Modeling Flow through
Wetlands
Wayne Dodgens
Chad E. Edwards
Amy Gross
Modeling Flow Through Wetlands

Groundwater

Surfacewater

GroundwaterSurfacewater
Interactions
Hydrologic Cycle
Groundwater

The water stored in interconnected pores
located below the water table in an unconfined
aquifer or located in a confined aquifer. (Fetter
2001)

That part of the subsurface water that is in the
zone of saturation, including underground
streams. (Glossary of Geology, 4th ed.)
Groundwater
Groundwater
Reasons groundwater is of concern
to wetlands studies:

Ecological concerns

Can store and also filter
contaminated fluids

Groundwatersurfacewater
interactions
Animation from www.mhhe.com
Saltwater Intrusion
www.mhhe.com
How do you model groundwater
flow in wetlands?
Treated the same as any groundwater investigation.
-Surface mapping
-Subsurface characterization:
1.
Soils
2.
Water
-Modeling
Darcy’s Law
Q = -k * i * a
Q = discharge
k = hydraulic conductivity
i = hydraulic gradient
a = area
Soils cont.

Data acquired from:




Soil borings
Well cuttings
Cores
Geophysical
techniques
Soils
Hydraulic Conductivity (~Permeability)

Gravel – 10-2 – 1 cm/s *
Fine sand – 10-5 - 10-3 cm/s *



Clays – 10-9 - 10-6 cm/s *
Peat – 10-3 – 108 m/day ††
*(Fetter 2001)
†† (Wise et. al.)
Hydraulic Conductivity cont.

Flow rates from tests run during and after drilling of the
monitoring wells

Inferred hydrologic parameters based on inspection of
samples.

Assumed values for materials from published values in
previous literature.

Estimates based upon the grain size distribution curve
for samples run through a sieve analysis
Hydraulic Gradient

Monitoring wells

Piezometers

Hydraulic head values

Hydraulic gradient = change in head over
distance or (Δh / Δl)
Wetland flow possibilities
Case Study
Study Area – Jensen Beach, Fla.
Study Area

Pine flatwoods of Savannas State
Preserve

Circular shape – 60m diameter

USFWS designation: palustrine,
persistent, emergent, nontidal and
seasonally flooded wetland
Vegetation - upland
Dahoon holly
Wax myrtle
Saw palmetto
http://www.gillespiemuseum.stets
on.edu/grounds/list.html
Vegetation - interior
St. John’s Wort
Blue Maidencane
Duck potato
Maidencane
http://sofia.er.usgs.gov/virtual_tour/pgbigcypress.html
http://www.gillespiemuseum.stetson.edu/grounds/list.html
Geology

Underlain by the surficial aquifer – Upper
Miocene to Pleistocene 45-52m thick

Upper 12-18m = fine to coarse grained sand
intermixed with shell beds

3-6m layer of fine sand with a few shells

Lower layer of limestone and calcarenite mixed
with shells and sand
Site Geometry

Sediment surface contouring during flooded
conditions

3m intervals along N-S & E-W, NW-SE & SWNE transects

Peat thickness was measured by pushing 1cm
rebar through the peat until higher resistance
indicated the sand layer
Methods

The basic idea behind this study is to pump
enough surfacewater from the wetland so that
its relationship to the underlying aquifer can be
assessed based on the rate at which the
wetland levels recover due to groundwater
seepage from below.

Monitoring of 6+ wells in the marsh interior, and
12+ wells outside the area, for initial head
values and the lowering and subsequent rise of
head values throughout the experiment.
WAIT – well transects
Results
Results
Conclusions

Model agrees with data for smaller time
increments while extrapolation to longer periods
may involve inclusion of more variables

WAIT quantifies the resistance to flow between
wetland and aquifer

AWIT – to determine variability in the vertical
hydraulic conductivity depending on direction
Computer Modeling

“Computer models are used to help
hydrologists understand how flow
systems work and sometimes to project
how flow systems might be affected by
changes in the hydrologic cycle. “
http://ut.water.usgs.gov/modelsb.html

More than 40 models have been
developed or are being developed.
Modeling

Different programs solve for parameters
dependant on the study design.

Current programs are combining the
capabilities of existing software into
packages that can deliver results or
predictions for numerous parameters
GMS v.4.0
All images: http://www.ems-i.com/GMS/gms.html
Visual Modflow Pro v3.1
Animation:http://www.visual-modflow.com/html/visual_modflow.html
Modeling Surface Water
Flow in Wetlands
A non-mathematical explanation of a
mathematical process
Development and evaluation of a
mathematical model for surfacewater flow within the Shark River
Slough of the Florida Everglades
Carl H. Bolster, James E. Saiers
Why develop a model for surface
water flow through wetlands?


