In a river system, the confluence of two rivers is a very important issue. This is due to the confluence can affect the morphology and hydraulics in both upstream and downstream. The aim of this study is to determine the effect of hydrodynamics on the spread pollutant of TSS in the confluence of two rivers, i.e., main stream and lateral stream, through a mathematical model. The model is built based on the law of conservation of mass, the law of conservation of momentum, partial differential equations in two-dimensional depth-averaged surface-water flow and the continuum principle. It is further solved numerically by using finite volume method, i.e., QUICK scheme, because it has both accuracy and numerical stability relatively good. These numerical results are then simulated using MATLAB software. For the numerical simulation, we take a case example of TSS dispersion in the Kali Surabaya River. Therefore, data of TSS and river hydrodynamic are obtained from the government company of Perum Jasa Tirta I. Numerical simulation of the model is further performed on location Karangpilang bridge until Sepanjang bridge, with pollutant discharge from a paper industry and an oil industry. The numerical results indicate that the TSS pollutant dispersion either in longitudinal, i.e., horizontal, or lateral, i.e., vertical, direction in the confluence of two rivers tends to decrease when the distance grows longer and decreasing when the time grows up.

confluence of two rivers, total suspended solid, finite volume methods, QUICK.