Effects of Subsurface Flows on Wetland Restoration at Juniper Bay and Surrounding Area.

groundwater modeling;subsurface flows;soil stratigraphy;wetland restoration

Pati, Swamy ; Rodney L. Huffman, Committee Chair,R. Wayne Skaggs, Committee Member,Michael J. Vepraskas, Committee Member,Michael R. Burchell II, Committee Member,Gary T. Roberson, Committee Member,Pati, Swamy ; Rodney L. Huffman ; Committee Chair ; R. Wayne Skaggs ; Committee Member ; Michael J. Vepraskas ; Committee Member ; Michael R. Burchell II ; Committee Member ; Gary T. Roberson ; Committee Member

University:North Carolina State University

关键词: groundwater modeling;    subsurface flows;    soil stratigraphy;    wetland restoration;   

Others  :  https://repository.lib.ncsu.edu/bitstream/handle/1840.16/4485/etd.pdf?sequence=1&isAllowed=y

美国|英语

来源: null

【 摘 要 】

The North Carolina Department of Transportation purchased a 270-hectare, roughly elliptical tract of agricultural land, known as Juniper Bay (a Carolina Bay), to convert to wetlands as part of their wetlands mitigation program. Preliminary water balance work suggested that there are significant flows of groundwater entering and leaving the tract. This study was initiated to examine the subsurface potentials and determine the degree to which a ditch around the perimeter of the tract controls the lateral fluxes of groundwater in the surficial aquifer. Five nests of piezometers were installed along each of four 150-m transects crossing the perimeter ditch at approximately the major and minor axes of the tract, which correspond to the suspected maxima of influx and efflux. Deep soil cores (up to 13 m) were collected along each transect to guide placement of piezometers for monitoring hydraulic heads. Piezometer water levels were recorded at 15-minute intervals. Meteorological data were collected with an on-site weather station. Models were developed for the four transects using Visual MODFLOW. Models were calibrated with observed groundwater pressure heads. Maximum absolute error in the calibration process was 0.5 m. The modeling results suggested that the ditch drained water from the surficial system from both sides. In the deeper sand layers, there was an indication of groundwater flowing into the bay at NW and NE transects. Groundwater flows in the SW transect indicated outflows. The SE transects showed water draining into the ditch from both sides. The models were extended to 800-m inside the bay to simulate conditions after the interior ditch system was blocked. Simulation results showed groundwater inflows through the NW, NE, and SE transect, and groundwater outflows through SW transect. The lateral influence of the perimeter ditch had a maximum of approximately of 100 m, observed at the SW transect, and a minimum of 30 m, observed at the SE transect. The extent of influence of the perimeter ditch was also dependent on the weather conditions, showing more influence in summer months compared to winter months. Influence of the perimeter ditch was entirely in the upper sands at the NE and SE transects, but some influence was seen in the middle sand layers at the NW and SW transects. Groundwater flow estimates from the transects were extrapolated over the whole perimeter of Juniper Bay to obtain net groundwater inflow. Net groundwater inflow was approximately 125 mm for the time period of 1 January 2004 to 30 June 2004. To develop recommendations for maintaining the perimeter ditch, the models were run for various scenarios focused on water levels in the perimeter ditch. Control levels were imposed on the ditch and options were investigated. A water level of 35.9 m MSL was identified as a critical point of control of the perimeter ditch. Controlling the water level in the perimeter ditch at 35.9 m will minimize offsite impacts and result in maximum wetland area.