenance means: The performance of tasks required to ensure the continuing airworthiness of an aircraft, including any one or combination of overhaul, replacement, defect rectification, the embodiment of a modification or a repair.
This definition covers all activities for which aviation regulations require issuance of a maintenance release document. The basic types of maintenance falling under MRO include: Preventive maintenance known as PM Corrective maintenance where equipment is repaired or replaced after wear, malfunction or break down. Predictive maintenance, which uses sensor data to monitor a system continuously evaluates it against historical trends to predict failure before it occurs. ReinforcementArchitectural conservation employs MRO to preserve, restore, or reconstruct historical structures with stone, glass and wood which match the original constituent materials where possible, or with suitable polymer technologies when not. Preventive maintenance is "a routine for periodically inspecting" with the goal of "noticing small problems and fixing them before major ones develop." Ideally, "nothing breaks down."The main goal behind PM is for the equipment to make it from one planned service to the next planned service without any failures caused by fatigue, neglect, or normal wear, which Planned Maintenance and Condition Based Maintenance help to achieve by replacing worn components before they fail.
Maintenance activities include partial or complete overhauls at specified periods, oil changes, minor adjustments, so on. In addition, workers can record equipment deterioration so they know to replace or repair worn parts before they cause system failure; the New York Times gave an example of "machinery, not lubricated on schedule" that functions "until a bearing burns out." Preventive maintenance contracts are a fixed cost, whereas improper maintenance introduces a variable cost: replacement of major equipment. Preventive maintenance or preventative maintenance has the following meanings: The care and servicing by personnel for the purpose of maintaining equipment in satisfactory operating condition by providing for systematic inspection and correction of incipient failures either before they occur or before they develop into major defects; the work carried out on equipment in order to avoid its malfunction. It is a routine action taken on equipment in order to prevent its breakdown. Maintenance, including tests, adjustments, parts replacement, cleaning, performed to prevent faults from occurring.
Other terms and abbreviations related to PM are: scheduled maintenance planned maintenance, which may include scheduled downtime for equipment replacement planned preventive maintenance is another name for PM breakdown maintenance: fixing things only when they break. This is known as "a reactive maintenance strategy" and may involve "consequential damage." Planned preventive maintenance, more referred to as planned maintenance or scheduled maintenance, is any variety of scheduled maintenance to an object or item of equipment. Planned maintenance is a scheduled service visit carried out by a competent and suitable agent, to ensure that an item of equipment is operating and to therefore avoid any unscheduled breakdown and downtime; the key factor as to when and why this work is being done is timing, involves a service, resource or facility being unavailable. By contrast, co
In navies and the maritime industry, damage control is the emergency control of situations that may cause the sinking of a watercraft. Examples are: rupture of a pipe or hull below the waterline and damage from grounding or hard berthing against a wharf. temporary fixing of bomb or explosive damage. Simple measures may stop flooding, such as: locking off the damaged area from other ship's compartments. More complicated measures may be needed if a repair must take the pressure of the ship moving through the water. For example: Thermal lance cutting around the rupture. Oxyacetylene welding or electric arc welding of plates over the rupture. Quick-drying cement is applied underwater over the rupture. Damage control training is undertaken by most seafarers, but the engineering staff are most experienced in making lasting repairs. Damage control is distinct from firefighting. Damage control methods of fighting fire are based on the class of ship and cater to ship specific equipment on board. Particular examples: USS Samuel B. Roberts: After an Iranian mine holed the frigate beneath the waterline in 1988, the crew fought fire and flooding that threatened to sink it.
