Study On Suspended Sediment Concentration Change By Remote Sensing

Qiantang River (QTR) is the biggest river in Zhejiang province, China. Its Basin is the area having the fastest economic growth and the largest population in the province. With the dramatic development of social and economy in the region, severe environmental and resources related issues have been emerged, for example, wide-spread water pollution, soil erosion, and land degradation, etc., which have become great concerns to government, academic cycle, and citizens.Suspended sediment concentration (SSC) is one of the important and widely used parameters in the measurement of water pollution. It influences not only the optical transparency, turbidity and color of water body, but also transportation and deposition of particles in both drainage basin and river channel. However, there are few cases applying RS in QTR Basin. Therefore, it is of great significance in terms of practical and methodological aspects to conduct this study.Remote sensing (RS) is the science/technology mainly developed after 1960's, which is specifically designed for earth observation. Many successful cases have been demonstrated that RS is an effective tool to study issues in many aspects of environment and resources. This study applies remote sensing to monitor the land use/cover changes and determine water quality in QTR Basin. By integrating routine survey data of land use in 1985 with RS information in 1991 and 2004, we obtained the land use changes in the region from 1985 to 2004. With the field measured data used as calibration, we developed a linear model that quantified the relationship between SSC and Remotely sensed information in QTR Basin. The main results were as follows:(1) From 1985 to 2004, a clear trend was found, with crop land dramatically shrunk, but Garden Plot, and Urban and Industrial Area expanded. This tendency was even more evident from 1991 to 2004 than that from 1985 to 1991. For example, average annual increase rate of Garden Plot from 1991 to 2004 was 6.60%, while from 1985 to 1991 it was 2.89%;meantime, we found from 1991 to 2004, there was 52.1% of total Garden Plot transformed to Cultivated land, Woodland, and Urban and Industrial land. This dynamic was of significance for further investigation.(2) The human activities are the essential causes of land use change in Qiangtang River Basin. Among them, the population, crop production value, wood production value andfundamental construction investment had more important effects on land use structure. From 1985 to 2004,the amount of fundamental construction investment rised from 1.086 billion yuan to 57.354 billion yuan, while the area of residential and industrial land rised from 106386.82 hm2 to 239598.58 hm2.(3) A regression equation was obtained:Suspended Sediment Concentration = 1.701 (TM3/TM1) - 1.740Correlation Coefficient R2 = 0.7677By using this equation, we predicted SSC for QTR Basin in 1978, 1991 and 2004, respectively. There was no significant change of SSC in Qiantang River among the three years, but we found a clear trend of a single SSC class. For example, the area with SSC >= 2137.5 mg/L accounted for 0.3% in 1978, 0.5% in 1991 and 0.8% in 2004, correspondingly, in QTR Basin.(4) The concentration change of suspended sediment concentration of water body was closely related with land use change in Qiantang River Basin, and the land use type changes of garden land, water area and residential and urban and Industrial land play more important roles on it.