the Goliad sand, Willis sand, Bently formation, Montgomery formation, Beaumont 

 clay, and the Quaternary alluvium. The formations dip toward the Gulf at an 

 angle greater than the slope of the land surface. They have greater depth and 

 thickness in the gulfward direction and consequently influence subsurface 

 hydrologic units and their water-bearing characteristics. The Chicot and 

 Evangeline aquifers are the only hydrologic units bearing fresh or slightly 

 saline water in Brazoria County (Sandeen and Wesselman, 1969). Except for a 

 few sands located in the upper unit of the Chicot aquifer, water-bearing forma- 

 tions crop out and are recharged in counties to the north. Recharge is mostly 

 from precipitation percolating through surface sands, but some recharge is also 

 attributable to the San Bernard River. Flow along the hydrologic gradient 

 follows a southeast direction toward Brazosport. Mixing of fresh and saline 

 groundwater depends on the sequence and nature of aquifer interbedding, presence 

 of nearby salt domes, and other subsurface features. 



Surface waters in the San Bernard Refuge area drain into the San Bernard 

 River and Intracoastal Waterway. Surface water in the Brazoria Refuge drain 

 into the Intracoastal Waterway as well as Christmas and Drum Bays. Since both 

 refuges are characterized by extensive lowlands and marshes with elevations of 

 less than 1.5 m (5 ft) above mean sea level, these areas are very poorly drained. 

 Internal drainage and runoff are ^^ery slow. Drainage occurs primarily through 

 a series of ponds, lakes, and interconnecting streams, which eventually discharge 

 into the Intracoastal Waterway or other flowing watercourses. A permanent water 

 •■able fluctuates from the soil surface to a depth of about 127 cm (50 inches) 

 ^JSDA, 1973). 



Periodic flooding of areas below the 1.5-m (5-ft) may result from (1) high 

 tides and hurricane-induced surges and (2) overflow from the San Bernard and 

 Brazos Rivers. Consequently, most marsh areas, ponds, and lakes below the 1.5- 

 m (5-ft) line contain brackish water; salinity varies according to the time of 

 year, available precipitation, and degree of flooding (Seadock, 1974), 



Vegetation . Floristical ly, the Brazoria and San Bernard Refuges are very 

 similar in composition and in structure. Both refuges lie in the Gulf Prairies 

 and Marshes vegetational area of Texas (Gould, 1969). Site elevation, which 

 regulates surface hydrologic regime, and site proximity to salt water are the 

 primary regulatory factors of the coastal vegetation. Brackish to freshwater 

 marsh flora and coastal grasses, primarily gulf cordgrass ( Spartina spartinae ), 

 are the two dominant vegetation types. 



The marsh systems are typically located in low-lying, often inundated sites. 

 Salinity varies locally, being influenced by the ratio of upland freshwater 

 drainage to saltwater inundation; marsh salinity decreases northward. Marshhay 

 cordgrass, saltgrass, and several species of bulrush are common brackish marsh 

 species. Smooth cordgrass dominates less extensively, chiefly along shores of 

 bays, bayous, the Intracoastal Waterway, and numerous low depressions frequently 

 exposed to saline water. Several fairly extensive stands of smooth cordgrass 

 exist in the Brazoria Refuge along the shores of Bastrop and Drum Bays. Areas 

 of high salinity represent an edaphic climax because soil salinity limits plant 



66 



