FLOODING AND HUMANS

FLOODING

This will occur when streams receive more water than their channels can hold,

i.e. when stream discharge is greater than stream capacity.

Streams water will overflow the banks of the stream.

The most common causes of flooding are extensive rainfall and/or rapid melting of snow in the spring of the year

FLOODPLAIN

When flooding occurs, water in the stream overflows its normal channel and covers the land adjacent to the stream banks.

The flat land bordering a stream is called the floodplain.

The floodplain is the area covered by water during a flood.

More flooding more land that is covered

LEVEES Parallel ridges on the sides of the stream bank form

when it floods. These are called natural levees. They are formed from sediment deposited during a

flood.

With the overflow during a flood, the velocity of the stream decreases and sediment is deposited.

After many floods the natural levees become larger, both in width and height.

The bed load of the stream is not deposited because it requires too much energy to be transported over the banks of the stream.

Floodplains are highly productive wetlands. The wetlands are created by floodwaters filling

depressions in the floodplain. Floodplains are popular places for human habitation

because the soil is fertile and quite useful for agriculture. A ready source of water is also available on a floodplain.

EFFECTS ON MAN Flooding being beneficial are

also quite harmful. It is estimated that flooding

is the most lethal of all natural disasters, responsible for almost 40% of human deaths by natural hazards.

Flooding is the most frequent of all natural disasters. Flooding is expensive, resulting from an extensive

loss of infrastructure during a flood.

MANS INVOLVEMENT

It is not all natures fault, as human activities have contributed to the sharp rise in flood deaths over the past century.

Vegetation removal through logging, overgrazing of animals, forest fires, mining and urbanization

cause a reduced infiltration of rainwater into the ground.

PREVENTION

Many techniques have been devised to reduce flood risks. Channelization – is where the stream is widened and

deepened. This allows for greater discharge.

Flood control dams – is where dam is built across a stream to hold back the water and the water flow is regulated. Results in sediment build-up up stream.

Artificial levees – levees generally constructed of soil are build along the stream banks. They result in an increased stream velocity. This intern creates more erosion and flooding down stream. Levees are good for small floods but may break during large floods