DOCUMENTATION FOR PREPARING THE INPUT FILE OF THE UPDATEDHYDRUS PACKAGE FOR MODFLOW-2000
Updated May 2008
Navin Kumar C. Twarakavi1, Hyeyoung Sophia Seo2 and Jirka Simunek1
12

University of California, Riverside, 900 University Ave. Riverside CA 92521, Jiri.Simunek@ucr.edu
Colorado School of Mines, 1500 Illinois St. Golden CO 80401, hseo@mines.edu, epoeter@mines.edu

The input to the HYDRUS Package is read from the file that is type “UNSF” in the name file.
Note that the HYDRUS package comes with an author supplied template for ease in preparing thepackage input file. The input files may have any number of comment lines. Unlike other
MODFLOW packages, the HYDRUS package can have any number of comment lines. However,each comment line must be distinguished by starting it with a ‘#’ sign. Input in ‘[ ]’ is notmandatory and is required under some conditions.

FOR EACH SIMULATION
0. [ #Text ]1. NPUNSP NUNSFOP IUNSFCB IUNSFpr
2. NMAT MAXNP MAXATM
3. Zonarr
4. MaxIt TolTh TolH
5. DT DTMIN DTMAX DMUL DMUL2 ITMIN ITMAX
6. HTAB1 HTABN iMODEL
7. THR THS ALPHA N KS L (Repeat item 7 NMAT times.)
8. PROPR[PROINF][PRINT TIMES, must be repeated PROpr times]
FOR EACH PROFILE
9. [IZ]
10. SINKF WLAYER LINITW NOMAT
11. NUMNP
12. N Z(n) H MAT BETA
(Repeat item 11 NUMNP times.)
13. [P0 P2H P2L P3 r2H r2L POPTM](Read when SINKF ≥ 0.)
14. MAXAL hCritS
15. tAtm Prec rSoil rRoot hCritA(Repeat item 14 MAXAL times.)EXPLANATION OF VARIABLES
TextCharacter variable (199 characters) that starts in column 2. Any characters
can be included in Text. The “#” character must be in column 1. Text is
printed when the file is read.

NPUNSP

Number of unsaturated flow profiles.

NUNSFOP

Unsaturated flux option code. The flux is either applied to the first layerin each vertical column or to the highest active layer.
1; Unsaturated flux is applied to layer one.
2; Unsaturated flux is applied to the highest active layer in each verticalcolumn.

IUNSFCB

Flag and a unit number.
If IUNSFCB > 0, it is the unit number to which cell-by-cell flow terms
will be written when “SAVE BUDGET” or a non-zero value for
IUNSFCB is specified in Output Control.
If IUNSFCB ≤ 0, cell-by-cell flow terms will not be written.

IUNSFprOutput flag. The possible values of IUNSFpr and their meanings are as
follows:
If IUNSFpr = 0, then only input is printed.
If IUNSFpr = 1, then an echo of input and the fluxes from the UNSF
package are printed at the end of each time period.
If IUNSFpr = 2, then no input is echoed but fluxes are printed at the end ofeach time step.

NMATTotal number of soil materials in the model domain. Materials are
identified by the material number, MatNum.

MAXNP

Maximum number of nodal points in a HYDRUS profile.

MAXATM

Maximum number of atmospheric data.

ZonarrName of the zone array to be used to define the cells that are associatedwith each profile. The name “ALL” means that there is no zone array andone HYDRUS profile is used for all MODFLOW grid cells. The name
“EACH” means that the HYDRUS profile is used for each MODFLOW
grid cell.

MaxIt

Maximum number of iterations allowed during any unsaturated flow
calculation time step, while solving the nonlinear Richards' equation usinga modified Picard method. The suggested value is 20.

2TolTh

Absolute water content tolerance for nodes in the unsaturated flow model(the suggested initial value is 0.0001). TolTh represents the maximum
desired absolute change in the value of the water content between two
successive iterations during a time step. If the numerical solution does notconverge, the user may try to relax these criteria, or use finer discretization.

TolH

Absolute pressure head tolerance for nodes in the saturated flow model (itsrecommended initial value is 0.1cm). TolH represents the maximum
desired absolute change in the value of the pressure head between two
successive iterations during a particular time step. If the numericalsolution does not converge, the user may try to relax these criteria, or use
finer discretization.

DTInitial time increment, Δt [T]. Initial time step should be estimated withrespect to the problem being solved. For problems with high pressure
gradients (e.g. infiltration into and initially dry soil), Δt should berelatively small.

DTMIN

Minimum permitted time increment for the unsaturated zone model, Δtmin
[T].

DTMAX

Maximum permitted time increment for the unsaturated zone model, Δtmax
[T].

DMUL

Dimensionless number to multiply Δt for the next time step when thenumber of required iterations at a particular time step is less than or equal
to ITMIN. The recommended value ranges between 1.0 and 1.3.

