降水在沙丘中的渗透过程研究

观测研究结果表明 :⑴降水在沙丘上下渗深度与降水量及降水强度成正相关 ,与气温成负相关。民勤沙区雨季降水量在 4 0mm以上时在沙丘中的下渗深度可以达到 5 0～ 90cm。在当地 ,秋季降水尤其是秋季连续降水是沙丘储存水分的主要来源。⑵降水在沙丘上的下渗速率与降水量正相关 ,降水量大 ,主要含水层的含水率则高 ,下渗速度自然就快。⑶降水后梭梭根部沙面 0～ 5cm含水率高于流动沙丘 ;降水停止 1d以后对应于流动沙丘的最大含水层梭梭根部的含水率明显降低 ;降水停止 1d后在流动沙丘降水下渗深度内的平均含水率高于梭梭沙丘对应层含水率 ,且随时间推移这个差值在增大。⑷在 0～ 4 5mm的降水量范围内 ,不论是流动沙丘还是有梭梭林的沙丘 ,其降水的主要含水层在表层 0～ 2 0cm范围内。⑸当地 8月上旬 <12mm的降水量在降水停止后的 7～ 8d内蒸发殆尽 ;4 3.5mm的降水量在降水停止后第 10天时 0～ 15 0cm沙层含水率折合水层深度较降水前多 17.2 8mm ;2 1.7mm的降水量在降水停止后第 10天时 0～ 15 0cm沙层含水率折合水层深度较降水前多 10 .6 6mm ;在降水过程中和降水后的 1d内水分蒸发损耗最大

PENETRATING PROCESS OF PRECIPITATION IN SAND DUNE IN MINQIN DESERT AREA

The observation results showed that: (1) The penetrating depth of precipitation in dune was positively correlated with amount of precipitation and precipitation intensity but negatively correlated with air temperature. In Minqin desert area, the penetrating depth could reach 50-90 cm when the precipitation is above 40 mm. Autumnal rainfall, in particular the continuous rainfall, is the main source of water storage for dune. (2) The penetration rate was positively correlated with amount of precipitation. That is strong rainfall may cause high water content in the main water bearing layer of dune, thus resulting in a quick penetration. (3) After a rainfall, the moisture percentage in the surface layer of 0-5 cm in depth around Holoxylen ammoden dron root was higher than that in moving dune, but one day later after rain, it obviously declined, and the moisture percentage of water bearing layer of moving dune was higher than that of Holoxylen ammoden dron dune, meanwhile, with lapse of time, the difference increased. (4) When the precipitation is in range of 0-45 mm, the main water bearing layers for both moving dune and Holoxylen ammoden dron dune were limited in the surface layer of 0-20 cm in depth. (5) In Minqin desert area, a less than 12 mm rainfall in early August was evaporated up in 7-8 days after rain stopped. For a 43.5-mm rainfall, at 10 days after rain the depth of waterlayer in 0-150 cm sandy layer was increased by 17.28 mm compared with that before rain, while for a 21.7-mm rainfall, it was increased by 10.66 mm. The largest evaporated loss of water occurred within the process of rainfall and one day after rainfall.