131C—Red River Alluvium

This MLRA (shown in red in the figure above) is in Louisiana (86 percent) and Arkansas (14 percent). It makes up about 2,410 square miles (6,245 square kilometers). The eastern half of the city of Shreveport and the towns of Alexandria and Bossier City, Louisiana, are in this MLRA. Interstate 20 crosses this area and intersects Interstate 49 in Shreveport. Interstate 30 crosses the northern tip of the area, in Arkansas. Small areas of the Kisatchie National Forest are along the southwest edge of this MLRA. The England and Barksdale Air Force Bases are in this area. The area is along a major flightpath of migratory waterfowl.

Physiography

Almost all of this area is in the West Gulf Coastal Plain Section of the Coastal Plain Province of the Atlantic Plain. The southern end is in the Mississippi Alluvial Plain Section of the same province and division. This MLRA is on the alluvial plain along the lower Red River in Arkansas and Louisiana. The landforms in the area are level or depressional to very gently undulating alluvial plains, backswamps, oxbows, natural levees, and terraces. Landform shapes range from convex on natural levees and undulating terraces to concave in oxbows. Landform shapes differentiate water-shedding positions from water-receiving positions, both of which have a major effect on soil formation and hydrology. Average elevations start at about 40 feet (12 meters) in the southern part of the area and gradually rise to about 270 feet (80 meters) in the northwestern part. Maximum local relief is about 10 feet (3 meters), but relief is considerably lower in most of the area.

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Red-Sulphur (1114), 63 percent; Louisiana Coastal (0808), 35 percent; and Lower Red-Ouachita (0804), 2 percent. The lower Red River and its tributaries drain the MLRA to its confluence with the Atchafalaya and Mississippi Rivers, which occurs in MLRA 131A.

Geology

Bedrock in this area consists of Tertiary and Cretaceous sands formed as beach deposits during the retreat of the Cretaceous ocean from the midsection of the U.S. Alluvial deposits from flooding and lateral migration of the Red River typically lie above the bedrock. These sediments are sandy to clayey fluvial deposits of Holocene to late Pleistocene age and are many meters thick. In some areas late Pleistocene terrace deposits are within several meters of the present surfaces, but they do not crop out in this MLRA. The geologic history of the area is greatly influenced by a large logjam that formed in the Red River channel in the middle part of the area during the late 18^th century and the early 19^th century. At the time of its largest extent, the logjam obstructed the river and its tributary outlets for a distance of 160 miles downstream from the Arkansas State boundary. Backwater flooding, reformation of natural levees, and crevasse splays caused by this logjam played a major role in covering large parts of the area with a mantle of recent clayey to sandy material. Destruction of the logjam in the late 1800s resulted in the drainage of many large lakes that had formed.

Climate

The average annual precipitation in this area ranges from 47 to 62 inches (1,195 to 1,575 millimeters), increasing from north to south. Most of the rainfall occurs as frontal storms during late fall, winter, and early spring, although an appreciable amount of precipitation also occurs as convective thunderstorms during the early part of the growing season. The total amount of the precipitation that occurs as snow ranges from less than 1 percent in the southern part of the area to 5 percent in the northern part. The average annual temperature ranges from 63 to 67 degrees F (17 to 19 degrees C). The freeze-free period averages 280 days. It ranges from 255 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, 3.1%; ground water, 3.3%
Livestock—surface water, 1.4%; ground water, 1.1%
Irrigation—surface water, 1.3%; ground water, 8.1%
Other—surface water, 77.3%; ground water, 4.4%

The total withdrawals average 840 million gallons per day (3,180 million liters per day). About 17 percent is from ground water sources, and 83 percent is from surface water sources. In most years the supply of moisture is adequate for maximum crop production. Surface water for public supply, industrial use, and some irrigation is available in quantity from bayous, oxbow lakes, canals, and rivers throughout the area. The dominant use of surface water in the area is for cooling thermoelectric power plants. Numerous small, above-ground water impoundments are used for raising commercial catfish throughout the MLRA. 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. Flooding is a major concern in most of the area.

