From Wikipedia, the free encyclopedia
Flood control
Flood control
For the protocol issue, see: Flood control (communications). The term "flood control" refers to all methods used to reduce or prevent the detrimental effects of flood waters.[1]
Unusual high tides
Coastal areas are sometimes flooded by unusually high tides induced by strong winds over the ocean surfaces. During a hurricane, a storm tide combines the normal tide plus the storm surge, with higher waves on top. In the USA, during Hurricane Katrina, the entire coastline of Mississippi was hit by a storm tide of convert|5|to(-)|9.5|m}}, flooding all coastal cities over 90%. The entire coastline of Alabama was also flooded with a storm tide of 4 to 6 metres (13–20 ft), flooding parts of downtown Mobile, Alabama|Mobile, several feet deep, and destroying yachts, fishing boats, and beach homes along the shoreline. Some eastern coastal areas of Louisiana were also flooded by high storm tides, but the flooding in New Orleans only reached 80% of outlying parts, not downtown New Orleans, because flooding there was mainly caused by levee failures in low-lying areas, not by high storm tide.
Causes of floods
Floods are caused by many factors: heavy precipitation, severe winds over water, unusual high tides, tsunamis, or failure of dams, levels, retention ponds, or other structures that contained the water. Periodic floods occur on many rivers, forming a surrounding region known as the flood plain.
Heavy precipitation
During times of rain or snow, some of the water is retained in ponds or soil, some is absorbed by grass and vegetation, some evaporates, but the rest, which reaches stream channels, is called Surface runoff. Floods occur when ponds, lakes, riverbeds, soil, and vegetation cannot absorb all the water. Water then runs off the land in quantities that cannot be carried within stream channels or retained in natural ponds and manmade reservoirs. About 30 percent of all precipitation is in the form of runoff small and that amount might be increased by water from melting snow. River flooding is often caused by heavy rain, sometimes increased by melting snow. A flood that rises rapidly, with little or no advance warning, is typically called a flash flood.Flash floods usually result from intense rainfall over a relatively small area, or if the area was already saturated from previous precipitation.
Tsunamis
Tsunamis are high, large waves, typically caused by undersea earthquakes or massive explosions, such as the eruption of an undersea volcano.
Effects of floods
Flooding produces many effects in the region. It not only damages property and endangers the lives of humans or animals, but can have other effects as well. Rapid water runoff causes soil erosion in addition to sediment deposition problems further downstream. The spawn biology spawning grounds for fish and other wildlife habitats can become polluted or completely destroyed. Some prolonged high floods can delay traffic in areas which lack elevated roadways. Floods can interfere with drainage and economic use of lands, such as interfering with farming. Structural damage can occur in bridge abutments, bank lines, sewer lines, and other structures within floodways. Waterway navigation and hydroelectric power are often
Severe winds over water
Even when rainfall is relatively light, the shorelines of lakes and bays can be flooded by severe winds, such as during hurricanes, that blow water into the shore areas, exceeding the capacity of the shoreline to contain the water.
1
From Wikipedia, the free encyclopedia
impaired. Financial losses due to floods are typically millions of dollars each year.
Flood control
Control of Floods
Some methods of flood control have been practiced since ancient times.[1] These methods include planting vegetation to retain extra water, terracing hillsides to slow the flow downhill, and the construction of floodways (man-made channels to divert floodwater).[1] Other techniques include the construction of levees, dikes, dams, reservoirs[1] or retention ponds to hold extra water during times of flooding.
Flood blocking the road in Jerusalem Currently the Saint Petersburg Flood Prevention Facility Complex is to be finished by 2008, in Russia, to protect Saint Petersburg from storm surges. It also has a main traffic function, as it completes a ring road around Saint Petersburg. Eleven dams extend for 25.4 kilometres and stand eight metres above water level.
Methods of control
In many countries, rivers prone to floods are often carefully managed. Defences such as levees, bunding|bunds,reservoirs, and weirs are used to prevent rivers from bursting their banks. When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used. Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands. A dike is another method of flood protection. Dikes lower the risk of having floods compaired to other methods. It can help prevent damage however it is better to combine the dike with other flood control methods to reduce the risk of a collaped dike.
