<p>The Caspian Sea, a treasure trove of biological diversity, is threatened by accumulated suspended sediments due to the river sediment plume during floods. This study, which uniquely assesses the sedimentary alterations occurring on the southeastern shores of the Caspian Sea due to sediment plume from the Talar, Tajan, and Neka rivers during flood conditions, is of considerable value. The initial phase involved simulating the flow rate and sediment flow rate of the rivers under flood conditions. Subsequently, a comprehensive model was devised for the southeastern coasts of the Caspian Sea, encompassing the simulation of waves, sea currents, and sediment transport. A numerical model was then deployed to ensure the accuracy and reliability of our findings. This model is developed by considering the presence and absence of the rivers’ flow, and the resulting data were meticulously compared, demonstrating the thoroughness and reliability of our research. The findings revealed a direct correlation between the increase in flow rate and sediment concentration from the rivers and the heightened concentration of suspended sediments in the model. However, it was noted that this concentration diminished rapidly due to the interplay of sedimentation, transport, and diffusion within the sea environment. Upon discharge into the sea, the sediments dispersed eastward, extending into deeper waters and eventually reaching the western coasts of Neka and Amirabad ports. This led to sedimentation along the neighboring beaches.</p>