128—Southern Appalachian Ridges and Valleys

This MLRA (shown in red in the figure above) is in Tennessee (36 percent), Alabama (27 percent), Virginia (25 percent), and Georgia (12 percent). It makes up about 21,095 square miles (54,660 square kilometers). It is heavily populated. It includes Decatur, Huntsville, and Hartselle in the separate area of the MLRA in northern Alabama; Scottsboro, Gadsden, Anniston, Talladega, and Birmingham in the part of the MLRA in northeastern Alabama; Dalton and Rome, Georgia; Knoxville, Chattanooga, Cleveland, Athens, Maryville, Oak Ridge, Morristown, Greeneville, Johnson City, and Bristol, Tennessee; and Blacksburg and Abingdon, Virginia. Interstates 20, 24, 40, 59, 65, 75, and 81 cross the area. Small areas of the Cherokee National Forest are on the eastern border of the MLRA, the Jefferson National Forest is in the part of the MLRA in Virginia, and the Chattahoochee National Forest is in the part in Georgia. Small parts of the Talladega National Forest are in the southeast corner of the area, in Alabama. The Chickamauga and Chattanooga National Military Park commemorates Civil War battles near the Georgia and Tennessee border. The National Aeronautics and Space Administration’s Marshall Space Flight Center and the Redstone Arsenal and Fort McClellan Military Reservations are in the part of the area in Alabama. The Oak Ridge National Laboratory is in the part in Tennessee.

Physiography

Most of this area is in the Tennessee Section of the Valley and Ridge Province of the Appalachian Highlands. The thin stringers in the western part of the area are mostly in the Cumberland Plateau Section of the Appalachian Plateaus Province of the Appalachian Highlands. A separate area of the MLRA in northern Alabama is in the Highland Rim Section of the Interior Low Plateaus Province of the Interior Plains. The western side of the area is dominantly hilly to very steep and is rougher and much steeper than the eastern side, much of which is rolling and hilly. Elevation ranges from 660 feet (200 meters) near the southern end of the area to more than 2,400 feet (730 meters) in the part of the area in the western tip of Virginia. Some isolated linear mountain ridges rise to nearly 4,920 feet (1,500 meters) above sea level. This area is highly diversified. It has many parallel ridges, narrow intervening valleys, and large areas of low, irregular hills. Many ridges and valleys have a difference in elevation of 660 feet (200 meters).

The extent of the major Hydrologic Unit Areas (identified by four-digit numbers) that make up this MLRA is as follows: Upper Tennessee (0601), 37 percent; Alabama (0315), 24 percent; Middle Tennessee-Elk (0603), 12 percent; Middle Tennessee-Hiwassee (0602), 11 percent; Kanawha (0505), 9 percent; Lower Chesapeake (0208), 3 percent; Chowan-Roanoke (0301), 2 percent; and Mobile-Tombigbee (0316), 2 percent. The Tennessee River and its main tributaries, the Clinch, Holston, Obed, Hiwassee, and Sequatchie Rivers, are in this area. Two other tributaries in the area, the French Broad and Little Rivers, have been designated National Wild and Scenic Rivers. The Tennessee River is one of the largest rivers in the United States. It is a navigable waterway because of the numerous locks and dams on the river.

Geology

The bedrock in this area consists of alternating beds of limestone, dolomite, shale, and sandstone of early Paleozoic age. Ridgetops are capped with more resistant carbonate and sandstone layers, and valleys have been eroded into the less resistant shale beds. These folded and faulted layers are at the southernmost extent of the Appalachian Mountains. The narrow river valleys are filled with unconsolidated deposits of clay, silt, sand, and gravel.

Climate

The average annual precipitation in most of this area is 41 to 55 inches (1,040 to 1,395 millimeters). It increases to the south and is as much as 66 inches (1,675 millimeters) at the highest elevations in east Tennessee and the northwest corner of Georgia. The maximum precipitation occurs in midwinter and midsummer, and the minimum occurs in autumn. Most of the rainfall occurs as high-intensity, convective thunderstorms. Snowfall may occur in winter. The average annual temperature is 52 to 63 degrees F (11 to 17 degrees C), increasing to the south. The freeze-free period averages 205 days and ranges from 165 to 245 days. It is longest in the southern part of the area and shortest at high elevations and at the northern end.

