Unraveling the effects of geomorphic restrictions on sediment connectivity in a debris flow small watershed

Abstract

Sediment (dis)connectivity plays a critical role in influencing the geomorphic processes and sediment delivery in debris flow areas. Similarly, changes in geomorphic constraints have a significant impact on sediment connectivity. Therefore, understanding the potential effects of geomorphic indicators on sediment connectivity can identify geomorphic adjustment hotspots and help to inform geo-geomorphic hazard prevention and control. To explore the effects of geomorphic restrictions on sediment connectivity, we applied an index of connectivity (IC) and the digital terrain analysis (DTA) in Jiangjiagou Gully, Yunnan Province, SW China, which is famous for its high annual occurrence of debris flow events. And according to the natural topography conditions, the watershed was separated into three sections from up to down. The IC and 13 geomorphic indicators are calculated for each cell of the watershed’s 5 m resolution digital elevation model (DEM). GeoDetector was used to investigate the geomorphic indicators and their interactions affecting the spatial distribution of sediment connectivity. The results showed that the IC and geomorphic indicators have significant spatial heterogeneity in different regions. The IC value varied from -20.74 to 1.42 and the high-value areas overlap with the river network. LS factor, Topographic Characterization Index (TCI), and Terrain Roughness (TR) are the three factors with the greatest impact on IC value for all regions. In addition, the interactions significantly enhanced the explanatory power of single indicators. Particularly, Topographic Wetness Index (TWI), while single explanatory power is extremely low, its interactions display higher influences than others. Therefore, carrying out low-cost geomorphic adjustments based on the key geomorphic indicators can reduce or block sediment connectivity, further achieving the aim of water and soil conservation and geo-geomorphic hazard control. This study contributes to improving our understanding of the geomorphic processes and provides a scientific basis for nature-based solutions in typical debris flow small watersheds.