DMUL2

Dimensionless number to multiply Δt for the next time step when thenumber of required iterations at a particular time step is less than or equal
to ITMAX. Usually DMUL2 is less than 1.0, and the recommended value is0.7.

ITMIN

Lower optimal iteration range. When the number of iterations necessary
to reach convergence for water flow is less than or equal to this number,the time step is multiplied by a dimensionless number DMUL.
Recommended value is 3.

ITMAX

Upper optimal iteration range. When the number of iterations necessary toreach convergence for water flow is higher than this number, the time stepis multiplied by a dimensionless number DMUL2. Recommended value is7.

HTAB1

Absolute value of the upper limit [L] of the pressure head interval below
which a table of hydraulic properties will be generated internally for eachmaterial (HTAB1 must be greater than 0.0; e.g. 0.001cm).

3HTABN

Absolute value of the lower limit [L] of the pressure head interval forwhich a table of hydraulic properties will be generated internally for eachmaterial (e.g. 1000m). If the absolute value of the pressure head during
program execution lies outside of the interval [HATB1, HTABN], thenappropriate values for the hydraulic properties are computed directly fromthe hydraulic functions (i.e. without interpolation in the table).

iModelSoil hydraulic properties model:= 0; van Genuchten= 1; van Genuchten with air entry value of 2 cm
= 2; Brooks and Corey

THR

Residual water content.

THS

Saturated water content.

ALPHA
NL

Inverse of the air-entry value (or bubbling pressure)
Pore size distribution index
Pore-connectivity parameter

KS

Saturated hydraulic conductivity.

PROPR

A flag that allows for printing HYDRUS profile information at selected
print times. The profiles are printed in ‘profile.out’.
≤0; Profile information not printed.
>0; Profile information printed for PROPR number of times.

PROINF

A flag that indicates what kind of profile information has to be printed,.
This is required only if PROPR >0.
≤0; pressure heads at each node is printed.
>0; water contents are printed.
PRINT TIMES A line with the times (number of times=PROPR) at which the profile
information needs to be printed.
IZ

Zone number that defines the cells associated with the profile. Thesevalues are omitted if Zonarr is specified as “ALL” or “EACH”. The
HYDRUS Profile starts with a cell at column 1 and row 1 and moves tocolumn 2 and row 1.

SINKF

Root water uptake flag.
If SINKF ≥ 0, water extraction from the root zone occurs.
If SINKF < 0, no water extraction from the root zone.

WLAYER

Water accumulation flag.

4

If WLAYER ≥ 0, water can accumulate at the surface (There is no surfacerunoff).
If WLAYER < 0, any excess water on the soil surface will be immediatelyremoved (It is assumed to runoff).
LINITW

Initial condition flag.
If LINITW ≥ 0, the initial condition is given in terms of water content.
If LINITW < 0, the initial condition is given in terms of pressure head.

NOMAT

Number of soil materials in the profile.

NUMNP

Number of nodal points.

NNodal number. Nodes are numbered sequentially from 1 to NumNP (total
number of nodes) from the soil surface to the bottom of the soil profile.

Z(n)Z-coordinate of node n. Z=0 at the sea level.

HInitial value of the pressure head at node n expressed in terms of height ofa column of water.

MAT

Index for material whose hydraulic properties are assigned to node n.

BETA

Value of water uptake distribution, b(z) [L-1], in the soil root zone at thenode n. Set beta (n) equal to zero if node n lies outside the root zone. b(z)is the normalized water uptake distribution in the equation (39).

P0

Value of the pressure head below which the roots start to extract waterfrom the soil. Required if SINKF≥0.

P2H

Value of the limiting pressure head at which the roots cannot extract waterat the maximum rate (assuming a potential transpiration rate of r2H).
Required if SINKF≥0.

P2L

Value of the limiting pressure head at which the roots cannot extract waterat the maximum rate (assuming a potential transpiration rate of r2L).
Required if SINKF≥0.

P3

Value of the pressure head below which root water uptake ceases (usuallyequal to the wilting point). Required if SINKF≥0.

r2H

Highest potential transpiration rate [LT-1]. Required if SINKF≥0.

r2L

Lowest potential transpiration rate [LT-1]. Required if SINKF≥0.

5

POPTM

Value of the pressure head below which roots start to extract water at themaximum possible rate. Required if SINKF≥0.

MAXAL

Number of atmospheric data records.

hCritS

Maximum allowed pressure head at the soil surface (usually 0.0).

tAtm

Time for which the i-th atmospheric data record is provided [T]. Time isspecified relative to the start of the MODLOFW simulation.

Prec

Precipitation rate [L/T]. Prec, rSoil, and rRoot are always positive. If a
negative value is entered, the absolute value will be used.

rSoil

Potential evaporation rate in absolute value [L/T].

rRoot

Potential transpiration rate in absolute value [L/T].

hCritA

Absolute value of the minimum allowed pressure head at the soil surface[L] (defined from equilibrium conditions between soil water andatmospheric vapor).

6