4.5 River Basins
Oak). Te other river basins have waters that drain across adjacent states (Georgia, South Carolina, Tennessee, and Virginia). Information about the river basins is available online at the NCDENR Division of Water Resources Basin Planning Branch web page http://portal. ncdenr.org/web/wq/ps/bpu. Five western basins in the state are part of the Interior Basin and drain to the Mississippi River and the Gulf of Mexico (Hiwassee, Little Tennessee, French Broad, Watauga, and New). North Carolina boundaries for these fve river basins, along with the Savannah River Basin, have boundaries entirely within the Mountain ecoregion, which dominates the western third of the state. Generally, streams in the Mountain ecoregion are relatively high gradient with cool waters, have boulder and cobble-gravel bottoms, and are of low to mod- erate fertility. Larger streams and rivers have historically supported exceptionally diverse warmwater communities. Te other 12 basins of the state are part of the Atlantic Slope and fow to the Atlantic Ocean. Te headwaters of the Broad, Catawba, and Yadkin–Pee Dee River Basins drain the eastern slopes of the Mountains. Tese river systems drain toward the ocean through the rolling topography of the Piedmont, where all but three of the remaining river basins originate. Te Piedmont is a mosaic of broad valleys interspersed with highlands of varying topog- raphy and geology. Streams in the Piedmont are generally warmwater systems, have cobble-gravel and sand bottoms, and are of intermediate gradient and fertility. Te Fall Line marks a change in topography from the Piedmont to the fat terrain of the Coastal Plain. Te North Carolina basins of the White Oak, Chowan, and Pasquotank rivers are entirely within the Coastal Plain ecoregion and are characterized by low gradi- ent warmwater streams with sand and mud bottoms and high fertility. Natural lakes and extensive wetlands are important aquatic habitats found only in North Carolina’s Coastal Plain ecoregion. A method developed by the US Geological Survey (USGS) spatially organizes drainage areas (DAs) by dividing watersheds into successively smaller hydrologic units based on four levels: regions, subregions, accounting units, and cataloging units (Seaber et al. 1987) . Te hydrologic units are arranged or nested within each other, from the largest geographic area (regions) to the smallest geographic area (cataloging units). Regional hydrologic units are identifed by a unique two-digit hydrologic unit code (HUC) but smaller units may repre- sent the most useful planning unit. Te HUCs and associated maps have undergone exten- sive review by principle federal, regional, and state water-resource agencies and are widely accepted for use in planning and data sharing (Seaber et al. 1987) . In North Carolina, 12-digit HUCs are commonly used for sharing aquatic resource data. Surface water classifcations are another tool used in North Carolina to manage and protect state waters. Te NC Division of Water Resources (NCDWR) assigns primary classifcations
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2015 NC Wildlife Action Plan
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