Abstract:

Monitoring and forecasting of the distribution and temporal change of SCC (suspended sediment concentration)is very important both for river water conservancy project and river ecology and environment protection. Retrieving SCC by remote sensing can compensate for the deficiency of the traditional timeconsume sampling method which acquires discrete data at high cost,and it provides information of SCC nearly in realtime at largescale. So far,the Three Gorges Project has been used nearly ten years,meanwhile the impoundment of the reservoir will fundamentally change SCC of the suspended of the Yangtze River water in time and space,its influence is a matter of concern. This study took the middle reaches of the Yangtze River as the study area.It aimed to develope the Moderateresolution Imaging Spectroradiometer (MODIS) imagebased SSC retrieval model for Middle River, use the model to predict the SSC of Middle Yangtze River during the flood period from 2002 to 2009,and analyze its spatial and temporal change characteristics. The results revealed that: the red band of MODIS Terra was significantly related to the SCC,and it may be applied to retrieve the SSC of Middle Yangtze River during the flood period. This study selected three images.After inversion,three sediment concentration profiles from 2002 to 2009 were obtained,in order to contrast SCC of the Yangtze River in wet season before and after the impoundment of the Three Gorges Project. During 2002-2009 years,the SCC from the Yangtze River downstream of the dam was reduced significant. In addition,the sediment from the Yangtze River into the Dongting Lake was also reduced significantly.SCC mainly concentrated in the 300-400 mg/L from Yichang to Chenglingji in the period of wet season in 2002,and it reduced to 150-200 mg/L or so in 2009.During 2002-2009 period,24.2% of the total area of the concentration reduced by 100-150 mg/L,48.4% of the total area of the concentration reduced by 150-200 mg/L.The Dongting Lake inflow was one of the most important sources of suspended sediment in the middle reaches of the Yangtze River under Chenglingji. It contained more suspended solids than that of the Yangtze River as we can see from the forecast results. It formed dozens of kilometers mixed area in the Yangtze River when the Dongting Lake inflow got into the Yangtze in Chenglingji and mixed with the river.This study proved that MODIS data was feasible for inland water suspended matters monitoring.The linear model was simple and feasible.The correlation coefficient R2 of the model was 0.877,and the rootmeansquare error was 40.57mg/L. Thus, it can be promoted as a suspended matters romote sensing retrieval method. The model is areaspecific and it needs further tested to identify whether it can be applied to other areas. These results would serve as a reference for studies of the evolution and regulation of rivers and lakes in the lower Yangtze reaches