Write a geographical account of flooding in urban areas under the following headings; (a) four causes (b) three effects (c) four measures that can be used t...

A geographical account of flooding in urban areas

Flooding in urban areas occurs when the volume of water on the land surface exceeds the capacity of the drainage system to carry it away, so that streets, compounds and buildings become submerged. The account below is written under the three required headings.

(a) Four causes of urban flooding

1. Excessive or prolonged rainfall. Heavy downpours release more water than the drains can discharge within a short time, so the excess spills onto roads and into buildings.
2. Dumping of refuse into drains and channels. Solid waste, silt and vegetation block gutters and culverts, obstructing the free flow of water so that it backs up and overflows.
3. Poor engineering and construction of the drainage system. Undersized, badly aligned or unlined drains cannot cope with peak run-off, and poor town planning allows settlements to be built on flood plains and across natural water channels.
4. Removal of vegetation and sealing of the ground with concrete and tarmac. Paving reduces infiltration and greatly increases surface run-off, sending a larger volume of water more quickly into the streets.

(b) Three effects of urban flooding

1. Loss of lives and properties. People are drowned or swept away, while buildings, roads, bridges, vehicles and household goods are destroyed or damaged.
2. Spread of water-borne diseases and health hazards. Flood water mixes with sewage and refuse, contaminating drinking-water sources and causing outbreaks of cholera, typhoid and other water-borne diseases.
3. Disruption of movement and economic activity. Submerged and eroded roads make transport difficult, businesses, schools and offices close, and people are displaced and rendered homeless.

(c) Four measures that can be used to control urban flooding

1. Provide adequate, well-engineered drainage and desilt it regularly. Construct wide, properly graded drains and culverts and clear them of silt and refuse before and during the rainy season.
2. Enforce efficient urban planning. Prohibit building on flood plains and across natural water channels, and reserve these areas as green or open space.
3. Ensure proper waste disposal and public enlightenment. Stop the dumping of refuse into drains and rivers, and educate residents on keeping gutters clear.
4. Construct dams, embankments and reservoirs and dredge rivers. These works store or divert excess water and increase channel capacity, controlling the overflow of rivers into the built-up area.