This study investigates the effects of drawdown flushing in hydraulic structures on sediment transport and morphological changes within and around reservoirs. Utilizing the Smoothed Particle Hydrodynamics (SPH) method, the research focuses on local erosion induced by drawdown flushing and examines the interaction between water and sediment. To validate sediment behavior, we analyzed a granular dam-break model using three rheological models: Herschel-Bulkley (H–B), Bingham, and μ(I). Two drawdown flushing scenarios are explored, considering mobile bed conditions at the reservoir's inlet and outlet. The study area is categorized into three zones: water, sediment, and the interface between water and sediment, with the μ(I) rheological model applied to the sediment portion. Within the interaction zone of sediment and water, the Shields parameter is defined based on Julien's relations to determine the yield stress of sediments. This value is then incorporated into the H–B model for sediment in this specific zone. Additionally, the drag force is introduced into the momentum equation within this zone. The study's findings are rigorously validated against existing numerical and experimental studies, affirming the credibility of the modeling approach. This research provides valuable insights into the complex dynamics of sediment transport during drawdown flushing in hydraulic structures.