Wetlands are beginning to be appreciated for
their value to society
The future management and restoration of
wetlands relies on a quantitative
understanding of surface water flows over
vegetation

Over the last 50 years, 1000 miles of
canals, 720 miles of levees, and nearly 200
water control measures have been
implemented in the Florida Everglades

The restoration plan of $7.8 billion will
include re-engineering the ecosystem to
capture most of the water that is now being
diverted to the ocean and use 80% of it for
environmental restoration and the remaining
20% for society’s water needs
Planners need to be able to predict
the effect on wetlands of actions
such as:
Removing canals and levees
Removing dams
Redirecting flow from canals to wetland
sloughs
The model developed in this study is
a two-dimensional model for surface
water movement
The model was tested against hydrologic data
measured in Shark River Slough in the Fl.
Everglades
Assumptions of the model include:





Uniform rates of evaporation
a constant ground surface slope
spatially homogenous vegetation cover
constant values for wetland porosity
exchanges between surface water and
subsurface water are negligible
Overland flow models are determined by the
properties of the wetland
Bed shape irregularities (such as hummocks and
depressions) and vegetation density control
resistance to flow and the magnitude of the
model’s friction coefficient
Variable data regarding the ground-surface slope
represent the effects of gravity on the movement of
water across the surface of the wetland
Data on evapotranspiration , rainfall, and groundwater
exchange also contribute to the designing of an
accurate surface water flow model for wetlands
Field measurements of hydraulic head (water level) were
obtained from databases operated by the USGS and
Everglades National Park.
Daily measurements were compiled by averaging 15minute interval data
Results of the Shark River study


The model successfully predicted two
observed decreases in hydrologic head
occurring from Jan. 17,1998-July 29, 1998
and from Aug. 14, 1998-Dec. 30, 1998.
Also, the model coincides with rainfallinduced head oscillations recorded at the
monitoring sites



The model is not perfect, however
Between May 1998 and July 1998 the
model overestimated the observations at
one recording station and underestimated
the observations at another
This was presumed to have been caused by
violations of the uniform wetland
properties assumption


The model did predict accurately the
temporal and spatial changes in surface
water levels over a 27 km long area of
Shark River Slough
Results suggest that good predictions of
wetland flow over relatively large scales
can be obtained with simple mathematical
models, without allowing for varying
wetland properties

The authors of the study conclude surface
water flow for extended time periods , over
larger expanses, can be predicted with
reasonable accuracy without the need to
model changes in wetland parameters
A 2-dimensional, diffusion-based wetland flow model
(WETFLOW) Ke Feng and F.J. Molz
Two cases are presented in this study: a laboratory testing of
the model and the model applied to a wetland pond in
Talladega National Forest near Moundville, AL
This model was developed to be applied to a general wetland
type
This small wetland was created when beavers
dammed a perennial stream
This is a Riparian wetland, one that is
adjacent to a body of water and is flooded
on a regular basis
Flow domain boundaries (outlines of study area) and
outlines of the islands must be defined
The varying boundaries of a wetland provide a problem to
the mathematical modeling of surface water flow
The boundaries of a wetland may change with time, due to
flooding events and drought
This model has many positive
attributes



The model allows for variations in wetland
characteristics
The model applies to both 1-D and 2-D flow
fields (evidenced by the laboratory study and
the wetland study)
During drought and flood events, the model
can identify changing wetland boundaries


This model can be used (as a
hydrodynamic basis) for wetland research
involving transport, chemistry, and biology
The authors of the study concluded that
micro-topography and the distribution of
flow resistance are the two parameters that
must be measured in detail, and not
assumed, in order to build an accurate
model
Numerical Representation of
dynamic flow and transport at the
Everglades/Florida bay interface
Dr. Eric Swain USGS

Southern Inland and Coastal Systems
Numerical Model (SICS)
This model was developed by starting with the
USGS Swift 2-D model, and was then modified to
make it applicable to the Everglades
Model input data


The model area is characterized by:
topography, vegetation, wind friction
coefficient, and bathymetry
Hydrologic data is then incorporated: rainfall,
evapotranspiration, salinity time series data,
and water discharge at the boundaries of the
study area


There must be observed data on hand to
compare to the results of the model: the
amount of water discharged at coastal creeks,
at the boundaries, and within the study area
Calibration data
The Southern Inland and Coastal Research
Systems (SICS) will be discussed more by the
next presenter (groundwater and surface water
interactions)
Several papers were researched in studying
modeling surface water flow through
wetlands, most of these papers deal with the
mathematical equations of the models
The models usually contain a series of
differential equations that work together
There will be separate equations for different
aspects of wetland hydrology
conclusions
There are a few mathematical models used for
modeling surface water flow through wetlands
 These models may be modified to apply to a
particular type of wetland: Everglades,
riparian, etc.
 All of these models attempt to provide a
relatively simple means to model wetland flow
without the need to account for minor changes
in topography, porosity,etc.

