The Dujiangyan Irrigation System (DIS), located in the western portion of the Chengdu Plain at the transitional junction between the Qinghai-Tibet Plateau and Sichuan Basin, has been in operation for about 2300 years. The system automatically uses natural topographical and hydrological features and provides automatic water diversion, sediment drainage and intake flow discharge control, thus preventing disastrous events in the region in a ‘natural’ way. Using a numerical modeling approach, this study aims to investigate the reasons behind this natural behavior of the system and provide a better understanding of the complex mechanisms which have caused the sustainability of the DIS for over two millennia. For this purpose, a two-phase flow model based on the Shallow Water Equations (SWEs) is developed to simulate the fluid and sediment motions in the DIS. A coupled explicit-implicit technique based on the Finite Element Method is applied for the fluid flow and a Sediment Mass (SM) model in the framework of the Lagrangian particle method is proposed to simulate the sediment motion under different flow discharge conditions. The results show how different components of the DIS make full use of the hydrodynamic and topographical characteristics of the river to effectively discharge sediment and excess flood to the downstream and create an environmentally sustainable irrigation system.

This study aims to develop a robust sediment transport model focusing on the vertical two-dimensional water–sediment two-phase flow in which sediments are constantly interacting, hitting each other, gradually becoming smoother and smaller, and accumulating when velocities decrease. The grid-based models currently available can be cumbersome when dealing with phenomena that require replication of this water–sediment interface. Therefore, a two-dimensional water–sediment two-phase flow model based on Smoothed Particle Hydrodynamics (SPH) is established in the macroscopic scale to simulate a large amount of sediment accumulation and propagation typical of a landslide caused by a dam break. In this study, water and sediments are treated as two kinds of fluids with different densities and viscosities to accurately simulate the flow structure, the sediment transport, and the water–sediment interaction process. The interaction model developed treats the interface of the two phases within a unified framework. The model developed was then tested against three applications, and the results obtained confirmed its accuracy in correctly replicating the movement of the sediment phase. The preliminary results obtained can be helpful in providing further insights into the mixing of water and sediments and their propagation following a dam break and the consequent wave profile generated.