O Level Notes : Geography - landforms and landscape processes - Rivers

This topic focuses on how rivers form different landforms, the distribution of arid and semi-arid areas and the action of wind in such regions. When landforms develop, they present certain hazards to human beings. As a result, this chapter also looks at the nature of hazards caused by landform development and the possible mitigation strategies.

RIVERS

There are different types of rivers, classified according to the nature of their flow. These are:

• Ephemeral streams

These are the streams which only flow after a storm. In Zimbabwe these are tiny streams flowing in summer only when rain has been received. They flow just for hours or days when storms are experienced. After the storm they simply run dry. They are useful for water harvesting through construction of small earth dams down these streams. The water collected can be used to irrigate crops during summer dry spells. Some of them feed water into bigger streams.

• Intermittent streams

These are much bigger than ephemeral ones. They flow only during the rainy season. In Zimbabwe these flow throughout the summer when rains are frequently received. After the summer they dry out. Their sources are dry and siltation has reduced most of these streams' water holding capacity making them unable to contain water through the year.

• Perennial streams

Perennial streams are those that flow throughout the year. These include big rivers cutting through inland Zimbabwe such as Odzi, Runde, Save, Devure, Shashe, Mazowe, Hunyani and others and those forming Zimbabwe's international borders which are Limpopo and Zambezi. Those forming international borders have their sources outside the country. In dry winters their discharge is reduced due to lack of rain, they do not completely dry out. In the summer, their discharge is increased due to replenishment from the rains.

• Exogenous

These are streams with their sources outside the regions they flow through. For example, Zambezi and Limpopo are exogenous to Zimbabwe.  The Nile River passing through Sahara Desert is exogenous since it does not originate from the desert.

Case Study: Zambezi River

Zambezi is the 4th longest River in Africa, after Nile, Congo, and Niger Rivers. In Africa it is the longest east flowing river. It passes through six countries as it flows from its source to its mouth. From the source to the mouth it is  2700km long and its source is about 1500m above sea level, that is, in Mwinilunga District where Zambia, Angola and Congo meet. It flows into the Indian ocean. The Zambezi River passes through Zambia, Angola, Namibia, Botswana, Zimbabwe and Mozambique on its way to the Indian Ocean. Hydroelectricity power is generated at 2 lakes constructed on the Zambezi and these are Lake Kariba for Zimbabwe and Zambia and Lake Cahora Bassa in Mozambique.