The Environmental And Hydrological Effect In Tidal Plain:time-spatial Variation And LID Respond

Shanghai is one of the largest metropolitan areas in the world, during the rapidurbanization of last decades, impervious surface expanded continually and became a mainfactor influencing environmental quality. This study discussed the time-spatial variation of threshold effect between impervious surfaces and water quality based on the Arc GIS and R segmented model. Otherwise, L-THIA-LID model was used to simulate whether and how LID practises influence hydrologic effect. This study can offer suggestions and references and help guide future planning efforts aimedat urban development, ecosystem health, environment management and LID practises projects.(1) Obviously time and spatial variation effects were found between the impervious surfaces and water quality. Results showed that the threshold value of average level grown from 30.93% to 47.04% during 1989 to 2010, which indicates that urbanization can reduce the impervious surfaces impact on river health. City centre, Pudong district and Nanhui district were three typical areas represented high, middle and low level of urbanization, threshold effect at these three levels were listed as Nanhui, Pudong and city centre from large to small, which shows that the threshold effect were more significant at low developed area. Otherwise, seven water quality indicators including CODMn, NH3-N, TN, TP, DO, Phenol and Oil have differences on the responding of threshold effect, CODMn has the closest relationship with threshold effect and Phenol and Oil have the worst. Because Phenol and Oil are mostly discharged from industry, so the threshold effect between impervious surfaces and Phenol and Oil were worse when industrial discharge was well controlled.(2) Percentages of building roofs, roads and green land are variational for different land uses. High density residential has the most roads with the percentage of 42.06%, industrial has the most building roofs with the percentage of 30.22% and low density residential has the most green land with the percentage of 49.88%. High density residential has the lowest standard deviation and industrial has the highest because of their construction distribution.(3) Runoff volume grows obviously form 2000 to 2010 due to the transforming of land uses. Nanhui district has the highest annual growth rate of 2.67% during ten years, followed by Pudong district and city centre. Also, reduction of impervious surfaces can cut runoff volume significantly, city centre has the most reduction of runoff than other area when decrease impervious surfaces at the same level. Results also shows that reduction rate of runoff volume was higher when rainfall was less.(4) When discussing the LID practises, porous pavements has a better result on reducing runoff volume, followed by green roofs. Green roofs combining with porous pavements and bio-retention performed better than Rain barrels combining with porous pavements and bio-retention. Porous pavements were the most suitable practises to industrial, commercial, high density residential, green roofs were the most suitable practice to middle density residential, and bio-retentions were the most suitable practise to low density residential.