Transcript Investigation of the Interaction Between the St. Johns River and the

St. Johns River Water Supply
Impact Study
Investigation of the interaction between St
Johns River and the underlying aquifers in
the Middle Basin
by
Getachew Belaineh Ph. D., P.H.1
Brian McGurk P.G.1
Louis Motz Ph. D., P.E2
Follow up Review meeting
March, 2010
1 St. Johns River Water Management District
2 University of Florida, (Expert assistance)
The National Academies Follow Up
Remarks
1. Show the stability of chloride concentration more explicitly
and for more locations.
2. What is the criteria used to determine whether the change
due to density gradient is significant or not?
3. (a) The committee is looking forward to further analysis
that might rule out the need for transient groundwater
model.
(b) How is the steady state assumption considered
conservative?
Remark #1
Factors used in evaluating
the stability of chloride
concentration in the aquifer
SJR Basin
Location of
Hydrogeologic
Cross-Section
& Data Points
4/13/2015
B. McGurk, GWP WSIS support
Ground Water Flow System: Orlando through USJRB
(figure 25 from Tibbals, 1990 {USGS Water Supply Paper 1403-E})
4/13/2015
B. McGurk, GWP WSIS support
Methods used to estimate
chloride loading to SJR
•
Data obtained from monitoring wells and chloride
concentration map produced by the District.
•
GIS was used to create a raster and calculate chloride
concentration for each ECF model grid.
•
Chloride loading to SJR was estimated as a product of
the flux calculated by ECF and chloride concentration
calculated by the above method.
Verification of stability of chloride concentration
in the aquifer
•
Data from eight monitoring in the upper
and middle basins used.
•
Period of record mostly 1990 - 2009
Location of monitoring wells from which data
was obtained for the analysis
Chloride concentration in
one of the monitoring wells, S-0025
8000
7000
Chloride
mg/L
6000
5000
4000
3000
2000
1000
0
Sep-87 Nov-89 Feb-92 Apr-94 Jun-96 Aug-98 Nov-00 Jan-03 Mar-05 Jun-07 Aug-09
Seasonal record
Mean
Chloride concentration in
one of the monitoring wells, L-0032
900
800
Chloride - mg/L
700
600
500
400
300
200
100
0
6/19/90
3/15/93
Seasonal…
Mean
12/10/95
9/5/98
6/1/01
2/26/04
11/22/06
Statistical analysis results
Data mostly covers 1990-2009
Well ID
BR-1526
S-0025
V-0083
L-0032
V-0818
S-1397
V-0165
L-0455
Mean
Concentration Variability about
(mg/L)
mean (%)
1722
5235
3198
753
663
42
28
9
1.9
1.6
1.7
0.7
0.8
1.5
1.3
2.2
Summary on the stability of chloride
concentration in the aquifer near SJR

Data showed noticeable spatial variability, but
temporal variability is consistently insignificant at all
the locations the test was conducted. Temporal
variability about the mean ranges between
0.7 and 2.2%.

Laboratory uncertainty ± 10 – 15%.
(Discussion with staffs of District Laboratory and Columbia Analytical
Service, Inc. )

