Relationship of sediment yield to connectivity index in small watersheds with similar erosion potentials

Purpose Sediment connectivity is an emerging term that explains the connected transfer of sediment from all sources within a watershed to its outlet. Validation and further development of this concept require considerable supporting data. This research aims to investigate the relationship between the connectivity index (IC) and specific sediment yield (SSY) of catchments with similar erosion potentials. Materials and methods Eleven small adjacent catchments identical in terms of general landscape in the Loess region of Iran were selected. First, the slope, USLE C-factor, and IC maps were made using 30-m spatial resolution data. Then, four IC30 statistics/metrics including average IC, median IC, area specific positive pixels, and IC at the outlet were calculated for the study catchments, followed by investigating their correlations (as well as the IC determinant factors) with the observed SSY (1.8 to 19.8 t ha(-1) year(-1)). In the next step, to examine the effects of pixel size on the behavior of IC in small basins, three coarser resolutions of 50, 100, and 200 m (i.e., IC50, IC100, IC200, respectively) were calculated by resampling the original 30 m input data. Results and discussion The correlation coefficients of the four aforementioned statistics/metrics with SSY were quite significant. Because the average IC30 showed the highest correlation, it was used in the subsequent analyses. The average IC30s for 11 sub-watersheds were obtained from -4.485 to -3.278. While this explained 71% of the 11-fold difference in the SSY, none of the IC determinant factors (i.e., area, slope, waterway length, and vegetation density) showed a R-2 greater than 50%. This indicates the high value of IC in predicting sediment delivery to the basin outlet. The larger pixel sizes gradually weakened the IC-SSY correlation in the study sub-watersheds. The occurrence of this phenomenon is due to the incompatibility of large pixels with the small size of the basins. Conclusion This study implies that a 30-m resolution IC can be implemented to assess sediment delivery quantitatively at small catchment scales, at least, when they have similar erosion potentials. Overall, the IC is a parsimonious method and can be promoted as a substitute for the traditional lumped sediment delivery models.

Automated summary

This study aims to investigate the relationship between the connectivity index and specific sediment yield of catchments with similar erosion potentials. The results show that a 30-m resolution IC can be implemented to assess sediment delivery quantitatively at small catchment scales, serving as a substitute for traditional models.