A coupled numerical hydrodynamic water quality model of the river environment

After 5 years of innovative research, Professor WANG Jianhua and his group, from the State Key Laboratory of Simulation and Regulation of the Water Cycle in River Basins of the China Institute of Water Resources and Hydropower Research, have developed a new coupled numerical hydrodynamic water quality model of the river environment.

The model has been applied in the Luan River Basin where the model parameters were calibrated and validated. Their work, entitled “Integrated Simulation and Assessment of Water Quantity and Quality for a River Under Changing Environmental Conditions”, has been published in the Chinese Science Bulletin (In Chinese, 2013, No.12).

Because of the increasing cumulative effects of the environment on water quality, many aquatic systems cannot meet the demands for water resource development and use. In general terms, water quantity and quality simulation and assessment methods have several shortcomings, for example, water quantity and quality are assessed separately, they are assessed at limited spatial and temporal scales, assessment is static rather than dynamic and objects are evaluated individually.

To address these problems, and to help us understand the interactions between water quantity and quality in different water bodies, we need to develop a comprehensive assessment method using current available information on water resources, and on pollutants that are generated by hydrological processes, such as runoff generation, conflux, and drainage. In short, we urgently need to establish dynamic methods for integrated simulation and assessment of river water quantity and quality.

The river hydrodynamic model was validated by comparing water level and flow data collected at the Guojiatun and Sandaohezi stations on the main stem of the Luan River in 2006. Water level and flow were simulated at these sites, and compared with actual data (Figure 1). The results showed that the difference between the simulated and observed flow was less than 10% for 85% and 82% of the flow data from the Guojiatun and Sandaohezi stations, while 90% of the differences between simulated and observed water level were less than 10%, all of which fully satisfied the accuracy requirements for the model application.

The area of the Panjiakou Reservoir fits into a maximum of 64 grid cells in the horizontal direction and 69 grid cells in the vertical direction. This means that, when the horizontal computing unit is 1 km and the vertical computing unit is1m, there are 2246 calculated grid cells. The measured TN and TP concentrations were used to validate the water quality characteristics of the reservoir. Validation results are shown in Figure 2. Comparison of the monitored and simulated values showed that the average error for each sampling site was 12% for TP and 9% for TN. Although some sites had relatively large errors, overall, the model satisfied the application requirements.

Under constantly changing environmental conditions, it is clear that dynamic changes in river water quantity and quality are closely related, so we need to develop new scientific methods for integrated simulation and assessment of these two characteristics of water. In this study, we constructed and validated an integrated model to simulate river system hydrodynamics and water quality. The validation indicated that the error between the simulated and monitored values was comparatively small, demonstrating that (1) the model satisfied the demands for its application and (2) it was possible to simulate integrated dynamic changes in water quantity and quality.

The water environment in the Luan River Basin has been dramatically altered because of global climatic change and highly insensitive human activities. Results of the integrated dynamic assessment model for water quantity and quality show that the water in the upper reaches of the Luan River Basin were classified from type I to type V as follows: 11.9% (type I), 16.9%, 32.3%, 14.2%, 19.4% and 5.3% (type V). In addition, the water quality of the main water body of the Panjiakou Reservoir was classified as type IV.

We need integrated water quality and quantity simulation and assessment for effective water resource management. Although we have achieved integrated simulation and assessment of river systems, we still need to improve statistical analyses of inflows of both point and diffuse source pollutants. In addition, the current hydrology and water quality monitoring data series are relatively short, so the conclusions from integrated simulation and assessment cannot show either the impacts of anthropogenic activities or climate change. Therefore, there is a need for further research on the integrated simulation and assessment of water quantity and quality under changing environmental conditions.

See the article: Wang J H, Xiao W H, Wang H, et al. Integrated simulation and assessment of water quantity and quality for a river under changing environmental conditions. Chin Sci Bull, 2013, 58(12): 1101-1108 doi: 10.1007/s11434-012-5622-0

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