Environmental Hazard – Flooding


Welcome to class! 

In today’s class, we will be talking about flooding. Enjoy the class!

Environmental Hazard – Flooding

Flooding classnotes.ng

Flood is an overflow of water that submerges land, which is usually dry. Flooding occurs mainly when a large amount of water covers a dried area of land or soil. It usually occurs aftermath of a heavy downpour of rain. A flood can also occur when a water body, such as river, lake, ocean, overflows its bank, which then results in water escaping its boundary into the environment.

Flooding has high potential to destroy lands, lives, houses, etc. The soil structure of land sometimes determines the size and the intensity of flood that can occur in such area of land.

Soil structure

Soil structure is the arrangement of so a downward 12 aggregates in a vertically downward position. It is divided into four regions called horizons. Planes separate each horizon. The horizons are Horizon A, Horizon B, Horizon C and Horizon D.

  • Horizon A: Horizon A refers to the so surface that is made up of granules and crumps.
  • Horizon B: In horizon B, soil particle is glued together in a square or angle shapes. This type of arrangement makes it difficult for water penetration.
  • Horizon C: In horizon C, soil particles from pillars and columns to make water penetration more difficult.
  • Horizon D: Horizon D forms the bedrock of the soil.

There is an impervious rock deep down the soil, which does not allow water to pass through it. When it rains in an area where the impervious rock layer is close to the ground surface, a small portion of water will be able to seep into the ground while some portion will move to the surface layer thereby making the soil flooded.

When the impervious rock is, however, deep down into the ground, the rainwater seeps down without causing flooding.

Drainage systems

Drainage systems are the patterns formed by the streams, rivers, and lakes in a particular drainage basin. It helps to channel water from the rainfall into the body of the water. However, a blocked drainage system in an environment can lead to flooding.

When drainage is blocked with refuse, water will not be able to flow freely, and this may lead to water overflowing the drain and spreading over the area.

Drainage patterns

There are four major kinds of drainage pattern, they are:

  1. Dendritic drainage pattern
  2. Trellised drainage pattern
  3. Deranged drainage pattern
  4. Radial drainage pattern
  • Dendritic drainage pattern:

Dendritic drainage pattern looks like the branching pattern of tree roots. This drainage system has many contributing streams, which join into tributaries of the main river. It is the most common type of drainage pattern and they develop where the river channel follows the slope of the terrain.

  • Trellis drainage pattern:

Trellis drainage pattern is a rectangular shaped drainage pattern that is mostly found between rocks, especially sedimentary rock.

  • Deranged drainage pattern:

Deranged drainage pattern can be found in an area where there is no coherent pattern to the rivers and lakes It is mostly found in areas where there has been much geological eruption such as volcanic eruption.

  • Radial drainage pattern:

The radial drainage pattern is a drainage system where the streams radiate outwards from a central high point. Volcanoes usually display this type of drainage pattern.

Causes of flooding

Some of the causes of flooding include:

  1. Heavy rainfall: When there is a heavy rainfall that is much more than what the drainage system can take, there will be an overflow of water, which mostly leads to flooding.
  2. River overflow: River overflow occurs mostly when there is a heavy downpour of water. The river water level rises which then leads to an overflow of water downstream to the adjacent low-lying areas.
  3. Dam breaking: Dams are mostly built by the government to generate electricity. When a dam breaks, there will be an overflow of water in that area.
  4. Winds in the coastal areas: Strong and massive winds in the coastal areas can blow and carry over water into dry coastal land and thereby leads to flooding.
  5. Sand filling of water paths.

Prevention of flooding

Flooding can be prevented by:

  1. Providing and maintaining a proper drainage system.
  2. Proper dredging of rivers.
  3. The building of walls along riverbanks.
  4. Diversion of streams so that they do not cause water overflow.
  5. Sand filling of lowlands.
  6. The building of detention basin which serves as temporary storage for flood water
  7. Mulching

Effects of flooding

  1. Flooding can lead to water pollution as a result of deposition of sands and some toxic chemicals into the body of water such as rivers, streams, oceans. This may, therefore, kill living organisms (plant and animal) living in such an environment.
  2. It can lead to the destruction of property, lives, etc.
  3. It can disturb the natural balance of an ecosystem.
  4. Flooding can destroy food crops.
  5. It may cause loss of soil fertility.


In our next class, we will be talking about Environmental Hazard – Deforestation.  We hope you enjoyed the class.

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