USS Princeton: After an Iraqi naval mine damaged the cruiser during the 1991 Gulf War, her crew fought fires and sealed cracks in the hull repaired electronic systems, bringing the Aegis combat system back on line within 2 hours. USS Cole: immediate measures to stop sinking after the ship was bombed in 2000. HMS Nottingham: measures to keep the ship afloat after, on 7 July 2002, the Nottingham ran aground on the submerged but well-charted Wolf Rock near Lord Howe Island. Naval architecture "Royal Navy Damage Control" on YouTube Media related to Damage control at Wikimedia Commons The dictionary definition of damage control at Wiktionary
United States Coast Guard
The United States Coast Guard is the coastal defense and maritime law enforcement branch of the United States Armed Forces and one of the country's seven uniformed services. The Coast Guard is a maritime, multi-mission service unique among the U. S. military branches for having a maritime law enforcement mission and a federal regulatory agency mission as part of its mission set. It operates under the U. S. Department of Homeland Security during peacetime, can be transferred to the U. S. Department of the Navy by the U. S. President at any time, or by the U. S. Congress during times of war; this has happened twice: in 1917, during World War I, in 1941, during World War II. Created by Congress on 4 August 1790 at the request of Alexander Hamilton as the Revenue-Marine, it is the oldest continuous seagoing service of the United States; as Secretary of the Treasury, Hamilton headed the Revenue-Marine, whose original purpose was collecting customs duties in the nation's seaports. By the 1860s, the service was known as the U.
S. Revenue Cutter Service and the term Revenue-Marine fell into disuse; the modern Coast Guard was formed by a merger of the Revenue Cutter Service and the U. S. Life-Saving Service on 28 January 1915, under the U. S. Department of the Treasury; as one of the country's five armed services, the Coast Guard has been involved in every U. S. war from 1790 to the Iraq War and the War in Afghanistan. The Coast Guard has 40,992 men and women on active duty, 7,000 reservists, 31,000 auxiliarists, 8,577 full-time civilian employees, for a total workforce of 87,569; the Coast Guard maintains an extensive fleet of 243 coastal and ocean-going patrol ships, tenders and icebreakers called "cutters", 1650 smaller boats, as well as an extensive aviation division consisting of 201 helicopters and fixed-wing aircraft. While the U. S. Coast Guard is the smallest of the U. S. military service branches in terms of membership, the U. S. Coast Guard by itself is the world's 12th largest naval force; the Coast Guard carries out three basic roles, which are further subdivided into eleven statutory missions.
The three roles are: Maritime safety Maritime security Maritime stewardshipWith a decentralized organization and much responsibility placed on the most junior personnel, the Coast Guard is lauded for its quick responsiveness and adaptability in a broad range of emergencies. In a 2005 article in Time magazine following Hurricane Katrina, the author wrote, "the Coast Guard's most valuable contribution to may be as a model of flexibility, most of all, spirit." Wil Milam, a rescue swimmer from Alaska told the magazine, "In the Navy, it was all about the mission. Practicing for war, training for war. In the Coast Guard, it was, take care of our people and the mission will take care of itself." The eleven statutory missions as defined by law are divided into homeland security missions and non-homeland security missions: Ice operations, including the International Ice Patrol Living marine resources Marine environmental protection Marine safety Aids to navigation Search and rescue Defense readiness Maritime law enforcement Migrant interdiction Ports and coastal security Drug interdiction See National Search and Rescue Committee See Joint Rescue Coordination CentersWhile the U.
S. Coast Guard Search and Rescue is not the oldest search and rescue organization in the world, it is one of the Coast Guard's best-known operations; the National Search and Rescue Plan designates the Coast Guard as the federal agency responsible for maritime SAR operations, the United States Air Force as the federal agency responsible for inland SAR. Both agencies maintain rescue coordination centers to coordinate this effort, have responsibility for both military and civilian search and rescue; the two services jointly provide instructor staff for the National Search and Rescue School that trains SAR mission planners and coordinators. Located on Governors Island, New York, the school is now located at Coast Guard Training Center Yorktown at Yorktown, Virginia. Operated by the Coast Guard, the National Response Center is the sole U. S. Government point of contact for reporting all oil, radiological and etiological spills and discharges into the environment, anywhere in the United States and its territories.
In addition to gathering and distributing spill/incident information for Federal On Scene Coordinators and serving as the communications and operations center for the National Response Team, the NRC maintains agreements with a variety of federal entities to make additional notifications regarding incidents meeting established trigger criteria. The NRC takes Maritime Suspicious Activity and Security Breach Reports. Details on the NRC organization and specific responsibilities can be found in the National Oil and Hazardous Substances Pollution Contingency Plan; the Marine Information for Safety and Law Enforcement database system is managed and used by the Coast Guard for tracking pollution and safety incidents in the nation's ports. The National Maritime Center is the merchant mariner credentialing authority for the USCG under the auspices of the Department of Homeland Security. To ensure a safe and environmentally sound marine transportation system, the mission of the NMC is to issue credentials to qualified mariners in the United States maritime jurisdiction.
