摘要
新月形沙丘是风蚀荒漠化过程中伴随的重要风积地貌类型,在以往的研究中主要侧重于沙丘体表面动力学过程,而关于沙丘在风蚀荒漠化过程中的作用鲜有报道。本文在台特玛湖的干涸湖盆区(曾经的塔里木河尾闾湖),采用测钎法,实地测定了新月形沙丘周围地表的蚀积变化,同时采用室内风洞模拟了典型新月形沙丘地表的气流分布模式,系统分析了新月形沙丘对地表蚀积影响的作用机理。结果表明:在新月形沙丘影响下,沙丘周围地表风蚀强度不均一,在沙丘迎风坡前区和沙丘左右翼,风蚀深度略大于不受沙丘影响区(CK),但单位面积平均净蚀积量接近平衡状态;在沙丘背风坡前区以风积为主,而在背风侧尾流区,地表以风蚀为主,且随着沙丘体积增加,单位面积平均净风蚀量也略有增大。在内陆干旱区干涸湖盆风蚀荒漠化过程中,新月形沙丘通过改变地表流场结构,使风沙流饱和度发生空间分异,从而影响了下伏地表蚀积的空间分布,尤其加剧了背风侧尾流区的风蚀,使新的风蚀面裸露,破坏沉积层结构,促进了河湖相沉积平原风蚀荒漠化的发展。
Barchan dune is an important type of aeolian landform and forms during the process of desertification.In the previous researches,more researchers focused mainly on the surface dynamic process of barchan dune but less on the influence of barchan dune on surface wind erosion during desertification process. In this paper,the plugging-brazing method was used to measure the distribution pattern of wind erosion/deposition on the surface around barchan dunes at the Taitema playa. The wind tunnel was used to simulate the distribution pattern of airflow over the typical barchan dune. The mechanism of barchan dune affecting surface wind erosion around dune was analyzed. The results showed that the airflow structure changed with the varying geometry shapes of barchan dunes,and it affected significantly the intensity of wind erosion/deposition over the surface. Although the wind erosion depth and sedimentary thickness were slightly greater than those on flat sand,the average volume of net wind erosion per unit area was close to an equilibrium in the frontal region of windward slope and on both sides of dunes.Deposition was dominant in the frontal region on leeward slope of barchan dune,but wind erosion was dominant on the surface of flank wake zone of leeward slope. The average volume of net wind erosion per unit area was slightly increased with the increase of dune size. In a word,the barchan dunes affect the intensity of surface wind erosion and deposition during the process of desertification in playa.
引文
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