USGS Scientific Investigations Report 2008-5005
Prepared in cooperation with the Mobile Area Water and Sewer System
By Carl S. Carlson and Stacey A. Archfield
U.S. Geological Survey Scientific Investigations Report 2008-5005, 21 pages
This report is available in PDF format:
SIR 2008-5005 (
) (1.55 MB)
J.B. Converse (Converse) Lake is the primary source of drinking water for the city of Mobile, Alabama. Concerns regarding the ability of the reservoir to meet current and future water demands during drought conditions have prompted this study. The 1991 through 2006 water years included a drought that occurred during 2000, and drought conditions currently (2007) are affecting the area. To assist officials of the Mobile Area Water and Sewer System in planning for future demands for drinking water in the Mobile metropolitan area, the firm yield for Converse Lake was estimated by the U.S. Geological Survey.
The firm yield of Converse Lake was estimated using the Massachusetts Department of Environmental Protection’s firm-yield-estimator (FYE) model, which recently was refined by the U.S. Geological Survey. The model uses a mass-balance approach to determine the maximum average daily withdrawal rate that can be sustained during a period of record that includes a drought of record. If the reservoir is in contact with an aquifer, the FYE also includes routines that estimate the volume of ground-water and surface-water exchange between the aquifer and the reservoir.
The average daily firm yield for Converse Lake was estimated to be 79 million gallons per day using the FYE routine that does not include ground-water exchange between the reservoir and the adjacent aquifer. Observed lake levels and withdrawals during the drought of 2000 indicate that more than 74 million gallons per day of water were withdrawn without complete depletion of reservoir storage. Therefore, it is likely that ground-water exchange with the reservoir may supplement available reservoir storage. If water exchange occurs between the aquifer and the reservoir, an increase in the volume of water available to the reservoir may occur during a drought. To quantify the potential ground-water contribution to reservoir storage, an analytical solution was applied to the FYE simulation of Converse Lake to estimate ground-water exchange between the reservoir and the aquifer. Aquifer properties required by the FYE were estimated by model calibration to observed water levels that occurred during the drought of 2000. When ground-water exchange between the reservoir and adjacent aquifer is included, the average daily firm yield increased to 83 million gallons per day.
The estimate of 83 million gallons per day incorporates both total surface-water flow and ground-water exchange components. This analysis indicated that direct ground-water interaction contributes about 5 percent of the firm yield of Converse Lake. However, the average daily firm yield of 83 million gallons per day, based in part on calibrated values for aquifer transmissivity and storage, can be used only as a guideline until these aquifer properties can be defined better by field investigation in the Converse Lake watershed.
Abstract
Introduction
Hydrogeology of the J.B. Converse Lake Watershed
Hydrologic Setting
Climatic Conditions
Surface-Water Inflows
Reservoir Characteristics
Reservoir Conditions: 1994 through 2006
Geologic Setting
Major Hydrogeologic Units
Aquifer Properties
Firm-Yield Estimator Methodology and Calibration
Firm-Yield Assessment of J.B. Converse Lake
Model Limitations and Uncertainty
Summary
References Cited
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Suggested citation: Carlson, C.S., and Archfield, S.A., 2009, Hydrogeologic conditions and a firm-yield assessment for J.B. Converse Lake, Mobile County, Alabama, 1991–2006: U.S. Geological Survey Scientific Investigations Report 2008–5005, Second Edition--February 2009, 21 p. (available online at http://pubs.water.usgs.gov/sir2008-5005).
For more information, please contact Carl S. Carlson.
U.S. Department of the Interior |
U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/sir2008-5005
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Page Last Modified: Thursday, 10-Jan-2013 19:03:20 EST