The five uniformed services that make up the U. S. Armed Forces are defined in Title 10 of the U. S. Code: The term "armed forces" means the Army, Air Force, Marine Corps, Coast Guard; the Coast Guard is further defined by Title 14 of the United States Code: The Coast Guar
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. It is the largest and most capable navy in the world and it has been estimated that in terms of tonnage of its active battle fleet alone, it is larger than the next 13 navies combined, which includes 11 U. S. allies or partner nations. With the highest combined battle fleet tonnage and the world's largest aircraft carrier fleet, with eleven in service, two new carriers under construction. With 319,421 personnel on active duty and 99,616 in the Ready Reserve, the Navy is the third largest of the service branches, it has 282 deployable combat vessels and more than 3,700 operational aircraft as of March 2018, making it the second-largest air force in the world, after the United States Air Force. The U. S. Navy traces its origins to the Continental Navy, established during the American Revolutionary War and was disbanded as a separate entity shortly thereafter.
The U. S. Navy played a major role in the American Civil War by blockading the Confederacy and seizing control of its rivers, it played the central role in the World War II defeat of Imperial Japan. The US Navy emerged from World War II as the most powerful navy in the world; the 21st century U. S. Navy maintains a sizable global presence, deploying in strength in such areas as the Western Pacific, the Mediterranean, the Indian Ocean, it is a blue-water navy with the ability to project force onto the littoral regions of the world, engage in forward deployments during peacetime and respond to regional crises, making it a frequent actor in U. S. foreign and military policy. The Navy is administratively managed by the Department of the Navy, headed by the civilian Secretary of the Navy; the Department of the Navy is itself a division of the Department of Defense, headed by the Secretary of Defense. The Chief of Naval Operations is the most senior naval officer serving in the Department of the Navy.
The mission of the Navy is to maintain and equip combat-ready Naval forces capable of winning wars, deterring aggression and maintaining freedom of the seas. The U. S. Navy is a seaborne branch of the military of the United States; the Navy's three primary areas of responsibility: The preparation of naval forces necessary for the effective prosecution of war. The maintenance of naval aviation, including land-based naval aviation, air transport essential for naval operations, all air weapons and air techniques involved in the operations and activities of the Navy; the development of aircraft, tactics, technique and equipment of naval combat and service elements. U. S. Navy training manuals state that the mission of the U. S. Armed Forces is "to be prepared to conduct prompt and sustained combat operations in support of the national interest." As part of that establishment, the U. S. Navy's functions comprise sea control, power projection and nuclear deterrence, in addition to "sealift" duties, it follows as certain as that night succeeds the day, that without a decisive naval force we can do nothing definitive, with it, everything honorable and glorious.
Naval power... is the natural defense of the United States The Navy was rooted in the colonial seafaring tradition, which produced a large community of sailors and shipbuilders. In the early stages of the American Revolutionary War, Massachusetts had its own Massachusetts Naval Militia; the rationale for establishing a national navy was debated in the Second Continental Congress. Supporters argued that a navy would protect shipping, defend the coast, make it easier to seek out support from foreign countries. Detractors countered that challenging the British Royal Navy the world's preeminent naval power, was a foolish undertaking. Commander in Chief George Washington resolved the debate when he commissioned the ocean-going schooner USS Hannah to interdict British merchant ships and reported the captures to the Congress. On 13 October 1775, the Continental Congress authorized the purchase of two vessels to be armed for a cruise against British merchant ships. S. Navy; the Continental Navy achieved mixed results.
In August 1785, after the Revolutionary War had drawn to a close, Congress had sold Alliance, the last ship remaining in the Continental Navy due to a lack of funds to maintain the ship or support a navy. In 1972, the Chief of Naval Operations, Admiral Elmo Zumwalt, authorized the Navy to celebrate its birthday on 13 October to honor the establishment of the Continental Navy in 1775; the United States was without a navy for nearly a decade, a state of affairs that exposed U. S. maritime merchant ships to a series of attacks by the Barbary pirates. The sole armed maritime presence between 1790 and the launching of the U. S. Navy's first warships in 1797 was the U. S. Revenue-Marine, the primary predecessor of the U. S. Coast Guard. Although the USRCS conducted operations against the pirates, their depredations far outstripped its abilities and Congress passed the Naval Act of 1794 that established a permanent standing navy on 27 March 1794; the Naval Act ordered the construction and manning of six frigates and, by October 1797, the first three were brought into service: USS United States, USS Constellation, USS Constitution.