Tibbals (1990) documented chloride concentration
in Floridan in the SJR area is temporally constant.
(U.S. Geological Survey Professional Paper 1403-E)
Remark #2
Factors used in evaluating the
significance of the impacts
resulting from potential density
stratification effects
Calculated effect of density stratification using
monitoring wells data
(calculation procedure presented in the previous meeting)
Well ID
Well Average
Depth Concen.
(m)
(mg/L)
Potentiometric surface
elevation (m_NGVD29)
Flux –m3 s-1
S-0025
47
5220
Uncorrected Corrected Uncorrected Corrected
2.3
2.4
0.15
0.16
V-0083
132
4047
2.0
2.3
0.08
0.10
1689
6.4
6.5
0.02
0.02
BR-1526 91
Summary on salinity change due to
density stratification
Salinity change due to density stratification in
Lake Harney area, which is one of the areas
with highest Cl concentration, is less than
0.012 psu (6.6 mg/L Cl).
Remark #3
Factors used to evaluate the difference
between steady-state and transient
ground water discharge and loading to
the Middle St. Johns River
Evaluation Approach
Since the primary purpose of the groundwater model
is to provide boundary condition to the MSJR
hydrodynamics and salinity model, sensitivity of the
model is considered as the best indicator whether or
not transient flux is needed.
Conceptual Model of Surface &
Ground Water Interaction
Transient interflow, Q(i,t), between SJR and Floridan was
estimated using the following relationship:
Q(i,t) = conductance (Hriver (i,t) - Haquifer (i,t))
Where ….
Hriver (i,t) = River stage near monitoring well i at time t.
Haquifer (i,t) = Aquifer head in monitoring well i at time t.
conductance = Aquifer property from ECF model.
Location of monitoring wells from which data
was obtained for the calculation
Comparison of surface and groundwater
discharges at the southern EFDC model boundary
Hydrodynamics and salinity
simulations
Middle St. Johns River system was simulated with EFDC for
the period of 1995 – 2005 to compare the effect of steady state
and transient groundwater fluxes on water level and salinity
using the following conditions:
1. Steady state groundwater flux (from ECF).
I. With 155 MGD withdrawal
II. Without withdrawal
2. Transient groundwater flux (estimated using data).
I. With 155 MGD withdrawal
II. Without withdrawal
Model outputs
The river response, water level and salinity,
were evaluated at the following five locations in
the river.
•
•
•
•
•
SR46 Bridge south of Lake Harney
Lake Jesup
US17 Bridge north of Lake Monroe
SR44 Bridge near DeLand
SR40 Bridge near Astor
Model output locations
Difference between response of the river to
steady state and transient fluxes
without the proposed withdrawal
Absolute
water level
difference
(cm)
Percentile
Absolute salinity differences(psu)
Top layer
Bottom layer
5%
0.000
0.000
0.000
25%
0.006
0.001
0.001
50%
0.053
0.006
0.005
75%
0.173
0.013
0.013
95%
0.499
0.035
0.034
99%
0.761
0.052
0.052
Largest
0.906*
0.206*
0.126*
* Occurred for one hour over the 10 year simulation period
Difference between response of the river
to steady state and transient fluxes
with the proposed 155 MGD withdrawal
Absolute
water level
difference
(cm)
Percentile
Absolute salinity differences(psu)
Top layer
Bottom layer
5%
0.000
0.000
0.000
25%
0.005
0.001
0.001
50%
0.049
0.005
0.005
75%
0.161
0.013
0.013
95%
0.489
0.035
0.035
99%
0.755
0.052
0.052
Largest
0.906*
0.206*
0.126*
* Occurred for one hour over the 10 year simulation period
Histogram showing water level difference between
the steady state and transient fluxes
with the 155 MGD withdrawal
μ = 0.03038 cm
σ. = 0.20159 cm
Histogram showing water level difference between the steady
state and transient groundwater flows
without withdrawal
μ = 0.02775 cm
σ. = 0.20742 cm
Histogram showing bottom layer salinity difference between
the steady state and transient fluxes
with the 155 MGD withdrawal
μ = 0.00000 psu
σ. = 0.01440 psu
Histogram showing top layer salinity difference
between the steady state and transient fluxes
without withdrawal
μ = 0.00000 psu
σ. = 0.01440 psu
Summary of the response of SJR
to steady state and transient
groundwater flows
Response of the river to the steady state & transient
groundwater flow match.
• Water level:
• Salinity:
95% of the time differences ≤ 0.489 cm
95 % of the time differences ≤ 0.035 psu
Steady state results capture the temporal variability
adequately.
The correlation between the steady state and transient
responses of the river exceeds 0.95; significant at 0.01
level.
What makes steady state a conservative
estimate?
•
In three of the four wells the mean of the
transient groundwater flow estimate was lower
than the steady state estimate for the cells the
wells are located. Well S-1397 is the exception.
Conclusions
1. Chloride stability: Data showed although there exists
noticeable spatial variability, temporal variability is
negligible.
2. Density stratification effect: Considering the highest Cl
concentration data, the correction for density gradient did
not show noticeable change in the river salinity.
Continued….conclusions
3. (a) Steady state/Transient Analysis: Statistical analysis of
the results of EFDC model sensitivity test showed the
assumption of steady state is valid for the purpose of the
groundwater model.
(b) Estimation of groundwater flow under steady state
assumption is not always higher than transient condition. In
this study comparisons showed the steady state groundwater
flow for the 1995 hydrologic condition higher than the average
transient flow for the period of 1995 – 2005 at three out of
four locations.
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