The State of Soil Erosion Control in Rwanda is the result of collaborative efforts between the Government of Rwanda through Rwanda Water Resources Board (RWB) and the International Union for Conservation of Nature (IUCN) as part of the Embedding Integrated Water Resources Management in Rwanda project, funded by the Embassy of Kingdom of the Netherlands in Rwanda.
In this report The results of the erosion control mapping shows that of the 30 districts of Rwanda, land under high erosion risk is about 1,080,168 hectares (45% of the total provinces land which is estimated to 2, 385, 830 hectares) of which 71 941 hectares (7% of the total risk areas) are at extremely high risk, 190, 433 hectares are at very high risk (18% of the total land at erosion risk), 300,805 hectares are at high risk (28% of the total risk identified), and 516,999 hectares (48% of the total land at risk) are at moderate risk.
Ngororero District has the highest risk with a total of 58,003 hectares i.e. 85% of its land at high erosion risk. Muhanga district is ranked the second-highest in erosion risk with 53, 352 hectares under risk (82% of the district land) while Rutsiro district comes third with 48,143 hectares prone to erosion estimated at 73% of the district land. Other districts such as Karongi, Gakenke, Huye, Nyaruguru, Rulindo and Nyamagabe districts needs considerable attention as the risk accounts for more than 60% of the district land.
The observed erosive features in risk areas have shown that about 70,433 hectares (17% of the country land at risk) are affected by Gullies (39% of the affected land), severe gullies on 13,584 hectares (8% of the land affected land), landslides on 2,823 hectares (2% of the affected land) and rill erosion (93,831 hectares, i.e. 52% of the affected land).
Within the catchment, the upper Nyabarongo is the worst affected with 45,961 hectares affected of which 28,123 hectares are affected by rill erosion, 14,337 hectares are affected by gullies, 2,353 hectares are affected by severe gullies, while 1,148 hectares are affected by landslides. Kivu catchment area follows with 34,050 hectares affected of which 15,085 hectares are affected by rill erosion, 16,033 hectares are affected by gullies, 2,426 hectares are affected by severe gullies and 506 hectares affected by landslides.
Efforts made in controlling erosion in Rwanda
In Rwanda, it was observed that the erosion control techniques i.e. proportion of land at erosion risk which are today protected against erosion for each district is very low. In fact, of 1,080,168 hectares of land at risk in all provinces, only 282,352 hectares are protected against erosion (26% of the country land at risk) of which 28,870 hectares are protected by contour bank terraces (commonly known as progressive terraces covering (10% of the land protected) while forests protect about 190,011 hectares at risk (67 % of land protected). There are other practices like bench terraces (42,379 ha: 15%), hedgerows and shrubs (318 hectares), etc. About 797,816 hectares are not protected yet which is about 74 % of the total country land at risk.
Recommended erosion control practices
The recommended erosion control practices are required in unprotected areas or where the existing erosion control techniques are judged inadequate with regard to the type of risks found and existing land use.
The contour bank terraces are recommended in high-risk agricultural lands while ditches in the forested area. Bench terraces are recommended in areas at high to extremely high risk where there has been started the bench terracing but which did not complete the entire area which is suitable for that recommendation.
Grassed waterways are recommended for existing terraces which was made without waterways or with but no grasses can cause severe gullies and destruction of bench terraces created. No-till agriculture (zero tillage) is recommended for perennial crops on the extremely high-risk area while Storm-water management facilities (SWMF) or water harvesting facilities is recommended in built-up areas. No-recommendation is provided where existing erosion control measures are adequate. Bamboos are recommended to close gullies or to protect rivers. Forests (Afforestation or reforestation) are recommended in extremely high-risk areas.
In the view of this concept, contour banks terraces are required on 510,096 hectares, which is about 47% of the total country land at risk, while afforestation and reforestation are required on 39,901 hectares (4% of the country land at risk), Agroforestry and Hedgerows are required on 101,232 hectares (9% of the total country land at risk). Bamboo planting is required on about 14,915 hectares of land affected by gullies and on riverside. No-tillage agriculture is required on 43,552 hectares for perennial crops established on land at very high risk.
Storm-water management facilities or water harvesting facilities are required in urbanized and settlement areas on about 89,679 hectares (8 % of the total land at risk).