Washout
Encyclopedia
A washout is the sudden erosion
of soft soil
or other support surfaces by a gush of water
, usually occurring during a heavy downpour
of rain
(a flash flood
) or other stream
flooding. These downpours may occur locally in a thunderstorm
(particularly in summer
, when they are often nearly stationary), or over a large area, such as following the landfall
of a tropical cyclone
. If a washout occurs in a crater
-like formation, it is called a sinkhole
, and usually involves a leaking or broken water main or sewerage
pipe
s. (Other types of sinkholes, such as collapsed cave
s, are not washouts.)
Widespread washouts can occur in mountain
ous areas after heavy rains, even in normally dry ravine
s. A severe washout can become a landslide
, or cause a dam break in an earthen dam. Like other forms of erosion, most washouts can be prevented by vegetation
whose root
s hold the soil and slow the flow of water. Deforestation
increases the risk of washouts. Retaining wall
s and culvert
s may be used, although particularly severe washouts may even destroy these if they are not large or strong enough.
In road and rail transport
, a washout is the result of a natural disaster
where the roadbed is eroded away by flowing water, usually as the result of a flood
. When a washout destroys a railroad's right-of-way
, the track
is sometimes left suspended in midair across the newly-formed gap, or it dips down into a ditch. The phenomenon is discussed in more detail under erosion
.
In 2004, the remnants of Hurricane Frances
and then Hurricane Ivan
caused a large number of washouts in western North Carolina
and other parts of the southern Appalachian Mountains
, closing some roads for days, and parts of the Blue Ridge Parkway
for months. Other washouts have also caused train wreck
s where tracks have been unknowingly undermined. Motorists have also driven into flooded streams at night, unaware of a new washout on the road in front of them until it is too late to brake
, and prompting a high-water rescue.
Major washouts can also ruin pipeline
s or undermine utility pole
s or underground lines, interrupting public utilities.
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...
of soft soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
or other support surfaces by a gush of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, usually occurring during a heavy downpour
Downpour
Downpour may refer to:*Heavy rain*Downpour , a 1999 music album by Mannafest*"Downpour", a song from Unbreakable *A fictional superhero in the animated series Justice League Unlimited...
of rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
(a flash flood
Flash flood
A flash flood is a rapid flooding of geomorphic low-lying areas—washes, rivers, dry lakes and basins. It may be caused by heavy rain associated with a storm, hurricane, or tropical storm or meltwater from ice or snow flowing over ice sheets or snowfields...
) or other stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
flooding. These downpours may occur locally in a thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
(particularly in summer
Summer
Summer is the warmest of the four temperate seasons, between spring and autumn. At the summer solstice, the days are longest and the nights are shortest, with day-length decreasing as the season progresses after the solstice...
, when they are often nearly stationary), or over a large area, such as following the landfall
Landfall (meteorology)
Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...
of a tropical cyclone
Tropical cyclone
A tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation of water vapor...
. If a washout occurs in a crater
Pit crater
A pit crater is a depression formed by a sinking of the ground surface lying above a void or empty chamber, rather than by the eruption of a volcano or lava vent. It is often found in chains or troughs. Several craters may merge into a linear alignment...
-like formation, it is called a sinkhole
Sinkhole
A sinkhole, also known as a sink, shake hole, swallow hole, swallet, doline or cenote, is a natural depression or hole in the Earth's surface caused by karst processes — the chemical dissolution of carbonate rocks or suffosion processes for example in sandstone...
, and usually involves a leaking or broken water main or sewerage
Storm drain
A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...
pipe
Water pipe
Water pipes are pipes or tubes, frequently made of polyvinyl chloride , ductile iron, steel, cast iron, polypropylene, polyethylene, or copper, that carry pressurized and treated fresh water to buildings , as well as inside the building.-History:For many centuries, lead was the favoured material...
s. (Other types of sinkholes, such as collapsed cave
Cave
A cave or cavern is a natural underground space large enough for a human to enter. The term applies to natural cavities some part of which is in total darkness. The word cave also includes smaller spaces like rock shelters, sea caves, and grottos.Speleology is the science of exploration and study...
s, are not washouts.)
