Multitype sediment deposits and sediment supply potential across alluvial–bedrock reaches of the Parlung Tsangpo River

: The Parlung Tsangpo Grand Canyon, located on the southeastern margin of the Tibetan Plateau, is one of the most tectonically active and sediment-dynamic regions in the alpine gorge zone. Frequent landslides, bank collapses, and flood events generate diverse multitype sediment deposits that strongly influence sediment supply and channel evolution. However, comprehensive investigations into the geometric characteristics of coexisting multitype sediment deposits, reach types, and associated sediment supply dynamics in river reaches subject to minimal human disturbance remain limited. In this study, the Parlung Tsangpo River (PTR) was selected as the study area. Focusing on the existing sediment deposits within the current river corridor, we identified and characterized four main types of sediment deposits—high-energy flood deposits (HFDs), confluence-zone alluvial deposits (CADs), bank-collapse deposits (BCDs), and landslide deposits (LSDs) —and the river was further divided into alluvial, mixed bedrock–alluvial, and bedrock reaches. The results indicate that variations in grain-size composition and geometric attributes among deposit types reflect distinct formative mechanisms and energy regimes, whereas reach type exerts a fundamental control on river morphology as well as the spatial scale and distribution of sediment deposits. Sediment supply is controlled by deposit geometry, spatial location, and discharge magnitude: HFD contributes most under low-flow conditions, whereas LSD and CAD dominate during high-flow and extreme flood events. This study elucidates the formation mechanisms, spatial differentiation, and sediment-supply processes of multitype sediment deposits in a high-mountain gorge environment, providing quantitative insights into potential sediment-supply dynamics and local channel adjustment in data-scarce alpine canyon rivers.