After a great downpour, an otherwise dry land is covered by standing water, which stays for a period of time. This is an example of flood. Flooding is caused by different situations.
In an area where the soil is sandy, rainwater sinks into the ground readily. This is however not the case if the soil is clayey. This is because clay retains water. As a result, the rain water does not sink readily. In areas where the soil is classy therefore, flooding is possible after a short rainfall.
In coastal areas like Port Harcourt, Lagos and other places where the land and sea meet, the level of water in the sea rises and falls. This rise and fall of the sea is referred to as the tide of the sea. Depending on the time if year and the season,tides can be low, high or very high. Tides are caused by the pull of the moon and the Sun. The flood caused by seawater is more severe during the rainy season when the water level rises and spreads across the land. There is also an overflow of water from the sea into nearby rivers. Excess water from the rivers also cause flooding of the land nearby.
Rivers may overflow their banks during the rainy season. If the rain is very heavy, the river may overflow it’s banks to the neighbouring land, making the land flooded. Thus occurs more often with large rivers like the River Niger and River Benue.
There are many ways to prevent flood. Construction of dams along rivers that overflow into neighbouring land can help in preventing flooding. This is because part if the water that us carried by the river us stored in the dam. The speed and the volume of water carried by the river are thereby reduced. This greatly reduces the tendency to flood. This is the case with river Niger in Nigeria, Mississippi and Missouri river in the United States.
Flooding can be prevented through the construction of river or sea embankments. An embankment is an artificial bank usually made with stones to hold back water. Gutters can also be cleared to allow for the free flow of rain water.
In urban areas, surface drainage paths should be designed and constricted by competent engineers. The floor of the gutter is made of concrete and designed to have a slope that allows water to flow away easily. The sides are made of concrete and therefore hold back water. The top of the drainage path may be covered with concrete slab to prevent cars and bicycles running into it or children falling inside it. Another reason is that some people may throw rubbish into the drainage to block it, thereby causing a flood.
(Adapted from Basic Science – An Integrated Science Course for JSS 3 by F. O. C. Ndu and E. O. Somoye.)
1. What is the tide?
2. What is the name given to an artificial bank in the passage?
3. What type of soil encourages flooding?
4. During which season of the year are foods more common?
5. Describe two ways of preventing floods.
6. According to the passage, in which of the following areas is a flood not like to happen?
B. coastal areas
D. Port Harcourt
7. The word downpour in the first paragraph means ————–.
A. a lot of sun
B. a lot of rain
C. a lot of water
D. a lot of clay
8. Floods can be prevented through all the following except
D. blocked drainage ditches
9. Which of the following should be constructed in urban areas to prevent flooding?
B. surface drainage ditches
10. A clayey soil is full of ———
C. black soil
Decide if the following statements about the passage you have read are true (T) or false (F).
1. Flooding is possible after a short rainfall.
2. The cause of tides is unknown.
3. Tides happen on seas.
4. Urban areas are too sophisticated to be flooded.
5. Drainage ditches should be constructed by competent engineers.
Give a word or phrase which can replace the following words in the passage.