Documentation of the Unsaturated-Zone Flow (UZF1) Package for modeling Unsaturated Flow Between the Land Surface and the Water Table with MODFLOW-2005
Documentation of the Unsaturated-Zone Flow (UZF1) Package for modeling Unsaturated Flow Between the Land Surface and the Water Table with MODFLOW-2005
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DOI：
10.3133/tm6a19
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
R. Niswonger;D. E. Prudic;R. Regan
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文献类型：
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作者：
R. Niswonger;D. E. Prudic;R. Regan
降水通过包气带的渗流对地下水的补给具有重要意义。降雨和融雪在地表被划分为不同的途径，包括径流，入渗，蒸散，非饱和带存储和补给。开发了一个新的MODFLOW 2005软件包，称为非饱和带流（UZF 1）包，以模拟非饱和带中的水流和储水，并将水流划分为蒸散和补给。这套方案还考虑了流向河流和湖泊的地表径流。用特征线法求解运动波近似的理查兹方程，模拟垂向非饱和水流。该方法假设，非饱和流发生在响应重力势梯度，忽略负势梯度;该方法进一步假设均匀的水力特性在非饱和区的每个垂直列的模型单元。Brooks-Corey函数用于定义非饱和导水率与含水量之间的关系。UZF 1程序包使用的变量包括初始和饱和含水量、饱和垂直导水率和Brooks-Corey函数中的指数。残余水含量由UZF 1软件包根据饱和水含量和单位产率之间的差异进行内部计算。UZF 1包是MODFLOW-2005的补给和蒸散包的替代品。UZF 1包与回灌包的不同之处在于，在陆地表面采用渗透率，而不是直接对地下水采用规定的回灌率。所施加的入渗速率进一步受到饱和垂直导水率的限制。UZF 1包与蒸散包的不同之处在于，蒸散损失首先从蒸散消失深度以上的非饱和带中去除，如果需求得不到满足，只要地下水深度小于消失深度，就可以直接从地下水中去除水。UZF 1包与蒸散包的不同之处还在于，只要地下水位高度超过陆地表面，水就直接排到陆地表面。排放到陆地表面的水，以及超过饱和垂直水力传导率的应用渗透，如果这些包是活动的，则可以直接作为流入指定的河流或湖泊的流入量;否则，将从模型中删除这些水。UZF 1软件包针对美国地质调查局的变饱和二维流动和传输模型进行了测试，用于解决包括蒸散损失在内的垂直非饱和流问题。本报告还包括一个例子，其中MODFLOW-2005与UZF 1包被用来模拟一个现实的地表水/地下水流问题，包括时间和空间变量的渗透，蒸散，径流，地下水排放到陆地表面和溪流。另一个更简单的问题，使用户可以使用输入文件作为模板的新问题，并验证正确的代码安装。
Percolation of precipitation through unsaturated zones is important for recharge of ground water. Rain and snowmelt at land surface are partitioned into different pathways including runoff, infiltration, evapotranspiration, unsaturated-zone storage, and recharge. A new package for MODFLOW2005 called the Unsaturated-Zone Flow (UZF1) Package was developed to simulate water flow and storage in the unsaturated zone and to partition flow into evapotranspiration and recharge. The package also accounts for land surface runoff to streams and lakes. A kinematic wave approximation to Richards’ equation is solved by the method of characteristics to simulate vertical unsaturated flow. The approach assumes that unsaturated flow occurs in response to gravity potential gradients only and ignores negative potential gradients; the approach further assumes uniform hydraulic properties in the unsaturated zone for each vertical column of model cells. The Brooks-Corey function is used to define the relation between unsaturated hydraulic conductivity and water content. Variables used by the UZF1 Package include initial and saturated water contents, saturated vertical hydraulic conductivity, and an exponent in the Brooks-Corey function. Residual water content is calculated internally by the UZF1 Package on the basis of the difference between saturated water content and specific yield. The UZF1 Package is a substitution for the Recharge and Evapotranspiration Packages of MODFLOW-2005. The UZF1 Package differs from the Recharge Package in that an infiltration rate is applied at land surface instead of a specified recharge rate directly to ground water. The applied infiltration rate is further limited by the saturated vertical hydraulic conductivity. The UZF1 Package differs from the Evapotranspiration Package in that evapotranspiration losses are first removed from the unsaturated zone above the evapotranspiration extinction depth, and if the demand is not met, water can be removed directly from ground water whenever the depth to ground water is less than the extinction depth. The UZF1 Package also differs from the Evapotranspiration Package in that water is discharged directly to land surface whenever the altitude of the water table exceeds land surface. Water that is discharged to land surface, as well as applied infiltration in excess of the saturated vertical hydraulic conductivity, may be routed directly as inflow to specified streams or lakes if these packages are active; otherwise, this water is removed from the model. The UZF1 Package was tested against the U.S. Geological Survey’s Variably-Saturated Two-Dimensional Flow and Transport Model for a vertical unsaturated flow problem that includes evapotranspiration losses. This report also includes an example in which MODFLOW-2005 with the UZF1 Package was used to simulate a realistic surfacewater/ground-water flow problem that includes time and space variable infiltration, evapotranspiration, runoff, and groundwater discharge to land surface and to streams. Another simpler problem is presented so that the user may use the input files as templates for new problems and to verify proper code installation.