Due to his strong posture on having a strong standing Navy during this period, John Adams is "often called the father of the American Navy". In 1798–99 the Navy was involved in an undeclared Quasi-War with France. From 18
A cutter is a small to medium-sized vessel, depending on its role and definition. It was a smallish single- or double-masted, decked sailcraft designed for speed rather than capacity; as such, it was gaff-rigged, with two or more headsails and a bowsprit of some length, with a mast sometimes set farther back than on a sloop. While a workboat, as used by harbor pilots, the military, privateers, sailing cutters today are most fore-and-aft rigged private yachts. Powered cutters vary in size depending on their function, with small boats for ferrying passengers between larger craft and shore sometimes referred to as cutters, rugged smallish vessels serving the traditional role of delivering harbor pilots, large ocean-going U. S. Coast Guard or UK Border Force ships referred to as cutters by tradition. Open oared cutters were carried aboard 18th century naval vessels and rowed by pairs of men sitting side-by-side on benches. A similar form that evolved among London watermen remains in use today in club racing.
The cutter is one of several types of sailboats. Traditionally the sloop rig was a rig with a single mast located forward of 70% of the length of the sailplan. In this traditional definition a sloop could have multiple jibs on a fixed bowsprit. Cutters had a rig with a single mast more centrally located, which could vary from 50% to 70% of the length of the sailplan, with multiple headsails and a running bowsprit. A mast located aft of 50% would be considered a mast aft rig. Somewhere in the 1950s or 2000s there was a shift in these definitions such that a sloop only flew one headsail and a cutter had multiple headsails and mast position became irrelevant. In this modern idiom, a cutter is a sailing vessel with one mast. Cutters carry a staysail directly in front of the mast, set from the forestay. A traditional vessel would normally have a bowsprit to carry one or more jibs from its end via jibstay on travelers. In modern vessels the jib may be set from a permanent stay fixed to the end of a fixed bowsprit, or directly to the stem fitting of the bow itself.
In these cases, that may be referred to as the forestay, the inner one, which will be less permanent in terms of keeping the mast up, may be called the stays'l stay. A sloop carries only one head sail, called either the foresail or jib.. The cutter rig a gaff rig version where the sails aft the mast were divided between a mainsail below the gaff and a topsail above, was useful for sailing with small crews as the total sail area was divided into smaller individual sails; these could be managed without the need for large crews, winches, or complex tackles, making the cutter suitable for pilot and coast guard duties. For example, a pilot cutter may only have two people on board for its outward trip—the pilot to be delivered to a ship and an assistant who had to sail the cutter back to port single-handed; the cutter sailing rig became so ubiquitous for these tasks that the modern-day motorised vessels now engaged in these duties are known as'cutters'. The open cutter carried aboard naval vessels in the 18th century was rowed by pairs of men sitting side-by-side on benches.
The cutter, with its transom, was broader in proportion compared to the longboat, which had finer lines. The watermen of London used similar boats in the 18th century decorated as depicted in historical prints and pictures of the River Thames in the 17th and 18th centuries; the modern waterman's cutter is based on drawings of these boats. They are 34 feet long with a beam of 4 ft 6 in, they can carry a cox and passengers. The organisers of the Great River Race developed the modern version in the 1980s and now many of the fleet of 24 compete annually in this "Marathon of the River". Watermen's cutters compete annually in the Port of London Challenge, the Port Admirals' Challenge. Cutter races are to be found at various town rowing and skiffing regattas. In addition the cutters perform the role of ceremonial Livery Barges with the canopies and armorial flags flying on special occasions. Cutters have been used for record-breaking attempts and crews have achieved record times for sculling the English Channel in 1996 and for sculling non-stop from London to Paris in 1999.
