133B—Western Coastal Plain

This MLRA (shown in orange in the figure above) is in Texas (47 percent), Louisiana (31 percent), Arkansas (21 percent), and Oklahoma (1 percent). It makes up about 45,450 square miles (117,770 square kilometers). The towns of Longview, Lufkin, Marshall, Nacogdoches, and Tyler, Texas, are in the southwestern part of the area. The towns of Minden, Ruston, and West Monroe, Louisiana, are in the southern part. The towns of Magnolia, Hope, Camden, El Dorado, and Pine Bluff, Arkansas, are in the northern part. Shreveport, Louisiana, and Little Rock, Arkansas, are major cities in this MLRA. Interstate 30 crosses the northernmost part of this area, in Texas and Arkansas, and Interstate 20 crosses the central part, in Texas and Louisiana. Interstate 49 runs from Shreveport south through Louisiana. The MLRA includes parts of Camp Joseph T. Robinson, the Little Rock Air Force Base, and the Pine Bluff Arsenal in Arkansas and Fort Polk in Louisiana. It also includes the Angelina, Davy Crockett, Kisatchie, Sabine, and Sam Houston National Forests, parts of the Ouchita National Forest, and the Big Thicket National Preserve. The northern half of the Alabama and Coushatta Indian Reservation is in the part of this area in Texas.

Physiography

This area is in the West Gulf Coastal Plain Section of the Coastal Plain Province of the Atlantic Plain. It consists of level to steep uplands that are intricately dissected by streams. Broad flood plains and terraces are along some streams. Elevation ranges from 80 to 650 feet (25 to 200 meters), increasing gradually from southeast to northwest. Local relief is generally less than 30 feet (9 meters).

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Lower Red-Ouachita (804), 29 percent; Red-Sulphur (1114), 26 percent; Neches (1202), 17 percent; Sabine (1201), 14 percent; Trinity (1203), 7 percent; Louisiana Coastal (0808), 3 percent; Galveston Bay-San Jacinto (1204), 3 percent; and Lower Arkansas (1111), 1 percent. The headwaters of the Angelina, Calcasieu, and Neches Rivers are in this area. The Trinity River passes through the far western part of the area. Tributaries of the Ouachita and the Sabine Rivers also drain the area. The Saline River in Arkansas and Louisiana and the Little, Black Lake Bayou, Calcasieu, and Bayou D’Arbonne Rivers in Louisiana are National Wild and Scenic Rivers.

Geology

Tertiary and Cretaceous marine sediments underlie most of this area. Tertiary units include the Wilcox and Midway Groups, the Claiborne Group, the Jackson Group, the Catahoula Formation, and the Willis Formation. They consist of interbedded sandstone, siltstone, and shale and unconsolidated sands, silts, and clays. The Reklaw and Weches Formations in the Claiborne Group form the Redland area in east Texas. The Cretaceous marine sediments of the Fleming and Oakville Formations are of minor extent in the area. They consist of calcareous clays and marls. Sand, silt, and clay alluvium is under the flood plains and terraces along the major drainages.

Climate

The average annual precipitation in this area is 39 to 63 inches (990 to 1,600 millimeters). It increases from northwest to southeast. Most of the rainfall occurs as frontal storms in spring and early summer. High-intensity, convective thunderstorms occur in late summer and in fall. Some heavy rains occur during tropical storms in winter. The average annual temperature is 61 to 68 degrees F (16 to 20 degrees C). The freeze-free period averages 270 days. It ranges from 235 days in the northern part of the area to 305 days in the southern part.

Water

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

Public supply—surface water, 6.5%; ground water, 7.8%
Livestock—surface water, 3.5%; ground water, 4.6%
Irrigation—surface water, 3.1%; ground water, 2.3%
Other—surface water, 21.0%; ground water, 51.3%

The total withdrawals average 3,050 million gallons per day (11,545 million liters per day). About 66 percent is from ground water sources, and 34 percent is from surface water sources. The water generally is abundant because of precipitation, perennial streams, and the supply of ground water. Even though summer rainfall is generally adequate for crops, droughts are common. There is a summer moisture deficit of 2 to 6 inches (50 to 150 millimeters). Wet soils must be drained before they can be used for crops. Several large reservoirs on the major streams provide municipal and industrial water and also serve as recreation sites. The surface water in the area is used dominantly for industry and for cooling thermoelectric power plants. Most of the surface water is of good quality and is suitable for most uses with some treatment. High concentrations of suspended sediments, agricultural chemicals, and municipal and industrial wastewater discharges contribute to some local water-quality problems. The lower tributaries of the Ouachita River are contaminated with wastes from oil and gas production. Fecal-coliform bacteria counts have caused water-quality problems on the Red River near Shreveport and in the Toledo Bend Reservoir on the Sabine River. A low level of dissolved oxygen is a problem in rivers below reservoirs where deep, oxygen-deficient water is released. Flooding is a concern in many parts of the area.

