Study on the collapse characteristics and threshold behavior of the subsurface stormflow mechanism

Abstract: Subsurface stormflow is the dominant runoff generation mechanism during certain flash flood events. The collapse characteristics and threshold behavior are critical to the transition from the slow runoff stage to the rapid runoff stage and the relevant study is not only essential for hydrology theory but also for flash flood disaster prevention. In recent years, efforts have been made to explore the common principles of hydrological processes under strong spatial heterogeneity, but findings from field experiments and numerical studies were difficult to apply to the modeling process. Furthermore, we have yet to develop a deeper understanding of the mechanisms for the impact of complex factors on subsurface stormflow and lack a comprehensive understanding of the formation mechanism of threshold.
This presentation discusses how we plan to address this research gap. Firstly, around the phenomenon of “burst-block-burst” in the subsurface stormflow runoff generation process, rainfall-runoff simulation experiments were carried out and factor analysis was conducted to determine the main influencing factors of subsurface stormflow runoff generation. The main influencing factors include soil texture factors, collapse state factors, initial state factors, and other factors, and the influence of these four types of factors decreases in turn. In the second step, we constructed a field hydrological station in the Huanggou Watershed located in Hubei Province, China, collected the rainfall-runoff data, and found that the subsurface stormflow process shows a three-stage-double-threshold behavior: the water storage stage, the initial flow stage, and the rapid flow stage. In the third step, synthesizing the main influencing factors, the three-stage double-threshold process was quantified. Further, the three-stage subsurface stormflow-based model (TSSM) was developed and applied to the Huanggou Hillslope and the Huanggou Watershed. The results show that TSSM performed well, with NSEs of 0.82 and 0.67 in the calibration and verification periods of the Huanggou slope, and NSEs of 0.76 and 0.74 in the calibration and verification periods of the Huanggou Watershed, respectively.
This study elucidated the collapse characteristics and threshold behavior of subsurface stormflow and developed an effective simulation model, which contributes to increasing our understanding of three-stage subsurface stormflow and is beneficial for hydrologists to develop more realistic hydrological models.

Keywords: Subsurface stormflow; Collapse characteristics; Threshold behavior; Three-stage subsurface stormflow mechanism; TSSM