Influence of Groundwater Influence of Groundwater flows on Wetland Restoration flows on Wetland Restoration

Project at Juniper BayProject at Juniper Bay

Swamy Pati

Bio. & Ag. Engineering Dept., NCSU

SSC 570 - Wetland Soils

Term Paper Presentation

Outline

• Introduction

• Carolina Bays

• Wetland Restoration Requirements

• Project Objectives

• Methodology

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.

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.

Arial Photograph

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.

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

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.

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.

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.

Juniper Bay

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

Stratigraphy

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.

Objectives

• Characterize the subsurface flows at four locations on the perimeter

• Interaction of the perimeter ditch

• Model the subsurface flows

• Develop the management recommendations.

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.

North-facing view of the Juniper Bay

Locations of Piezometer Transects

Transect of Piezometer Nests

NW - Transect

SE - Transect

SW - Transect

NE - Transect

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.

Ksat tableDescribed By: A. Adams Core Diameter (cm) 7.62Ksat Test By: Swamy PatiCore Location: NW-IN-75 Core Height (cm) 7

Horizon DEPTH (ft) COLOR TEXTURE CORE # COMMENTS time, min Q, ml H20 ht, cm Ksat, cm/min0 - 0.5 10YR2/1 SL 18 diffuse or gradual boundary

0.5 - 1.17 10YR6/1 S/SL 1013 diffuse or gradual boundary 1 13 6.1 0.07371.17 - 2.5 10YR4/2 C 1000 1.33 15 5.5 0.0612.5 - 3.1 10YR 4/3 SCL 1077 all roots or wood 1.5 5 5.8 0.0183.1 - 3.67 10YR5/2 & 10YR5/3 SCL 86R seems to be transition zone 6.2

3.67 - 540% 10YR5/2 & 60%

10YR6/2 C w/ SCL 1083 packets of SCL, at bottom all SCL 2.33 14 6 0.033

5 - 5.8390% 2.5Y6/2 & 10%

10YR2/1 SC 1102 black at top 5.95.83 - 7.58 2.5Y6/2 SCL 1109 reduced Fe++ througout 5.87.58 - 8.58 2.5Y6/2 SL 28R varying sand content 1440 15 5 5.25E-058.58 - 9.5 2.5Y7/2 LS 1119 Fe oxidized throughout 55 15 4.2 0.00139.5 - 10.1 2.5Y6/2 SL 51 Fe oxidized throughout 9.66 9 5.4 0.01

10.1 - 10.58 2.5Y8/1 S 1016 Fe oxidized throughout 5.510.58 - 11.58 2.5Y6/1 CL 1126 Fe oxidized throughout 5.511.58 - 13.25 2.5Y6/2 SL 1024 Fe oxidized throughout 2.1 50 6 0.134

13.25 - 15 2.5Y4/1 SCL 182R Fe oxidized throughout 33.83 11 4.5 0.001615 - 16.58 2.5Y3/1 SCL 1055 Fe oxidized throughout 1.67 60 5.5 0.196

16.58 - 18.67 2.5Y3/2 & 6/2 LS/S 20R(top) Fe oxidized throughout 1 15 5 0.0814R (bottom) 2.58 35 4.4 0.067

18.67 - 19.83 2.5Y3/1 SL 119R Fe oxidized throughout 3 9 5.2 0.01619.83 - 21.25 2.5Y3/1 SL 1044 Fe oxidized throughout 1 24 4.7 0.12321.25 - 22.25 N4 C 10-R Fe oxidized throughout 4.922.25 - 22.5 2.5Y3/1 SL not enough for sample22.5 - 24.83 2.5Y3/1 C 988 top same as 21'5'' - 22'5''' 6 9 4.4 0.007

51-R bottom 524.83 - 29.83 2.5Y3/1 C 1041 top material contained from section above Fe is oxidized

1079 middle 3 16 5.2 0.01061087 bottom 4.2

29.83 - 34.83 2.5Y3/1 C 1106 top same as 25' - 30' 41078 middle 5.81043 bottom 5.5

34.83 - 37.33 2.5Y3/1 C 1037 top white sand grains throughout but very very firm1083 bottom 600 10 5.8 0.000094

37.33 - 39.83 10YR3/1 C 70R top white sand grains throughout in 5% of matrix1063 bottom contains some packets of sand

39.83 - 42.33 10YR3/1 C 30-H4 top sand samples are present in same percentages, soil is brittle1045 bottom

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

Future Work - Additional Field Work

• Perimeter cores (8-12) for stratigraphic data

• Ground-penetrating radar surveys

Additional Coring

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.

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.

MODFLOW

• Input parameters: Aquifer parameters, hydraulic parameters, dimensionality, initial conditions boundary conditions.

• Some of the input parameters will be estimated from the field data.

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.

MODFLOW

MODFLOW

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

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

THANK YOU

Questions?