Transcript Dougherty Karst Plain/Chipola Upper Floridan Aqfuifer

The Floridan Aquifer/Chipola River
System Study
Funded by: U.S. Geological Survey
National Water Quality Assessment Program (NAWQA)
and
Florida Department of Environmental Protection (FDEP)
Christy Crandall
U.S. Geological Survey
Tallahassee, Florida
850 942-9500 ext. 3030
[email protected]
STUDY OBJECTIVES
• Identify significant sources of nutrients to the Floridan aquifer
system in the lower ACF basin and in the Chipola River basin.
• Characterize hydrologic and transport processes occurring
along flowpaths from areas contributing recharge to discharge
points of interest using a ground-water flow and particle
tracking model.
• Use flow and tracking model to match nitrate concentrations in
ground water from areas contributing recharge to 6 NAWQA
trend wells, Jackson Blue Spring, Baltzell spring group, and
Sandbag Spring—springs that flow into the Chipola River.
• Use the ground-water flow and tracking model to test
hypothetical scenarios changing management practices in
using the flow and tracking model.
Contaminant occurrence in the Upper
Floridan aquifer and recharging Rivers
Purpose of study is to determine:
Factors affecting nitrate occurrence and distribution in the Upper
Floridan aquifer in the Dougherty Karst Plain
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Distribution of travel times from recharge to discharge
Land use effects on nitrate concentrations
Transport processes in ground water
Effects of Withdrawals on flowpaths and travel times
Background and Study Area
Floridan Aquifer System
• Vertically contiguous sequence of limestone and
dolostone of late Paleocene to early Miocene age
ranging from 0 to 1250 feet thick in the study area
• Sand overlying clay and limestone
• Clay lenses in places between the sand and
Limestone
• Highly potable
• Contains numerous springs, sinks and other karst
features—highly vulnerable.
Extent of Floridan
Topography
of the
Dougherty
Karst Plain
Floridan Aquifer System in the
Dougherty Karst Plain
• High rates of direct recharge through sinkholes and
indirect recharge through overburden—mostly sand and
silty sand
• High rates of discharge to large incised streams through
springs.
Flow system Conceptualization
Northern Extent of
Floridan Aquifer System
•Confinement--Recharge occurs mainly in unconfined and semi-confined areas
•Potentiometric surface—flows southward to rivers from northern extent
• Ground water makes up the
majority of discharge during
low-flow conditions in the
Dougherty Karst Plain.
•For example at least 63
springs identified and sampled
along the Chipola River.
•(Barrios and Chellette, 2004)
Existing Models 2006
Models from Elliott Jones and Lynn
Torak 1996 and 2006
•
MODFE Finite element transient
2-D model developed to simulate
the effects of 4000 irrigation wells
on baseflow conditiotns in the Flint
river.
Current
MODFLOW
Active ModelGrid Boundary
Tallahassee
Jones and Torak
MODFE Model
Boundaries
Comparison of Model Features
MODFE Developed to simulate the
MODFLOW Developed to simulate
effects of irrigation on the
Flint/Apalachicola Rivers baseflow
nitrate tracking and concentrations
recharging rivers
• Steady State (Torak and
others, 1996) and then 1year transient (19992000) (Jones and Torak,
• Steady State
• Uniform cell-size (1000
m)
• 2 layer surficial/residuum,
UFA fully 3-D model
• Over 4000 Wells
simulated
2006)
• Variable Element Size
• 1 layer 2-D model
• 4000 Wells simulated
•
MODLFOW model derived the following
starting parameters where available
from Torak and Jones
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Hydraulic parameters
Aquifer tops and bottoms
Pumping data
Recharge
Boundary conditions
River and drain stage and conductance
Starting heads
Boundary Conditions in the MODFLOW Model
Simulated Withdrawals in the Upper Floridan aquifer
Model Calibration Data
• 329 head observations in the Floridan
aquifer
• 65 flow observations including perennial
and non-perennial streams
MODFLOW Budget
Components Flow in CFS
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CONSTANT HEAD 3,397
WELLS = 0.00
NONPERENNIALS = 0.00
PERENNIALS = 253
HEAD DEP 5332
RECHARGE = 1,909
•CONSTANT HEAD 2,772
•WELLS = 810
•NONPERENNIALS = 188
•PERENNIALS = 3124
•HEAD DEP 3,996
•RECHARGE = 0.00
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TOTAL IN 10,890
•TOTAL OUT 10,890
Simulated
UFA
Heads
Observed v. Simulated Head
300
250
200
150
simulated
100
50
0
0
50
100
150
200
250
300
Simulated v. Observed flows
sim_cfs
0
-800
-600
-400
-200
0
-100
-200
-300
sim_cfs
-400
-500
-600
-700
Additional Modeling to define
Areas Contributing Recharge
Regional Model
• UFA broken into 3 layers
• Local Grid Refinement in areas of interest
• Karst Features added throughout—
– Sinkhole
– Conduit layer
Local Grid Refinement
Local Grid Refinement
• 12 layers—
– 3 in the surficial
– 9 in the Floridan
Improves flow path accuracy and travel time
estimates
Better areas contributing recharge definition
Flow Paths
Areas Contributing Recharge
and Age of Water
Summary
• Add local grids at Balztell and Sandbag
Spring Group as well
• Finalize nitrate travel time estimates and
area contributing recharge with these
models
• Finish report