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Water-Resources Investigations Report 99–4225

Prepared in cooperation with the Groundwater Resources Program

WTAQ—A Computer Program for Calculating Drawdowns and Estimating Hydraulic Properties for Confined and Water-Table Aquifers

By Paul M. Barlow and Allen F. Moench

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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 ground-water flow in a homogeneous and anisotropic aquifer. The program allows for well-bore storage and well-bore skin at the pumped well and for delayed drawdown response at an observation well; by including these factors, it is possible to accurately evaluate the specific storage of a water-table aquifer from early-time drawdown data in observation wells and piezometers. 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. Three sample problems illustrate use of WTAQ for estimating horizontal and vertical hydraulic conductivity, specific storage, and specific yield of a water-table aquifer by type-curve methods and by an automatic parameter-estimation method.

Posted December 2009

For additional information contact:
Paul Barlow,
Massachusetts and Rhode Island
Water Science Center
U.S. Geological Survey
10 Bearfoot Road
Northborough, MA 01532
http://ma.water.usgs.gov

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Suggested citation:

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, 84 p.



Contents

Abstract

Introduction

Axial-Symmetric Flow in Confined and Water-Table Aquifers

Program WTAQ

Simplifying Assumptions

Description of Selected Program Options and Variables

Data-Input Files

Type-Curve Format

Dimensional Format

Result and Plot Files

Sample Problems

Sample Problem 1—Estimation of Horizontal and Vertical Hydraulic Conductivity and
Specific Yield Using Type-Curve Format

Sample Problem 2—Estimation of Specific Storage Using Dimensional Format

Sample Problem 3—Automatic Parameter Estimation Using Dimensional Format

Summary

References

Attachment 1: Narrative for Program WTAQ

Attachment 2: Sample Input Files for use of WTAQ with UCODE



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