潜水位动态计算灌溉回渗强度动力学方法研究

Study on dynamic method of calculating irrigation infiltration intensity based on unconfined groundwater table

在沟渠侧渗与田间下渗都不可忽略的灌区,由于潜水水位动态数据分项计算田间下渗与沟渠侧渗的困难,研究基于地下水动力学原理,当田间下渗强度ε为常数,将ε作源汇项构建沟渠附近潜水非稳定流模型,对模型进行线性化、齐次化处理,利用Laplace变换,求出模型解;对随时间变化的下渗强度,利用分段函数将其离散,按叠加原理求出解.然后,基于模型解,构建利用潜水水位动态数据计算田间下渗强度的递推公式,结合Darcy定律给出计算沟渠侧渗算式,讨论沟渠边界对潜水位变动及对侧渗强度的影响规律.以淮北平原某干渠附近潜水位动态为例,演示上述过程:在48 h计算期内,沟渠侧渗对潜水位变动的贡献比例,从初期的4.3%迅速上升到末期的62.8%.据此所提出的计算灌溉回渗强度的动力学方法可为灌溉水入渗地下水计算提供参考.

In irrigation areas where both ditch lateral infiltration and field infiltration are not negligible,it is difficult to calculate field infiltration and ditch lateral infiltration on the basis of the dynamic data of unconfined groundwater table.According to the basic principle of groundwater dynamics,when the field infiltration intensityεis a constant,εis used as the source and sink term,the basic model of unsteady seepage of phreatic water near the ditch is constructed.The model was linearized and homogenized,and the model solution was obtained by Laplace transform.For the infiltration intensity varying with time,using the segmented function,ε(t)is discretized,and the model solution is obtained according to the superposition principle.By using the model solution,a recursive formula for retrieving the field infiltration intensity using the dynamic data of unconfined groundwater table is established.Combined with Darcy's law,the formula for retrieving the lateral infiltration of ditches is given,and the influence of ditch boundary on the variation of unconfined groundwater table and the lateral infiltration intensity is discussed.The above calculation process is demonstrated by taking the dynamics of unconfined groundwater table near a trunk canal in the North Huaibei Plain as an example;the contribution of ditch lateral seepage to the change of submersible water level increases rapidly from 4.3%at the beginning to 62.8%at the end of the 48-h calculation period.The proposed dynamic method for calculating irrigation infiltration intensity can provide reference for the calculation of irrigation water infiltration into groundwater.