Techniques and Methods 6-A19
U.S. GEOLOGICAL SURVEY
Techniques and Methods 6-A19
Documentation of the Unsaturated-Zone Flow (UZF1) Package for Modeling Unsaturated
Flow Between the Land Surface and the Water Table with MODFLOW-2005
A Product of the Ground-Water Resources Program
Chapter 19 of Section A, Ground Water, of Book 6, Modeling Techniques
By Richard G. Niswonger, David E. Prudic, and R. Steven Regan
Table of Contents
Conversion Factors, Datums, and Acronyms
PREFACE
Abstract
Introduction
Theory and Conceptualization of Unsaturated-Zone
Flow
Comparison of UZF1 and VS2DT Simulations
Test Simulations
Implementation of UZF1 With MODFLOW-2005
Summary
References Cited
Appendix 1. Data Input Instructions
for the Unsaturated-Zone Flow (UZF1) Package (PDF, 91 KB)
Appendix 2. Selected Input Datasets and Printed Results for Test Simulation 2 (PDF, 305 KB)
Figures
Figure 1. One-dimensional unsaturated-zone
flow coupled to three-dimensional ground-water flow.
Figure 2. A wetting front moving through
a uniform column of unsaturated material affected by a decrease in surface flux,
and results from a kinematic-wave solution of the wetting front represented
by leading and trailing waves.
Figure 3. Kinematic-wave approximation
of a wetting front moving through a uniform column of unsaturated material affected
by a constant evapotranspiration rate of 4.35 millimeters per day.
Figure 4. Comparison of results from
the kinematic-wave approximation used to simulate unsaturated flow (UZF1) with
a two-dimensional finite-difference solution of Richards’ equation (VS2DT; Healy,
1990) assuming evapotranspiration demand rates of: (A) 5 ×
10-8 meter per second, (B)
5 × 10-7 meter per second, and (C) 1 ×
10-6 meter per second.
Figure 5. Distribution of hydraulic
conductivity from ground-water model used for test simulation 1.
Figure 6. Distribution of steady-state
ground-water depths used for test simulation 1.
Figure 7. Infiltration rate and evapotranspiration
demand used for test simulation 1.
Figure 8. Distribution of infiltration
factors used for test simulation 1.
Figure 9. Volumetric rates of infiltration,
recharge, and evapotranspiration summed over the model domain for test simulation
1.
Figure 10. Streamflow at the basin
outlet, ground-water discharge to land surface plus saturation excess, and ground-water
discharge to streams for test simulation 1.
Figure 11. Distribution of ground-water
seepage to land surface for (A) steady state, and (B) July
1.
Figure 12. Water-content profiles
in the unsaturated zone of a model cell located in an upland area (column 9,
row 36) at selected dates for test simulation 1.
Figure 13. Well locations, elevation
of top of consolidated rocks beneath basin-fill aquifer, and distribution of
hydraulic conductivity and specific yield of the basin-fill aquifer used in
test simulation 2.
Figure 14. Hypothetical basin-fill
aquifer with model grid, land-surface contours, active cells, and stream segment
and reach numbering for test simulation 2.
Tables
Table 1. Unsaturated zone variables
used in comparison of results from the Unsaturated-Zone Flow (UZF1) Package
in MODFLOW-2005 with those from the Variably-Saturated Two-Dimensional Flow
and Transport (VS2DT) Model.
Table 2. MODFLOW-2005 Packages and files
used for test simulation 1.
Table 3. Hydraulic properties and other
selected variables used in the Layer-Property Flow (LPF) and the Unsaturated-Zone
Flow (UZF1) Packages for test simulation 1.
Table 4. Method for calculating stream
depth and width, inflow rates, streambed properties, stream dimensions, and
Manning’s roughness coefficients for stream segments used in test simulation
2.
Table 5. Specified infiltration and
pumping rates for the 12 stress periods used in test simulation 2.
Table 6. Hydraulic properties and other
selected variables used in the Layer-Property Flow (LPF) and Unsaturated-Zone
Flow (UZF1) Packages for test simulation 2.
Table 7. Computed ground-water budget
for test simulation 2.
Table 8. Computed unsaturated-zone budget
for test simulation 2.
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Send questions or comments about this report to the author, R.G. Niswonger, (775) 887-7639.
U.S.
Department of the Interior | U.S. Geological
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