层状非均质包气带渗透性特征及其对降水入渗的影响

Permeability characteristics of layered-heterogeneous vadose zone and influence on precipitation infiltration

不同的岩性界面影响了降水在包气带中的入渗、运移与再分布过程,其影响机制仍是有待研究的学科前沿问题。针对上述问题,基于层状非均质包气带6 m×4 m×5 m样方,开展了多场次自然降水入渗过程的原位试验监测,研究结果表明层状非均质结构对降水入渗过程和速率影响明显:(1)地层分界面处土壤含水率呈现陡降变化特征;(2)220 cm深度以上包气带中土壤含水率对降水入渗响应变化敏感,呈含水率陡变的多峰谷式脉冲响应变化特征,其中20~100 cm地层土壤含水率变化幅度为22.58%~29.76%,120~200 cm地层土壤含水率变化幅度为13.74%~20.74%;220 cm深度以下包气带中土壤含水率对降水入渗响应滞缓,年内呈现平缓单峰响应变化特征,反映了多场次降雨的累积效应,其中220~400 cm地层土壤含水率变化幅度为2.3%~12.15%,430~460 cm地层土壤含水率变化幅度为2.5%~3.41%;(3)层状非均质结构阻滞了水分的运移(湿润锋通过亚砂土-粉砂界面时,平均运移速度由10.53 cm·d^-1下降为0.77 cm·d^-1;湿润锋通过亚砂土-亚粘土界面时,平均运移速度由12 cm·d^-1下降为1.86 cm·d^-1),当岩性界面处水分不断蓄积克服阻力后才能向下运移;受上部界面水分蓄积的影响,下部层状非均质结构的阻滞作用将被减弱甚至不明显。

The mechanism of how lithologic interfaces influence the process of infiltration,migration and redistribution of precipitation in the vadose zone is still a frontier problem to be studied.In view of the question,in-situ experiments of natural precipitation infiltration have were carried out based on the layered heterogeneous vadose zone(6 m×4 m×5 m).The results showed that the layered heterogeneous structure had obvious influence on the infiltration process and rate of precipitation:(1)Soil water content showed the characteristics of sharp down at the stratigraphic interfaces;(2)The response of soil water content above 220 cm depth to precipitation infiltration in vadose zone was sensitive,and showed the characteristics of multi-peak-valley type with quick changes of water content,for instance,the variation range of water content was 22.58%~29.76%in 20~100 cm stratum and 13.74%~20.74%in 120~200 cm stratum while not sensitive below 220 cm depth and showed small fluctuation,which reflected that with the cumulative effect of multiple rainfall events,the variation range of water content in 220~400 cm stratum was 2.3%~12.15%.The variation in 430~460 cm stratum was only 2.5%~3.41%;(3)The layered heterogeneous structure blocked the movement of water(the average migration velocity of the wetting front decreased from 10.53 cm·d^-1 to 0.77 cm·d^-1 when it passed through the interface of sandy loam and silty sand,and from 12 cm·d^-1 to 1.86 cm·d^-1 when it passed through the interface of sandy loam and clay loam),when the water accumulated at the lithological interface until to overcome the resistance,it moved downwards.Due to the effect of water accumulation in the upper interface,the blocking effect of the lower layered heterogeneous structure was weakened or even eliminated.