基于水量平衡原理的裂隙优先流双域渗透模型及其应用

Dual-permeability Model for Crack Preferential Flow Based on Principle of Water Volume Balance and Its Application

针对农田裂隙在灌溉过程中造成灌水效率降低和养分淋失等现象,基于表层入渗、裂隙边壁层流通量、裂隙边壁水平吸渗三者与灌水强度平衡原理,构建了基于水量平衡的优先流双域渗透模型,采用染色示踪试验进行了验证,并基于该模型进行了初始/边界条件旋转设计模拟应用。结果表明,试验优先流模式可显著区分为基质流态(土层深度0~10 cm)和优先流态(土层深度大于10 cm),染色覆盖率在土层深度大于10 cm的区域内呈线性骤降趋势;对比分析实测和模拟流态可知,本文提出的裂隙流双域渗透模型可有效预测土壤上边界入渗特征、基质流入渗深度和染色覆盖率随深度的变化,实测和模拟染色覆盖率极显著相关(P<0.01,R^(2)为0.981),裂隙流发育可分为供水强度控制、表层入渗能力/裂隙边壁层流控制、表层/裂隙边壁入渗能力控制3个阶段。基于该模型采用初始体积含水率(θ_(i)为0.20、0.25、0.30、0.35 cm^(3)/cm^(3))和灌水强度(R_(0)为0.10、0.08、0.06、0.04、0.03、0.02 cm/min)旋转设计,分析了初始及边界条件下优先流特征,模拟结果表明,增大灌水强度可使优先流指数增加而降低灌水均匀度,而当初始含水率升高时,优先流强度减弱且基质流深度增加。本文基于水量平衡原理模拟了裂隙流湿润锋推移过程,消除了传统双域渗透模型难以量化裂隙边壁糙率和层流厚度的缺点,丰富了膨缩性土壤裂隙优先流预测理论,可为农田水分管理和水肥渗漏淋失抑制提供依据。

Soil desiccation cracks result in a decrease in irrigation efficiency and nutrients loss during irrigation events,and the prediction of crack preferential flow would provide theoretical basis for soil water management during crop planting.A dual-permeability model was proposed for crack preferential flow,based on the principle of water volume balance in which the sum of surface infiltration rate,laminar flow flux and lateral flow rate through crack walls equaled the surface irrigation intensity.The dual-permeability model was validated with help of dye tracer experiments of preferential flow.Furthermore,this preferential flow model was applied to practical use with rotation-combination design of initial/boundary conditions,i.e.antecedent water content and irrigation intensity.The results showed that the preferential flow patterns could be markedly classified into matrix flow(soil depth was 0~10 cm)and preferential flow(soil depth was greater than 10 cm).The variations of dye coverage were rapidly decreased when the soil depth exceeded 10 cm.A comparison of the measured and simulated data showed that the dual-permeability preferential flow model was remarkably valid in predicting the characteristics of the surface infiltration rate,matrix flow depth and the dye coverage variations with depth.The Pearson correlation coefficient between the measured and the simulated data showed a significant level(P<0.01,R^(2)was 0.981).The propagation of crack preferential flow process could be divided into supply dominated phase,surface infiltration capacity/crack wall laminar flow dominated phase and surface/crack wall infiltration capacity dominated phase.Based on this model,a rotation-combination numerical simulation containing four levels of antecedent water content(θ_(i) was 0.20 cm^(3)/cm^(3),0.25 cm3/cm3,0.30 cm^(3)/cm^(3) and 0.35 cm^(3)/cm^(3))and six levels of irrigation intensity(R_(0) was 0.10 cm/min,0.08 cm/min,0.06 cm/min,0.04 cm/min,0.03 cm/min and 0.02 cm/min)was conducted.The simulated preferential flow patterns were analyzed under 24 treatments.The results showed an increase in preferential flow fraction and a decrease in irrigation uniformity when the irrigation intensity was increased.As the antecedent water content was increased,the strength of preferential flow was decreased and the matrix flow depth became larger.In general,the proposed model was valid in predicting the propagating wetting fronts of crack preferential flow by adopting the water volume balance principle,which eliminated the disadvantages of the traditional dual-permeability preferential flow model that the roughness of the crack walls and the thickness of the laminar flow can not be accurately quantified.The proposed model provides a novel perspective into crack preferential flow prediction,and the simulation results would provide theoretical basis for the farmland water management and percolation loss.