The Evaluation and Modeling of the Effects of Surface Treatments on the Hydrology of a Restored Wetland in the Coastal Plain of North Carolina.

Show full item record

Title: The Evaluation and Modeling of the Effects of Surface Treatments on the Hydrology of a Restored Wetland in the Coastal Plain of North Carolina.
Author: Wright, Jason Dee
Advisors: Dr. Michael Burchell II, Committee Member
Dr. Robert Evans, Committee Chair
Dr. Stephen Broome, Committee Member
Dr. Garry Grabow, Committee Member
Abstract: Wetlands can be valuable for removing sediment and pollutants from drainage waters. Many wetlands are being restored through state and federal incentive programs, however more research is needed to develop and document the success of restoration practices. Wetland hydrology is critical in the success of wetland restoration. This study was conducted to determine the effects of surface treatments on the hydrology of a 100 ha prior converted wetland in coastal North Carolina that was restored in March of 2003. A depressional non-riverine bottomland hardwood wetland was also evaluated to serve as a reference for comparison of the hydrologic conditions in the restored wetland. A natural stream in the reference wetland served as the drainage outlet. Water table monitoring wells were installed along three different transects across the reference. Approximately 60 ha of the prior converted crop land was restored using three types of surface treatments; plug and plant, crown removal, and microtopography. In each of the treatments the ditches were plugged and wetland vegetation was planted. Plug and plant left the ground surface as it was during agricultural production, crown removal leveled the approximately 20 cm of crown in order to reduce runoff, and microtopography was added to provide storage and slow runoff. The three surface treatments were replicated in three blocks, approximately 20 ha each. Each of the 6.5 ha plots were separated by berms to allow measurement of surface runoff. Water table monitoring wells were installed in a single transect across each treatment. Water control structures with weirs were used to control outlet stage and outflow from each treatment. Continuous water level recorders were installed in each well and at the outlets. The water table depth in the treatments was analyzed using eight criteria to characterize the hydrology of the site. The criteria were the 1) number of times that jurisdictional wetland criteria was met; 2) the range of the water table fluctuation; 3) the number of days that the water table was at or above the surface during the study period and 4) the growing season; 5) the number of days that the water table was within 30 cm of the surface during the study period and 6) the growing season; 7) SEW30 for the study period and 8) the growing season. SEW30 is a measure of the duration and frequency that the water table is above a threshold depth. The average water table in the crown removal treatment was deeper than in the plug and plant and the microtopography treatment across all three blocks. The water table was also closer to the surface in the microtopography treatment than in the plug and plant treatment. Outflows from the crown removal treatment were less than from the microtopography and plug and plant treatments. A ditch plug near the outlet of plot 9 (Block 3) failed which likely affected the hydrology of this plot. When the criteria were applied to only block 1 and block 2, the crown removal treatment was wetter (water table closer to the surface) than the microtopography treatment and the plug and plant treatment. These latter results showed that crown removal was the most effective practice to maintain the water table within 30 cm, or closer to the surface, compared to adding microtopography or just plug and plant. DRAINMOD was calibrated using the 20 months of water table data and used to simulate the hydrology of each plot in blocks 1 and 2. Long term simulation results were similar to the observed results. The simulated water table was at the surface for more days in the crown removal treatment than in the reference or the microtopography and the plug and plant treatments. The water table was within 30 cm of the surface for more days and the SEW30 was greater in the crown removal treatment indicating that it was wetter. DRAINMOD was also used to model the expected conditions in the wetland once mature wetland vegetation was established. Minimal jurisdictional wetland criteria (water table within 30 cm of the surface for 5% of the growing season) was satisfied for more than 41 out of 50 years in the treatments and 46 out of 50 years in the center of the reference. The restored surface treatments were saturated continuously above 30 cm for 12.5% or more of the growing season in 17 to 22 years out of 50 compared to 24 out of 50 for the center of the reference. Both the reference and the restored treatments satisfied the drier range of the jurisdictional criteria but neither satisfied the wet end of the range. Finally, outflow was simulated for a wetland with mature vegetation and compared to conventional row crop conditions. Each of the restored treatments showed an approximate 30% reduction in flow compared to conventionally drained row crops.
Date: 2005-04-21
Degree: MS
Discipline: Biological and Agricultural Engineering
URI: http://www.lib.ncsu.edu/resolver/1840.16/1972


Files in this item

Files Size Format View
etd.pdf 4.062Mb PDF View/Open

This item appears in the following Collection(s)

Show full item record