Link to USGS home page.
Texas Water Science Center

Estimated Depth to the Water Table and Estimated Rate of Recharge in Outcrops of the Chicot and Evangeline Aquifers near Houston, Texas

By J.E. Noble, P.W. Bush, M.C. Kasmarek, and D.L. Barbie

U.S. Geological Survey
Water-Resources Investigations Report 96–4018

In cooperation with the Harris-Galveston Coastal Subsidence District


Abstract

In 1989, the U.S. Geological Survey, in cooperation with the Harris-Galveston Coastal Subsidence District, began a field study to determine the depth to the water table and to estimate the rate of recharge in outcrops of the Chicot and Evangeline aquifers near Houston, Texas. The study area comprises about 2,000 square miles of outcrops of the Chicot and Evangeline aquifers in northwest Harris County, Montgomery County, and southern Walker County. Because of the scarcity of measurable water-table wells, depth to the water table below land surface was estimated using a surface geophysical technique, seismic refraction. The water table in the study area generally ranges from about 10 to 30 feet below land surface and typically is deeper in areas of relatively high land-surface altitude than in areas of relatively low land-surface altitude. The water table has demonstrated no long-term trends since ground-water development began, with the probable exception of the water table in the Katy area: There the water table is more than 75 feet deep, probably due to ground-water pumpage from deeper zones. An estimated rate of recharge in the aquifer outcrops was computed using the interface method in which environmental tritium is a ground-water tracer. The estimated average total recharge rate in the study area is 6 inches per year. This rate is an upper bound on the average recharge rate during the 37 years 1953–90 because it is based on the deepest penetration (about 80 feet) of postnuclear-testing tritium concentrations. The rate, which represents one of several components of a complex regional hydrologic budget, is considered reasonable but is not definitive because of uncertainty regarding the assumptions and parameters used in its computation.

Table of Contents

Abstract

Introduction

Purpose and Scope

Geology and Hydrogeology

Acknowledgments

Estimated Depth to the Water Table

Seismic-Refraction Method and Field Application

Water-Table Depth from Seismic Refraction

Estimated Rate of Recharge

Method of Computing Recharge Rate Using Environmental Tritium

Field Application of the Method and Computation of Recharge Rate

Evaluation of Recharge Rate

Conclusions

References Cited

Plate

1.   Map showing estimated depth to the water table near Houston, Texas, 1989–90

Figures

1.   Map showing location of study area and outcrops of the Chicot and Evangeline aquifers near Houston, Texas
2.   Correlation chart showing geologic and hydrogeologic units in the study area near Houston, Texas
3.   Diagrams showing (A) sound-wave propagation in unsaturated and saturated zones and detection at land surface, and (B) the corresponding time-distance curve
4.   Hydrographs of water-table wells (A) LJ–65–02–311, (B) LJ–65–12–725, and (C) TS–60–45–803 completed in the Chicot aquifer near Houston, Texas
5.   Map showing location of tritium sampling sites near Houston, Texas
6.   Graph showing sample depth below the water table as a function of tritium concentration in samples from selected wells in the Chicot and Evangeline aquifers near Houston, Texas, 1989–90

Tables

1.   Measured and seismic-computed water-table depths at seismic-verification sites near Houston, Texas
2.   Environmental tritium concentrations in samples from selected wells in the Chicot and Evangeline aquifers near Houston, Texas, 1989–90

This report is available as a pdf (541 KB)

plate (16.3 MB, 21" x 24")

To view this document, you need the Adobe Acrobat® Reader installed on your computer.
(A free copy of the Acrobat® Reader may be downloaded from Adobe Systems Incorporated.)


U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/wri964018
Page Contact Information: USGS Publishing Network
Last modified: October 12 2006, 04:28:33 AM
FirstGov button  Take Pride in America button