An environmental gradient of vegetative controls upon channel planform in the source region of the Yangtze and Yellow Rivers

Abstract

Alluvial reaches in the source region of the Yangtze and Yellow Rivers, located atop the Qinghai–Tibetan Plateau and mostly at elevations that are typically higher than 3500m, have similar slope and valley setting conditions. However, alluvial reaches in the source region of the Yangtze River exhibit predominantly braided channel planforms, while equivalent reaches in the source region of the Yellow River have more diverse planform morphologies including anastomosing/braided, anabranching/braided, and anabranching/anastomosing reaches. The regional gradient of variation in riparian vegetation and interactions between vegetation development and hydrologic process are shown to be major factors influencing this difference in channel planforms. A short period above freezing, coincident with recurrent yet pulsed flows in the source region of the Yangtze River, suppress riparian vegetation growth, promoting the development of braided channel morphologies. In contrast, a milder climate, coincident with less variable flows in the source region of the Yellow River, permit the establishment of different forms of riparian vegetation, thereby supporting the development of a wider range of channel planform morphologies.