The principal sources of ground water in this area are bedrock aquifers. They include the Carrizo-Wilcox aquifer in Texas and Louisiana, the Trinity Group in Texas, the Cockfield and Sparta aquifers in Arkansas and Louisiana, the Wilcox aquifer in Arkansas, and the Pliocene-Miocene aquifers in Louisiana. The Wilcox aquifer in southwest Arkansas is not used extensively in this area. The ground water is used primarily for industry, but it also is used for public supply. Most rural landowners rely on the bedrock aquifers for domestic and livestock water. The median level of total dissolved solids is typically less than 400 parts per million (milligrams per liter), but water in the Trinity Group near the Texas-Oklahoma State line has a median level of 619 parts per million (milligrams per liter). The ground water is soft in Louisiana and Arkansas, but it is moderately hard to very hard in Texas. The iron content can be very high in some areas in Arkansas, and it may also cause some problems in the part of the area in Louisiana. A declining water level is a problem in the Trinity Group aquifer in Texas. About 30 percent of the samples from this aquifer exceeded the 10 parts per million (milligrams per liter) national standard for nitrate in drinking water. The water in the Pliocene-Miocene sands in west-central Louisiana has high levels of fluoride, and its color limits its use for drinking water. Locally, the color of the water in the Cockfield and Sparta aquifers in Louisiana limits the use of those aquifers for public supply.

Soils

The dominant soil orders in this MLRA are Alfisols and Ultisols. The soils in the area dominantly have a thermic soil temperature regime, a udic or aquic soil moisture regime, and siliceous, mixed, or smectitic mineralogy. They generally are very deep, well drained to poorly drained, and loamy or clayey. Hapludults formed in residuum (Cuthbert and Kirvin series) and marine sediments (Sacul series) on hills and ridges. Paleudults formed in marine sediments (Bowie and Malbis series) and mixed marine sediments and alluvium (Ruston series) on uplands. Endoaquults (Amy series) formed in old alluvium on stream terraces. Fragiudults (Savannah series) formed in mixed marine sediments and alluvium on uplands and stream terraces. Hapludalfs (Eastwood and Woodtell series) formed in marine sediments on hills and ridges. Glossaqualfs formed in alluvium on flood plains and stream terraces (Guyton series) and in old alluvium on stream terraces (Wrightsville series).

Biological Resources

This area supports pine-hardwood vegetation. The dominant trees are loblolly pine, shortleaf pine, sweetgum, southern red oak, white oak, flowering dogwood, and post oak. American beautyberry, greenbrier, hawthorns, and berry vines are included in the woody understory. Little bluestem and pinhole bluestem are the dominant herbaceous species. Other major grasses include beaked panicum, longleaf uniola, spike uniola, and yellow Indiangrass. The plant community has many species of low-growing panicums and paspalums and perennial forbs.

The major wildlife species in this area include white-tailed deer, coyote, beaver, raccoon, skunk, opossum, muskrat, mink, cottontail, squirrel, weasel, armadillo, and mourning dove.

Land Use

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

Cropland—private, 2%
Grassland—private, 18%
Forest—private, 65%; Federal, 4%
Urban development—private, 6%
Water—private, 3%; Federal, 1%
Other—private, 1%

The forested areas in this MLRA are used for the production of lumber and pulpwood. The cleared land is used mostly for pasture and hay. Where the water supply is adequate, such crops as corn, grain sorghum, oats, soybeans, peanuts, rice, and vegetables are grown.

The major resource concerns are water erosion, wetland restoration, and water supplies for livestock. Conservation practices on cropland generally include buffer strips, which help to control erosion and runoff. They also include the proper use and timing of irrigation.

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