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8/10/2019 Rec Seawater intrusion
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8/10/2019 Rec Seawater intrusion
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number of groundwater models, spatial variations in fluid
density can affect groundwater flow patterns significantly
(Bear et al. 1999; Christensen et al. 2001). For example,
groundwater flow near the coast is often influenced by
density variation, and more complex density-dependent
models are required to simulate the processes such as
saltwater intrusion and submarine groundwater discharges.
Efforts have been made to simulate density-dependentflow with a MODFLOW base code coupled with an
advective and dispersive transport program (Langevin and
Guo 2006). The SEAWAT model uses a combination of
the approaches used by MODFLOW and MT3DMS model
to represent solute transport processes (Guo and Langevin
2002; McDonald and Harbaugh 2003).
This paper discusses a numerical study of saltwater
intrusion in the central Godavari delta region situated
adjacent to the Bay of Bengal coast in East Godavari
District of Andhra Pradesh, India. Significant quantity of
groundwater is withdrawn from the Ravva On-shore Ter-
minal located in the study area. The main aim of this workis to provide useful information that can aid in the pro-
tection of groundwater resources in the study area from
saltwater ingress. A three-dimensional numerical ground-
water flow and solute transport model were developed with
SEAWAT, which draws upon hydrogeological and hyd-
rochemical data collected as part of this study.
Description of the study area
The Godavari delta region is situated in the East Godavari
District of Andhra Pradesh, situated on the east coast of
India. The study region, spread over an area of 295 km2 in
the southern part of Godavari delta, is bounded by the Bay
of Bengal on the east, the Vainateya River on the west, and
alluvial plains on the north (Fig. 1). The exploration wells
for oil are located 1.1 km from the coastline of the Bay of
Bengal, while the Ravva On-shore Terminal wells are
located 0.6 km inland from the coastline. The area has
extensive tidal flats and inlets that receive sea water during
high tides. The area also experiences periodic flooding by
the Godavari River (Gurunadha Rao et al. 2011). Paddy
cultivation and fresh water aquaculture are the major land
uses within the region. The well-distributed Godavari
irrigation canal network acts as a source for irrigation and
drinking water throughout the year. Vasalatippa, Kunava-
ram, and Pikaleru drains are carrying out the irrigation
return flows through the Ravva On-shore Terminal area and
flow into the Bay of Bengal. This 100-year-old canal net-
work contributes significantly to groundwater recharge,
thereby reducing the potential for saltwater intrusion into
shallow aquifers (Chachadi and Teresa 2002; Gurunadha
Rao et al.2011; Naidu et al. 2013).
Geology
The area is underlain by deltaic sediments of early Holo-
cene age with varying proportions of clay, silt, sand, and
gravel with a gentle slope of 0.001 km/km toward the
coast. Groundwater occurs under water table conditions.
However, semi-confined and confined conditions tend to
develop in the area where impervious clay layers overliethe saturated granular zones. Groundwater is being tapped
from shallow open wells with depth range of 38 m as well
as filter point wells penetrating up to 20 m depth. A series
of marine transgression and regression events have greatly
influenced the depositional environments of the delta in the
past. The beach ridges are associated with the delta pro-
gradation (Rengamannar and Pradhan 1991). The study
area includes fluvial landforms such as channels, levees,
back swamps, and geologic floodplains as well as land-
forms influenced by marine processes, such as tidal flats,
beach ridge complexes, and mangrove swamps. The area is
rich in Quaternary alluvial sediments derived from theGodavari River (Rao 1993; Bobba 2002). Since the Qua-
ternary period, the Godavari River has been discharging
large amounts of sediments into the Bay of Bengal, thereby
supporting the delta building processes. The upper delta
region sediments are essentially fluvial, while those in the
lower delta region are fluvio-marine in origin (GSI2006).
The concentrations of iron, manganese, sodium and pH are
increased towards the delta where they approach the mar-
ine environment. The distribution patterns of calcium and
magnesium are mostly controlled by the amounts of shell
fragments and clay minerals, particularly montmorillonite
(Seetaramaswamy and Poornachandra Rao1975).
