Two-dimensional unsteady modeling of the Bamdej wetland hydrodynamic and quality

One of the most important issues in modeling wetland basins is estimating water balance by simulating its hydrological components, For which, various software was developed. DYRESM model was applied to indicate the water quality conditions of the Torogh Dam reservoir (KHAYAMI et al., 2009) and Fifteen-Khordad dam reservoir (ETEMAD et al., 2009) by examining the temporal changes of temperature, salinity, wind speed and dissolved oxygen parameters. Using MIKE SHE model, water balance in Paya Indah Wetlands (PIW) watershed in Malaysian was estimated (Rahim et al., 2012). CE-QUAL-W2 2D model was used for thermal and oxygen modeling in the Sefidrood dam reservoir (Taheri et al., 2014). Modeling of water level changes due to breakwaters in Anzali International Wetland was investigated using MIKE 21 numerical model (Juston and Kadlec, 2019).In this research, a qualitative and quantitative two-dimensional model of Bamdej wetland is developed using MIKE 21 software to operate and manage the wetland for the first time. The model is calibrated and validated using measured data over a one-year period. Finally, changes in hydrodynamic parameters of water depth and velocity in x and y directions and qualitative parameters such as temperature, dissolved oxygen, nitrate, ammonia are analyzed.

Bamdej wetland is located between 48˚ 33’ to 48 ˚ 39’ longitude and between 31˚ 41’ to 31˚ 47’ latitude in Khuzestan province which is far from northwestern Ahvaz city about 40 kilometers.The two-dimensional model, conducted on Bamdej wetland using the MIKE 21 model, is an unsteady model which applies laterally averaged depth-(in X- and Y-direction), revealed by equations 1-4. The hydrodynamic and quality parameters used in this study were shown in ‎Table 1. Using field surveying data initial values of Manning’s roughness for the river bed and the flood plain of the wetland were chosen. ‎Fig. 3 shows the points at which flow and pollution resources were considered. Then, the model results were validated by changing the initial values of the roughness. Finally, boundary conditions, ‎Table 4, were applied and run. The parameters related to determining the time step of the calculations were considered according to ‎Table 5.

Taking into account different values ​​of the Manning coefficient, the final values ​​of the Manning roughness coefficient are equal to 0.04 for the riverbed and 0.06 for the right and left floodplains. Due to the limited data available in the hydrodynamic model, only the roughness coefficient and the pollutant transfer model, only the scattering coefficient parameter (as the most important parameters) were calibrated. For calibrating the roughness coefficient, the most agreement was made between the computational and observational zones of the wetland.The model outputs include the mentioned hydrodynamic and qualitative parameters during one year of simulation time with 2.5 hours. Run times for a year take about 36 hours, and since wet and dry seasons are experienced during the year, an acceptable methodology can be enumerated. We applied ArcGIS software for analysis and zoning of variables. the results are presented only for a limited time in ‎Fig. 4 to 11.The amount of water depth in Bamdej wetland is mostly less than one meter, although it reaches about 2 meters and even up to 2.6 meters in some places. The average depth velocity varies between 0.05 to 0.2 m / s in Bamadj wetland (‎Fig. 3 and 4). Comparing depth magnitudes (‎Fig. 4) and the amounts of water quality parameters (‎Fig. 5 to ‎11) throughout Bamdej wetland revealed that where the depth is greater the values of quality parameters are higher, consistent with the results of previous research.The high concentration of dissolved oxygen in the lagoon reaches up to 5 mg / l, but high levels occur in the main bed. The same is true of biochemical oxygen demand values. However, the maximum ​biochemical oxygen concentration (2 mg / l) is less than the dissolved oxygen concentration.Ammonia concentration varies between 1 and 3; however, the slightest changes and high values ​​ observe only in a few points among the qualitative parameters.In general, the results showed that the simulation accuracy is about one percent, concluded that the prepared two-dimensional and unsteady hydrodynamic model has good accuracy and can calculate the flow parameters and the lagoon area with acceptable accuracy.

Hydrodynamic and quality maps of the wetland procured by two-dimensional modeling of hydrodynamic and quality of Bamdej wetland, developed in this research, show the proper Manning's roughness coefficients for the river and flood plain are 0.04 and 0.06, respectively. Furthermore, the hydrodynamic and quality model is accurate and could precisely calculate flow parameters and wetland zones.