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GEOGRAPHIC SETTING


The CPYRW encompasses approximately 3,636 square miles (mi2) in parts of 10 counties of southeast Alabama. Table 3 lists each county, and its land area in square miles within the watershed (U.S. Census Bureau, 2002). Plate 1 illustrates the watershed area relative to adjacent states and includes hydrologic unit boundaries for each subwatershed.

The northern boundary of the CPYRW begins at the headwaters of the Pea River at Bluff Creek between Union Springs and Midway in Bullock County. The western boundary follows the eastern boundary of the Conecuh River watershed through Pike and Crenshaw Counties. The southwestern boundary is formed by the Yellow River watershed in portions of Covington and Crenshaw Counties. The southern boundary is the Alabama-Florida state line from near Florala in Covington County eastward to central Houston County. The eastern boundary is the drainage divide between the Choctawhatchee and Chattahoochee River watersheds and extends from Barbour County southward through central Henry and Houston Counties (fig. 1).


PHYSIOGRAPHY AND TOPOGRAPHY


The CPYRW lies within the East Gulf Coastal Plain physiographic section of Alabama and is characterized by gently rolling hills, sharp ridges, prairies, and alluvial flood plains (Clean Water Partnership (CWP) and Geological Survey of Alabama (GSA), 2005). The highest elevations are in the northern portion of the watershed where ridge crests are approximately 640 feet (ft) above mean sea level (MSL). Elevation data is expressed on the CPYRW Digital Elevation Model map below (fig. 2).

Geologic units underlying the Coastal Plain are of sedimentary origin and consist of sand, gravel, porous limestone, chalk, marl, and clay. These strata dip in the subsurface south-southwest at approximately 35 to 40 feet per mile (ft/mi) and strike generally westward. Some of the strata are more resistant to erosion and underlie broad saw-toothed ridges known as cuestas that slope gently to the south with steep north-facing slopes. Eight physiographic districts are delineated in the East Gulf Coastal Plain of Alabama including the Fall Line Hills, Black Belt, Chunnenuggee Hills, Southern Red Hills, Lime Hills, Dougherty Plain, Southern Pine Hills, and Coastal Lowlands (Sapp and Emplaincourt, 1975). Four of these districts including Chunnenuggee Hills, Southern Red Hills, Dougherty Plain, and Southern Pine Hills are present in the CPYRW area (fig. 3).

The Chunnenuggee Hills (CH) district consists of a series of pine-forested sand hills developed on hardened beds of clay, sandstone, siltstone, and chalk. The CPYRWMA management area northern boundary closely follows the Enon Cuesta. The headwaters of the Pea River are in Chunnenuggee Hills district on the south side of the Enon Cuesta.

The Southern Red Hills district extends in a belt more than 60 miles wide across the CPYRW area. The Southern Red Hills is characterized by cuesta type ridges with steep, serrate north slopes and gentle back slopes. Topographic relief in the Southern Red Hills is among the greatest in the Coastal Plain of Alabama. Streams in this area acquire upland characteristics with high gradient, hard-rock bottoms, and swifter flows. The headwaters of the Choctawhatchee River are on the southern slope of the Ripley Cuesta in the Southern Red Hills.

The Dougherty Plain district or “wiregrass region” of the CPYRW area includes portions of Henry, Dale, Houston, Geneva, Coffee, Crenshaw, and Covington Counties. It is composed of limestone, sand, and clay. Active solution of the underlying limestone produces many shallow, flat-bottomed depressions that dot the landscape. Small headwater streams are noticeably absent from the Dougherty Plain because active limestone solution or karst transfers many of the drainages to underground channels. The name “wiregrass” originates from the common occurrence of needlerush in the wet, shallow depressions. The confluence of the Choctawhatchee and Pea Rivers occurs in the Dougherty Plain in southern Geneva County.

The Southern Pine Hills (SPH) district in the CPYRW area includes extreme southern Covington County. Topography is low-relief with broad, rounded ridges and V-shaped valleys with sand and clay sediments. The portion of the region in Covington County has thin sand and clay sediments overlying limestone. In this area, karst features similar to the Dougherty Plain are common. The most prominent of these features is Lake Jackson in Florala (Baker and others, 2005). Flat uplands with shallow ponds, bogs, and marshes occur throughout the district and many of the valleys are saucer-like perpetually wetted by seepage from nearby hills. The abundance of warm summer rains is a major factor in leaching fertility from the soil and favoring the growth of pines in this region. Yellow River drains the Southern Pine Hills in the CPYRW area.


LAND USE


Current land use in the CPYRW is comprised of these main categories: forest (64%), agriculture (22.2%), urban (6.7%), wetlands (6.3%), and water bodies (0.9%) (plate 2). The region is heavily forested with the prominent forest type being evergreen. Other common vegetation classes are deciduous, shrubland, mixed forest, and grassland herbaceous. Agriculture is the second largest land use category. The majority of agricultural land is comprised of these classes: grassland/pasture/hay, crops, fallow/idle cropland, and aquaculture. Crop classifications in the CPYRW include cotton, corn, peanuts, soybeans, pecans, sorghum, sod/grass seed, herbs, millet, winter wheat, rye, oats, tomatoes, sweet potatoes, blueberries, cucumbers, watermelons, peas, and several varieties of double crops.

There are two distinct areas of intense agriculture observed within the watershed. The boundaries of these areas, designated A and B and shown on figure 4, were derived by assessing the geology, soils, physiography, topography, and land-use patterns. Area A extends from the Pea River in Pike County and eastward to central Barbour County, and area B extends from Andalusia in Covington County to Dothan in Houston County. Clayton, Porters Creek, and Nanafalia Formations, all of which are composed of sand, clay, and limestone, dominate the geology of area A. Area B is underlain primarily by the Gosport Sand, Lisbon Formation, Tallahatta Formation, Jackson Group undifferentiated, and residuum that contains sand, clay, claystone, chert, and limestone. Boundaries of intensive agricultural land use conform closely to geologic contacts. The geology of these regions is the basis for soils, which are conducive to row crop agriculture.



Urban areas are defined by four categories: developed/open space, developed/low intensity, developed/medium intensity, and developed/high intensity. Wetland classes include woody wetlands and herbaceous wetlands. General land use classifications were derived from the 2011 Multi-Resolution Land Characteristics Consortiums (MRLC) National Land Cover Data (NLCD) and detailed agricultural classes were derived from the U.S. Department of Agriculture (USDA) Cropland Data Layer for Delta States (USDA, National Agricultural Statistics Service, 2013) (plate 2). All detailed land use classes, areas, and percentages are displayed in Appendix 1 (LULC_Appendix). Land use change is discussed in “Watershed Trends.”


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