Monday, September 20, 2010
FLOOD. (PART 1)
FLOOD. (PART 1)
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. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries. While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a significant flood unless such escapes of water endanger land areas used by man like a village, city or other inhabited area.
Floods can also occur in rivers, when flow exceeds the capacity of the river channel, particularly at bends or meanders. Floods often cause damage to homes and business if they are placed in natural flood plains of rivers. While flood damage can be virtually eliminated by moving away from rivers and other bodies of water, since time out of mind, people have lived and worked by the water to seek sustenance and capitalize on the gains of cheap and easy travel and commerce by being near water. That humans continue to inhabit areas threatened by flood damage is evidence that the perceived value of living near the water exceeds the cost of repeated periodic flooding.
PRINCIPAL TYPES and CAUSES.
Flooding of a creek is due to heavy monsoonal rain and high tide, and flash flooding is caused by a severe thunderstorm.
Riverine. Slow kinds: Runoff from sustained rainfall or rapid snow melt exceeding the capacity of a river´s channel. Causes include heavy rains from monsoons, hurricanes and tropical depressions, foreign winds and warm rain affecting snow pack. Unexpected drainage obstructions such as landslides, ice, or debris can cause slow flooding upstream of the obstruction.
Fast kinds: Include flash floods resulting from convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier.
Estuarine. Commonly caused by a combination of sea tidal surges caused by storm-force winds. A storm surge, from either a tropical cyclone or an extratropical cyclone.
Coastal. Caused by severe sea storms, or a result of another hazard (e.g. tsunami or hurricane). A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category.
Catastrophic. Caused by a significant and unexpected event, e.g. dam breakage, or a result of another hazard (e.g. earthquake or volcanic eruption).
Muddy. A muddy flood or mud slide is generated by run off on crop land. A muddy flood is produced by an accumulation of runoff generated on cropland. Sediments are then detached by runoff and carried as suspended matter or bedload. Muddy runoff is more likely detected when it reaches inhabited areas. Muddy floods are therefore a hillslope process, and confusion with mudflows produced by mass movements should be avoided.
Other. Floods can occur if water accumulates across an impermeable surface (e.g. from rainfall) and cannot rapidly dissipate (i.e. gentle orientation or low evaporation). When a series of storms are moving over the same area. Dam-building beavers can flood low-lying urban and rural areas, often causing significant damage.
Primary effects. Physical damage. Can damage any type of structure, including bridges, cars, buildings, sewer systems, roadways, and canals.
Casualties. People and livestock die due to drowning. It can also lead to epidemics and waterborne diseases.
Secondary effects. Water supplies. Contamination of water. Clean drinking water becomes scarce. Diseases. Unhygienic conditions. Spread of water-borne diseases. Crops and food supplies. Shortage of food crops can be caused due to loss of entire harvest. However, lowlands near rivers depend upon river silt deposited by floods in order to add nutrients to the local soil.
Trees. Non-tolerant species can die from suffocation.
Economic. Economic hardship, due to: temporary decline in tourism, rebuilding costs, food shortage leading to price increase, etc.
Part 2 will follow...
Thank you for reading!!