A pulling cutter was a boat carried by sailing ships for work in sheltered water in which load-carrying capacity was needed, for example in laying a kedge. This operation was the placing of a light anchor at a distance from the ship so as to be able to haul her off in its direction; the oars were double-banked. That is, there were two oarsmen on each thwart. In a seaway, the longboat was preferred to the cutter as the finer lines of the stern of the former meant that it was less to broach to in a following sea. In the Royal Navy the cutters were replaced by 32-foot motor cutters. However, the cutters' traditional work had grown beyond the capacity of a boat as ships became larger. Though a pulling boat, this cutter could be rigged for sailing; some small powered fishing craft are referred to as cutters. Cutters were used by several navies in the 17th and 18th centuries and were the smallest commissioned ships in the fleet; as with cutters in general they were distinguished by their large fore-aft sail plans with multiple headsails carried on a long bowsprit, sometimes as long as half the length of the boat's hull.
The rig gave the cutter excellent maneuverability and they were much better at sailing to windward than a larger square rigged ship. Larger naval cutters had the ability to hoist two or
Firefighting is the act of attempting to prevent the spread of and extinguish significant unwanted fires in buildings, woodlands, etc. A firefighter suppresses fires to protect lives and the environment. Firefighters undergo a high degree of technical training; this involves wildland firefighting. Specialized training includes aircraft firefighting, shipboard firefighting, aerial firefighting, maritime firefighting, proximity firefighting. One of the major hazards associated with firefighting operations is the toxic environment created by combustible materials; the four major risks are smoke, oxygen deficiency, elevated temperatures, poisonous atmospheres. Additional hazards include falls and structural collapse that can exacerbate the problems entailed in a toxic environment. To combat some of these risks, firefighters carry self-contained breathing equipment; the first step in a firefighting operation is reconnaissance to search for the origin of the fire and to identify the specific risks. Fires can be extinguished by fuel or oxidant removal, or chemical flame inhibition.
The earliest known firefighters were in the city of Rome. In 60 A. D. emperor Nero established a Corps of Vigils to protect Rome after a disastrous fire. It consisted of 7,000 people equipped with buckets and axes, they fought fires and served as police. In the 4th century B. C. an Alexandrian Greek named Ctesibius made a double force pump called a siphona. As water rose in the chamber, it compressed the air inside, which forced the water to eject in a steady stream through a pipe and nozzle. In the 16th century, syringes were used as firefighting tools, the larger ones being mounted on wheels. Another traditional method that survived was the bucket brigade, involving two lines of people formed between the water source and the fire. Men in one of the lines would pass along the full buckets of water toward the fire while in the other line women and children would pass back the empty buckets to be refilled. In the 17th century,'fire engines' were made, notably in Amsterdam. In 1721, the English inventor Richard Newsham made a popular fire engine, a rectangular box on wheels filled using a bucket brigade to provide a reservoir while hand-powered pumps supplied sufficient water pressure to douse fires at a distance.
Ancient Rome did not have municipal firefighters. Instead, private individuals relied on their supporters to take action, they would not only form bucket brigades or attempt to smother smaller fires, but would demolish or raze nearby buildings to slow the spread of the fire. However, there is no mention of fires being extinguished, rather they were contained and burned themselves out. Ancient Rome did not have an organized firefighting force until the Vigiles were formed in the reign of Augustus. Prior to the Great Fire of London in 1666, some parishes in the UK had begun to organize rudimentary firefighting. After the Great Fire, Nicholas Barbon introduced the first fire insurance. In order to reduce insurance costs, Barbon formed his own fire brigade, other companies followed suit. By the start of the 1800s, insured buildings were identified with a badge or mark indicating that they were eligible for a company's firefighting services. Buildings not insured with a particular company were left by its firefighters to burn, unless they happened to be adjacent to an insured building, in which case it was in the company's interest to prevent the fire from spreading.
In 1833 fire insurance companies in London merged to form The London Fire Company Establishment. Steam-powered apparatuses were first introduced in the 1850s, allowing a greater quantity of water to be directed onto a fire. In World War II the Auxiliary Fire Service, the National Fire Service, were established to supplement local fire services. At that time, there was no countrywide standard for firefighting terms, ranks, or equipment; these were standardized after the war. In January 1608, a fire destroyed many of the colonists' provisions and lodgings in Jamestown, Virginia. Boston, New York City, Philadelphia were all plagued by fires, volunteer fire brigades formed soon after such disasters. In 1736, Benjamin Franklin founded the Union Fire Company in Philadelphia, which became the standard for volunteer fire organizations; these firefighters had two critical tools: so-called bed keys. Salvage bags were used to collect and save valuables, bed keys were used to separate the wooden frame of a bed into pieces for safe and rapid removal from the fire.
