(a) Define the term flooding. (b) Highlight four causes of flooding. (c) Outline four effects of flooding (d) What two measures can be taken to control floo...

Answer Details

(a) Definition of flooding

Flooding is the overflow of a large body of water (usually a river, lake or the sea) onto adjoining land that is normally dry. It occurs when the volume of water in a channel or basin exceeds the capacity that the channel, drainage system or land surface can hold or discharge, so the excess spreads over the surrounding area.

(b) Four causes of flooding

1. Heavy and prolonged rainfall: when rain falls faster than the soil can absorb it or the rivers can carry it away, the excess water spills over the banks.
2. Overflow of rivers: when a river receives more water than its channel can hold, especially at its lower course, it overtops its banks and floods the flood plain.
3. Poor or blocked drainage: in urban areas, drains blocked by refuse, silting, or inadequate drainage channels cause water to accumulate on the surface.
4. Coastal storm surges and tidal action: strong onshore winds and high tides push sea water inland, flooding low-lying coastal land.

Other accepted causes include deforestation which reduces interception and infiltration, dam failure or excessive release from dams, and rapid melting of snow.

(c) Four effects of flooding

1. Loss of lives and displacement: people and livestock are drowned or swept away, and many are rendered homeless.
2. Destruction of property and infrastructure: houses, roads, bridges, railways and electricity installations are damaged.
3. Destruction of crops and farmland: farm produce is washed away or submerged, leading to food shortage and famine.
4. Outbreak of water-borne diseases: contamination of water sources spreads cholera, typhoid and diarrhoea; stagnant water also breeds mosquitoes.

(d) Two measures to control flooding

1. Construction of dams and dykes: dams store excess water while embankments (dykes) and levees are raised along river banks to prevent overflow.
2. Provision of good drainage and afforestation: constructing and clearing wide drainage channels to carry away excess water, together with planting trees to increase interception and infiltration and reduce surface run-off.