Due to increasing number of world population and deficiency of the reliable resources of suitable water, there is a highly request for optimal use of both surface and ground water. The continuous growth of surface water pollution especially in developing countries is one of the most critical issues for human communities. In this regard, using mixing processes of the pollutants to refine and make the possibility of reusing the polluted water is one of the valuable methods to increase the amount of usable water. Transverse mixing coefficient is one of the hydraulic parameters of flow by which the amount of self-refinement and dilatation of rivers can be estimated. This thesis investigates an experimental method for measuring and evaluating the hydraulic parameters of a surface water flow which are useful for refinement and re-using polluted waters. The investigation focuses on effects of local roughness on transverse mixing coefficients of a flow that are key parameters to estimate the amount of self-refinement and dilatation of rivers. To investigate these effects, the experimental method was initially employed to determine the transverse mixing coefficients of a flow by injecting a pollutant in the center of an open channel flow and measuring its concentration at several sections located downstream of the injection point. To demonstrate and evaluate the method, two rectangular straight open channels were used. The length, width, and depth of the channels were 7m x 0.32m x 0.35m for the first one and 20m x 0.6m x 0.6m for the second one, respectively. The maximum flow rate of the first channel was 16.4 lit/s and for the second channel it was 75 lit/s. Water was circulated in the channels, the flow was uniform and the depth of water was controlled with a gate way. Subsequently, by means of submerged blocks, various bottom roughness configurations were arranged and tested for the channels to investigate their effects on the measured coefficients. Using the mass conservation equation for calculating the spreading rate of materials and their concentration in channels, the results showed that for the first channel, the arrangements of blocks could increased or decreased the transverse mixing coefficients of the flow, depending on the shape of roughness. However, for the second channel the existence of blocks with any configuration overall increased the transverse mixing coefficient. Also, increasing the distance of the blocks from the polluting source increased the effects of the bottom roughness on the coefficients and mixing length for the first channel, however, no significant changes was observed in the coefficient of the second channel. Furthermore, the test results showed that decreasing the alternative Keywords : Transverse mixing coefficients, surface water pollution, self-refinement of surface water, alternative local roughness, complete mixing length.