**4.2 Numerical modeling**

60 Hydrodynamics – Natural Water Bodies

Fig. 8. Comparison between measured and calculated velocities for the river middle part

Fig. 9. Concentration profiles for measured and calculated DO, BOD and Vanadium

The initial step in the methodology implemented was the numerical grid generation, using specialized software. Initial and boundary conditions (tide, the level of free water surface, and hydrodynamic condition) were imposed; the model was set up with information gathered in the measurement campaigns, as well as water balances to determine the river dynamics.

The mesh or numerical grid was created using the program ARGUS ONE (http://www.argusint.com), Fig. 10 shows the calculation grid system for Coatzacoalcos river stretch, which has a length of about 25 km, spacing of Δx = Δy = 100 m. The grid has 163 element in the X direction and 211 points in Y direction, giving a total of 34393 elements.

Fig. 10. Grid configuration

Two simulation scenarios were performed representing dry season and rain season. The input data required are shown in Table 2: Manning roughness coefficient, hydrological flow, cross-sectional area, flow velocity and direction.


Table 2. Initial data for simulations
