The Broad and Saluda River basins encompass over 20,000 km 2 of the upper reaches of the Santee River basin , the second largest watershed in the eastern United States . Only the Susquehanna River basin is bigger. The Santee River Basin is a part of the USGS National Water Quality Assessment Program (NAWQA).
The 13,630 km2 Broad River basin has its headwaters in North Carolina and has three large tributary watersheds to the west and a number of smaller watersheds to the east. The three large tributaries, from north to south, are the Pacolet, Tyger, and Enoree Rivers . The 6535 km2 Saluda River basin has a number of large tributaries including the North Saluda, Middle Saluda and Oolenoy Rivers in the northern reaches of the basin, Big Brushy Creek and the Reedy River in the middle reaches of the basin, and Little River and the Bush River in the southern reaches of the basin. At the fall line in Columbia , SC , the Broad River and Saluda River converge in the upper most Coastal Plain to form the Congaree River. Further downstream from Columbia , SC , the Congaree and Wateree rivers converge to form the Santee River which discharges into the ocean.
The Saluda and Enoree River Basins, about 8500 km2, have been the major focus of our efforts so far. Over the past decade, we have sampled nearly 700 localities in these two River Basins. We also have sampled a few localities in the lower Tyger River basin. As of summer 2008, we have expanded our studies in the Tyger River basin and have begun studies in the Pacolet River basin, including studies of headwater streams within the Nature Conservancy's Blue Wall Preserve.
Physiographic Provinces
The Broad and Saluda River Basins headwaters are in the Blue Ridge physiographic province. The Blue Ridge province is mountainous, with peaks as high as 1200 m (4000 ft). Peaks as high as 1920 m (6300 ft) are found in the adjacent French Broad River Basin . Downstream is the Piedmont Province , characterized by low rolling hills. The Lower Broad River Basin ends near the fall line, where the Piedmont Province transitions to the Coastal Plain.
Climate
Climate in the Lower Broad River Basin is subtropical to temperate. Temperature ranges from a low average daily maximum of 11 o C (52 o F) in January to a high average daily maximum of 31 o C (88 o F) in July. July and August, however, can be very hot with numerous days with highs in the mid 30s o C (90s o F). Rainfall averages 123 cm per year (48 in) with average monthly precipitation between 10 cm to 15 cm per month. Rainfall is not distinctly seasonal, though late winter and early spring tend to be slightly wetter than the rest of the year and early fall slightly drier. Recently, the Greenville region has had drought conditions in eight of the last ten years. The worst drought conditions were between 1999 and 2001 when rain deficits were between 10 and 15 inches each year.
Hydrology
In South Carolina alone there are up to 50,000 dams, many of which are in the Santee River basin . Thus, the hydrology of the streams and rivers in the Santee River basin is highly regulated by dams, which also extensively fragment the river ecosystem. In the Lower Broad River basin , there are several major dams in the Saluda River basin , as well as one major dam on the Broad River . Additionally, there are many small impoundments throughout the watershed.
The discharge of rivers in the basin is relatively low. The Broad River at Alston has a long term mean discharge of 81 m 3 /s and the Saluda River near Columbia has a long-term mean discharge of 72 m 3 /s. The Enoree River , a tributary to the Broad, has a long-term mean discharge of 6.3 m 3 /s. In 2007, most of the rivers in South Carolina had discharges less than 10% of the mean discharge, with many as low as 2%.
Geology and Soils
The Piedmont and Blue Ridge provinces are characterized by Paleozoic age high grade metamorphic rocks, typically biotite gniesses and muscovite and silmanite schists. These metamorphic rocks are intruded by Late Paleozoic granites and Mesozoic diabase dikes. Gabbros are found at a few localites, as are even rarer marbles. Numerous thrust faults trending about N30E divide the rocks into thrust sheets.
Soils in the Lower Broad River Basin are dominantly ulitsols having the characteristic red color of deeply weathered kaolinite/gibbsite/ferrihydrite soil mineral composition. Ferrihydrite is an iron oxide mineral responsible for the red color. Soils overlying mafic and ultramafic rocks often are alfisols, but are only local in extent. Ultisols are typically low in organic carbon content and base cations (sodium, potassium, magnesium, calcium). Below the ultisols are thick saprolites, partially weathered bedrock with a high percentage of residual primary minerals. Erosion of saprolite and bedrock and deposition of the sediment in floodplains form inceptisols in riparian zones.
In much of the area, top soils are thin because of erosion during intensive cotton farming in the late 19 th to mid 20 th centuries. In the Piedmont Province , these soils are characterized by a thick C horizon called saprolite, which is isovolumetrically weathered bedrock.
Ecosystems and Land Cover
Typical of southeastern Atlantic river basins, the Broad and Saluda River Basins are located within the Temperate Deciduous Biome. The Blue Ridge mountains are located within the Applachian/Blue Ridge Forests ecoregion and the Piedmont corresponds to the Southeastern Mixed Forests ecoregion. Streams in the basins are part of the South Atlantic Freshwater ecoregion.
In the late 1800s and early 1900s much of the region was completely deforested and converted to cotton farm. As a result, virgin forests are extremely rare in the region. Now, agricultural land is rapidly being transformed to urban/suburban land cover in the I-85 corridor between Spartanburg , SC and Greenville , SC. Watersheds in the Enoree River Basin range from dominantly forested to as much as 65% urban.