The effect of prevailing wind on shoreline landform evolution - Illustrated by the case of Buha River Delta and Hargai River Delta in the Qinghai Lake, western China

Lacustrine sedimentation, which is considered to be relatively simple, can be dominated by high-energy wind-driven process. Qinghai Lake, located at the northeastern margin of the Qinghai-Tibet Plateau, western China, is a typical “wind-driven lake”, of which the sedimentation and evolution of shorelines are impacted by prevailing wind. In this research, Buha River Delta and Hargai River Delta, located at the northwestern and northeastern of the lake respectively, are studied through field investigation and remote sensing images analysis. The outcrop section of Buha River Delta is characterized by channel lag deposits, planar cross-beds, and trough cross-beds, indicating a dominant effect of river. However, the section of Hargai River Delta displays planar cross-beds, as well as swash cross-beds (beach deposits) and high-angle cross-beds dip to land (washover deposits), revealing a combined effect of river and waves. Remote sensing images in recent 40 years showed that Buha River Delta remained a stable shape except for the migration of mouth bars, which may be caused by lake level fluctuation. Nevertheless, Hargai River Delta has recorded a noteworthy change in its appearance, which was characterized by the formation of a barrier bar outside the estuary. Meteorological Data reveals that the Qinghai Lake is mainly affected by north-west wind and north wind, thus Buha River Delta is located at the leeward side, while Hargai River Delta is situated at the windward side and significantly influenced by high-energy wind-driven lake currents and waves. When the prevailing wind direction is oblique to the lake shoreline, the coastal current parallel to the shoreline formed by the decomposition of wind-driven waves would transport the clastic materials provided by Hargai River and then deposit them along the lake bank, finally forming a barrier bar parallel to the shoreline. This study reveals that wind-driven process could have totally different effects on either side of a “wind-driven lake”, thus can help us anticipate the evolution of shoreline landform of a “wind-driven lake” in the near future.