VG模型参数对灌溉补给系数的敏感性分析

Analysis on sensitivities of VG model parameters to irrigation recharge coefficient

运用模型手段,计算灌溉补给系数时,VG模型中水力参数的不确定性严重影响了灌溉入渗补给系数的可靠性,且目前针对非均质岩土层入渗及其水力参数敏感性的研究较少。基于新疆伊犁霍城县原位试验场灌溉试验,运用HYDRUS-2D软件建立二维饱和-非饱和带水分运移数值模型,利用EFAST法和Morris筛选法分析了VG模型中水力参数对灌溉补给系数的敏感性,并分析比较两种方法的一致性。研究表明:当包气带岩性为均质结构时,θs(土壤的饱和含水率)及n(VG模型的形状参数)共同影响着灌溉补给系数。当包气带岩性处于上粗下细的结构时,θs对灌溉补给系数影响最大,即表明θs最为敏感,而且细颗粒θs相对于其他水力参数的耦合程度最大。n直接影响着土壤水分特征曲线的整体形状。同时EFAST法和Morris筛选法对参数敏感性分析结果呈现较高的相关性。由于VG模型中水力参数数量适中,EFAST法较Morris筛选法工作量合理,同时对模型参数敏感性分析更加贴近实际。研究成果对获取包气带水分运移模型参数有着重要意义。

When the irrigation recharge coefficient is calculated by means of model,the uncertainty of hydraulic parameters in VG(Van Genuchten)model seriously affects the reliability of irrigation infiltration recharge coefficient,while few studies are there on the infiltration and the sensitivities of the hydraulic parameters of heterogeneous rock-soil layer at present.Based on the irrigation experiment made in the in-situ experiment field in Huocheng County of Yili Prefecture in XinJiang,a 2-D numerical model of moisture transfer in the saturated-unsaturated zone is established with the software of HYDRUS-2D,and then the sensitivities of the hydraulic parameters in VG model to the irrigation recharge coefficient are analyzed through EFAST method and Morris’s screening method,while the consistency of both the methods is comparatively analyzed as well.The study result shows that when the lithology of vadose zone consists of a homogeneous structure,both theθs(saturated soil moisture content)and the n(shape parameter of VG model)jointly affect the irrigation recharge coefficient.When the lithology of vadose zone consists of a structure of upper coarse layer with lower fine layer,the impact from theθs on the irrigation recharge coefficient is the largest,that is to say,theθs is the most sensitive,while the coupling degree of theθs of the fine particle is the largest relative to the other hydraulic parameters.the n direrctly impacts the whole shape of the soil moisture characteristic curve.Meanwhile,the parameter sensitivity analysis results from both EFAST method and Morris’s screening method exhibit higher correlation.Due to the moderate number of the hydraulic parameters in VG model,the workload of EFAST method is more reasonable than that of Morris’s screening method,and simultaneously,the sensitivity analysis on the model parameter is closer to the reality.The study result has an important significance for obtaining the model parameters of the moisture transfer in vadose zone.