User's guide of Proceessing Modflow 5.0

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6.5.3 Seepage Surface through a Dam
Folder: \pm5\examples\geotechniques\geo3\
Overview of the Problem
This example demonstrates how to calculate the seepage surface using a vertical cross-sectional
model. As shown in Fig. 6.49, the length of the dam is 100 m, the thickness and height are 10m.
The water table is 10 m at the upstream side of the dam and 2 m at the downstream side. The
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material of the dam is homogeneous and isotropic with a hydraulic conductivity of 1 × 10 m/s.
The unrealistic bank is used here to simplify the data input.
Your task is to calculate the seepage surface and the seepage rate by using a vertical cross-
sectional numerical model. Compare the seepage rate with an analytical solution after Dupuit.
Fig. 6.49 Seepage surface through a dam
Modeling Approach and Simulation Results
To compute the head distribution and the seepage surface, it is sufficient to consider a vertical
cross-section of the aquifer with a uniform thickness of 1 m. The aquifer is simulated using a
grid of one layer, 21 columns and 20 rows. A regular grid space of 0.5 m is used for each
column. The layer type is 0:confined. The boundary at the upstream side of the dam is modeled
as fixed-head boundary with the hydraulic head h = 10 m. On the right-hand side of the dam,
there are four fixed-head cells with h = 2 m. The other cells on this boundary are modelled as
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drain cells with a high drain hydraulic conductance [L T ] value. The elevation of the drain is
set the same as the bottom elevation of each cell, for example the 2.0 m for the cell [21, 16, 1]
and 2.5 m for the cell [21, 15, 1]. The drain cells are activated only if water table is higher than
the level of the drain. The selected model grid and the boundary conditions are shown in Fig.
6.5.3 Seepage Surface through a Dam