the basic equations used in the qual2kw model and the practical guide of model

human activities in the fields of agriculture, municipal and industry introduce significant amounts of nutrients and organic materials into the rivers and streams resulting in their contamination. computer models such as qual2kw are used extensively for water quality management of rivers and streams. the qual2kw model is a one dimensional, non-uniform, steady water quality model, which has been used by the united state environmental protection bureau and was developed based on the qual2e model. a water quality model provides a feasible framework by simulating the important physical, chemical and biological processes. qual2kw is able to simulate a number of components including temperature, ph, carbonaceous biochemical demand, sediment oxygen demand, dissolved oxygen, organic nitrogen, ammonia nitrogen, nitrite and nitrate nitrogen, organic phosphorus, inorganic phosphorus, total nitrogen, total phosphorus, phytoplankton and bottom algae. the main equation which the aforementioned model attempts to solve is the one-dimensional convection-diffusion equation which is applied for each constituent, except for variables related to river-bottom algae. applications of qual2kw are found in numerous cited literature. in this paper, based on the model manual, the equations used in the modelling process are described. also a practical guide for users who want to use this model has been presented.