(a) On an outline map of Nigeria, locate and name (i) an inland drainage basin (ii) a delta (iii) a man-made lake (iv) a confluence town (b) In what four wa...

As shown on the map above, the required features are:

• Inland drainage basin: Chad Basin, in north-eastern Nigeria.
• Delta: Niger Delta, on the southern coast where the River Niger enters the Atlantic Ocean.
• Man-made lake: Kainji Lake, on the River Niger in north-western/central Nigeria.
• Confluence town: Lokoja, where the River Niger and River Benue meet.

(b) Physical factors which limit river transportation in Nigeria include:

1. Rapids and waterfalls: These occur where there is a steep gradient and prevent boats and larger vessels from moving freely along the river.
2. Seasonal fluctuation in water level: During the dry season, many rivers become shallow, narrow or partly dry, making navigation difficult.
3. Water weeds and floating vegetation: Weeds such as water hyacinth may block channels, slow down boats and damage engines.
4. Sandbanks, silt and shallow channels: Deposition of sand and silt reduces the depth of rivers and may prevent vessels from passing.

(c) These limitations can be overcome by:

1. Constructing dams and reservoirs to regulate the flow of water and maintain a more regular water level during the dry season.
2. Dredging river channels regularly to remove silt, sandbanks and other obstructions, thereby deepening and widening navigable routes.
3. Clearing water weeds and floating vegetation continuously, and controlling their growth through appropriate weed-control measures.
4. Constructing canals, locks and bypass channels around rapids and waterfalls to enable boats to move from one navigable section to another.

In addition, navigation aids such as buoys, beacons and properly marked channels can improve the safety and efficiency of river transport.