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A numerical model and semi-analytic equations for determining water table elevations and discharges in non-homogeneous subsurface drainage systems.

机译：用于确定非均匀地下排水系统中地下水位高程和流量的数值模型和半解析方程式。

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摘要

A free water surface finite element model was developed. The method was implemented with the Galerkin approach to solve the Laplace equation in the saturated region. It was developed in the object oriented Visual C ++ computer language to permit easy update and drawing of the adaptive mesh. For each time step, the new water table position was calculated based on flux across the water table, a Brooks-Corey equation mass balance for the unsaturated region, and an equation that calculates water table position for the saturated region. An equation was developed to calculate a drainage transfer coefficient, α, based on percentage of perforated area in the drain tube wall. The drainage transfer coefficient was incorporated into the finite element model as a Fourier boundary condition. To validate the finite element model, its results were compared with the Kirkham equation results for steady state recharge of three subsurface drainage systems.; The finite element model was used to calibrate a semi-analytical frozen stream tube model for subsurface drainage of heterogeneous soils. The first step in the calibration procedure is to run the finite element model for steady state recharge and calculate the water table height divided by recharge rate (the stream tube resistance to flow) as a function of distance between drains. Least squares regression is used to fit a polynomial logarithmic equation, called the resistance function, to the stream tube resistance to flow vs. distance from the drain curve. A differential equation based on the principle of conservation of mass and application of Darcy's law to the frozen stream tube was solved to obtain an equation that calculates stream tube flow rate and final water table elevation as a function of the resistance function and initial water table elevation.; An example was developed for a non-homogeneous subsurface drainage system to illustrate the use of the semi-analytical model to predict water table fall and discharge.
机译：建立了自由水面有限元模型。该方法是用Galerkin方法实现的，用于在饱和区域中求解拉普拉斯方程。它是使用面向对象的Visual C ++ 计算机语言开发的，可轻松更新和绘制自适应网格。对于每个时间步，将根据跨水位的通量，不饱和区域的Brooks-Corey方程质量平衡以及计算饱和区的地下水位的方程来计算新的地下水位。根据排水管壁上的穿孔面积百分比，开发了一个公式来计算排水传递系数α。排水传递系数作为傅立叶边界条件并入有限元模型。为了验证有限元模型，将其结果与Kirkham方程结果进行了比较，以实现三个地下排水系统的稳态补给。有限元模型被用来校准非均质土壤地下排水的半解析冻结流管模型。校准程序的第一步是运行用于稳态补给的有限元模型，并计算水位高度除以补给率（流管对水的阻力）作为排水口之间距离的函数。最小二乘回归用于将多项式对数方程（称为阻力函数）拟合到流管的阻力与距排水曲线的距离之间的关系。解决了基于质量守恒原理并将达西定律应用于冻结流管的微分方程，从而获得了一个方程，该方程计算出流管流量和最终水位高程是阻力函数和初始水位高程的函数。;针对非均质地下排水系统开发了一个示例，以说明使用半分析模型预测地下水位下降和流量的情况。

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  • 作者

    Uribe-Chavez, Armando.;

  • 作者单位

    The University of Arizona.;

  • 授予单位 The University of Arizona.;
  • 学科 Engineering Agricultural.; Agriculture Soil Science.
  • 学位 Ph.D.
  • 年度 2001
  • 页码 125 p.
  • 总页数 125
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 农业工程;土壤学;
  • 关键词

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