Influence of Groundwater flows on Wetland Restoration Project at Juniper Bay

1. Influence of Groundwater flows on Wetland Restoration Project at Juniper Bay SSC 570 - Wetland Soils Term Paper Presentation Swamy Pati Bio. & Ag. Engineering Dept., NCSU

2. Outline • Introduction • Carolina Bays • Wetland Restoration Requirements • Project Objectives • Methodology

3. Introduction • Research project – Assessment of Groundwater flows at Juniper Bay and their impacts on the surrounding area. • This project is a supplement to the wetland restoration project underway at Juniper Bay. • Project mainly focuses on the influence of the subsurface flows on wetland restoration. • Juniper Bay is one of the Carolina Bays, which are spread throughout the Southeastern Coastal plain of US.

4. Literature review – Origin of Carolina Bays • Carolina Bays are small orientated depressions, elliptical to ovate in shape, that the south-eastern coastal plain of the united states in incredible density and range. • Extend from the Delmarva Peninsula in north to the Okefenokee swamp in Northern Florida.

5. Arial Photograph

6. Origin of Carolina Bays • D.W. Johnson, 1936 – shape and orientation, as well as presence of sandy rims are attributed to wind and wave action and depressions are attributed to the artesian process. • W.F. Prouty, 1952 – comet or asteroidal body entering the earth atmosphere at an oblique angle from a relatively northwesterly direction. • Bruce G. Thom, 1970 – Humate allows for a perched water table near the surface that would eventually evolve into shallow, wet depressions, orientated later by wind and wave action.

7. Origin of Carolina Bays • J. Ronald Eyton & Judith I. Parkhurst, 1975 – considered the theory stated by Prouty, 1952 and then they stated finally that comets are the cause for the creation of Carolina Bays. • Raymond T. Kaczorowski, 1977 – ruled out the extraterrestrial theory as a cause for Bay formation and supported Thom’s water table perching theory. He suggested that the only requirement for Bay existence is poor drainage leading to ponding mechanisms. • Reference: http://bss.sfsu.edu/jdavis/geog810/1999/black.html

8. Hydrology of Carolina Bays • The hydrology of Carolina Bays is influenced by subsurface flows inputs and fine textured soil or parent material layers that restrict the downward movement of stored water in the Bay. • Studies on the complex hydrology of Carolina Bays have shown complex subsurface interaction with the surrounding area • Local depressional hydrology superimposed on the regional subsurface hydraulic gradients of the landscape in which the bay occurred.

9. Wetland restoration Requirements • Wetland restoration projects needs assessment of the site in all factors to meet the restoration goals set by the US Army Corps of Engineers. • Wetlands hydrology, hydric soils, and plant community similar to the reference ecosystem be restored. • Site assessment, identification of potential functions, methodologies to restore wetland functions, and effective assessment of progress of functional restoration.

10. Hydrologic aspects of Wetland Restoration • Ditching and pumping in the surrounding area of the site • Regional subsurface hydraulic gradients • Filling the ditches is not suffice • Regional hydrology must be assessed and restoration methods must account for restoration of historical regional surface and subsurface hydraulic gradients.

11. Juniper Bay

12. Groundwater flows at Juniper Bay • Lateral Groundwater Flows • Preliminary work suggests non-negligible gradients across JB boundary • Core data suggest an effective bottom to the surficial system – Black Creek Confining Unit • Current well/piezometer network insufficient to assess lateral flows

13. Stratigraphy

14. Importance of Perimeter Ditch • Lateral boundary of the project is the perimeter ditch. • It influences the flows in the surficial aquifer and prevents the flows between interior and exterior of the bay. • It can effectively drain 100 feet to either side. • Influence of the perimeter ditch through the partially confined sand layers underlying the surficial aquifer is one of the main trusts of the project.

15. Objectives • Characterize the subsurface flows at four locations on the perimeter • Interaction of the perimeter ditch • Model the subsurface flows • Develop the management recommendations.

16. Characterize the subsurface flows • Four locations are selected around the perimeter of the project site. • Coring work was started in these locations. • Coring is being done at 5 points at each transect. • These are the same points at which nests of piezometers will be installed.

17. North-facing view of the Juniper Bay

18. Locations of Piezometer Transects

19. Transect of Piezometer Nests

20. NW - Transect

21. SE - Transect

22. SW - Transect

23. NE - Transect

24. Characterize the subsurface flows • With the cores collected at different locations saturated hydraulic conductivity tests are conducted and values are estimated. • Then flows crossing site boundaries will be calculated.

25. Ksat table

26. Piezometers • Piezometers are installed at these locations at all significant sand layer at each point on the transect. • Hydraulic heads will be monitored in the piezometers and perimeter ditch. • Instrumentation is installed with all the piezometers to monitoring the water levels. • Hydraulic gradients, Hydraulic conductivities, lateral and vertical fluxes will be estimated

27. Future Work - Additional Field Work • Perimeter cores (8-12) for stratigraphic data • Ground-penetrating radar surveys

28. Additional Coring

29. Role of the Perimeter Ditch • How deeply does the perimeter ditch influence subsurface flows? • Could/should it be preserved to control boundary flows? What management scheme? • Elimination of the perimeter ditch could increase wetland area by 30-100 acres.

30. Groundwater Modeling • There are various different kinds of modeling software available to model groundwater. • Some of them are CFEST, MIGRATE, DYNFLOW, MODFLOW, etc. • Except MODFLOW most of the other groundwater flow models are used to simulate the solute or chemical transport phenomena. • In this project we are mainly dealing with the hydraulic aspects of the groundwater flow, MODFLOW will be appropriate to use.

31. MODFLOW • Input parameters: Aquifer parameters, hydraulic parameters, dimensionality, initial conditions boundary conditions. • Some of the input parameters will be estimated from the field data.

32. MODFLOW • MODFLOW simulates hydraulic head and velocity field distribution and they solve the groundwater flow equation. • This model can handle multiple layer porous media, with either confined, unconfined or semiconfined. Heterogeneous, anisotropic or compressible porous media can also be modelled. • Finite difference solution technique is used in this model.

33. MODFLOW

34. MODFLOW • Number of layers and the input parameters change depending on the scenario the model is run for.

35. Modeling • Using the model we predict the flows in the surficial aquifer for the entire site • Model will be run for different management scenarios – w/ & w/o the perimeter ditch • Predict the impacts of the conversion on the water table levels in adjacent properties

36. THANK YOU Questions?