Overall, the authors of the papers presented report
relatively successful models, that have correctly
predicted observed changes in the surface water
flows in the wetlands studied
It is important to have reliable models that allow us
to understand and predict changes that may occur
in surface water flows in a wetland due to human
intervention; whether those changes are for better
(tearing down control structures) or for worse
(building structures that resist wetland flow)
References

Development and evaluation of a mathematical model
for surface water flow within the Shark River Slough
of the Florida Everglades. Carl H. Bolster, James E.
Saiers. Journal of Hydrology 259 (2002)221-235
 A 2-D, diffusion-based, wetland flow model. Ke

Feng, F.J. Molz. Journal of Hydrology 196 (1997)
230-250
Numerical representation of dynamic flow and
transport at the Everglades/Florida Bay interface. Dr.
Eric D. Swain, USGS
Ground and Surface Water
Interaction


Examine the effects of fluxes in water
between the ground and surface
Study the effects of these movements on
solutes: Organic (carbon), inorganic
(nitrogen), pollution (mercury)
Ground and Surface Water
Interaction


Ecological effects: salinity front movements
Used to study the effects of management
practices on hydrology
QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.
Interactions Between Groundwater
and Surface Water Models
Case Study:
The Tides and Inflows in the
Mangroves of the Everglades (TIME)
And
Southern Inland and Coastal Systems
(SICS)
Introduction

A critical goal of the Comprehensive
Everglades Restoration Plan (CERP) is to
restore and preserve the hydrology of the
predrainage ecosystem to provide ecological
conditions that are consistent with habitat
requirements.
Introduction

SICS will investigate wetland response to
freshwater inflows and to compute resultant
salinity patterns and concentrations in the
subtidal embayments of Florida Bay as
functions of freshwater inflows
SICS Study Area
The dynamic
surface-water
model is
connected to a
threedimensional
ground -water
model
SICS




What effects hydrologic changes to Taylor
Slough and C-111 will have on:
Hydroperiods and Hydropatterns
Quantity, timing, and location of freshwater
flow
Development of hypersaline conditions and
excess nutrients and contaminants
SICS

An existing, generic, two-dimensional
surface-water flow and transport model was
coupled to a fully developed, generic, threedimensional variable-density ground-water
flow and solute-transport model
QuickTime™ and a Cinepak decompressor are needed to see this picture.
TIME

TIME is an investigation into the interacting
effects of freshwater inflows and coastal
driving forces in and along the mangrove
ecotone of southern Florida within Everglades
National Park
Satellite image of
south Florida covering
Everglades National
Park, 1:500,000 scale
Satellite image showing
TIME model boundary
Scale 1:500,000
Development of the TIME Model


An extension of the SICS model westward
Required many new, high resolution data sets
to be created including, topography,
vegetation, and other hydrographic data
Primary Objectives of the TIME
Project



Develop, implement, and use a mathematical
model to study the interaction of overland sheet
flow and dynamic tidal forces
Including flow exchanges and salinity fluxes
between the surface- and ground-water systems
In the mangrove-dominated transition zone
between the Everglades wetlands and adjacent
coastal-marine ecosystems
Goals of the TIME project
to provide
 new scientific insight,
 additional quantitative information,
 more comprehensive data
 a refined hydrodynamic model to help guide
and assess restoration and management
decisions for this critical ecosystem.
Questions Addressed by TIME


How do the Everglades freshwater-wetland
and coastal-marine ecosystems respond
concurrently, both hydrologically and
ecologically, to regulation of inflow?
Will upland restoration actions affect the
transformation of freshwater wetlands to
brackish and marine marshes and
subsequently to mangrove marsh ecotones?
Questions Addressed by TIME


How will changes in inflows act in concert with
predicted increases in sea level to affect migration of
the freshwater/saltwater interface within the surface
and subsurface flow systems?
What key factors influence salt concentrations in the
coastal mixing zone and how do these factors
interact to affect wildlife habitat areas?
Questions Addressed by TIME


How will external dynamic forcing factors,
such as sea level rise or meteorological
effects, adversely affect upland regulatory
plans?
What concurrent changes in wetland
hydroperiods and coastal salinities are likely
to occur in response to various proposed
restoration and management plans?
Data sets used in model










vegetation characteristics
aquifer properties
surface-water levels,
ground-water heads,
flow velocities,
structure discharges,
tidal fluctuations,
salt concentrations,
Rainfall events,
and meteorological conditions
Findings to Date


Water management has increased recharge
and discharge in the north-central Everglades
above pre-drainage conditions
Mercury is being recharged from surface
water to groundwater and stored in the
surficial aquifer
Findings to Date


Ungaged freshwater flows discharging from
groundwater into Taylor Slough were
quantified for the first time
Significant recharge and discharge occurs by
vertical flow through Everglades peat in areas
that are far from boundaries with levees and
canals
Findings to Date

Discharge of deep groundwater from relict
seawater origin beneath WCAs cannot explain
the contaminant-level concentrations of
sulfate in Water Conservation Areas
Conclusions




Models are very useful and powerful tools:
Predict effects of management practices
Allow officials to make management
decisions based on more than speculation
Predict effects of natural phenomena