Identification of runoff type and an assessment of water balance for the megadune area of the Badain Jaran Desert

摘要

The Badain Jaran Desert contains numerous megadunes that are characterised by the largest height difference in the world. Various rare landforms are also found on the slopes of the Badain Jaran megadunes, including spring streams, surface infiltration-excess runoff, erosion rills caused by surface runoff, slow-seepage runoff, as well as physical and chemical sediment resulting from subsurface lateral flow outflows. A variety of analyses were performed using electron microscope observation, X-ray diffraction, particle size analysis and field survey, investigating properties such as the mineral composition of the chemical sediment, the particle size composition of the physical sediment and aeolian sand, runoff type, the recharge conditions of precipitation to groundwater and lake water, and the water balance of the megadune area. The formation of the different types of runoff demonstrates that although precipitation in this area is low, effective heavy precipitation processes characterised by single events of more than 15 mm are present that likely act as a source for groundwater. Seven indicators, including the formation of spring water at the bottom of megadunes, multiple runoff types, as well as both physical and chemical sediments, clearly show that precipitation in the area reaches the bottom of megadunes via infiltration, which constitutes an effective supply of lake water and groundwater. The water-resisting property of the fine sand layer is likely the reason why the region is characterised by an outflow of subsurface runoff, with the latter and its sediment further confirming that the area also possesses a positive water balance. This positive water balance is the result of four unique characteristics: the presence of effective heavy precipitation, low transpiration due to scarce vegetation, the high infiltration rate of the sand layer and the small depth of the sand layer affected by evaporation. This in turn means that atmospheric precipitation is sufficient to supply groundwater, leading to the development of the numerous lakes found in the desert area. Water balance calculations revealed that, after accounting for evaporation, transpiration and other sources of consumption of atmospheric precipitation, around 134,648.4-135,976.9 m(3) of water per square kilometre per year is still supplied to the groundwater and lake water.