**4.1 Model validation**

For validation purpose, a sampling and measurement campaign was carried out in the Coatzacoalcos river stretch from upstream of Minatitlan city (17º 57' 00" N - 94º 33' 00" W) to its mouth in Gulf of Mexico (18º 09' 32" N – 94º 24' 41.33" W). The main objective was to obtain velocities, bathymetry and water quality at 10 points of the Coatzacoalcos River (Fig. 6). The information obtained through direct measurements and chemical analysis is primarily used for testing and numerical model validation.

Fig. 6. Measurements and sampling sites

Table 1 shows the water velocity magnitude, direction and location measured on the ten stations. These values were compared with the model results. Fig. 7 and Fig. 8 show a comparison between measured and calculated water velocities.

As shown in Fig. 7 and 8, the hydrodynamics numerical results correspond fairly well with field measurements. The model results show agreement in direction and magnitude of the measured velocity, which demonstrate that the model results are consistent and reliable to the real river behaviour. Therefore, it is considered that the developed model can be implemented and applied to different situations for the studied area.

Likewise, the water quality modules were validated by comparison with field measurements, observing that the model results are consistent with these measurements


and they are in the same order of magnitude. Fig. 9 shows some of the obtained results (each point represents a measurement station and the solid line the model result).

Table 1. Measurements of water velocity

58 Hydrodynamics – Natural Water Bodies

The model results show agreement with measurements of velocity direction and magnitude, as well with water quality parameters. Therefore, it is considered that the developed model can be implemented and applied to different situations for this study area and others rivers

For validation purpose, a sampling and measurement campaign was carried out in the Coatzacoalcos river stretch from upstream of Minatitlan city (17º 57' 00" N - 94º 33' 00" W) to its mouth in Gulf of Mexico (18º 09' 32" N – 94º 24' 41.33" W). The main objective was to obtain velocities, bathymetry and water quality at 10 points of the Coatzacoalcos River (Fig. 6). The information obtained through direct measurements and chemical analysis is

Table 1 shows the water velocity magnitude, direction and location measured on the ten stations. These values were compared with the model results. Fig. 7 and Fig. 8 show a

As shown in Fig. 7 and 8, the hydrodynamics numerical results correspond fairly well with field measurements. The model results show agreement in direction and magnitude of the measured velocity, which demonstrate that the model results are consistent and reliable to the real river behaviour. Therefore, it is considered that the developed model can be

Likewise, the water quality modules were validated by comparison with field measurements, observing that the model results are consistent with these measurements

primarily used for testing and numerical model validation.

Fig. 6. Measurements and sampling sites

comparison between measured and calculated water velocities.

implemented and applied to different situations for the studied area.

with similar characteristics.

**4.1 Model validation** 

Fig. 7. Comparison between measured and calculated velocities for the river mouth

A Study Case of Hydrodynamics and Water Quality Modelling: Coatzacoalcos River, Mexico 61

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.

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,

The simulation represents 30 days corresponding to dry and rain season. The numerical integration time or time step was, ∆t = 2.0 s. Fig. 11 shows the obtained result for resultant

**Parameter Dry season Rain season Flow rate (m3/s)** 405 1104.9 **Cross section (m2)** 812.4 2216.7 **Flow velocity (m/s)** 0.5 0.5 **Flow direction (°)** 58.78° 60.39 **Manning coefficient** 0.025 0.025

**4.2 Numerical modeling** 

Fig. 10. Grid configuration

Table 2. Initial data for simulations

velocity.

**4.3 Results of hydrodynamics simulations** 

cross-sectional area, flow velocity and direction.

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
