非饱和黄土中降雨入渗规律的现场监测研究

In-situ observation on regularities of rainfall infiltration in loess

在甘肃省正宁县建立一监测站,对天然降雨入渗后的10.0 m深度范围内土壤含水率变化进行全年观测,结合降雨量、蒸发量及气温数据分析黄土中的水分迁移规律。研究结果表明:研究区土壤中水分通过降雨补给,蒸发排泄;1.2 m内土壤水分受降雨和蒸发影响较大,具有周年的背景变化趋势,当降雨量小于18mm/d时,水分仅在表层循环,土壤含水率在其背景趋势上波动很小,大于该值时,才会引起土壤含水率骤升,该趋势和蒸发量的变化趋势吻合;降雨量越大,土壤含水率增幅越大,影响深度越大,随着深度增加,增幅减小,时间上渐有滞后。深部的非饱和黄土中,水分以非饱和渗流或水汽形式迁移,水汽迁移量很小,因此土壤含水率增幅小且非周年性变化,遇到透水性差的土层时,会在其顶部富集,利用有限元软件模拟降雨入渗过程,模拟结果也很好地反映了这一规律。

One monitoring site was set up in Zhengning county, Gansu province, the changes of soil moisture content within 10.0 m under the condition of natural rainfall were observed continuously in a whole year, and the rules of water migration in loess were analyzed combined with precipitation, evaporation and temperature data. The results show that soil moisture is recharged by rainfall and drains through evaporation in the area. Soil moisture within 1.2 m is affected greatly by rainfall and evaporation, changing in annual cycle, and when the precipitation is more than 18 mm/d, soil moisture content skip suddenly saltatory change, but on the contrary, the circulation of soil moisture occurs mainly in surface layer; soil moisture content almost has no obvious fluctuations on the background trend. The trend is consistent with the change of evaporation. The growth of moisture content increases and the affected depth deepens when the precipitation increases, and the growth decreases and the change of moisture content lags with the depth. Water moves in unsaturated loess in the deep mainly in the form of unsaturated seepage or vapor form, and the motion of vapor is very small, resulting in that soil moisture content grow not only weakly but non-annually, and the water can gather on the surface as encountering layers with low permeability, which is also well reflected by simulated results of the process of rainfall infiltration by finite element software.