The principal sources of ground water in this area are sandy and loamy materials within the Red River alluvial deposits. Impermeable or very slowly permeable smectitic clays overlie these aquifers in many parts of the MLRA, and these clay layers are many meters thick in some areas. Water moves through the smectitic clays via large desiccation cracks that open during dry periods and swell closed and form slickensides during wet periods. The ground water is used primarily for irrigation, but it also is used for public supply and industry. The median level of total dissolved solids is 330 parts per million (milligrams per liter), and the water is very hard. The iron content is generally high in the part of this area in Arkansas, but it generally is not a significant problem in the part in Louisiana. The level of total dissolved solids can reach 4,000 parts per million (micrograms per liter) in the southwest corner of the part of the area in Arkansas, making the water from the alluvial aquifer unusable. The Sparta and Cockfield bedrock aquifers are used in the northern end of this area, in Arkansas. The ground water in these aquifers has a lower mineral content than the water in the alluvial aquifer, and it is soft. The iron content generally is below the national secondary standard for drinking water of 300 parts per billion (micrograms per million). These aquifers provide drinking water for rural landowners and small communities. They also provide water for public water supply in the larger communities. More and more irrigation wells are being developed in the Sparta aquifer.

Soils

The dominant soil orders in this MLRA are Vertisols, Entisols, Inceptisols, and Alfisols. The soils in the area have a thermic soil temperature regime. They dominantly have an aquic soil moisture regime, smectitic clay mineralogy, and mixed sand and silt fraction mineralogy. They are very deep and generally are poorly drained to moderately well drained and loamy or clayey. Nearly level Epiaquerts (Moreland series) and Vertic Endoaquepts (Yorktown series) dominate the Holocene-age alluvial flats and backswamps. Nearly level to gently sloping Endoaquepts (Coushatta series), Udifluvents (Severn and Roxana series), and Vertic Epiaquepts (Latanier series) dominate the Holocene-age natural levees. Nearly level to gently undulating, coarse-silty over clayey Udifluvents (Caplis series) and sandy Udifluvents (Kiomatia series) dominate the Holocene-age levee splays and point bars. Nearly level to gently undulating Hapludalfs (Gallion and Rilla series) and Argiudolls (Caspiana series) dominate the Holocene-age natural levees along the older meander scars.

Biological Resources

This area once consisted entirely of bottom-land hardwood deciduous forest and mixed hardwood and cypress swamps. The major tree species in the native plant communities in the areas of bottom-land hardwoods formerly were and currently are water oak, Nuttall oak, cherrybark oak, native pecan, red maple, sweetgum, eastern cottonwood, and hickory. The major tree species in the native plant communities in the swamps formerly were and currently are cypress, water tupelo, water oak, green ash, red maple, and black willow. The important native understory species are palmetto, greenbrier, wild grape, and poison ivy in the areas of bottom-land hardwoods and buttonbush, lizardtail, waterlily, water hyacinth, sedges, and rushes in the swamps.

Some of the major wildlife species in this area are white-tailed deer, feral hogs, red fox, coyote, rabbit, gray squirrel, American alligator, water turtles, water snakes, frogs, otters, beavers, armadillo, crawfish, wild turkey, mourning doves, ducks, and geese. Fishing is mainly in oxbow lakes, rivers, and bayous. The species of fish in the area include largemouth bass, smallmouth bass, catfish, drum, bluegill, gar, and yellow perch.

Land Use

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

Cropland—private, 37%
Grassland—private, 20%
Forest—private, 30%; Federal, 1%
Urban development—private, 5%
Water—private, 5%
Other—private, 2%

Farms and scattered tracts of forested wetlands make up nearly all of this area. The farms produce mainly cash crops. Cotton, soybeans, milo, and corn are the main crops. Sugarcane is a major crop in the southernmost part of the area. In many areas furrow irrigation is used during droughty parts of the growing season. Throughout the area, catfish are produced commercially on farm ponds that are contained by levees. Migratory waterfowl are harvested throughout the area. Hardwood timber is harvested on some forested wetlands, and most forested areas are managed for wildlife.

About 22 percent of this MLRA is not protected from flooding, and flooding occurs occasionally or frequently. Levees protect nearly all of the cropland from flooding. Most of the forested wetlands are not protected from flooding. Networks of drainage canals and ditches help to remove excess surface water from the cropland.

The major resource concerns are control of surface water, management of soil moisture, and maintenance of the content of organic matter and productivity of the soils. Conservation practices on cropland generally include nutrient management, crop residue management, and alternative tillage systems, especially no-till systems. In many areas land leveling or shaping optimizes the control of surface water. Other major cropland management practices are control of competing vegetation and insects through aerial or ground spraying of herbicides and insecticides and fertility management programs that make use of chemical fertilizers.

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