Operational restoration of the Pen Branch bottomland hardwood and swamp wetlands — the research setting

• Published in: Ecological engineering 2000-09, Vol.15, p.S23-S33
• Main Authors: Nelson, Eric A, Dulohery, Neil C, Kolka, Randall K, McKee, William H
• Format: Article
• Language: English
• Subjects: Bottomland hardwoods; Freshwater; Mitigation; Nyssa aquatica; Pen Branch; Planting; Riparian; Savannah River; Site preparation; Swamp habitats; Taxodium distichum; USA, South Carolina; Wetland restoration
• ISSN: 0925-8574; 1872-6992
• DOI: 10.1016/S0925-8574(99)00069-5

The Savannah River swamp, a 3020 ha forested wetland on the floodplain of the Savannah River, USA is located on the Department of Energy's Savannah River site (SRS) near Aiken, SC. Historically, the swamp consisted of approximately 50% bald cypress–water tupelo ( Taxodium distichum– Nyssa aquatica) stands, 40% mixed bottomland hardwood stands, and 10% shrub, marsh, and open water. Creek corridors were typical of southeastern bottomland hardwood forests. Hydrology was controlled by flooding of the Savannah River and by flow from four creeks that drain into the swamp prior to flow into the Savannah River. Upstream dams have caused some alteration of the water levels and timing of flooding within the floodplain. Major impacts to the swamp hydrology occurred with the completion of the production reactors and one coal-fired powerhouse at the SRS in the early 1950s. Flow in one of the tributaries, Pen Branch, was typically 0.3 m 3 s −1 (10–20 cfs) prior to reactor pumping and 11.0 m 3 s −1 (400 cfs) during pumping from 1954 to 1988. Sustained increases in water volume resulted in overflow of the original stream banks, the creation of additional floodplains, considerable erosion of the original stream corridor, and deposition of a deep silt layer on the newly formed delta. Heated water was discharged directly into Pen Branch and water temperature in the stream often exceeded 65°C. The nearly continuous flooding of the swamp, the thermal load of the water, and the heavy silting resulted in complete mortality of the original vegetation in large areas of the floodplain. In the years since pumping was reduced, no volunteer seedlings of heavy-seeded hardwoods or cypress have been found in the floodplain corridor. Research was conducted to determine methods to reintroduce tree species characteristic of more mature forested wetlands. Species composition and selection were altered based on the current and expected hydrological regimes that the reforestation areas will be experiencing.