Americas
Another elaborate system of floodway defenses can be found in the Canadian province of Manitoba. The Red River flows northward from the United States, passing through the city of Winnipeg (where it meets the Assiniboine River) and into Lake Winnipeg. As is the case with all north-flowing rivers in the temperate zone of the Northern Hemisphere, snowmelt in southern sections may cause river levels to rise before northern sections have had a chance to completely thaw. This can lead to devastating flooding, as occurred in Winnipeg during the spring of 1950. To protect the city from future floods, the Manitoba government undertook the construction of a massive system of diversions, dikes, and floodways (including the Red River Floodway and the Portage Diversion). The system kept Winnipeg safe during the 1997 flood which devastated many communities upriver from Winnipeg, including Grand Forks, North Dakota and Ste. Agathe, Manitoba. In the U.S., the New Orleans Metropolitan Area, 35% of which sits below sea level, is protected by hundreds of miles of levees and flood gates. This system failed catastrophically, with numerous breaks, during Hurricane Katrina in the city proper and in eastern sections of the Metro Area, resulting in the inundation of approximately 50% of the
Europe
London is protected from flooding by a huge mechanical barrier across the River Thames, which is raised when the water level reaches a certain point (see: Thames Barrier). Venice has a similar arrangement, although it is already unable to cope with very high tides. The defenses of both London and Venice will be rendered inadequate if sea levels continue to rise. The largest and most elaborate flood defenses can be found in the Netherlands, where they are referred to as Delta Works with the Oosterschelde dam as its crowning achievement. These works were built in response to the North Sea flood of 1953, in the southwestern part of the Netherlands. The Dutch had already built one of the world’s largest dams in the north of the country: the Afsluitdijk (closing occurred in 1932).
2
From Wikipedia, the free encyclopedia
Metropolitan area, ranging from a few inches to twenty feet in coastal communities. In an act of successful flood prevention, the Federal Government of the United States offered to buy out flood-prone properties in the United States in order to prevent repeated disasters after the 1993 flood across the Midwest. Several communities accepted and the government, in partnership with the state, bought 25,000 properties which they converted into wetlands. These wetlands act as a sponge in storms and in 1995, when the floods returned, the government did not have to expend resources in those areas.[2]
Flood control
jackets, and watertight boots with steel toes and insoles.[6]
Benefits of flooding
There are many disruptive effects of flooding on human settlements and economic activities. However, flooding can bring benefits, such as making soil more fertile and providing nutrients in which it is deficient. Periodic flooding was essential to the well-being of ancient communities along the Tigris-Euphrates Rivers, the Nile River, the Indus River, the Ganges and the Yellow River, among others. The viability for hydrologically based renewable sources of energy is higher in floodprone regions.
Asia
In China, flood diversion areas are rural areas that are deliberately flooded in emergencies in order to protect cities.[3] Many have proposed that loss of vegetation (deforestation) will lead to a risk increase. With the natural forest cover, the flood duration should decrease. Reducing the rate of deforestation should improve the incidents and severity of floods.[4]
Notes
[1] ^ "Flood Control", MSN Encarta, 2008 (see below: References). [2] Floods, Tornadoes, Hurricanes, Wildfires, Earthquakes... Why We Don’t Prepare. Amanda Ripley. Time. August 28, 2006. [3] [1] [4] Bradshaw CJ, Sodhi NS, Peh SH, Brook BW. (2007). Global evidence that deforestation amplifies flood risk and severity in the developing world. Global Change Biology, 13: 2379-2395. [5] National Institute for Occupational Safety and Health. Storm and Flood Cleanup. Accessed 09/23/2008. [6] The National Institute for Occupational Safety and Health. NIOSH Publication No. 94-123: NIOSH Warns of Hazards of Flood Cleanup Work.
Flood clean-up safety
Clean-up activities following floods often pose hazards to workers and volunteers involved in the effort. Potential dangers include electrical hazards, carbon monoxide exposure, musculoskeletal hazards, heat or cold stress, motor vehicle-related dangers, fire, drowning, and exposure to hazardous materials.[5] Because flooded disaster sites are unstable, clean-up workers might encounter sharp jagged debris, biological hazards in the flood water, exposed electrical lines, blood or other body fluids, and animal and human remains. In planning for and reacting to flood disasters, managers provide workers with hard hats, goggles, heavy work gloves, life
References
• "Flood Control", MSN Encarta, 2008, webpage: Encarta-flood-control.
Retrieved from "http://en.wikipedia.org/wiki/Flood_control" Categories: Flood This page was last modified on 27 April 2009, at 07:36 (UTC). All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.) Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) taxdeductible nonprofit charity. Privacy policy About Wikipedia Disclaimers
3