## 5 Soil Erodibility Factor of the Dam
Even within the moderate erodibility category, the considerable variation (e.g., 0.106 for sample 3 vs. 0.145 for sample 6) highlights the need for targeted conservation measures in areas with higher K values. In the context of tropical soils, these results suggest that the downstream region of the Tiga Dam has generally favorable soil erodibility characteristics. However, moderately erodible soils in over half of the samples underscore the importance of implementing and maintaining appropriate soil conservation practices to mitigate erosion risks. The original Universal Soil Loss Equation (USLE) used a nomograph based on soil texture, organic matter, structure, and permeability [40]. For a silty clay loam with 1% organic matter, granular structure, and slow permeability (typical of the Tiga Dam soils), K ranges from 0.055 to 0.145. This value falls within the range of most Tiga Dam samples, validating the RUSLE approach. However, the nomograph does not capture the full variability in the RUSLE results, as it does not directly account for mineralogy or ion exchange capacity. [PERSON] et al. used runoff plots in the Three Gorges area, China, finding K values between 0.0010 and 0.0054 for clay loams [9]. The Water Erosion Prediction Project (WEPP) model uses interrill erodibility (K\({}_{\rm i}\)), rill erodibility (K\({}_{\rm r}\)), and critical shear stress (\(\tau_{\rm c}\)) to  
Figure 14: The soil erodibility factor was determined by twelve soil samples from the downstream area of the Tiga Dam in Kano State, Nigeria. define soil erodibility [59]. [PERSON] et al. found for a clay loam: K\({}_{\text{i}}\) = 2,728,133 kg\(\cdot\)s/m\({}^{4}\), K\({}_{\text{r}}\) = 0.0058 s/m, and \(\tau_{\text{c}}\) = 3.5 Pa [56]. Another common technique is the rainfall simulation method. In a study of Nigerian soils, [PERSON] and [PERSON] employed this method and found K values between 0.012 and 0.078 Mg h MJ\({}^{-1}\) mm\({}^{-1}\)[9]. The primary novelty lies in applying the RUSLE, traditionally an agricultural soil loss model, to assess earth dam stability. This interdisciplinary approach breaks silos between soil science, agricultural engineering, and geotechnical engineering, fostering innovative problem-solving. Standard RUSLE applications use generic soil properties. The model is fed with site-specific data--grain size, plasticity, and compaction characteristics--tailoring it to the unique geotechnical properties of dam soils. This customization enhances the model's accuracy and relevance. Conventionally, dam engineers treat erosion, slope stability, and seepage as separate issues. Using RUSLE's K factor, this study integrates surface erosion risk into a broader geotechnical framework. For example, linking sample 4's K value with its low cohesion and high permeability provides a multi-faceted view of its vulnerability. Climate change is intensifying rainfall patterns globally. The RUSLE, designed to predict long-term soil loss, is now being used to infer soil behavior under extreme events--a novel extension. Like sample 4's, K values may flag areas that could rapidly erode during unusually intense storms, a critical consideration in our changing climate. While our study primarily utilized the Revised Universal Soil Loss Equation (RUSLE) to assess soil erodibility, it is crucial to consider how our soil properties might be interpreted within frameworks developed explicitly for assessing internal erosion in dams. Recent advancements in understanding backward erosion piping (BEP) and internal erosion mechanisms provide valuable perspectives for interpreting our soil data. Considering the rate process perspective outlined by [PERSON] et al., our soil samples with higher clay content and plasticity index (e.g., samples 1) would likely exhibit higher critical shear stress (\(\tau_{\text{c}}\)) values. This suggests a potentially lower susceptibility to initiation of internal erosion.