Abstract:Sediment delivery ratio （SDR) is a critical transfer parameter for investigating soil erosion and sediment yield in a watershed, which is a matter of concern not only because of the sediment yield input to river but also due to its important effects such as safety-operation and flood control in reservoirs. Currently, there is limited information on the quantitatively estimation of SDR for different periods in the catchments of the Three Gorges Reservoir Region (TGRR), and its temporal changes of estimates are also scarcely analyzed. Thus, Huangchongzi and Gongnonggou catchments, located in the central part of the TGRR were selected as study areas, which represented one of the typical purple soil areas. In order to investigate the SDR of the past 52 years in the central part of the TGRR strictly according to the definition of SDR, annual average soil erosion was precisely estimated with an integration of geographic information system (GIS) and the revised universal loss equation (RUSLE). Sediment yields for different periods from 1963 to 2014 were identified by pond sedimentation amount based on the dating results of the comprehensive utilization of 137Cs and 210Pb tracer techniques, and these results made use of calculation of SDR for different time-interval. Results showed that the average soil erosion amount was 119.72t and 86.86t and its coefficient of variation (CV) was 0.76 and 0.86 during 1963—2014 in Huangchongzi and Gongnonggou catchments, respectively. The average soil erosion amounts in 2001—2014 were obviously lower than that in 1963—2000 for these two catchments. The main reason was the benefit of grain to green, which started in 2001. The 137Cs time mark dating-results were in agreement with results by 210Pbex constant rate of supply (CRS) model. Based on this analysis, sedimentation core for Huangchongzi and Gongnonggou ponds was segmented with 19 and 12 time-intervals and its CV of the corresponding sediment yields was 0.28 and 0.19 from 1963 to 2014, respectively. The SDR fluctuated distinctly from 1963 to 2014, which were especially intensity after human-activities. The CV of the SDR for different time-interval was 0.33 and 0.82 from 1963 to 2014 for Huangchongzi and Gongnonggou catchments, respectively. The results estimated strong variations in SDR from 0.07 to 0.9 for different time-intervals in the catchments, and this emphasized that the reasonable selection of time-interval played an critical role in estimating SDR, particularly when benefit assessment for soil and water conservation was implemented.