The first American attempt at fire insurance failed after a large fire in Charlestown, Massachusetts in 1736. In 1740, Benjamin Franklin organized the Philadelphia Contributionship to provide fire insurance, more successful; the Contributionship adopted "fire marks" to identify insured buildings. Firefighting started to become formalized with rules for providing buckets and hooks, with the formation of volunteer companies. A chain of command was established. A firefighter's goals are to save lives and the environment. A fire can spread and endanger many lives, but with modern firefighting techniques, catastrophe can be avoided. To prevent fires from starting, a firefighter's duties may include public education about fire safety and conducting fire inspections of locations to verify their adherence to local fire codes. Firefighting requires skills in fire suppression and hazardous materials mitigation. Firefighters must have, or be able to acquire, kno
A flood is an overflow of water that submerges land, dry. In the sense of "flowing water", the word may be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Flooding may occur as an overflow of water from water bodies, such as a river, lake, or ocean, in which the water overtops or breaks levees, resulting in some of that water escaping its usual boundaries, or it may occur due to an accumulation of rainwater on saturated ground in an areal flood. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, these changes in size are unlikely to be considered significant unless they flood property or drown domestic animals. Floods can occur in rivers when the flow rate exceeds the capacity of the river channel at bends or meanders in the waterway. Floods cause damage to homes and businesses if they are in the natural flood plains of rivers.
While riverine flood damage can be eliminated by moving away from rivers and other bodies of water, people have traditionally lived and worked by rivers because the land is flat and fertile and because rivers provide easy travel and access to commerce and industry. Some floods develop while others such as flash floods can develop in just a few minutes and without visible signs of rain. Additionally, floods can be local, impacting a neighborhood or community, or large, affecting entire river basins; the word "flood" comes from a word common to Germanic languages. Floods can happen on flat or low-lying areas when water is supplied by rainfall or snowmelt more than it can either infiltrate or run off; the excess accumulates in place, sometimes to hazardous depths. Surface soil can become saturated, which stops infiltration, where the water table is shallow, such as a floodplain, or from intense rain from one or a series of storms. Infiltration is slow to negligible through frozen ground, concrete, paving, or roofs.
Areal flooding begins in flat areas like floodplains and in local depressions not connected to a stream channel, because the velocity of overland flow depends on the surface slope. Endorheic basins may experience areal flooding during periods when precipitation exceeds evaporation. Floods occur in all types of river and stream channels, from the smallest ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers; when overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, debris, or beaver dams. Slow-rising floods most occur in large rivers with large catchment areas; the increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. However, large rivers may have rapid flooding events in areas with dry climate, since they may have large basins but small river channels and rainfall can be intense in smaller areas of those basins.
Rapid flooding events, including flash floods, more occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation or sudden release from an upstream impoundment created behind a dam, landslide, or glacier. In one instance, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the flow rate increased from about 50 to 1,500 cubic feet per second in just one minute. Two larger floods occurred at the same site within a week, but no one was at the waterfall on those days; the deadly flood resulted from a thunderstorm over part of the drainage basin, where steep, bare rock slopes are common and the thin soil was saturated. Flash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere.
In that setting, the first flood water to arrive is depleted. The leading edge of the flood thus advances more than and higher flows; as a result, the rising limb of the hydrograph becomes quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant. Flooding in estuaries is caused by a combination of sea tidal surges caused by winds and low barometric pressure, they may be exacerbated by high upstream river flow. Coastal areas may be flooded by storm events at sea, resulting in waves over-topping defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. Research from the NHC explains: "Storm surge is an abnormal rise of water generated by a storm and above the predicted astronomical tides. Storm surge should not be confused with storm tide, defined as the water level rise due to the combination of storm surge and the astronomical tide.
This rise in water level can cause extreme flooding in coastal areas when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases." Urban flooding is the inundation of land or property in a built environment in more densely populated areas, caused by rainfall overwhelmi