Study On Hydrodynamic, Pollutant Transport And Dispersion Processes In The South Yellow Sea

Based on the planned Wastewater Marine Disposal Project of Nantong, Jiangsu Province, the studies on the characteristics of hydrodynamics, pollutant transport and dispersion in the marine area near the sea outfall and the potential biological impact of the Project have been conducted considering the complex conditions of shoal and fishery in the study area. The methodology followed the system engineering concept in that a complete modelling system consisting of two- and three- dimensional, integrated hydrodynamic and water quality numerical models were applied to analyse the hydrodynamic conditions and characteristics of pollutant transport and dispersion after the wastewater is discharged into the sea. The environmental impact has been analysed from the mixing zone, dilution field, potential biologically affected area and plume intrusion probability. The study results possess a general significance theoretically and practically.The main study results are as follows:1. System engineering concept: The wastewater marine disposal project is regarded as an integrated system considering such factors as the location selection, modelling, and environmental and biological impact. The modelling system comprises models with the coarse, medium and fine resolutions in order to study the general and detailed hydrodynamic and water quality conditions in the area in question;the characteristics of hydrodynamics and pollutant transport and dispersion in the study area, and the potential biological impact were analysed in a systemic and hierarchical way.2. Hydrodynamic study: A new bathymetry processing technique including horizontally no-seam connection and vertically smooth processing was presented for complex bathymetry condition such as the beaming shoal in the study area;a two dimensional hydrodynamic model with the orthogonal curve grid system was established covering the beaming-shaped shoal area in North Jiangsu and the South Yellow Sea near the Yangtze Estuary. A two dimensional hydrodynamic model with the rectangular grid system was established covering the offshore area between the Haozi Port and Tanglu Port. A three dimensional hydrodynamic model with the horizontally rectangular grid system and vertically fixed coordinate system was established for the sea area near the outfall. Calibration and verification of these models showed a good agreement with the historic measurements. Two new AEBL46 and AEBL 46 algorithms were presented for transfer of water level information and flow velocity information respectively atthe boundary of a three dimensional model from a broader, two dimensional model. The algorithms have been successfully applied in the three dimensional model.3. Pollutant transport and dispersion: A two dimensional water quality model was established covering the offshore area between the Haozi Port and Tanglu Port and a three dimensional water quality model was established for the sea area near the outfall to simulate the pollutant transport and dispersion process in different spatial and temporal scale;Four factors four levels orthogonal test was carried out to determine the COD decay coefficient used in the model;the two dimensional model was applied to identify the mixing zones of different project options;a new concept of hierarchical mixing zones was put forward which can be analysed by a three dimensional model;the dilution field for conservative matters was focused on in the study so as to evaluate the distribution and mixing zones of other pollutants;pollutant intrusion probability to sensitive areas and mixing zones was analysed using statistics theory to reflect the exposure strength by the pollutants.4. Study of potential biological affected area: A new concept of safe dilution degree and potential biologically affected area was put forward based on the safe concentration of chronical impact in sensitive fishery area;the potential biologically affect areas were calculated for all project schemes and the distribution of these areas in stipulated marine function areas were analysed to determine the compatibility;the probability of the dilution degree and concentration distribution in the biologically affected area was calculated using statistics theory.The study has systemically analysed the characteristics of hydrodynamics and pollutant transport and dispersion in the offshore area of the South Yellow Sea. The results form a scientific basis for decision-making, design and construction support of the Wastewater Marine Disposal Project of Nantong, and for marine pollution control and resources utilization in general as well. A few new concepts and methods raised in the study will provide new research topics for wastewater marine disposal engineering. Suggestions of future research and study topics have been put forward in the report.