Widespread washouts can occur in mountain
Mountain
Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...
ous areas after heavy rains, even in normally dry ravine
Ravine
A ravine is a landform narrower than a canyon and is often the product of streamcutting erosion. Ravines are typically classified as larger in scale than gullies, although smaller than valleys. A ravine is generally a fluvial slope landform of relatively steep sides, on the order of twenty to...
s. A severe washout can become a 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...
, or cause a dam break in an earthen dam. Like other forms of erosion, most washouts can be prevented by vegetation
Vegetation
Vegetation is a general term for the plant life of a region; it refers to the ground cover provided by plants. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader...
whose root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s hold the soil and slow the flow of water. Deforestation
Deforestation
Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....
increases the risk of washouts. Retaining wall
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...
s and culvert
Culvert
A culvert is a device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common...
s may be used, although particularly severe washouts may even destroy these if they are not large or strong enough.
Effect on road and rail transport
Rail transport
Rail transport is a means of conveyance of passengers and goods by way of wheeled vehicles running on rail tracks. In contrast to road transport, where vehicles merely run on a prepared surface, rail vehicles are also directionally guided by the tracks they run on...
, a washout is the result of a natural disaster
Natural disaster
A natural disaster is the effect of a natural hazard . It leads to financial, environmental or human losses...
where the roadbed is eroded away by flowing water, usually as the result of a flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
. When a washout destroys a railroad's right-of-way
Right-of-way (railroad)
A right-of-way is a strip of land that is granted, through an easement or other mechanism, for transportation purposes, such as for a trail, driveway, rail line or highway. A right-of-way is reserved for the purposes of maintenance or expansion of existing services with the right-of-way...
, the track
Rail tracks
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast , plus the underlying subgrade...
is sometimes left suspended in midair across the newly-formed gap, or it dips down into a ditch. The phenomenon is discussed in more detail under 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...
.
In 2004, the remnants of Hurricane Frances
Hurricane Frances
Hurricane Frances was the sixth named storm, the fourth hurricane, and the third major hurricane of the 2004 Atlantic hurricane season. The system crossing the open Atlantic during mid to late August, moving to the north of the Lesser Antilles while strengthening. Its outer bands affected Puerto...
and then Hurricane Ivan
Hurricane Ivan
Hurricane Ivan was a large, long-lived, Cape Verde-type hurricane that caused widespread damage in the Caribbean and United States. The cyclone was the ninth named storm, the sixth hurricane and the fourth major hurricane of the active 2004 Atlantic hurricane season...
caused a large number of washouts in western North Carolina
Western North Carolina
Western North Carolina is the region of North Carolina which includes the Appalachian Mountains, thus it is often known geographically as the state's Mountain Region. It is sometimes included with upstate South Carolina as the "Western Carolinas", which is also counted as a single media market...
and other parts of the southern Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...
, closing some roads for days, and parts of the Blue Ridge Parkway
Blue Ridge Parkway
The Blue Ridge Parkway is a National Parkway and All-American Road in the United States, noted for its scenic beauty. It runs for 469 miles , mostly along the famous Blue Ridge, a major mountain chain that is part of the Appalachian Mountains...
for months. Other washouts have also caused train wreck
Train wreck
A train wreck or train crash is a type of disaster involving one or more trains. Train wrecks often occur as a result of miscommunication, as when a moving train meets another train on the same track; or an accident, such as when a train wheel jumps off a track in a derailment; or when a boiler...
s where tracks have been unknowingly undermined. Motorists have also driven into flooded streams at night, unaware of a new washout on the road in front of them until it is too late to brake
Brake
A brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
, and prompting a high-water rescue.
Major washouts can also ruin pipeline
Pipeline transport
Pipeline transport is the transportation of goods through a pipe. Most commonly, liquids and gases are sent, but pneumatic tubes that transport solid capsules using compressed air are also used....
s or undermine utility pole
Utility pole
A utility pole is a pole used to support overhead power lines and various other public utilities, such as cable, fibre optic cable, and related equipment such as transformers and street lights. It can be referred to as a telephone pole, power pole, hydro pole, telegraph pole, or telegraph post,...
s or underground lines, interrupting public utilities.