Hydrology and water quality of the Great Dismal Swamp, Virginia and North Carolina, and implications for hydrologic-management goals and strategies

First posted October 21, 2021 For additional information, contact: Center Director, Virginia and West Water Science CenterU.S. Geological Survey1730 East Parham RoadRichmond, VA 23228 The Great Dismal Swamp is a peat wetland in the Coastal Plain of southeastern northeastern North Carolina. Timber harvesting construction ditches to drain swamp facilitate are collectively implicated changes that altered forests, caused subsidence decomposition peat, increased risk fire. In response these changes, managers have implemented strategies control water levels rewet using network 64 adjustable-height, water-control structures on ditches. Rewetting intended re-establish original wetland-forest types, reduce fire, enhance accretion, Knowledge responses hydrologic controls, however, critical developing implementing effective management goals strategies. Because 2008 South One fire reemphasized need for this knowledge, U.S. Survey cooperation with Fish Wildlife Service began studies 2009 identify controls controls.These identified sources, topography, two-layered hydraulic characteristics absence some areas, ditch road network, ditches, Canal associated infrastructure, forests as primary controls. Precipitation only source across much swamp. eastward flow streams groundwater from Isle Wight Plain, Suffolk scarp, into sources western part Vertical differences reflect an upper having high conductivity specific yield overlying lower sand yield. forms main aquifer storage, flow, release Maintaining availability because properties.Groundwater flows where it discharges nearby streams. Discharge typically closest except spoil-pile impedes intervenes between ditch. When about 2 feet than other three surrounding swamp, most level. This occurs even if Flow single shifts watershed boundaries divides toward higher demonstrates how discharge controlled by levels. Consequently, managing based achieving objectives.The chemistry shows effects peat. Dissolved organic carbon concentrations among highest reported globally, ranging 55 195 milligrams per liter. pH commonly less 4.0 standard units acids. A relation conductance reflects paths, chemical evolution, waters different mix along paths.