The Value of Rivers, Lakes, Wetlands, Oceans and Seas – Drainage in Africa and the World (Senior 3 Geography) | Ganzaa

Drainage in Africa and the World

Lessons

Senior 3 · Geography

Drainage in Africa and the World

4 lessons

Lesson 3 of 4

The Value of Rivers, Lakes, Wetlands, Oceans and Seas

25 min

Let's begin

For years, some of Kigali's valley-bottom wetlands were built on, farmed or used as dumps. Now the Rwanda Environment Management Authority has restored five of them, because, in REMA's words, during heavy rain they "absorb and temporarily store excess stormwater, reducing flood risks". A swamp that looks like wasted land can be doing work worth more than the houses that might be built on it. This lesson weighs what water bodies do for people, and why each is worth protecting.

Definition

Wetland: land that is soaked or covered by shallow water for all or part of the year, with plants adapted to wet soil, such as papyrus. Examples: Rugezi in northern Rwanda, the Sudd in South Sudan, the Okavango Delta in Botswana. In Kinyarwanda, REMA uses the terms ibishanga n'ibibaya.

Rivers and lakes

Use	How it works	African example
Water supply	Drinking water, industry, livestock	Cairo and the other cities of Egypt depend almost entirely on the Nile
Irrigation	Water led to crops in the dry season or in deserts	The Nile valley and delta in Egypt; the Gezira scheme between the Blue and White Niles in Sudan
Hydro-electric power (HEP)	Falling water turns turbines	The Aswan High Dam on the Nile; Kariba on the Zambezi; the Inga dams on the lower Congo
Fishing	Food and income	Nile perch and tilapia in Lake Victoria; isambaza in Lake Kivu
Transport	Cheap carriage of heavy goods	Barges on the Congo between Kinshasa and Kisangani; ferries on Lake Victoria and Lake Kivu
Tourism	Waterfalls, boat trips, beaches	Victoria Falls on the Zambezi; boat trips on Lake Ihema in Akagera
Boundaries	Rivers form easily seen borders	The Akagera along part of the Rwanda–Tanzania border

Wetlands

REMA lists what Rwanda's wetlands do: they "protect water quality, maintain water supplies by replenishing rivers and streams during the dry season", "reduce the risk of flooding, sequester carbon", and give habitat to wildlife "that cannot survive elsewhere". Figure 5 shows the sponge effect.

Figure 5: the sponge effect of a valley wetland. Drawn by Ganzaa.

Wetlands also supply papyrus for mats and roofs, fish, and grazing in the dry season, and draw birdwatchers and tourists. Their risk is that their flat, fertile, wet floors are tempting to drain for crops, bricks and building.

Oceans and seas

Trade. Most of Africa's imports and exports travel by sea. Land-locked Rwanda's overseas trade passes through the ports of Mombasa (Kenya) and Dar es Salaam (Tanzania).
Fishing. Cold, nutrient-rich currents such as the Benguela off Namibia and Angola support rich fishing grounds (Unit 11).
Climate. Oceans store heat and moderate the temperature of coasts; warm currents bring rain, cold currents bring dry, foggy coasts such as the Namib.
Minerals and energy. Offshore oil and gas (Nigeria, Angola), salt from sea water.
Tourism. Beaches and coral reefs, for example along the Kenyan coast and in Zanzibar.

Wisconsin Wetlands Association: How Wetlands Manage Water. The wetlands shown are in the USA, but the processes are the same as in Rwanda's valleys: watch for storage of floodwater and slow release in dry weather.

Definition

Hydro-electric power (HEP): electricity generated when falling water turns turbines, usually at a dam or waterfall. Land-locked country: a country with no coastline, which must send its sea trade through a neighbour's ports. Example: Rwanda.

Worked example

Worked example 1: why rivers carry heavy goods. Explain why the Congo between Kinshasa and Kisangani is used for transport, but the lower Congo below Kinshasa is not.

Between Kinshasa and Kisangani the river is wide, deep and gently sloping, so barges can travel about 1,700 km without obstruction.
Below Kinshasa, the river drops steeply through a series of rapids and falls (where the Inga dams are built), so boats cannot pass; goods go to the coast by rail and road instead.
So the same river can be both a highway and a barrier: its usefulness depends on its gradient.

Worked example

Worked example 2: a land-use decision. A district must choose between draining a valley wetland for rice and protecting it. Give one argument for each side and a judgement.

For draining: flat, wet, fertile land can grow rice and feed many families; more income in the short term.
For protecting: the wetland stores floodwater, filters sediment, keeps the river flowing in the dry season and shelters wildlife (REMA); once drained, these services are lost and floods downstream can get worse.
Judgement: a balanced plan protects the core of the wetland and allows careful, regulated farming at its edges, which keeps most of its services while still producing food.

Warning

A wetland is not wasteland. In an exam, never describe swamps only as "breeding grounds for mosquitoes". Give their functions first (flood control, water storage, filtering, habitat, carbon storage), then their problems.

Tip

FIT-TECH for the uses of water bodies: Fishing, Irrigation, Transport, Tourism, Energy (HEP), Climate, Home water supply.

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Practice

Define a wetland and give one Rwandan example.
Give four uses of rivers, with an African example of each.
Using Figure 5, explain how a wetland reduces floods in the rainy season.
Why is the sea important to Rwanda even though Rwanda has no coast?
Name the dam and river that supply HEP at (a) Aswan, (b) Kariba.
Explain why the Congo carries more barge traffic upstream of Kinshasa than downstream.
"Wetlands in towns should be drained to make room for houses." Evaluate this view.

Show answersHide answers

Land soaked or covered by shallow water for all or part of the year, with plants such as papyrus; e.g. Rugezi.
Any four, e.g.: water supply (Nile for Cairo); irrigation (Gezira, Sudan); HEP (Kariba, Zambezi); fishing (Lake Victoria); transport (Congo barges); tourism (Victoria Falls); boundaries (Akagera).
Rain running off the hills is held in the wetland's soil and plants, which spread and slow the water and store it, so less reaches the river at once and the flood peak downstream is lower.
Its overseas imports and exports pass through the ports of Mombasa and Dar es Salaam; the oceans also shape its climate (moist air for rain) and supply sea fish and salt.
(a) the Aswan High Dam on the Nile; (b) the Kariba Dam on the Zambezi.
Upstream the river is wide, deep and gently sloping; downstream of Kinshasa it falls through rapids and waterfalls that boats cannot pass.
Draining gives land for housing, but it removes flood storage (REMA), so heavy rain floods nearby homes and roads; it also loses water filtering, dry-season flow and habitat. Kigali has chosen to restore five wetlands instead. A strong answer concludes that the costs usually outweigh the benefits, and that houses belong on safer, higher ground.

Sources and credits

Rwanda Environment Management Authority (REMA): Wetlands and Kigali wetlands restoration project nears completion, read on 1 October 2026. Facts used as stated.
Aswan Dam, Inga dams, Congo River, Wetland and Benguela Current: Wikipedia contributors, Wikipedia, CC BY-SA 4.0, adapted by Ganzaa.
Video: How Wetlands Manage Water, Wisconsin Wetlands Association, embedded from YouTube.
Figure 5, explanations, worked examples and exercises: written and drawn by Ganzaa.

This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.

1Rivers and lakes

2Wetlands

3Oceans and seas

Rivers and lakes

Wetlands

Oceans and seas