Effect of Environmental Factors on Numerical Simulation of Coliform in Riverine Basins

Dynamic modelling of fecal coliform is now very important to the environmental managers, since keeping the concentrations of those pathogens around the accepted and universal standard values is one of the essential principles for healthy biological environment. One of the main parts of modelling FC is an accurate estimation of mortality rate. In many commercial numerical models, the users are only able to define a constant value for this coefficient for the whole simulation time. But the mortality rate or decay coefficient is highly dependent on the environmental conditions, such as temperature, turbidity, pH, EC, and etc. In this research Karoon River (Mollasani-Farsiat reach) is selected as a case study and the hydrodynamic and water quality numerical FASTER model was used to find the best relationship between the decay coefficient and environmental parameters. A 3 year period (2006-2009) was used for model calibration and developing of those relationships, and a 1 year period (2009-2010) was used for model verification. Comparison of the measured and predicted FC values for the both calibration and verification periods showed that, using the dynamic variable decay coefficient as a function of environmental parameters (turbidity and temperature) was able to improve the model accuracy more than 23% and 20% in error estimation of FC concentration values in comparison with the corresponding results obtained for a constant decay coefficient (0.05 (1/hr)).