Georgia Water Science Center
This report is available online in pdf format (18.4 MB): USGS SIR 2006-5234 (
)
L. Elliott Jones and Lynn J. Torak
U.S. Geological Survey Scientific Investigations Report 2006-5234, 83 pages (Published December 2006)
To determine the effects of seasonal ground-water pumpage
for irrigation, a finite-element ground-water flow model
was developed for the Upper Floridan aquifer in the lower
Flint River Basin area, including adjacent parts of the Chattahoochee
and Apalachicola River Basins. The model simulates
withdrawal from the aquifer at 3,280 irrigation, municipal,
and industrial wells; stream-aquifer flow between the aquifer
and 36 area streams; leakage to and from the overlying
upper semiconfining unit; regional ground-water flow at the
lateral boundaries of the model; and water-table recharge in
areas where the aquifer is at or near land surface. Steady-state
calibration to drought conditions of October 1999 indicated
that the model could adequately simulate measured groundwater
levels at 275 well locations and streamflow gains and
losses along 53 reaches of area streams. A transient simulation
having 12 monthly stress periods from March 2001 to February
2002 incorporated time-varying stress from irrigation
pumpage, stream and lake stage, head in the overlying upper
semiconfining unit, and infiltration rates.
Analysis of simulated water budgets of the Upper Floridan aquifer provides estimates of the source of water pumped for irrigation. During October 1999, an estimated 127 million gallons per day (Mgal/d) of irrigation pumpage from the Upper Floridan aquifer in the model area were simulated to be derived from changes in: stream-aquifer flux (about 56 Mgal/d, or 44 percent); leakage to or from the upper semiconfining unit (about 49 Mgal/d, or 39 percent); regional flow (about 18 Mgal/d, or 14 percent); leakage to or from Lakes Seminole and Blackshear (about 2.7 Mgal/d, or 2 percent); and flux at the Upper Floridan aquifer updip boundary (about 1.8 Mgal/d, or 1 percent). During the 2001 growing season (May–August), estimated irrigation pumpage ranged from about 310 to 830 Mgal/ d, about 79 percent of the 12-month total. During the growing season, irrigation pumpage was derived from decreased discharge or increased recharge of stream-aquifer flux (from about 23 to 39 percent), leakage to or from the upper semiconfining unit (from about 30 to 36 percent), regional flow (from about 8 to 11 percent), Lakes Seminole and Blackshear (about 2 percent), and flux at the Upper Floridan aquifer updip boundary (about 1 percent). Storage effects (decreased storage gain or increased storage loss) contributed from about 11 to 36 percent of irrigation pumpage during the growing season.
Water managers can use the model to determine where and how much additional ground-water pumpage for irrigation should be permitted based on a variety of hydrologic constraints. For example, the model results may indicate that in some critical locations, additional ground-water pumpage during a prolonged drought might reduce stream-aquifer flux enough to cause noncompliance of established minimum instream flow conditions.
Abstract
Introduction
Purpose and Scope
Previous Studies
Model Area
Climate
Physiography and Drainage
Geohydrologic Setting
Well and Surface-Water Station Numbering System
Acknowledgments
Simulated Effects of Seasonal Ground-Water Pumpage
Ground-Water Flow Model Development
Conceptualization of Geohydrologic Flow System
Governing Equations and Simulation Approach
Finite-Element Mesh
Specified-Head Boundary: Upper Floridan Aquifer Updip Limit
Specified-Flux Boundaries
Irrigation Pumpage
Industrial and Municipal Pumpage and Off-Channel Springflow
Infiltration
Head-Dependent Flux Boundaries
Regional Ground-Water Flow
Flow Across Streambeds
Upper Semiconfining Unit and Lake-Bed Leakage
Upper Floridan Aquifer Characteristics
Ground-Water Flow Model Performance and Analysis
Steady-State Calibration, October 1999
Calibration Strategy
Ground-Water Level Residuals
Stream-Aquifer Flow
Sensitivity Analysis
Parameter Uncertainty
Ground-Water Flow Direction
Transient Simulation, March 2001—February 2002
Water-Budget Components
Source of Seasonal Ground-Water Pumpage
Model Limitations
Summary and Conclusions
References Cited
Appendix A
This report is available online in pdf format (50 MB): USGS SIR 2006-5234 ()
To view the PDF 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.)
Recent USGS publications on Georgia or Georgia Water-Resources Information
For more information, please contact webmaster-ga@usgs.gov.
U.S. Department of the Interior |
U.S. Geological Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065234
Page Contact Information: USGS Publishing Network
Page Last Modified: Thursday, 01-Dec-2016 19:28:55 EST
