Water Quality Simulation And Total Maximum Daily Load Of The Old Haihe River

As one of Chinese seven major river systems, the Haihe River always plays an important role in the development of politics, economy and culture of Tianjin. For the past few years, there was a direct relationship between the deterioration of the water quality of Haihe River and the mismanagement of its tributaries. As one of the main tributaries influencing the water quality of Haihe River, the research on hydrodynamic, water quality and pollution total control of the old Haihe River is of great theoretical and practical significance.This paper analyzed the characteristics of pollution sources and pollutants of the old Haihe River, and evaluated its water quality. Then MIKE 21 was chosen to simulate hydrodynamic and water quality. At last, the river total maximum daily load was calculated. The main work and conclusions can be seen from the following.(1) The investigation and study of the basic conditions such as geographical location, natural conditions and channel status of the old Haihe River, and the collection of topography, hydrology and meteorology information of research area provide data conditions for hydrodynamic model building. The rainfall runoff was confirmed as existing main pollution sources.(2) According to the continuous water quality monitoring by setting the monitoring cross sections, the varieties, morphology and properties of the main pollutants were mastered. Based on the evaluation on water quality using single factor index evaluation method, COD was chosen as the key pollution indicators to analysis the changing trend and total amount controlling.(3) The calculation principles and characteristics of MIKE 21 were fully studied. HD and AD modules were used to simulate Hydrodynamic force and water quality. After the definite condition setting and parameter calibration using trial and error, empirical value and inverse method, the hydrodynamic and water quality coupling model was established. Verification results showed that the model was reliable.(4) The changes of COD under different conditions were simulated and analysed. When the weather was not rainy, the water quality of the old Haihe River would become better with each passing day until the steady concentration by degradation. When the COD background concentration was 15 mg/L, the water quality would be above the surface water Class V water standard under rainfall of 20 mm. Then it needed 11.5 days to recover to the initial level. If the COD background concentration was 30 mg/L, it needed 3.5 days to meet the standard and 7 days to the initial level. After a rainfall of 83 mm, the gate would be opened. Under the background concentration of 15 mg/L, it needed 11 days to meet the standard and 22 days to the initial level.(5) Using the selected model to calculate the total maximum daily load of COD under background concentration of 15 and 30 mg/L, the results were 198.4 kg/d and 175.4 kg/d. Guarantee suggestions and measures for the total amount control target were put forward according to the actual situation of the old Haihe River.