渠道土壤含水率的时空变化及渗漏模拟研究

Numerical Simulation of Spatiotemporal Variation in Exfiltration and Moisture Content in the Proximal Soil of Channel

【目的】探明渠道土壤含水率的时空变化及不同水深条件下渠道渗漏规律。【方法】采用恒水位静水试验,试验设置8个入渗水头,分析渠道土壤含水率的时空变化规律及不同水深、质地条件下渠道的累积入渗量及入渗速率的变化规律。基于田间层状土壤条件下开展的渠道渗漏试验,建立了二维空间上饱和-非饱和有压水头的土壤水分入渗模型,采用HYDRUS-2D软件对试验渠道及均质粉土、粉壤土的渠道进行模拟。【结果】①当土壤剖面存在分层界面时,临界面对水分入渗具有缓阻作用,分层界面底部达到饱和含水率的时间相应增长。到达一定时间后,缓阻现象消失,水分通过分层界面后,入渗呈线性均匀的变化。②利用HYDRUS-2D软件对试验渠道的水分入渗速率及累积入渗量进行模拟,经实测数据验证,试验模拟效果较好,用于渠道渗漏评价入渗速率和累积入渗量是可行的。随着渠道水深的增大,入渗速率增大,累积入渗量的变化越大。渠道水深与土壤水势梯度正相关,因而与渗漏通量正相关。③渠道土质越黏重,土粒间孔隙就越小,水流渗漏的阻力越大,水力传导度越小,土壤持水能力越大,渠道的渗漏损失越小。【结论】HYDRUS-2D软件可较好的模拟复杂条件下渠道渗漏规律,土壤的层状性对水分入渗具有缓阻现象,灌区改造优选黏性土壤可减小土壤水分入渗。

【Objective】Channel exfiltration is impacted by numerous factors and the objective of this paper is to study spatiotemporal variation in water content in the proximal soil of channel and its impact on channel exfiltration.【Method】Channel exfiltration was measured using constant water head method.We measured exfiltration rate and spatiotemporal variation in soil water content by setting the water head at eight different levels.Saturated-unsaturated water flow in the proximal soil of the channel was simulated using the Hydrus-2D software from which we calculated the exfiltrating rate at different part of the channel,and compared the impact of water depth in the channel and three soil textures:stratified soil as seen at the experiment site,homogenous sandy loam and loam soil.【Result】①The soil-interface in the stratified soil had a moderate effect on water infiltration,and it took more time for the underlaid layer to become saturated compared to the homogenous soil.Once breaking through the soil interface,the infiltration increased linearly with time.②Comparison with experimental data revealed that the Hydrus-2D was able to simulate infiltration rate and cumulative infiltration into the soil.It is found that with the depth of water in the channel increasing,both infiltration rate and accumulative infiltration increased.Because water flow in soil is driven by potential energy gradient,the depth of the water in the channel was positively correlated with matric potential gradient in the soil and the channel exfiltration rate.③The stickier and denser the soil was,the smaller the pores were,and,as a result,it reduced soil hydraulic conductivity and improved soil capacity.【Conclusion】The Hydrus-2D software was able to simulate water flow in the proximal soil of channel and the channel exfiltration under complicated conditions.The stratified soil could slow down water infiltration;increasing sticky and density of the soil can reduce water infiltration.The results of this study provide a means to evaluate the efficacy of irrigation channel improvement in alleviating channel exfiltration.