Spatiotemporally varied contributions of primary bank-derived materials from ungaged areas to the Three Gorges Reservoir: Insight from decadal continuous sediment archives (2012–2022)

Accurate quantification of sediment sources is essential for assessing bank erosion, mitigating reservoir sedimentation, and ensuring long-term sustainability. However, estimates for ungaged areas remain uncertain due to systematic monitoring gaps, and modeling efforts often lack reliability because of insufficient sediment records. To address this issue, grain size distributions (GSDs) were analyzed for two sediment cores, approximately 2.7 m in length, collected from the RangDu (RD) and ZhongXian (ZX) areas in the Three Gorges Reservoir (TGR), China. Suspended sediment from the mainstream and primary bank-derived materials from ungaged areas served as end members for quantitative source apportionment. Sedimentation periods were inferred by correlating temporal grain-size variations with precipitation intensity. The results indicate that both cores recorded continuous sedimentation from 2012 to 2022. The contribution of primary bank-derived materials from ungaged areas exhibited significant seasonal and spatial variations, averaging 36 % in the RD core (2012–2019) and 3.6 % in the slow-flow ZX core (2015–2022). Topographic and hydrodynamic conditions facilitated greater deposition of suspended materials in slow-flow areas compared to the main channel. The substantial contribution of bank-derived materials to reservoir sediment systems highlights the critical influence of wet-season rainfall on bank erosion and associated reservoir sediment. Nevertheless, given the current limitations in core sample quantity and temporal coverage, future studies should extend sedimentary conditions and temporal scope of sediment records for better understanding the impacts of precipitation, particularly extreme precipitation events, on bank erosion and reservoir sedimentation processes under global climate change.