Drainage System in Rwanda
Senior 4 · Geography
Drainage System in Rwanda
Lesson 3 of 3
25 min
In 2003 and 2004 Rwanda suffered repeated power cuts. The cause was not a broken machine but a damaged wetland about 50 km north of Kigali. Follow the chain in Figure 5.
Figure 5. The Rugezi wetland case, drawn by Ganzaa from REMA (2021).
The case shows the main idea of this lesson: rivers, lakes and wetlands are one connected system, so what people do on the hills and in the marshes affects water, energy and health far downstream.
Worked example 1: what did the damage cost?
Problem. During the shortage the government paid almost US$60,000 a day for diesel generators. Estimate the cost of one year of this, and compare it with the US$375 million total economic value given for Rugezi (2014).
Interpretation. One year of emergency fuel cost about one-seventeenth of the wetland's estimated total value, and the fuel bought nothing lasting. Protecting the wetland was far cheaper than replacing its services. This is the economic argument for conservation.
| Activity | Water bodies used | Rwandan examples |
|---|---|---|
| Hydroelectric power | Rivers and lakes with a drop in level | Ntaruka (water from Burera to Ruhondo); Rusumo on the Akagera, shared with Burundi and Tanzania |
| Energy from gas | Lake Kivu | Methane dissolved in the deep water is extracted to generate electricity |
| Irrigation and livestock water | Marshlands, rivers, valley dams | Rice and vegetables in valley marshes; valley dams in Nyagatare (42), Kayonza (23) and Gatsibo (12); 813 small water ponds, most in Bugesera and Kirehe (RWB, in REMA, 2021) |
| Fishing and fish farming | Lakes, ponds | Sambaza (Limnothrissa miodon), introduced to Lake Kivu at the end of the 1950s; tilapia |
| Transport | Lake Kivu, large rivers | Boats on Lake Kivu linking lakeside towns such as Rubavu, Karongi and Rusizi; dugout canoes (ibyombe) as river ferries |
| Water supply | Rivers, lakes, springs, groundwater | 87.4% of households had an improved drinking-water source in 2017 (95.8% urban, 85.4% rural) (NISR, in REMA, 2021) |
| Tourism and recreation | Lakes, wetlands | Lake Kivu beaches, boat trips on Muhazi and Ihema, urban wetland eco-parks in Kigali |
| Crafts and building | Wetlands | Papyrus mats, roofing and ceilings; clay for bricks |
Water bodies also cause problems: floods on valley floors, mosquitoes and water-borne diseases near stagnant water, and rivers that block roads until bridges are built.
Definition
Water pollution: the addition of substances or organisms that make water harmful to living things or unfit for use.
Turbidity: cloudiness of water caused by suspended particles such as soil. Siltation: the settling of this sediment on river beds, lake floors and in reservoirs.
Eutrophication: over-enrichment of water with nutrients (nitrates, phosphates), which feeds algae and weeds; when they decay, dissolved oxygen falls and fish die.
Invasive species: an introduced plant or animal that spreads and harms native ecosystems. Example: water hyacinth.
In 2018–2019 the former Rwanda Water and Forestry Authority (RWFA) assessed 36 water bodies (30 rivers and lakes, 6 groundwater sources). On five core parameters (oxygen, salinity, nitrogen, phosphorus, pH), 85% had good water quality. When turbidity, suspended solids and E. coli bacteria were added, only 18.75% did. No water body met the standard for E. coli, and in 2018–2019 only Kivu and Muhazi met the standard for turbidity (RWFA, 2019, in REMA, 2021).
| Cause | How it pollutes | Effects |
|---|---|---|
| Soil erosion from farms and bare slopes | Soil, fertiliser and pesticide wash into rivers | High turbidity, siltation of reservoirs and lakes, eutrophication |
| Mining | Washing ore releases sediment-laden water; most mine sites add heavily to siltation | Turbid rivers even in dry weather |
| Domestic wastewater and poor sanitation | Septic tanks, soak pits and direct discharge into wetlands | E. coli, water-borne diseases, smells, low oxygen |
| Industry | Effluent that does not meet standards | Chemical pollution, fish deaths |
| Invasive species | Water hyacinth spread from the Nyabarongo into the lakes from Muhazi to Rweru and the Akagera complex; Lake Mihindi became completely covered (REMA, 2009) | Blocks light and boats, removes oxygen, harms fish and fishing |
Worked example 2: why did the score fall from 85% to 18.75%?
Question. The same 2018–2019 samples gave 85% "good" on five parameters but 18.75% "good" on eight. What does this tell us about Rwanda's water?
Answer.
Conclusion. The most effective controls are on the land: terraces, trees and buffer strips to keep soil out of rivers, and sewers and treatment to keep sewage out. An index is only as useful as the parameters it includes.
Warning
Sediment is a pollutant. Many students list only chemicals and rubbish. In Rwanda the measured problems are mainly soil (turbidity) and bacteria (E. coli). Also, do not say "Rwanda has no water problems because it is wet": per person, renewable water is under 1,000 m³ a year, so Rwanda is classified as water-scarce (NISR, 2019, in REMA, 2021).
DW (Eco-at-Africa): "Saving Rwanda's wetlands". How Rwanda is restoring wetlands and what this means for people who farmed them. Note one benefit and one cost of restoration.
Practice
Key points
Further reading
Sources and credits
Sources: Rwanda State of Environment and Outlook Report 2021, REMA, citing RWFA, RWB, WASAC and NISR (Rugezi case and valuation, water quality 2016–2019, causes of pollution, wastewater systems, valley dams, wetland zoning, drinking water access, water scarcity); Rwanda State of Environment and Outlook Report, REMA, 2009 (water hyacinth, sambaza, papyrus uses); Upper Nyabarongo Catchment Plan 2018–2024, Rwanda Water Resources Board (catchment planning); Lake Kivu and Rusumo Hydroelectric Power Station, Wikipedia contributors, CC BY-SA 4.0, adapted by Ganzaa (methane extraction; the shared Rusumo station).
Figure 5 and the worked examples were drawn and written by Ganzaa.
Photos: Crossing Nyabarongo river in Rwanda from North to South using ICYOMBE, Davyimage, CC BY-SA 4.0; A view of Nyabarongo river, Doltography, CC BY-SA 4.0; via Wikimedia Commons.
Video: "Saving Rwanda's wetlands | Eco-at-Africa", DW News, embedded from YouTube. The rest of the lesson and the exercises were written by Ganzaa.
This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.
Quick check
Put the Rugezi chain in order, from cause to effect.
Tap the cards in the right order.
