Write explanatory notes on flooding under the following; (a) areas of occurrence (b) Causes (c) negative effects (d) control

Explanatory notes on flooding

(a) Areas of occurrence

• River flood plains and valleys such as those of the Niger and Benue in Nigeria.
• Low-lying coastal areas and deltas (the Niger Delta, Lagos and other coastal lowlands).
• Poorly drained towns and cities where drainage cannot cope with heavy rain, and areas below dams.

(b) Causes

1. Heavy and prolonged rainfall that makes rivers overflow their banks.
2. Poor or blocked drainage and the dumping of refuse in drains and channels.
3. Release of water from over-filled dams, and high sea tides or storm surges on the coast.
4. Building on flood plains, deforestation and silting of river channels, which reduce the land ability to absorb or carry water.

(c) Negative effects

• Loss of life and outbreak of water-borne diseases such as cholera.
• Destruction of houses, roads, bridges and other property, and displacement of people (homelessness).
• Destruction of farmland and crops, leading to food shortage, and pollution of water sources.

(d) Control

• Construction of drainage channels, dams and embankments (dykes) to hold and guide flood water.
• Dredging of rivers and regular clearing of drains and refuse to keep channels open.
• Afforestation and control of building so that people do not settle on flood plains, plus early warning and public education.