The Effect of Suspended Load on the Lower Discharge of Large Dams using Flow-۳D Numerical Model

Bottom outlets in dams are critical structures for regulating flow and releasing sediment, particularly during floods and emergency situations. These systems play a vital role in ensuring dam safety and effective water management. While previous studies have primarily focused on flow simulation without considering suspended sediments, this omission overlooks a significant factor influencing outlet performance under flood conditions. Suspended sediments increase the density of the flow, which can substantially alter the hydraulic characteristics of the outlet system. This study investigates the effect of suspended sediment concentration on the hydraulic efficiency of bottom outlets, using Flow-۳D software to model the flow dynamics within the bottom outlet of Siazakh Dam. Siazakh Dam is located ۷ km south of Diwandara and ۹۵ km north of Sanandaj city in the Kurdistan province of Iran. Initial calibration and validation of the model were performed using laboratory data. Simulations were conducted with suspended sediment concentrations of ۳۰۰۰, ۶۰۰۰, ۹۰۰۰, and ۱۲,۰۰۰ ppm to examine the impacts on discharge and key hydraulic parameters such as flow velocity and pressure distribution. The results reveal that as sediment concentration increases, the discharge rate decreases significantly due to higher flow density, which alters both velocity profiles and pressure distributions. At higher concentrations, discharge reduction exceeded ۲۰%, accompanied by notable variations in pressure and flow velocity across different sections of the outlet system. This study highlights the importance of accounting for sediment load in the design and operational management of dam outlet systems, as this factor can significantly influence performance. Future studies could further investigate the impact of varying sediment shapes and sizes on system efficiency.

کلیدواژه ها:

Bottom Outlet ، Suspended Sediment ، Flow-۳D ، Numerical Modeling ، Hydrodynamic