FLOOD

FLOOD

The only thing left to do is

SURVIVE

_ _ _ _ is usually an overflow of an expanse of water that submerges land and the inflow of tide onto land.

Floods are categorized into _A_U_A_ and A_ _I_I_IA_ floods in terms of their specific causes.

Flood is basically a natural hydrological phenomenon. Its occurrence is usually the aftermath of meteorological events.

These included an intense and prolonged _ai_ _a_ _ spells and unusually high coastal and estuarine waters due to _ _o_ _ _u_ _e_, seiches, etc.

Floods are also caused, indirectly, by seismic activities.

Coastal areas are particularly susceptible to flooding due to _ _u_a_i_ (seismic sea waves).

Sinking of land due to ea_ _ _ _ua_e_ reduces the elevation of land areas. In the vicinity of lakes and rivers, these areas become flood-prone.

Likewise, the uplifting of lake and river beds from seismic causes sometime results in the overflowing of these bodies of water. The water then i_u_ _a_e_ the surrounding and adjacent areas.

To a certain extent, flooding is an astronomically influenced phenomena such as _i_ _ _i_e_ coinciding with the occurrence of heavy rainfall frequently cause flooding.

Flooding is also believed to be caused by sea-level rise.

Sea-level rise is defined as the mean rise in sea level as an effect of thermal e_ _a_ _io_ and melting of i_e _a_ _.

Occasionally, floods occur unnaturally. These are usually the result of _u_a_ a_ _i_i_ie_. Such activities include:

• Blasting - this causes landslides in the slopes of hills and mountains which may result in the unintentional damming of rivers and streams;

• Construction of temporary dams - this produces an impediment to the flow of a river or stream which then results in an overflow;

• Failure of hydraulic and other control structures - accidents like the breaking of a dike result in the entry of an enormous quantity of water in a protected area; and

• Mismanagement of hydraulic structures - control structures like dams which are utilized for various purposes are usually operated according to what is known as an "operation rule" and mismanagement which results in the violation of the rule may necessitate an untimely and sudden release of large amounts of excess water.

Types of Flooding

_i_a_ Flooding

Both sea and river defences may be overtopped or breached by a combination of low pressure weather systems and peak high tides. Storms with high wind speeds cause tall and powerful waves and low pressure fronts cause sea levels to rise above normal levels. High tide levels vary through the lunar and solar cycle and when superimposed upon other tidal variations exceptionally high tides result.

_ _u_ia_ Flooding

Flooding occurs in the floodplains of rivers when the capacity of water courses is exceeded as a result of rainfall or snow and ice melts within catchment areas further upstream. Blockages of water courses and flood channels or tide locking may also lead to ponding and rising water levels.

_ _ou_ _ _a_e_ Flooding

Low lying areas sitting over aquifers may periodically flood as ground water levels rise. This type of flooding is often seasonal and therefore can be forecasted with good accuracy. It is often slow in its onset.

_ _u_ia_ Flooding

Surface water flooding is caused by rainwater run-off from urban and rural land with low absorbency. These circumstances, combined with intense rainfall, can give rise to localised flooding.

Flooding from Sewers

Flooding from sewers can occur where there are combined storm and foul sewers and their capacity is exceeded due to large amounts of surface water run-off in a short time. Poor cleaning and maintenance can lead to blockages that can also cause local flooding.

Flooding from Man Made Infrastructure

Canals, reservoirs and other manmade structures can fail causing flooding to areas downstream. Industrial activities, water mains and pumping stations can also give rise to flooding due to failure.

Flood Classifications

_A_O_ Flooding

This causes inundation of large areas, isolating towns and cities. Major disruptions occur to road and rail links. Evacuation of many houses and business premises may be required. In rural areas widespread flooding of farmland is likely.

_O_E_A_E Flooding

This causes the inundation of low lying areas requiring the removal of stock and/or the evacuation of some houses. Main traffic bridges may be closed by floodwaters.

_I_O_ Flooding

This causes inconvenience such as closing of minor roads and the submergence of low level bridges and makes the removal of pumps located adjacent to the river necessary.

Flood Progression

F_A_ H floods often occur in deserts where it rains in one place and the water starts to rush to an area further down stream.

G_A_UA_ floods, some floods may take a few days to build up to dangerous levels.

How do floods cause damage?

There are two main types of damage caused by floods:

_ _ai_ water damage.

This damage basically soaks everything, sometimes it can dissolve foundations and make the ground unstable and muddy.

_u_ _i_ _ water damage.

This is damage due to the water crashing into buildings, cars and other things, this is flood water that often kills people and animals.

