Rwanda has experienced accelerated soil erosion as a result of unsustainable human activities and changes in land use. Therefore, this study aimed at applying the RUSLE (Revised Universal Soil Loss Equation) model using GIS (Geographical Information System) and remote sensing to assess water erosion in Rwanda, focusing on the erosion-prone lands for the time span 2000 to 2015. The estimated mean annual soil losses were 48.6 t ha⁻¹ y⁻¹ and 39.2 t ha⁻¹ y⁻¹ in 2000 and 2015, respectively, resulting in total nationwide losses of approximately 110 and 89 million tons. Over the 15 years, 34.6% of the total area of evaluated LULC (land use/land cover) types have undergone changes. The highest mean soil loss of 91.6 t ha⁻¹ y⁻¹ occurred in the area changing from grassland to forestland (0.5%) while a mean soil loss of 10.0 t ha⁻¹ y⁻¹ was observed for grassland converting to cropland (4.4%). An attempt has been made to identify the embedded driving forces of soil erosion in Rwanda. As a result, we found that mean soil loss for Rwanda’s districts in 2015 was significantly correlated with poverty (r = 0.45, p = 0.013), increased use of chemical fertilizers (r = 0.77, p = 0.005), and especially was related to extreme poverty (r = 0.77, p = 0.000). The soil conservation scenario analysis for Rwanda’s cropland in 2015 revealed that terracing could reduce the soil loss by 24.8% (from 14.6 t ha⁻¹ y⁻¹ to 11.7 t ha⁻¹ y⁻¹). Most importantly, the study suggests that (1) terracing integrated with mulching and cover crops could effectively control water erosion while ameliorating soil quality and fertility, and (2) reforestation schemes targeting the rapid-growing tree species are therefore recommended as an important feature for erosion control in the study area.

The riparian zone of the Three Gorges Reservoir (TGR) has experienced substantial erosion that may severely deteriorate the reservoir ecosystem. To calculate soil erosion characteristics, field investigations have been conducted in the TGR area and 12 erosion-monitoring transects have been set in the middle TGR. The results showed that the dominating drive forces are water wave, gravity and surface runoff. In summer when the reservoir ran at lower water levels, wave erosion led to bank instability and bank collapses. Simultaneously, due to a number of heavy storms, surface runoff erosion was also severe. In other seasons when the reservoir ran at relative higher levels reaching the highest level in winter, water wave prevailed due to the wide range of water surface and heavy waterway transportation. Soil erosion was the most severe in the mainstream where higher frequency and intensity of waves occurred. The rates of wave erosion were around 37 mm/year with the highest being 53 mm/year, and surface runoff erosion was up to 15 mm/year in the main stream riparian zone.

Aggregate is the basic unit of soil structure, which is crucial to the sustainability of soil system functions such as structural stability and Fertility Maintenance. Three Gorges Dam (TGD) has extensively led to a dramatic hydrological regime alteration, which may consequently affect various soil physical properties. The aim of this study was to investigate the long-run temporal variation of soil aggregate stability as induced by water-level fluctuations in the riparian zone of the Three Gorges Reservoir (TGR). Sampling plots were established along different elevations considering the interval of 5 m, starting from 150 m to 175 m. A Laser Diffraction based analysis that allows the measurement of soil aggregate stability after the removal of soil organic matter helped to particularly study the effect of external factors on soil aggregate stability of the study area. In addition, wet-sieving method considering the effect of chemical binding agents was used to quantify aggregate stability. The present results indicated a significant increase of Mean Volume Diameter, MVD (p < 0.05) within the study period. Continuous drying-wetting cycles mended soil aggregate stability with a 14.25% increase of the MVD from 2012 to 2016. In the Water-Level Fluctuation Zone (WLFZ), the lower land has predominantly contributed to the increase of soil aggregate stability compared to upper land, with an increase of 62.19% and 37.81% for MVD, 60.88% and 39.12% for D₁₀, 95.34% and 4.66% for D₉₀ at lower and upper elevations, respectively. Sediment deposition below 165 m has precluded a direct effect of water stress on soil aggregates, which certainly declined soil disaggregation. The removal of SOM while analyzing aggregate stability by LD may explain the contradiction between the resulted MVD, and the MWD and GMD. The increase of MWD and GMD was mainly attributed to the increase of SOM with r² = 0.89 (p < 0.01) and r² = 0.90 (p < 0.01), while the increase of MVD was highly predicted by the decrease of SOM with r² = 0.88 (p < 0.01). Since this study presents a remarkable change of soil in the riparian area due to dry-wet cycles, our results may help to deeply understand the soil ecology and environmental changes in the WLFZ.