Hydrogeology
The average annual rainfall in the study area is about
1,137 mm distributed unevenly among an average of 57
rainy days of the year (Gurunadha Rao et al. 2008). About
72 % of the rainfall occurs during the southwest monsoon
season (JuneSeptember), while the rest occur during the
northeast monsoon (OctoberDecember). The area consists
of alluvium with thickness varying from a few meters to
300 m. Clay is present in varying proportions along with
silt and gravel. The alluvium overlies the Rajahmundry
sandstones (CGWB1999). The hydrogeology of the study
area is mainly derived from borehole geophysical logs
collected at Amalapuram, Vodalarevu, and Surasanayanam
villages. Geophysical imaging was carried out with Multi
Electrode Resistivity Tomography (ERT) at 13 different
locations in the Godavari deltaic region, the results of
which indicate that loamy sandy soils are underlain by
thick clay beds of about 3035 m and followed by coarse-
grained sands (Gurunadha Rao et al. 2011, 2013; Lagudu
L. Surinaidu et al.
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et al. 2013). The geophysical logs collected from three
locations at Ravva On-shore Terminal revealed that sandy
clay is underlain by 4555-m-thick clay with fine sand
followed by medium-to-coarse-grained sands up to a depthof 120 m below which clays saturated with saline water are
found up to a depth of 143 m (Gurunadha Rao et al. 2011;
Naidu et al. 2013).
Groundwater occurrence and flow direction
The occurrence and behavior of groundwater are controlled
by topography, soils, climate, geology, and land use of the
area. In the central deltaic region, the groundwater slope is
very gentle with an average hydraulic gradient of 0.3 m/km.
Groundwater levels in the entire Godavari delta fluctuate
significantly in response to recharge and groundwater
withdrawals (CGWB 1999). Forty-two observation wellswere selected to monitor groundwater levels and ground-
water quality in the area. In general, the groundwater levels
near canals and ditches fluctuate 34 m between the pre-
monsoon and post-monsoon season (CGWB1999). How-
ever, during the study period (20062007), they were
observed to be less than 2 m. Maximum groundwater ele-
vation of 5 m above mean sea level (MSL) has been
observed at Amalapuram, while a minimum of -12 m
(MSL) is observed inside the Ravva On-shore Terminal
A
B
AB Profile
Fig. 1 Location map of the
central Godavari delta, East
Godavari District, A.P, India
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wells. The groundwater elevation contours during the pre-
monsoon (2006) period indicate the groundwater flow
direction to be toward the Bay of Bengal coast with a
groundwater gradient of 0.43 m/km from Amalapuram to
coast (Fig.2), and the same trend was observed for
remaining three monitoring periods (Post-monsoon 2006,
Pre- and Post-monsoon 2007).
Materials and methods
For the assessment of groundwater quality, groundwater
samples were collected in the pre- and post-monsoon
periods in 2006 and 2007 from 42 representative dug wells,
bore wells, and hand pumps (filter point wells) distributed
throughout the area (Fig. 1). Samples were analyzed for
pH, electrical conductivity, major ions calcium (Ca2?),
magnesium (Mg2?), sodium (Na?), bicarbonate (HCO3-),
chloride (Cl-), sulfate (SO42-), fluoride (F-), and nitrate
(NO3-) using standard methods recommended by the
American Public Health Association (APHA 2005). The
net groundwater recharge due to monsoon rainfall and
irrigation return flow was estimated using a water level
fluctuation method (GEC 2009) with the following
equation:
Recharge R SyDhArea
where Sy is specific yield and Dh is water level fluctuation
from pre-monsoon to post-monsoon.
SEAWAT, a computer program for simulation of three-
dimensional, variable density, transient groundwater flow
in porous media (Langevin et al. 2003), was constructed
using geophysical data collected during field investigations
in April 2007 by Gurunadha Rao et al. (2011); Naidu et al.
(2013); and Lagudu et al. (2013) and supported with geo-
physical logs collected by Central Ground Water Board
(CGWB), Southern region, India, and Cairn Energy India
Ltd.
N
Amalapuram
Rave terminal
Gudilanka
Vodalarevu
N.Kottaplli
Anantavaram
Fig. 2 Groundwater elevation
contours in m (amsl) in the pre-
monsoon period (2006)
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Major ion chemistry
The pre- and post-monsoon variations in total dissolved
solids (TDS) in the groundwater during the years 2006 and
2007 are presented in Fig. 3. The TDS values of wells C1,
C4, C5, and C6 show very high variations over the 2 years.
