Impacts Of Land Use Change On Runoff Of Shanghai Central City And Relevant Environmental Effects

The paper was based on the project Study on the Effect of Runoff Storage and Pollution Reduction of Urban Green Space which was sponsored by Science and Technology Commission of Shanghai Municipality (No.04DZ12024) . The data in this paper was based on three ways, including collecting historical literature, selecting the data from related government offices, and field monitoring, etc. Both qualitative and quantitative methods were used to analyze the impacts of land use change on runoff and relevant environmental effects.On the basis of brief analysis on the land use change over 10 years (1994-2003) , the paper modeled the hydrological behaviors of a study area (48km~2), which was composed of 28 discrete small watersheds along the Suzhou River, through the application of the Soil Conservation Service curve number (CN) method. According to the results, modified the SCS model and extendedly applied to estimate the direct runoff in Shanghai central city. The possible effects of land use change on runoff generation and pollutant load of runoff were discussed in this paper.The main research contents and conclusions can be summarized as the following:According to the CN tables given in the National Engineering Hand Book-Part630, the suitable CN values for Shanghai central city were preliminarily determined. Implemented the SCS model to two land-use scenarios (2000, 2003) and calculated the runoff yield of the study area for 45 rainfall events associated with different amount of precipitation. The results of lower approved rate (28.57%) showed that the application of SCS model in Shanghai needed some amendment. The initial abstraction (I_a) - potential maximum retention (S) relation in the SCS method was assumed as I_a=λS. Adjusted the X value in response to the ratio of I_a to P (total rainfall) in a specific watershed. The pilot calculation results indicated X values of about 0.03 for AMC I , 0.08 for AMCII and 0.20 for AMCIII would be more appropriate for using in determination of direct runoff from given rainfall with a higher approved rate (71.34%) .Based on the contradistinction of land use among 1994, 2000 and 2003, using the data of land use and rainfall estimated the runoff amounts in three assumed typical hydrological years through the modified SCS model. From 1994 to 2003, land use change due to urbanization led to decrease of 0.0474, 0.0522 and 0.0399 in runoff coefficient under the assumption of 900mm, 1100mm and 1300mm annual precipitation in Shanghai central city. Besides, the pollutant loading amounts of surface runoff increased obvious. The variance both on runoff coefficient and the pollutant load amounts demonstrated the land use change had crucial influence on runoff.With the same rainfall, the comparison of runoff producing capacity in variant intensive of land use showed the rainfall-runoff relationship was affected by the change of land use and treatment. Particularly, the urban green space had standout representation on storing runoff and postponing the runoff producing time.By using the laboratory rainfall analog facility, quantitatively analyzed on the difference of water holding capacity between exposed soil and covered soil under three given rainfall intensities. At the meantime, the pollutant concentrations of yield water infiltrating through two sample soils were measured and contrasted. Finally, the digital information approved that the covered soil was better than exposed soil both on holding water and reducing pollutants, such as COD, TN and TP.In accordance with the current situation of general plans for the utilization of land, urban drainage, flood prevention and non-point pollution in Shanghai, the integrated management for land use was discussed on the basis of the foregoing study.