## 5 Soil Erodibility Factor of the Dam  
Figure 14 presents a novel application of the Revised Universal Soil Loss Equation (RUSLE) to estimate the soil erodibility factor (K) for twelve soil samples from the downstream area of the Tiga Dam in Nigeria. Traditionally, the RUSLE is employed in agricultural contexts to predict long-term average annual soil loss. Its adaptation to assess earth dam stability represents an innovative cross-disciplinary approach, leveraging established soil erosion models to enhance geotechnical risk assessment. The K factor in the RUSLE quantifies a soil's inherent susceptibility to detachment and transport by rainfall and runoff. In this study, the K values are expressed in SI units (ton-ha-h/ha-MJ-mm), differing from the conventional US customary units. The distribution of K factors does not appear to follow a clear pattern for sample number, suggesting that spatial variability in soil erodibility may be complex and influenced by local factors such as topography, land use, or soil composition. These findings have important implications for soil conservation and management strategies in the downstream area of the Tiga Dam. Areas with higher K factors may require more intensive erosion control measures, while those with lower values might be more suitable for specific land uses. Further investigation into the factors contributing to this variability in soil erodibility would be valuable for developing targeted conservation practices. The soil erodibility factor values exhibit considerable variation across the samples, ranging from a minimum of 0.055 for sample 4 to a maximum of 0.145 for sample 6. This substantial range (0.09) indicates significant heterogeneity in soil erodibility characteristics within the study area. The mean K factor across all samples is approximately 0.109, with a standard deviation of about 0.025. This relatively high standard deviation (about 23% of the mean) further underscores the variability in soil erodibility among the sampled locations. Several samples (6, 8, 7, 10, and 5) show K factors above 0.12, suggesting areas of higher susceptibility to erosion. In particular, sample 6 stands out with the highest K factor of 0.145, indicating potentially critical erosion vulnerability at this location. Conversely, samples 4, 12, 2, and 1 exhibit lower K factors (below 0.09), implying relatively lower erodibility. Sample 4, with the lowest K factor of 0.055, represents the least erodible soil among the samples analyzed. The results from the RUSLE method for estimating soil erodibility factors (K) can be interpreted using [PERSON]'s classification for tropical soils [58]. This classification categorizes K values into low erodibility (K \(<\) 0.10), moderate erodibility (0.10 \(\leq\) K \(\leq\) 0.30), and high erodibility (K \(>\) 0.30). Applying this framework to the result reveals that five samples (1, 2, 4, 9, and 12) fall into the low erodibility category, with K values ranging from 0.055 to 0.092. This suggests that approximately 41.7% of the sampled areas have relatively low susceptibility to erosion. The remaining seven samples (3, 5, 6, 7, 8, 10, and 11) exhibit moderate erodibility, with K values between 0.106 and 0.145, indicating that about 58.3% of the sampled areas have moderate erosion potential. None of the samples displays high erodibility according to [PERSON]'s classification. These findings have several implications for soil management in the study area. The predominance of moderately erodible soils suggests that while erosion is a concern, it may be manageable with appropriate conservation practices. The substantial portion of samples showing low erodibility is a positive aspect of soil conservation efforts. The absence of highly erodible soils (K \(>\) 0.30) is encouraging, indicating that extreme erosion vulnerability is not widespread in the studied area. The variation in K values within both the low and moderate categories points to the influence of site-specific factors on soil erodibility, necessitating localized approaches to soil management.