The release of storm water for city catchment is increasing because of urbanization with rapid economic growth, which directly reduces permeable surfaces and influences environmental self-purification. As a potential pollutant medium, storm water transfers considerable amounts of pollutants into bodies of water, which displays a potential environmental risk. There are several passive technologies available for storm water treatment, including best management practices. Lamella settlers are passive treatment systems, traditionally used in wastewater and industrial water treatment that have the potential application in urban, agricultural, and construction runoff treatment. Another treatment mechanism used in wastewater and industrial applications is electrocoagulation (EC). EC works to remove the pollutants by enhancing the flocculation process. As a type of passive technology, lamella settler is widely applied to treat water runoff from urbanization, agriculture, and construction sites, from which the impact of water quality in environment by human can be limited. The efficiency of lamella settler is well concerned by people to optimize the treatment process, the turbidity/concentration distribution through the system should be modeling according to dimension of the tank. This project will develop a model to predict turbidity/concentration at effluent using mass balance considering unsteadiness, advection, transport, settling, and dispersion in the settler. The developed model will be applied to assist design of lamella settler in large scale, which will also be compared with the experimental measurements.