Water

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

Public supply—surface water, 6.9%; ground water, 2.4%
Livestock—surface water, 0.3%; ground water, 0.2%
Irrigation—surface water, 0.2%; ground water, 0.3%
Other—surface water, 87.9%; ground water, 1.9%

The total withdrawals average 5,905 million gallons per day (22,350 million liters per day). About 5 percent is from ground water sources, and 95 percent is from surface water sources. In most years precipitation is adequate for crops, but in some years yields are reduced by short dry periods early in summer. Permanent streams, originating on either side of the mountains, carry water to nearly all parts of the area. Several dams, constructed by the Tennessee Valley Authority on the Tennessee River and its major tributaries, provide flood control, facilitate navigation and power production, provide opportunities for recreation, and provide municipal and industrial water. The surface water generally is suitable for all uses. Rivers below reservoirs in this area commonly contain water with low levels of dissolved oxygen because of the release of water from the bottom of the reservoirs. This water is very cold, and the releases can cause water temperature fluctuations, which can cause problems for fish and wildlife and for recreational uses.

The ground water used in this area is from a Cambrian- to Mississippian-age carbonate aquifer system that has beds of limestone, dolomite, shale, and sandstone. The water occurs in solution openings, joints, and fractures in these units. It is hard or very hard but is otherwise of excellent quality. Wells in this aquifer generally are less than 300 feet (90 meters) deep, and the aquifer is constantly recharged with freshwater (rainfall), so the level of total dissolved solids is fairly low for a carbonate aquifer. The median level of total dissolved solids is about 150, 126, and 270 parts per million (milligrams per liter) in Alabama, Georgia, and Tennessee, respectively. High levels of iron occur in some areas, such as the areas in the part of this MLRA in Tennessee. These high levels of iron may exceed the national secondary standard for drinking water, which is 300 parts per billion (micrograms per liter). The secondary standard is esthetic. The iron can stain ceramic and porcelain and precipitate in pipes. Since this aquifer is close to the surface and water moves through it quickly, it is highly susceptible to contamination from runoff. Many communities and rural landowners in areas away from surface water supplies rely on this aquifer for drinking water.

Soils

The soils in this area are mainly Udults and, to a lesser extent, Udepts. They have a udic soil moisture regime and a thermic or mesic soil temperature regime; are dominantly well drained, strongly acid, and highly leached; and have a clay-enriched subsoil. They range from shallow on sandstone and shale ridges to very deep in valleys and on large limestone formations.

Paleudults (Decatur, Dewey, Frederick, Fullerton, and Pailo series, commonly cherty) are in the many extensive areas underlain by limestone that traverse the MLRA from southwest to northeast. Hapludults (Townley and Armuchee series) are dominant in valleys underlain by acid shale. Steep, shallow or moderately deep, shaly and stony Dystrudepts (Weikert, Wallen, Montevallo, and Calvin series) are on the sides of steep ridges. Shallow, shaly Eutrudepts (Bays and Dandridge series) are in areas of the shale formation extending along the eastern side of the MLRA. Eutrudepts (Hamblen, Sullivan, and Pettyjon series) are on narrow bottom land.

Biological Resources

This area supports hardwoods or mixed hardwoods and pine. The deeper soils support good oak-hickory stands. The shallower soils, mostly on south and west aspects, support pine or oak-pine types. The understory vegetation also is affected by aspect. Little bluestem is the dominant grass species.

Some of the major wildlife species in this area are red fox, gray fox, raccoon, skunk, opossum, muskrat, mink, cottontail, gray squirrel, fox squirrel, bobwhite quail, and mourning dove. The species of fish in the area include carp, bullhead, largemouth bass, and bluegill.

Land Use

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

Cropland—private, 12%
Grassland—private, 21%; Federal, 1%
Forest—private, 41%; Federal, 2%
Urban development—private, 16%
Water—private, 5%
Other—private, 2%

Most of this area consists of small and medium-size farms. More than two-fifths of the area supports mixed hardwoods. Most of the forestland, except for a few wooded mountain ridges, is in small farm woodlots. Hay, pasture, and some grain for beef cattle and dairy cattle are the principal crops grown in this area. Burley tobacco is the important cash crop in the southern two-thirds of the area, excluding Georgia. Some cotton is grown south of Chattanooga. Corn and soybeans are grown on small acreages throughout the area, mainly in narrow strips of bottom land and on the adjacent low terraces.

The major soil resource concerns are sheet and rill erosion on pasture, land slippage, streambank erosion, gullying, surface compaction caused by livestock trampling, and a reduced content of organic matter on cropland. Conservation practices on cropland generally include crop rotations, contour farming, nutrient management, grassed and forested riparian buffers, cover crops, hayland planting, diversions, and grassed waterways. Pasture management includes rotational grazing, watering systems, fencing, managed livestock access to streams, pasture planting, and nutrient management. Forest management includes properly constructed forest harvest trails, critical area planting, and water bars on trails.

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