(a) With the aid of annotated diagram, describe the various stages of a river course (b) Mention four ways in w rivers are of importance to man

Answer Details

As shown in the annotated river-course diagram above, a river passes through three main stages from its source in the highlands to its mouth in the sea, lake or another river.

(a) Stages of a river course

1. Upper course or youthful stage

   This is the section near the source, usually in mountainous or hilly areas. The gradient is steep, so the river flows swiftly and has great energy. Vertical erosion, especially hydraulic action and abrasion, is dominant. The valley is therefore narrow and deep, producing a V-shaped valley.

   Typical features shown or associated with this stage include interlocking spurs, rapids, waterfalls, cataracts, plunge pools and gorges. Where a waterfall retreats upstream, it may leave a steep-sided gorge. River capture may also occur where one river erodes backwards and diverts the headwaters of another river.

2. Middle course or mature stage

   Here the gradient becomes gentler and the river channel becomes wider and deeper. Tributaries join the main river, increasing its volume and discharge. Lateral erosion

   The valley becomes wider, often with a broad V-shape. The river swings from side to side to form meanders. Erosion occurs on the outer bend, producing a river cliff or bluff, while deposition occurs on the inner bend, forming a slip-off slope. River terraces may also be found along the valley sides. This stage may be suitable for navigation in some places because the channel is wider and deeper.

3. Lower course or old stage

   This is the final section near the mouth of the river. The land is very gently sloping, the river is wide, deep and slow-moving, and it carries a large volume of water. Lateral erosion continues, but deposition

   The main features are a wide flood plain, large meanders, ox-bow lakes, natural levees, braided channels and distributaries. At the mouth, deposition may build up a delta where the river enters a calm sea or lake. In some cases, tributaries may join the main river close to its mouth, forming deferred confluences.

(b) Four importance of rivers to man

• Water supply: Rivers provide water for drinking, cooking, washing and watering animals.
• Irrigation and farming: River water is used to irrigate crops, while flood plains usually have fertile alluvial soils suitable for agriculture.
• Hydroelectric power: Fast-flowing rivers and waterfalls can be harnessed to generate hydroelectric power.
• Transport and trade: Navigable rivers provide routes for moving people and goods, especially in areas with poor road or rail networks.

Other benefits include fishing, industrial water supply, tourism and recreation, and the use of rivers as natural boundaries between areas or countries.