Drainage
Senior 1 · Geography
Drainage
Lesson 4 of 4
22 min
At Rusumo, on the Akagera, a power station finished in 2024 turns the fall of the river into 80 megawatts of electricity, shared equally by Rwanda, Burundi and Tanzania. Elsewhere along the same river, floods drown farmers' fields in the rainy season. The water bodies of Rwanda give people light, food, work and journeys, and they can also take them away. This lesson weighs both sides.
| Activity | How the water body helps | Rwandan example |
|---|---|---|
| Hydroelectric power (HEP) | Falling water turns turbines; the bigger the drop and the flow, the more power | Ntaruka (11.5 MW) on the stream from Lake Burera to Lake Ruhondo; Nyabarongo I (28 MW) in Muhanga District; Rusumo (80 MW, shared) |
| Gas for power | Methane dissolved in deep water is pumped up and burned in gas engines | The KivuWatt plant on Lake Kivu, whose first stage supplies 26 MW |
| Water supply | Rivers, lakes and springs supply homes, schools and factories | Around Kigali the Nyabarongo is used for washing, cooking and drinking |
| Farming and irrigation | Valley marshes stay wet in the dry season; river water can be led onto fields | Rice and vegetables in drained valley-bottom marshes |
| Fishing | Lakes and rivers provide fish, an important protein | Isambaza sardines in Lake Kivu, brought from Lake Tanganyika in 1959; tilapia and other fish in smaller lakes and fish ponds |
| Transport | Large, calm lakes carry boats; most Rwandan rivers are too steep or rocky for ships | Boats between Rubavu, Karongi and Rusizi on Lake Kivu |
| Tourism and recreation | Beaches, boat trips, birds and wildlife attract visitors | Lake Kivu beaches at Rubavu and Karongi; boat trips on Lake Ihema in Akagera National Park |
| Raw materials | River beds and swamps provide sand, clay and papyrus | Sand for building dug from river beds; clay for bricks and tiles; papyrus mats |
| Wildlife and water storage | Swamps store floods, filter water and shelter birds and fish | The Rugezi marsh, called the "kidneys" of the land because it filters water for Burera and Ruhondo |
Definition
Hydroelectric power (HEP): electricity made when moving water, usually falling from a height, turns a turbine linked to a generator. It is renewable: the rain refills the rivers. Example: the Ntaruka power station, where the stream between Lakes Burera and Ruhondo drops about 100 m.
Definition
Siltation: the filling of a river, lake or reservoir with fine soil (silt) washed off the land by erosion. It makes water muddy, harms fish and fills up dams. Example: the brown colour of the Nyabarongo and the Akanyaru in the rainy seasons.
Worked example 1: why build a power station at Ntaruka?
The stream from Lake Burera to Lake Ruhondo is about 600 m long and drops about 100 m. Find its gradient and compare it with the lower Akanyaru (1 in 1,231, lesson 2).
Answer. 1 in 6: the water falls 1 m for every 6 m it flows, about 200 times steeper than the lower Akanyaru. A big drop in a short distance is exactly what a hydroelectric station needs; a flat, swampy river is not.
Worked example 2: sharing Rusumo's power
The Rusumo station can produce 80 MW, shared equally by three countries. How much is Rwanda's share, and how does it compare with the 26 MW from the first stage of KivuWatt?
Answer. About 26.7 MW, almost exactly the same as KivuWatt's first stage (about 3% more). One river shared by three countries gives Rwanda as much power as one gas plant on its biggest lake.
Important
Case study: one river, three countries
Rusumo Falls has been a crossing point for centuries, because the river narrows over hard rock. Today the Rusumo power project is owned jointly by Rwanda, Burundi and Tanzania, all members of the East African Community. It was built as a run-of-river scheme: a larger 90 MW design with a big reservoir was dropped because it would have flooded more land. The power is carried by 220 kV lines to Kigali (115 km), Gitega in Burundi (158 km) and Nyakanazi in Tanzania (98 km). Because rivers cross borders, the countries of a basin must plan together: what is done to the Nyabarongo in Rwanda affects Lake Victoria and every country downstream. The project was managed for the three owners by NELSAP, part of the Nile Basin Initiative, in which the Nile countries, Rwanda among them, work together on sharing the river.
Warning
Name the water body and the place. "Rivers give fish" earns little. "Lake Kivu supports a fishery for isambaza sardines" earns the mark. For every use or problem, give a named Rwandan water body.
Regional Rusumo Falls Hydroelectric Project, a documentary by Rusumo NELSAP (5 min), filmed during construction. Watch for how the river is diverted and why three countries share one plant.
A district wants to drain part of a large valley swamp to grow rice for a growing population. An environmental officer wants the swamp protected, like Rugezi. Give two arguments for each side, and then suggest a compromise that uses the valley without destroying it.
Tip
Exam technique: group your points. Economic (power, fishing, farming, transport, tourism, raw materials), social (water supply, recreation) and environmental (storage, filtering, wildlife). Then give the problems in the same order, each with a solution: siltation → terraces and trees; pollution → treating waste; wetland loss → protected buffer zones.
Practice
Remember
Further reading
Books and resources for this unit
Sources and credits
The lesson text, table, worked examples and practice are written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
