Study On Water Renewal Capacity And The Transport And Diffusion Processes Of Pollutants In A Landscape Lagoon

In recent years, the development of water landscape is becoming a new hotspotgradually with the improvement of city modernization and the people’s livingstandard. During the process of the waterfront district landscape design, the designersoften lack of full attention to the water environment problems and lack of systemtheory knowledge, so that some water environment problems (poor hydrodynamic,deteriorated water quality et al) will be emerged during long term operation of waterlandscape. The health of a water ecosystem is governed by its physical, chemical, andbiological processes. One physical process that affects the health and water quality ofthe system and indicates its susceptibility to impairment is water renewal capacitybetween the lagoon and the open sea. Through the advection and diffusionmechanisms, the water mass is transported to the open sea where it is mixed with thesea. During this process, the pollutant is neutralized and mechanically removed fromthe ecological compartment.So it is important to study on water renewal capacity andthe transport and diffusion processes of pollutants for a landscape ecosystem system.In the study, we take a landscape lagoon as an example, to study the transport anddiffusion process in a reconstructed lagoon (Qilihai Lagoon) using residence time,exposure time using a three-dimensional numerical model. The model was calibratedand verified by using field measured data. The main works of this study are asfollows:(1) A three-dimensional numerical model-Environmental Fluid Dynamics Code（EFDC）was introduced in detail. The case of the Qilihai Lagoon was proposedbased on EFDC in this study and two structured grids were used to model it. One gridrepresented the present configuration of the lagoon and was applied for modelcalibration and validation. The other grid represented the configuration of the lagoonafter reconstruction and was used for studying the water renewal capacity in thereconstructed lagoon. The Qilihai Lagoon model was calibrated and verified by usingfield data measured, and the main parameters about the model was confirmed. Theresults showed that the model could accurately and effectively simulate hydrodynamicconditions in the lagoon.(2) The the reconstructed lagoon model was used to study the flow field in thelagoon. The influences of wind on flow field were also investigated. It would help usto understand the transport and diffusion processes of conservative substances. (3) The the reconstructed lagoon model was used to study the water renewalcapacity in the lagoon. The renewal time, residence time and exposure time were usedas timescales. The influences of wind and the depth and the number of the tidal inletof the lagoon on water renewal capacity were also investigated. It would help us tounderstand the spatial and temporal distribution the transport and diffusion ofconservative substances in the lagoon.(4) The the reconstructed lagoon model was used to study the transport anddiffusion processes of pollutants in the lagoon. The connectivity were used astimescales. The influences of wind and the depth and the number of the tidal inlet ofthe lagoon on transport and diffusion processes of pollutants were also investigated. Itwould help manager control the pollution and manage the water quality scientifically.