Environmental Hazard: Flooding – JSS3 Basic Science Lesson Note (First Term)

A flood is defined as an overflow of water that submerges land which is usually dry. Flooding occurs when a part of the soil or land is submerged under water. Some parts of the land are prone to flooding, this is due to the soil structure.

Types of Flooding

Flash floods- This occurs within a very short time and it is usually a result of heavy rain.

Rapid On-set Floods- This type of takes a longer time to accumulate and the flood can last for a day or two days.

Slow On-set Floods –This is caused by water bodies overflowing their banks, it develops slowly and can last for days and weeks.

Drainage Pattern-This is a system of watercourses or drains for carrying off excess water. The drainage pattern in a city or town may be blocked by refuse when rain falls and water cannot flow freely in the blocked drainage.

Types of Drainage Patterns

-parallel drainage pattern

-Rectangular drainage pattern

-Dendritic drainage pattern

-Radial drainage pattern

Causes of Flooding

-Presence of impervious rock deep in the soil which will not permit water to pass through them.

-Heavy downpour of rain

-Blockage of drainages

-Overflowing of water from the dam

-Natural disasters such as tsunamis, earthquakes, and hurricanes cause disturbances to the oceans to cause floods.

-Flood can occur as a long period of rainlessness as the soil will not absorb the water.

-The melting of ice when the subsoil is still frozen.

-Absence of gutters on either side of the roads.

 Prevention of Flood

-Construction of canals or drainages by government or individuals in an area with impervious rock layers surface.

-Proper drainage of rivers especially where dams are built.

-Prevention of buildings or construction of roads, houses, etc. across canals, drainages, and water courses.

-Erection of walls along banks of rivers, seas, and oceans to prevent tidal waves from pushing water upshore.

-Planting trees, shrubs, and grasses will help in breaking the power of moving floods and also reduce erosion.

The public should be enlightened about the danger of floods and what should be done to minimize their occurrence.

 Effects of Flood

-It damages houses other valuable properties.

-It can lead to loss of lives in most cases.

-It can increase the spread of disease due to contamination of water bodies.

-It makes soil infertile by removing soil nutrients.

-It reduces the available land for cultivation.

ASSIGNMENT

1. Release of excess water in dams can cause  A.erosion  B. flooding  C. precipitation   Evaporation
2. Where there are no gutters on either side of the road…………… may occur A. precipitation  Drainage Erosion  Flooding.
3. Dumping of refuse and industrial wastes in rivers can cause  A. erosion  B. flooding C. water movement  D. rise in water level
4. Blockage of drainage and gutter can cause A.flooding  Erosion  Sedimentation   Desertification
5. Which of the following predisposes an area to flood?  A. low rainfall  B. drought C. low wind  High rainfall.

6…………….. is a good example of natural disaster A.fermentation B.  Rainfall   C. Flooding  D. Animal husbandry

7a.List four causes of flooding in your community.

b.State four methods of controlling floods.