150A—Gulf Coast Prairies

This MLRA (shown in red in the figure above) is in Texas (83 percent) and Louisiana (17 percent). It makes up about 16,365 square miles (42,410 square kilometers). It includes the towns of Crowley, Eunice, and Lake Charles, Louisiana, and Beaumont, Houston, Bay City, Victoria, Corpus Christi, Robstown, and Kingsville, Texas. Interstates 10 and 45 are in the northeastern part of the area, and Interstate 37 is in the southwestern part. U.S. Highways 90 and 190 are in the eastern part, in Louisiana. U.S. Highway 77 passes through Kingsville, Texas. The Chase and Kingsville Naval Air Stations are in this area. The Attwater Prairie Chicken National Wildlife Refuge and the Fannin Battleground State Historic Site are in the part of the area in Texas. The area has a few State parks.

Physiography

This area is in the West Gulf Coastal Plain Section of the Coastal Plain Province of the Atlantic Plain. It is characterized by nearly level plains that have low local relief and are dissected by rivers and streams that flow toward the Gulf of Mexico. Elevation ranges from sea level to about 165 feet (0 to 50 meters) along the interior margin.

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Central Texas Coastal (1210), 28 percent; Galveston Bay-San Jacinto (1204), 22 percent; Louisiana Coastal (0808), 17 percent; Lower Colorado-San Bernard Coastal (1209), 13 percent; Nueces-Southwestern Texas Coastal (1211), 7 percent; Lower Brazos (1207), 7 percent; Trinity (1203), 3 percent; Neches (1202), 2 percent; and Sabine (1201), 1 percent. The Beckwith and Calcasieu Rivers are in the eastern end of this area, in Louisiana. The Sabine River forms the boundary between Texas and Louisiana. From north to south, the Neches, Trinity, San Jacinto, Brazos, San Bernard, Navidad, Lavaca, Guadalupe, San Antonio, Nueces, and Agua Dulce Rivers cross the part of this area in Texas.

Geology

This area is mostly a strip of land that is about 50 to 80 miles (80 to 130 kilometers) wide and runs along the Gulf of Mexico. The sedimentary rocks at the surface are of Pleistocene age. They were laid down during the last 2 million years. The deposits are deltaic and lagoonal clays and loams derived from older rocks to the west. At the western edge of this area, mostly within Texas, the sediments are older and more weathered and contain more sands. At the eastern edge, mostly within Louisiana, a cap of mixed loess and alluvium occurs on most soils. The loess was derived from the flood plain along the Mississippi River. Some Tertiary deposits occur along the interior edge of this MLRA. The weight of the recent deposits has caused them to tilt towards the Gulf of Mexico, so successively older deposits crop out from the coastal edge to the interior edge of the area. Salt domes, natural gas, and petroleum deposits are commonly below the surface throughout this area. Recent deposits of alluvial sand fill the valleys of the Brazos and Trinity Rivers and the other large rivers in the area.

Climate

The average annual precipitation in the northern two-thirds of this area is 45 to 63 inches (1,145 to 1,600 millimeters). It is 28 inches (710 millimeters) at the extreme southern tip of the area and 30 to 45 inches (760 to 1,145 millimeters) in the southwestern third of the area. The precipitation is fairly evenly distributed, but it is slightly higher in late summer and midsummer in the western part of the area and slightly higher in winter in the eastern part. Rainfall typically occurs as moderate-intensity, tropical storms that produce large amounts of rain during the winter. The average annual temperature is 66 to 72 degrees F (19 to 22 degrees C). The freeze-free period averages 325 days and ranges from 290 to 365 days, increasing in length to the southwest.

Water

Following are the estimated withdrawals of freshwater by use in this MLRA:

Public supply—surface water, 8.5%; ground water, 6.0%
Livestock—surface water, 0.6%; ground water, 0.5%
Irrigation—surface water, 7.7%; ground water, 20.2%
Other—surface water, 53.6%; ground water, 2.8%

The total withdrawals average 4,390 million gallons per day (16,615 million liters per day). About 30 percent is from ground water sources, and 70 percent is from surface water sources. Rainfall and perennial streams provide abundant water that is suitable for almost all uses. Water for irrigating rice is often obtained from streams. The surface water also is used for municipal and industrial supplies and for cooling thermoelectric power plants. Treated sewage effluent from upstream sources makes up a significant portion of the low flow in the San Antonio River in this area. Urbanization and industrial wastes are threatening the surface and ground water supplies in the Houston area. Most of the soils must be drained for optimum growth of general farm crops.

Ground water is abundant in the Gulf Coast aquifer system in this area. The water from this system has a median level of 420 parts per million (milligrams per liter) total dissolved solids and typically is moderately hard. This system provides much of the domestic, public supply, and irrigation water used in this area.

Soils

The dominant soil orders in this MLRA are Alfisols, Mollisols, and Vertisols. The soils have a hyperthermic soil temperature regime in the southwestern part of the area and a thermic soil temperature regime in the northeastern part. The soils in the MLRA generally have an ustic soil moisture regime and smectitic mineralogy. Drainage ranges from well drained in very gently sloping and gently sloping soils in convex areas to very poorly drained in soils in enclosed depressions. Soils that formed in early Pleistocene sediments, generally occurring north of Interstate 10, are very deep and have a loamy surface layer and subsoil and siliceous mineralogy. Soils that formed in late Pleistocene sediments, generally occurring south of Interstate 10, are very deep and have a loamy or clayey surface layer and a clayey, very slowly permeable subsoil. Aqualfs and Udalfs (Crowley, Aris, and Vidrine series) are dominant in Louisiana and southeastern Texas. Uderts and Udalfs (League, Lake Charles, Laewest, Hockley, Katy, and Telferner series) are dominant in the eastern and central parts of the area. Usterts and Ustolls (Banquete, Cranell, Orelia, and Victoria series) are dominant in the western and southwestern parts.

Biological Resources

This area was originally a natural grass prairie with hardwood trees along the rivers and streams. Little bluestem, Indiangrass, switchgrass, and big bluestem are the dominant species. A few groves of live oak dot the landscape.

Some of the major wildlife species in this area are white-tailed deer, raccoon, opossum, rabbit, fox, coyote, squirrel, armadillo, nutria, quail, and mourning dove. Migratory waterfowl, such as ducks and geese, and neotropical migratory Major Land Resource Areas songbirds winter in this area. The species of fish in the area include bass, channel catfish, and bream.

Land Use

Following are the various kinds of land use in this MLRA:

Cropland—private, 32%
Grassland—private, 39%; Federal, 1%
Forest—private, 5%
Urban development—private, 16%
Water—private, 5%
Other—private, 2%

Most of this area is in farms. Rice, soybeans, grain sorghum, cotton, corn, and hay are the chief crops. About two-fifths of the area is rangeland or pasture. The forested areas, consisting chiefly of hardwoods, border the rivers and streams that cross the MLRA. Urban development is rapidly expanding onto agricultural land throughout the area.

The major soil resource concerns are wind erosion, water erosion, maintenance of the content of organic matter and tilth of the soils, and management of soil moisture. Increasing salinity is a problem in some areas. Conservation practices on cropland generally include systems of crop residue management, which help to control erosion and maintain the content of organic matter in the soils. Timely tillage and planting can help to maintain tilth and the supply of soil moisture. Conservation practices on pasture and rangeland generally include prescribed grazing, fences, watering facilities, and nutrient and pest management.

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