Techniques and Methods 6-A19
U.S. GEOLOGICAL SURVEY
Techniques and Methods 6-A19
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
Conversion Factors, Datums, and Acronyms
Theory and Conceptualization of Unsaturated-Zone Flow
Comparison of UZF1 and VS2DT Simulations
Implementation of UZF1 With MODFLOW-2005
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)
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.
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.