降水在沙丘中的运动特征研究——以甘肃民勤沙区为例

Motion Characteristics of Precipitation in Sand Dunes A case study in Minqin sandy area, Gansu

自然降水和辅助人工模拟降水试验表明在民勤沙区,降水在沙丘上的下渗深度主要受沙面状况的影响。沙丘表层土壤田间持水量大小影响降水下渗,表层粉粒和粘粒含量影响田间持水量,降水量的大小与水分下渗深度的相关性并不显著;降水强度在29.8mm·d-1以内时,固定沙丘上的最大含水层为10～15cm,降水的下渗速率只有10～15cm·d-1;在半固定沙丘上,28.2mm·d-1以内的降水的最大含水层为30～35cm,降水的下渗速率只有15.0～17.5cm·d-1;在流动沙丘上,21.7mm·d-1以内的降水强度的最大含水层为130～135cm,降水的下渗速率可达32.5～33.8cm·d-1;在固定沙丘和流动沙丘上,8mm·d-1以内的降水很快蒸发损失,而在半固定沙丘上能保存较长时间;与固定和半固定沙丘相比,流动沙丘表面水分(即7～8mm以内的降水)最易在短期内蒸发损耗。

A study on natural precipitation supplemented by artificial precipitation imitation showed that in Minqin sandy area the depth of rainfall permeation was related to the property of sand surface: rainfall permeation was affected by field capacity of the upper layer of surface soil, which was influenced by the content of silt and clay particles in the sand layer; the correlation between rainfall and its permeation was less significant. In fixed sand dunes when precipitation intensity was within 29.8 mm5d -1 the maximum moistened soil depth by rainfall was 10~15 cm and the permeation rate was 15 cm5d -1 ; in semi-fixed dunes when precipitation intensity was within 28.2 mm5d -1 the maximum depth of soil moistened by rainfall was 30~35 cm and the permeation rate was 15~17.5 cm5d -1 ; in shifting dunes while precipitation intensity was within 21.7 mm5d -1 the maximum depth of soil moistened by rainfall was 130~135 cm and the permeation rate can reach 32.5~33.8 cm5d -1 . In fixed and shifting dunes the precipitation with intensity less than 8 mm5d -1 would vapor soon, whereas in semi-fixed dunes it can stay longer. In contrast with fixed and semi-fixed dunes the moisture in the surface of shifting dunes would vapor most likely (i.e. under 8 mm precipitation) in a short time.