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The Mississippi Gulf Coast region extends from the MississippiLouisiana boundary at Pearl River eastward to the Mississippi-Alabama boundary and includes Hancock, Harrison, ' and Jackson Counties, Mississippi Sound, and the barrier islands. The region is underlain by southward sloping irregular beds of sand and clay that range from Minrono tn Hnlnrono in ana iu un cu u biu y eyuu Miocene to Holocene in age. The Miocene aquifer system in the Gulf Coast area includes waterbearing zones in the Pascagoula and Graham Ferry Formations. The Citronelle aquifer and younger strata overlie the Miocene aquifer system. Freshwater extends to depths ranging from about 1,200 feet east of Pascagoula to slightly more than 3,000 feet in western Hancock County. Most large wells in the area range from 400 to about 1,000 feet in depth and commonly produce 500 to 1,000 gallons per minute. Water-levels have declined regionally about 2 feet per year during the past 30 years. In the Pascagoula-Moss Point area, concentrated large withdrawals since about 1900 have caused declines of as much as 136 feet. In the Biloxi-Gulfport area declines have been as much as 100 feet from above land surface to about 50 feet below land surface. Although these declines seem large, most of the region can accomodate much larger declines, and the aquifers are capable of yielding much larger quantities of water. The major streams in the region include the Pearl, Jourdan, Wolf, Tchoutachabouffa, Biloxi, Escatawpa, and Pascagoula Rivers. Back Bay of Biloxi and St. Louis Bay are promiment estuarine features. The Pearl and Pascagoula Rivers are the principal drainage from central and southern Mississippi. The Escatawpa River is a tributary to the Pascagoula River. The other rivers drain directly into Mississippi Sound, Back Bay of Biloxi, or St. Louis Bay. The region is subject to flooding from land surface runoff from excessive precipitation and from hurricane-induced flood tides. Surface water in the region generally is soft, acidic, and low in dissolved solids. Suspended sediment concentrations are low; however, some streams are high in organic color. All streams are subject to saltwater intrusion. Ground water is generally of good quality but locally contains excessive concentrations of dissolved solids. Saltwater intrusion has not been observed except in shallow aquifers that are hydraulically connected to estuarine streams. Water-quality problems in deeper aquifers are related to freshwater-saJ.twa.ter.--jji.terfaces that occur in all confined aquifers. Water otemperatures range from about 68 F in very shallow wells to over 100 F in the deepest aquifers. From Biloxi westward, the deeper aquifers are virtually undeveloped. Fresh surface water is used by industry in the Pascagoula area. Brackish surface water is used in the Biloxi area for thermoelectric cooling. All public water supplies and some industrial water supplies use ground water; however, most of the water .^sed in the area in terms of volume is brackish surface water. Total water use in 1980 was about 50 mi 11 ion gallons per day from ground-water sources and about 720 million gallons per day from surface sources. INTRODUCTION The U.S. Army Corps of Engineers, Mobile District, is making a water-resources management study that includes the three counties that border the Mississippi Gulf Coast. The Corps of Engineers study was authorized by resolutions adopted in June 1972 and March 1973 by the Committees on Public Works of the Senate and House of Representatives, 92d and 93d Congresses of the United States. In 1984, the U.S. Geological Survey entered into agreement with the U.S. Army Corps of Engineers to provide a summary of available hydrologic information for the area. PURPOSE AND SCOPE This report summarizes the published and open-file hydrologic information available for the three-county Mississippi Gulf Coast area. The sources of information include the publications and files of the U.S. Geological Survey and other agencies. Surface-water records were run on standard analytical programs to compute statistical relations for low-flow, average flow, and high-flow conditions in major streams. Particular attention was directed to the hydrology of streams at points of entry to the area, and to the problem reaches of the streams within the area. Available publications and file data on ground-water resources are summarized from the standpoint of recharge areas, delineation of aquifers, ground-water use, changes in water levels, and changes in water quality. No previously unreleased data or interpretative information are presented. PHYSICAL SETTING The Mississippi Gulf Coast region is bounded on the east by the Mississippi-Alabama state line and on the west by the Pearl River, the common state boundary with Louisiana. The region includes Hancock, Harrison, and Jackson Countries,. Mississippi Sound, and the barrier islands situated 10 to 12 miles south of the shoreline. The three counties have a combined area of about 1,800 mi'2. The Mississippi Sound comprises about 800 mi 2 of additional area. The four principal islands, subject to changes in area, include a total of about 50 mi2 (fig. 1). The climate of the study area is characterized by heavy rainfall, hot summers, and mild winters. Rainfall averages about 60 inches annually, and relative humidity generally remains high throughout the year. Temperatures during the summer months seldom exceed 100° but often reach 90° (Newcome and others, 1968). i Land forms in the coastal area, described in detail by Brown and others (1944, p. 17-31), include the Long Leaf Pine Hills, the Coastal Pine Meadows, the alluvial plains of the larger streams, beach ridges, sand dunes, and barrier islands. The beds exposed at the surface in the area range in age from Miocene to Holocene (fig. 2 and table 1) The area is underlain by a south-southwestward dipping series of deltaic and estuarine sediments that are composed mostly of clay, silt, sand, and irregular beds of gravel. The oldest exposed strata have been assigned to the Pascagoula Formation and are Miocene in age whereas the younger Graham Ferry and Citronelle Formations were considered to be of Pliocene age in Mississippi by Newcome and others (1968). The Citronelle is a blanket deposit that overlies both the Graham Ferry and the Pascagoula and extends beyond the study area to the north (Boswell, 1979). The Citronelle in the coastal area is overlain by Pleistocene and Holocene coastal and terrace deposits and alluvium. The south-southwestward slope that is characteristic of the older units is the result of gradual subsidence (sinking) in the Gulf Coast geosyncline. The younger beds exhibit successively less southwestward slope. Most of the units thicken down the dip to the southwest (Brown and others, 1944). The major streams in the area (fig. 1) include the Pearl, Jourdan, Wolf, Tchoutachabouffa, Biloxi, Escatawpa, and Pascagoula Rivers. These streams have well-defined inland channels that provide drainage for the mostly rural area. Back Bay of Biloxi and St. Louis Bay are large estuarine features. Major population centers within the area of investigation include Pascagoula-Moss Point, Biloxi-Ocean Springs, Gulfport-Long Beach-Pass Christian and Bay St. Louis-Waveland. Also included is the National Space Technology Laboratories area, Keesler Air Force Base, and U.S. Naval Construction Battalion Center. E X P L A N A T IO N G a g in g S ta tio n s A ct iv e D is co n tin u e d A 2 A 5A le ss t h a n 10 y e a r*

Water-resources overview of the Mississippi Gulf Coast area