Hydrologic Evaluation of a Restored Wetland in Eastern North Carolina

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Title: Hydrologic Evaluation of a Restored Wetland in Eastern North Carolina
Author: Jarzemsky, Robert David
Advisors: Michael Burchell, Committee Chair
Gregory Jennings, Committee Member
Michael Vepraskas, Committee Member
Abstract: A prior-converted wetland in coastal North Carolina was restored in an attempt to re-establish a non-riverine hardwood wet forest Community. Topography was restored using three surface techniques to determine the effect surface topography had on wetland hydrology in coastal areas. The three treatments were: plugging field ditches without altering the surface (PLUG), plugging the field ditches and contouring the surface (CONT), and plugging the field ditches and removing the field crown (CR). The treatments were replicated three times forming a randomized complete block design. It was hypothesized that CR would produce the wettest site followed by CONT and then PLUG. Water table response and surface outflow was evaluated for 2006-2008. Few significant differences were found between the water tables of each treatment; however CR and PLUG appeared wetter than CONT. Surveying of the restoration revealed that the as-built topography of the PLUG and CONT treatments in block 3 were different than their intended design causing PLUG to produce wetter conditions and CR to produce drier conditions than intended. Based on these observations, the treatments were re-evaluated using only blocks 1 and 2, and using all three blocks with block 3 PLUG and CR data switched. These evaluations found CR produced the wettest hydrology followed by CONT then PLUG, which matched the original hypothesis. Based on the alternate evaluations, CR produced wetter conditions than the reference (3 of 4 hydrologic criteria were significantly wetter) while PLUG produced drier conditions than the reference (3 of 4 hydrologic criteria were drier). CONT matched reference hydrology the closest but only one hydrologic criteria was not significantly different than the reference (α = 0.05). All three treatments produced significantly more surface inundation than the reference likely due to pre-restoration surface compaction by farming equipment. Surface outflow evaluation found that CONT produced significantly more outflow than PLUG and CR. PLUG was hypothesized to produce the most outflow, but that CONT produced the most outflow likely due to unintended conveyance pathways created during construction. A second study, evaluated the hydrology of the restored wetland during tropical weather. Three periods were evaluated from 2004 – 2007. In 2004, a 34 day period of tropical weather including, Hurricane Alex and Tropical Storm Charley produced 41 cm of rainfall and 21 cm of outflow. In 2005, a 15 day period including Hurricane Ophelia produced 33 cm of rainfall and 11 cm of outflow, and in 2007, an 11 day period including Tropical Storm Gabrielle produced 21 cm of rainfall and 7.5 cm of outflow. The restored wetland performed similarly during 2005 and 2007, retaining 67% and 64% of the rainfall. During 2004, the restored wetland retained only 49% of the rainfall. It performed less efficiently due to lower antecedent soil moisture condition and increased rainfall. Soil moisture conditions were high prior to both Alex and Charley which limited the wetlands ability to store water. Prior to Ophelia and Gabrielle, soil moisture conditions were low which provided large amounts of water-free pore space in the soil for storage. DRAINMOD was used to simulate pre-restoration, agricultural hydrology. DRAINMOD predicted the restoration reduced peak daily outflow during all three storm periods by at least 70%. Total outflow reduction was found to be dependent on soil moisture conditions. In 2005 and 2007 antecedent soil moisture conditions were low; the simulation predicted the restoration reduced total outflow by 44% and 29%. In 2004, soil moisture conditions were high prior to Hurricane Alex and Tropical Storm Charley and the simulation predicted the restoration did not reduce total outflow. The modeling predicted the restoration reduced annual outflow by 6 – 31% depending on the year.
Date: 2009-06-18
Degree: MS
Discipline: Biological and Agricultural Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/1652

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