Numerical Modeling of Pollution Caused by Nutrients in the Wetland by Using Two-dimension Equations of Hydraulic Flow Behavior of their Feeding Rivers

The present research studies the prediction of the changes and distribution of nutrients concentration (nitrogen and phosphor) by using a two-dimensional numerical model on the behavior of hydraulic water flow in the estuaries of the main river, Anzali Wetland and also show the location and time distribution of water quality parameters along with the horizontal category of velocity as well as water flow path. The modeling has been made by using the numerical model and based on mass transfer equation. In this research, the transport processes (advection) and penetration (diffusion - dispersion) have been considered separately in predicting nutrients concentration. To solve the equations that govern the water quality and flow, the finite volume and fractional step method has been used. The simulation of the concentration and water flow in the main river ending to the wetland (the estuaries and delta) was carried out by Flow 3D software which is a finite volume numerical model. In addition, a sub -model (auxiliary) was used for this model to predict the concentration of each one of the nutrients for different years and the geometric compatibility between this software and water quality model in which, the second degree multinomial interpolation regression method was used. This model was run for a 18 months period based on taking samples from the region subject of study and the lab tests. The standard method was employed for tests. The concentration of nutrients was calculated and measured for research period duration. The amounts calculated by the model showed good agreement with average amounts of lab measurement. To establish an increase in convergence in the results of numerical calculations and reducing fluctuations, the results obtained in two-dimensional calculation field (including speed of water and concentration of nutrients in it) were compared with the one-dimensional information extracted via HEC-RAS software and if necessary, the results obtained are corrected. After measuring the accuracy of the model by making different tests and certainty of its suitable function, the presented model could be used for predicting the quality of water in water environments.

کلیدواژه ها:

Wetland ، Water flow ، Finite volume method ، Water quality ، 2D Hydrodynamic model