Roads

The study calculated the difference in sediment export between the baseline, mitigated, and unmitigated road scenarios in order to highlight areas where erosion is expected to increase the most between the unmitigated and mitigated scenarios. These sub-basins are most vulnerable to impacts from unmitigated road construction, based on their topography, soils, and land management characteristics. These areas tend to be those that have both the steepest slopes, the most erodible soils, and the lowest vegetation cover (e.g., barren land, sand, and certain types of crops such as maize).

• Across the lower basin (high mountains and middle mountains), sediment export modeled by SDR is 7,333,638 tons/year for the baseline scenario, 8,453,199 tons/year for the mitigated scenario (a 15.3% increase from baseline), and 8,967,234 in the unmitigated scenario (a 22.3% increase).
• Results suggest that proper engineering practices can reduce sediment impacts of new construction to the Kaligandaki river by 31%, compared to construction done without sediment management.