Shifted Flood and Ecology Regimes Due To Channel Bar Greening and Increased Flow Resistance in a Large Dammed River

Abstract

Damming profoundly affects downstream flow-sediment regimes, altering channel bar dynamics and thereby affecting floods and riverine biodiversity. Here, we investigate the response of bars to upstream damming by examining patterns, mechanisms, and impacts in the Middle Yangtze River (∼1,000 km). Over a decade of post-damming observational data reveal substantial increases in bar revegetation and Leaf Area Index. Shorter flood duration and stable bar size collectively drive bar greening. Consequently, denser vegetation has slowed flow velocity by 17% ± 2% and increased flow resistance by 21% ± 5%, offsetting the water-level decrease from channel expansion due to scouring and even causing a slight rise in floodwater levels. Furthermore, damming has markedly altered river connectivity, thermal regimes, and solute dynamics, detrimentally affecting fish habitats and aquatic life. These findings, along with refined river stage simulation considering flow-sediment-vegetation interactions, facilitate sustainable reservoir operation and river management in big river systems.