Stream networks and knickpoints in the Sanjiangyuan Region

Abstract

Stream networks and knickpoints in the Sanjiangyuan RegionThe source area of the Lancang (Mekong), Yangtze and Yellow rivers is named in Chinese Sanjiangyuan (source of three rivers). Geographical characteristics of these rivers, and various rivers at the margin of the Qinghai-Tibetan Plateau (Jialing, Minjiang, Dadu, Yalong and Jinsha) are summarized from field investigations along with digital elevation model (DEM) analyses and satellite images. Uplift of the Qinghai-Tibetan Plateau has resulted in an asymmetrical distribution of tributaries for stream networks at the margins of the plateau. Almost all tributaries join the trunk stream from the northwest. Three types of drainage network are evident: plume, nervation and dendritic. In general, plume networks have a large number of first order streams. Nervation networks have a main stream and parallel tributaries. Dentritic networks are characrterized by continuous bifurcation and have a branch-like appearance. Most stream networks in the Sanjiangyuan region are of the nervation type. Several large knickpoints are evident along the longitudinal profiles of the Yellow and Yangtze Rivers. Channel aggradation immediately upstream of these knickpoints marks a transition in river processes from vertical bed evolution (i.e. incision) to horizontal channel adjustment (and associated braided and anabranching channels).