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The hydrodynamic model is essential for building a water quality model for rivers, lakes, estuaries, and other water systems. Most model software, such as HEC-RAS, can perform a complex hydrodynamic surface water body and limitations to represent water quality for the corresponding area. In contrast, other models, like WASP, can simulate a wide range of contaminants in a multidimensional geometry of rivers, estuaries, lakes, and reservoirs. Still, it requires flow information from separate hydrodynamic models. This article aims to develop a comprehensive water quality model of the Shatt Al Arab River south of Iraq by linking HEC-RAS with WASP. A variety of software techniques has sequentially been used. This software includes GIS for DEM modification, HEC-RAS for the hydrodynamic model, Python code with PyCharm to run the external coupler, WASP software for advective and dispersive contaminant transport, and finally, WRDB software for full calibration process and results display. The results showed successful transportation of flow information had been achieved. Moreover, the article described an effective calibration process by plotting comparison graphs and statistical summaries to make the appropriate decision. Another goal of this work is to collect the equations and associated reaction rates of source/sink kinetic for eutrophication’s state variables.

In this study, the analysis was carried out concerning previous changes in land use/land cover (LULC) for 2 years, 2000 and 2020, and their impact on water resources in the Diyala River Watershed in Iraq was assessed. The Soil and Water Assessment Tool (SWAT) model is a hydrological model used to perform the hydrological modeling process for LULC maps. The data for LULC were collected using the Landsat satellite with a resolution of 30 m, and it was classified using geographical information systems (ArcGIS). Using the confusion matrix, the accuracy of the maps for the years 2000 and 2020 was evaluated, the overall accuracy was more than 90%, and the kappa coefficient (ka) was more than 88%, which indicates the accuracy of the classification and is ideal for use in modeling work. SUFI-2 included with the SWATCUP program was used to perform the calibration and the results were validated for the outflow of the two gauging stations within the study area of Hemren station and Derbendikhan station as a monthly time step for a baseline map LULC 2000, in the period 1996–2020 with 4 years as warm up. Coefficient of determination (R 2), Nash–Sutcliffe efficiency (NSE), and percent bias (Pbias) were used, which were the most common indicators for evaluating the performance of the statistical model. The results indicated that the values of R 2 during the calibration and validation processes were (0.84–0.88) and (0.85–0.87), respectively; the NSE was (0.87–0.85), and the Pbias was (4.2–6.8)% and (5.8 to −4.1)%, respectively. Therefore, the calibration and verification results were good and satisfactory. In addition to the two LULC maps for 2000 and 2020, the parameters of the modified SWAT model were utilized to estimate the effects on the Diyala River Basin. The study found that LULC change affects basins and sub-basins differently. At the basin, hydrological parameters were largely unaffected by LULC changes. However, at the sub-basin level, the water yield and the surface runoff were changed between (−6.45 to 4.67)% and (−2.9 to 9.88)%, respectively.

In this study, a comprehensive 2D hydrodynamic model, integrating HEC-RAS with the Water Quality Analysis Simulation Program (WASP), was developed to assess the water quality and eutrophication levels of the Shatt Al-Arab River in Basrah, southern Iraq. The Shatt Al-Arab River, as the primary water source for Basrah province, features numerous branches along its course, necessitating a detailed analysis of its water quality dynamics. The focus of this investigation was to simulate the river's behavior through a model encompassing a seven-branch network within Basrah city. Employing the EUTRO module, the model simulated key state variables, namely temperature (T), ammonia (NH3), nitrite/nitrate (NO2/NO3), organic nitrogen (ON), total phosphorus (TP), inorganic phosphorus (IP), phytoplankton (PHYTO), dissolved oxygen (DO), and carbonaceous biochemical oxygen demand (CBOD), over a four-day period. The model's outcomes revealed significant fluctuations in the concentrations of ON, NH3, NO3, organic phosphorus (OP), IP, and CBOD at the Basrah Center site, attributed primarily to point source pollution from the river's main branches. Furthermore, the tidal influences were observed to significantly impact the concentrations of these state variables. Notably, the Shatt Al-Arab River exhibited a mesotrophic state throughout most of its course, indicating a moderate level of productivity. This finding is crucial for understanding the river's ecological status and for guiding effective water management strategies. In-depth analysis of the model's results offers valuable insights into the river's water quality dynamics, highlighting the significant impact of local anthropogenic activities and natural tidal phenomena on nutrient concentrations and overall river health. These findings are instrumental for environmental planning and management in the region, particularly in addressing eutrophication and its associated challenges. The study underscores the need for integrated hydrodynamic and water quality modeling to effectively manage and preserve vital water resources in riverine ecosystems. [ABSTRACT FROM AUTHOR]