Abstract
Compared with floods occurring over plains, alpine flash floods are formed over scattered locations with complex terrain and data is often lacking regarding the land topography, flow and sedimentation, causing difficulties when developing mathematical models to predict flash floods. The existing flash flood models mainly focus on the influence of water flow, such as the sharp increase in flow discharge caused by convergence at steep slopes, disregarding the sediment load carried by the water flow. However, under the effect of high-intensity sediment transport, the sedimentation in gullies may lead to surges in water level, causing the phenomenon of “great disasters resulting from minor flooding”. In this study, an efficient and accurate water-sediment coupling model was established with a Godunov-type finite volume method based 2D flow model, and a sediment module and OPENMP parallel computing module were added as well. Firstly, a common gully in mountainous area with large gradient variations was used as a generalized model to explore the impact of sedimentation on the flow field of the gully and compared with the physical model. Then, the alpine flash flood incident in Gengdi Village was simulated with the computer model. The calculation results show that the high-intensity sedimentation significantly increased the magnitude of alpine flash floods. Calculated by this mathematical model, the research results verified that this mathematic model can efficiently, accurately and concisely predict the occurrence of flash floods in gullies with large gradient variations. The model also provides a flow and sediment modeling method that incorporates the effect of high-intensity sediment transport into the traditional flash flood flow model. Thus, this model can be a powerful tool for detecting flash floods.
Highlights
Short-term high-intensity rainfall may cause flash flooding in mountainous regions, bringing large amounts of sediment (Reid et al, 1998)
2.1.1 2D Shallow Water Equation During flash floods, the water flow movement and the load transported by the flow generally behave like 3D flow, and the mathematical model should simulate the hydrodynamic process in 3D form in order to fully reflect its features
After a large amount of sediment enters an alpine gully with large gradient, the frontal deposition can develop quickly and in retrograde, potentially causing the water level to increase to twice the normal level with clear water
Summary
Short-term high-intensity rainfall may cause flash flooding in mountainous regions, bringing large amounts of sediment (Reid et al, 1998). Regarding the additional damage caused by high-intensity sediment transport during flash floods, Zheng et al (2019) used a 2D bed flow model to simulate the dynamic and hydraulic processes of a steep river channel with varying degrees of steepness, and under conditions of sufficient sediment replenishment They proposed the critical triggers for retrograde deposition in alpine gullies during flash floods. A new set of models is proposed in this paper to efficiently and accurately simulate the dynamic water flow and sedimentation processes during alpine flash flooding events in gullies with large varying gradients and high-intensity sediment transport The reliability of this mathematical model was verified with data from a variable-slope gully model and the flash flood event in Gengdi Village. An OPENMP interface was added to the model based on the flow and sediment modules to perform multicore parallel calculations of the flash flooding process, which greatly improved the calculation efficiency compared with conventional serial computation methods
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
