Applying stream power gradient in the investigation on spatial susceptibility of debris flow: A case of the Jinsha River Basin, China

Investigation of spatial susceptibility of debris flow is a basis for carrying out geological hazard prevention and developing ecological restoration plans. It is difficult to efficiently and accurately identify potential debris flow gullies on a large spatial scale simply by relying on field surveys combined with remote sensing observations or debris flow simulations with small watersheds as units. Taking the Jinsha River Basin of China as an example, we propose a quantitative scheme to describe the intensity of extrinsic forces by calculating the stream power gradient (ω). We extracted gullies prone to debris flow, assuming that there is no spatial heterogeneity in the provenance supply conditions based on the fundamental understanding that debris flow is a high-energy gravity flow. In the situation where the threshold (ω=1×10⁻⁴ W/m²) is the mutational site of the gradient change trend of the relation curve between the number of debris flow gullies and ω value, a total of about 32 thousand debris flow gullies with lengths of more than 200 m were found. In the middle and lower reaches of the basin, these gullies are located within a 30-kilometer buffer zone along the Jinsha and Yalong Rivers, and there is a power function relationship between the number of debris flow gullies and the width of a buffer zone. However, extreme weather events are likely to increase in the future under global warming, and these areas should be the critical prevention areas of debris flow disasters, especially the cascade reservoir area. The results of this study provide a lattice data set of spatial locations of the gullies prone to debris flow and the stream power gradients in the Jinsha River basin, which can be used to retrieve the exact location of the high-energy gullies and can also be used as the basic data for the study of related geological hazards and surface processes in general.