U.S. Geological Survey (USGS) wtaq
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NAME
wtaq - A computer program for calculating drawdowns and estimating
hydraulic properties for confined and water-table aquifers
ABSTRACT
The computer program WTAQ calculates hydraulic-head drawdowns in a
confined or water-table aquifer that result from pumping at a well
of finite or infinitesimal diameter. The program is based on
analytical models of axial-symmetric groundwater flow in a homogeneous
and anisotropic aquifer developed by Moench (1997) and Mathias and
Butler (2006). The program allows for well-bore storage and well-bore
skin at the pumped well and for delayed drawdown response at observation
wells or piezometers. For water-table aquifers, the program allows three
options for simulating drainage from the unsaturated zone: instantaneous
drainage, gradual drainage, or drainage that explicitly accounts for
hydraulic characteristics of the unsaturated zone (specifically, the
moisture retention and relative hydraulic conductivity of the soil).
WTAQ calculates dimensionless or dimensional theoretical drawdowns that
can be used with measured drawdowns at observation points to estimate
the hydraulic properties of confined and water-table aquifers.
METHOD
Program WTAQ implements the Laplace-transform solutions for drawdown
at a pumped well, observation well, or observation piezometer that
are given in equations 18-27 and 30-31 in Moench (1997) and equation 42
in Mathias and Butler (2006). The Laplace-transform solutions are
numerically inverted to the time domain by means of either the Stehfest
(1970) or de Hoog (1982) algorithms. The program calculates dimensionless
or dimensional drawdowns for a given set of input conditions that are
specified by the user in a data-input file.
HISTORY
WTAQ version 2.1 06/29/2012 - Minor bug fix to allow code to run when
SIGMA is specified as 0 (for confined aquifers); previous versions
stopped, with an error message, if SIGMA was specified as 0.
WTAQ version 2.0 04/29/2011 - Added analytical model of Mathias and
Butler (2006) for improved representation of drainage to water-
table aquifers from the unsaturated zone.
WTAQ version 1.2 04/29/2011 - Minor bug fix to variable name IOWS.
WTAQ version 1.1 11/13/2009 - Improved internal checks for incorrect
data values.
WTAQ version 1.0 10/01/1999 - Initial release.
DATA REQUIREMENTS
To use WTAQ, the user must prepare a data-input file that contains
information on the type of aquifer being simulated (confined or water
table), hydraulic properties of the aquifer, characteristics of the pumped
well and of all observation wells and(or) observation piezometers at
which drawdowns will be calculated, and additional information for model
solution. Input-data requirements are explained in the documentation
reports by Barlow and Moench (1999 and 2011).
OUTPUT OPTIONS
Primary output is drawdown calculated as a function of time at the pumped
well and at up to 25 observation-well and(or) observation-piezometer
locations. A result file and plot file are generated by the program. The
result file contains detailed information on the model simulation,
whereas the plot file contains an abbreviated listing of model results
that can be used for graphing.
SYSTEM REQUIREMENTS
WTAQ is written in Fortran 77. Input and result file names are queried by
the program and read from the screen. The program also can be run in
batch mode by redirecting program execution from the screen to a batch
file that contains the names of the input and output files.
DOCUMENTATION
Barlow, P.M., and Moench, A.F., 1999, WTAQ--A computer program for calculating
drawdowns and estimating hydraulic properties for confined and water-table
aquifers: U.S. Geological Survey Water-Resources Investigations Report
99-4225, 74 p.
Barlow, P.M., and Moench, A.F., 2011, WTAQ Version 2--A computer program for
analysis of aquifer tests in confined and water-table aquifers with alternative
representations of drainage from the unsaturated zone: U.S. Geological Survey
Techniques and Methods 3-B9, 41 p.
REFERENCES
de Hoog, F.R., Knight, J.H., and Stokes, A.N., 1982, An improved method for
numerical inversion of Laplace transforms: SIAM Journal of Scientific Computing,
v. 3, no. 4, p. 1059-1071.
Mathias,S.A., and Butler, A.P., 2006, Linearized Richards' equation approach
to pumping test analysis in compressible aquifers: Water Resources Research,
v. 42, W06408, doi:10.1029/2005WR004680, 10 p.
Moench, A.F., 1997, Flow to a well of finite diameter in a homogeneous,
anisotropic water table aquifer: Water Resources Research, v. 33, no. 6,
p. 1397-1407.
Stehfest, Harald, 1970, Numerical inversion of Laplace transforms:
Communications of the Association for Computing Machinery (ACM), v. 13, no. 1,
p. 47-49.
CONTACTS
Paul Barlow
U.S. Geological Survey
10 Bearfoot Road
Northborough, MA 01532
pbarlow@usgs.gov
Allen Moench
U.S. Geological Survey
MS 496
345 Middlefield Road
Menlo Park, CA 94025
afmoench@usgs.gov