Impacts of Flooding

Loss of lives and property:

Immediate impacts of flooding include loss of human life, damage to property, destruction of crops, loss of livestock, non-functioning of infrastructure facilities and deterioration of health condition owing to waterborne diseases. Flash floods, with little or no warning time, cause more deaths than slow-rising riverine floods.

Loss of livelihoods:

As communication links and infrastructure such as power plants, roads and bridges are damaged and disrupted, economic activities come to a standstill, resulting in dislocation and the dysfunction of normal life for a period much beyond the duration of the flooding. Similarly, the direct effect on production assets, be it in agriculture or industry, can inhibit regularly activity and lead to loss of livelihoods. The spill over effects of the loss of livelihoods can be felt in business and commercial activities even in adjacent non-flooded areas.

Decreased purchasing and production power:

Damage to infrastructure also causes long-term impacts, such as disruptions to clean water and electricity, transport, communication, education and health care. Loss of livelihoods, reduction in purchasing power and loss of land value in the flood plains lead to increased vulnerabilities of communities living in the area. The additional cost of rehabilitation, relocation of people and removal of property from flood-affected areas can divert the capital required for maintaining production.

Mass migration:

Frequent flooding, resulting in loss of livelihoods, production and other prolonged economic impacts and types of suffering can trigger mass migration or population displacement. Migration to developed urban areas contributes to the overcrowding in the cities. These migrants swell the ranks of the urban poor and end up living in marginal lands in cities that are prone to floods or other risks. Selective out-migration of the workforce sometimes creates complex social problems.

Psychosocial effects:

The huge psycho-social effects on flood victims and their families can traumatize them for long periods of time. The loss of loved ones can generate deep impacts, especially on children. Displacement from one's home, loss of property and livelihoods and disruption to business and social affairs can cause continuing stress. The stress of overcoming these losses can be overwhelming and produce lasting psychological impacts.

Hindering economic growth and development:

The high cost of relief and recovery may adversely impact investment in infrastructure and other development activities in the area and in certain cases may cripple the frail economy of the region. Recurrent flooding in a region may discourage long-term investments by the government and private sector alike. Lack of livelihoods, combined with migration of skilled labour and inflation may have a negative impact on a region's economic growth. Loss of resources can lead to high costs of goods and services, delaying its development programmes.

Political implications:

Ineffective response to relief operations during major flood events may lead to public discontent or loss of trust in the authorities or the state and national governments. Lack of development in flood-prone areas may cause social inequity and even social unrest posing threat to peace and stability in the region.

These Effects are Categorized into Three

Primary Effects

The primary effects of floods are those due to direct contact with the flood waters. As seen in the video last lecture, water velocities tend to be high in floods. As discharge increases velocity increases.

• With higher velocities, streams are able to transport larger particles as suspended load. Such large particles include not only rocks and sediment, but, during a flood, could include such large objects as automobiles, houses and bridges.

• Massive amounts of erosion can be accomplished by flood waters. Such erosion can undermine bridge structures, levees, and buildings causing their collapse.

• Water entering human built structures cause water damage. Even with minor flooding of homes, furniture is ruined, floors and walls are damaged, and anything that comes in contact with the water is likely to be damaged or lost. Flooding of automobiles usually results in damage that cannot easily be repaired.

• The high velocity of flood waters allows the water to carry more sediment as suspended load. When the flood waters retreat, velocity is generally much lower and sediment is deposited. After retreat of the floodwaters everything is usually covered with a thick layer of stream deposited mud, including the interior of buildings.

• Flooding of farmland usually results in crop loss. Livestock, pets, and other animals are often carried away and drown.

• Humans that get caught in the high velocity flood waters are often drowned by the water.

• Floodwaters can concentrate garbage, debris, and toxic pollutants that can cause the secondary effects of health hazards.

Secondary Effects

Secondary effects are those that occur because of the primary effect.

• Drinking water supplies may become polluted, especially if sewerage treatment plants are flooded. This may result in disease and other health effects, especially in under developed countries.

• Gas and electrical service may be disrupted.

• Transportation systems may be disrupted, resulting in shortages of food and clean-up supplies. In under developed countries food shortages often lead to starvation.

Tertiary Effects

Tertiary effects are the long term changes that take place.

• Location of river channels may change as the result of flooding, new channels develop, leaving the old channels dry.

• Sediment deposited by flooding may destroy farm land (although silt deposited by floodwaters could also help to increase agricultural productivity).

• Jobs may be lost due to the disruption of services, destruction of business, etc. (although jobs may be gained in the construction industry to help rebuild or repair flood damage).

• Insurance rates may increase.

• Corruption may result from misuse of relief funds.

• Destruction of wildlife habitat.