Towards quantification of soil conservation performance using sediment connectivity concept at hillslope scale: proposing a new framework for data-scarce regions

Purpose: Although contour trenching is one of the widely used nature-based solutions for soil conservation around the world, its efficiency has not been quantitatively investigated. This study aimed to scrutinize the performance of the contour trenching program, a nature-based solution and common soil erosion prevention measure in hillslopes of a data-scarce region based on the sediment connectivity approach. Materials and methods: Six different hillslopes (A-F) were selected in the Khamsan watershed in Iran, a representative area where contour trenching has been implemented. The sediment connectivity map of each hillslope was generated using the index of connectivity (IC) based on two real scenarios: with (scenario I) and without (scenario II) contour trenching. Two different field-based validation methods were applied on the base of (i) in situ measurements of the sediment depth in contour trenches and Pearson's correlation analysis, and (ii) field index of connectivity (FIC). The validity of the sediment connectivity results was verified using both validation approaches. The sediment connectivity in two scenarios was compared and the impact of the contour trenching was analyzed. The performance of the contour trenching program was quantitatively determined for each hillslope. Results and discussion: The results revealed that contour trenching significantly affected sediment routing and reduced the IC values of all selected hillslopes. The differences in IC value between the two scenarios (?IC) for hillslopes A, B, C, D, E, and F were found to be 22.6%, 11.27%, 14.69%, 5.83%, 15%, and 7.27%, respectively. Therefore, the spatial pattern of sediment connectivity also differed significantly after implementing contour trenching. Furthermore, Pearson's correlation coefficients revealed that the sediment connectivity and the sediment depth in contours in all hillslopes had a significant negative relationship, resulting in confirming the validity of the sediment connectivity results for all six hillslopes in the current study. Conclusion: Contour trenching significantly reduced the sediment connectivity on all six hillslopes studied. Furthermore, in situ measurements of the sediment depth in contour trenches should be conducted to verify the simulation of sediment connectivity. The proposed methodology can be applied in other data-scarce regions to evaluate the performance of the contour trenching program.