Soils in Rwanda
Senior 2 · Geography and Environment
Soils in Rwanda
Lesson 2 of 3
18 min
It takes hundreds of years for a few centimetres of topsoil to form, and a single heavy storm can wash them off a bare, steep field. That soil turns rivers brown, fills reservoirs with mud and leaves the farmer with poorer land every year. In a country where most people farm small plots on steep hills, soil erosion is one of the most serious environmental problems.
Soil erosion is the removal of the top layer of soil by water, wind or gravity faster than new soil can form.
They usually happen in this order as runoff increases:
Other forms: landslides (whole masses of soil sliding downhill), riverbank erosion, and wind erosion of dry, bare sandy soils in parts of the east.
| Natural causes | Human causes |
|---|---|
|
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A bare, steep 2-hectare field loses about 50 tonnes of soil per hectare each year. How much soil does it lose in 5 years?
That is roughly the load of fifty large lorries, all of it the most fertile layer of the field.
Tip
Memory hook. Water erosion climbs a ladder: splash → sheet → rill → gully. Each step means more water collected in fewer, deeper channels, and more damage.
Solution: the removal of topsoil by water, wind or gravity faster than new soil forms.
Solution: it removes the fertile topsoil evenly from the whole field, so yields fall before the farmer notices.
Solution: any two of: deforestation, overgrazing, cultivating up and down slopes, bush burning, mining, road building.
Solution: 40 × 3 = 120 t per year; 120 × 2 = 240 tonnes.
Solution: eroded soil settles in reservoirs (siltation), reducing the water they can store and damaging turbines.
Summary
Sources and credits
The worked example and practice items are written by Ganzaa; the soil-loss figures are illustrative.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
