Evolution of channel networks and morphology of a dryland River under human impacts – A case from Tarim River in Northwest China

Guoan Yu, Markus Disse, Ling Tong, Yang Yu

Tuesday 30 june 2015

8:30 - 8:45h at Oceania (level 0)

Themes: (T) Sediment management and morphodynamics, (ST) River morphodynamics

Parallel session: 4B. Sediment - River

Tarim River, the longest dryland river in China with extreme aridity, has undergone ever-increasing human impacts over the recent centuries (particularly since the 1950’s). Human activities in Tarim Basin impacted on three major controls on channel pattern: flow regime, sediment transport and vegetation, and have caused major changes in its channel network composition and river morphology (especially planform patterns). Consequently, an original (quasi-) anastomosing channel network system with nine tributaries in history gradually disintegrated into several isolated river systems and currently with only four tributaries flowing into main stem river, dominantly in braided and meandering (typically with distorted bend) channel patterns. Gauged hydrological data in past five decades showed obvious reduction of runoff and sediment load to the Tarim River, even though changes in a fluctuation. Vegetation status, represented with Populus euphratica, the typical and dominant vegetation in the basin along river channel, has declined and its area sharply reduced. Sinuosity degrees of current Tarim River channel are distinctively lower than those of old channel abandoned decades or centuries ago, implying natural evolution of channel forms has been restrained under the impacts of human interventions (dykes, reservoirs and water diversions). Human activities have objectively (sometimes subjectively) controlled, both in spatial range and time frequency, the morphologic variations (avulsion and lateral migration) of the Tarim River, and have reduced the complexity and diversity of the river network system.