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 an analytical model of axial-symmetric groundwater flow in a homogeneous and anisotropic aquifer (Moench, 1997; complete reference below). The program allows for well-bore storage and well-bore skin at the pumped well and for delayed drawdown response at an observation well. For water-table aquifers, the program allows for either delayed or instantaneous drainage from the unsaturated zone. 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). The Laplace-transform solutions are numerically inverted to the time domain by means of the Stehfest (1970) algorithm in the same manner as was done in Moench (1996, 1997). 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
Version 1.0, released 10/01/1999.
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 report by Barlow and Moench (1999).
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
The program is documented in:
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.
REFERENCES
Moench, A.F., 1996, Flow to a well in a water-table aquifer--an improved Laplace transform solution: Groundwater, v. 34, no. 4, p. 593-596.
_____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
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U.S. Geological Survey
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U.S. Department of the Interior, U.S. Geological Survey
10 Bearfoot Road
Northborough, MA 01532
(508) 490-5000