Hydrologic conditions and a firm-yield assessment for J.B. Converse Lake, Mobile County, Alabama, 1991-2006

Abstract

Vertical coordinate information is referenced to the North American Vertical Datum of 1929 (NGVD 29).Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).Elevation, as used in this report, refers to distance above the vertical datum. *Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times foot of aquifer thickness [(ft 3 /d)/ft 2 ]ft. In this report, the mathematically reduced form, foot squared per day (ft 2 /d), is used for convenience. Abbreviationsa Average distance from reservoir shoreline to aquifer boundary FYE Firm-yield estimator GIS Geographic Information System L Length of reservoir shoreline in contact with the aquifer MassDEP Massachusetts Department of Environmental Protection MAWSS Mobile Area Water and Sewer System Mgal Million gallons NWIS National Water Information System S Aquifer storage value T Aquifer transmissivity value USGS U.S. Geological Survey 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.