Further, the pre-monsoon values tend to be very high in
shallow wells due to seawater infiltration and mixing ofseawater through mudflats. In wells in the Ravva On-shore
Terminal, tapped from greater depth ([67 m), groundwater
is also observed to possess very high salinity.
The mean, minimum, and maximum values for major
ions in groundwater during both pre- and post-monsoon
seasons for the years 2006 and 2007 are shown in Tables 1
and2. In general, the groundwater samples were found to
be brackish in nature with pH varying from 7.5 to 8.9. The
increase in pH during the post-monsoon season suggests
that dissolution has been enhanced due to high interaction
between soil and rainwater as well as due to dilution from
the influx of rainwater of lower alkalinity (Subramanianand Saxena 1983). Total dissolved solids in the pre-mon-
soon season ranged from 256 to 25,088 mgL-1 with an
average value of 5,149 mgL-1, whereas in the post-mon-
soon, the range was from 141 to 28,536 mgL-1 with a
mean value of 6,486 mgL-1. Chloride during the pre-
monsoon ranges from 43 to 13,490 mgL-1 with a mean
value of 2,104 mgL-1, whereas during the post-monsoon,
the mean value increased to 2,943 mgL-1. The seasonal
increase in total dissolved solids and chloride possibly
indicates the dissolution of marine clays by rain water and
irrigation return flows (Gurunadha Rao et al. 2013).
Nitrate, sulfate, and bicarbonate values were found to
increase during the post-monsoon period, which may be
due to the addition of sulfate by organic substances of
weathered soils, sulfate leaching from fertilizers, and other
anthropogenic influences (Kumar et al. 2007). Concentra-
tions of the major cations (Ca2?, Mg2?, Na?, K?) in the
groundwater are very high compared to Bureau of Indian
Standards (BIS) for drinking water in both the pre- and
post-monsoon seasons (BIS2012). The high salinity levels
in the central Godavari delta are attributed to dissolution of
marine sediments and upconing of brines (Gurunadha Rao
et al. 2013; Lagudu et al. 2013).
SEAWAT modeling
The SEAWAT model is a useful tool for simulating various
types of variable density fluid flow through complex
geometries and geological settings, including saltwater
intrusion in coastal aquifers, submarine groundwater dis-
charge, brine transport, and groundwater flow near salt
domes (Ding et al.2014). The fundamental concept of the
SEAWAT model is to combine the two commonly used
groundwater flow and solute transport modeling programs,
MODFLOW (Anderson and Woessner1992; Harbaugh and
McDonald1996) and MT3DMS (Zheng and Wang 1999;
Zheng and Bennett2002) into a single program that solvesthe density-dependent groundwater flow and solute trans-
port equations. The governing equation for density-
dependent groundwater flow in terms of freshwater head as
represented in MODFLOW routines and SEAWAT is well
described by Andersen et al. (1988), Zheng and Bennett
(2002), Langevin et al. (2003), Bakker et al. (2004),
Zimmermann et al. (2006), and Lin et al. (2009).
Model discretization
In this study, the SEAWAT model was applied to Ravva
On-shore Terminal area, in the Godavari Delta region to
simulate three-dimensional, variable density groundwater
flow in porous media. The study area has been divided into
125 rows and 115 columns with a spacing of 200 m. The
aquifer thickness and layer thicknesses were determined by
geophysical investigations at 13 locations and borehole
Cairn Pumping Wells
TDS
(mg/l)
Wells near the coast
Fig. 3 Total dissolved solids
(TDS) in mg/l in the central
Godavari delta in year
(20062007)
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well data at 5 locations (Gurunadha Rao et al.2011; Naidu
et al.2013). A six-layer model was developed to represent
the entire hydrogeological conditions of the study area
using the available borehole geologic logs, largely pro-
vided by Cairn Energy India Ltd. and CGWB. In the
model, layers 1, 3, and 5 represent aquifers, whereas layer
2, 4, and 6 represent confining layers. In the region, there is
no major groundwater fluctuation (Gurunadha Rao et al.
2008), and therefore, the modeling was performed in
steady state with a total 50-year simulation period.
Hydrogeological parameters
Hydraulic conductivity of the groundwater system was
determined through pumping tests conducted in the study
area using Cooper and Jacob (1946) method. Water sam-
ples were also collected for analyses during the pumping
test. Packer tests were also adopted to estimate the
hydraulic properties of different horizons within the aquifer
system (CGWB1999). Average values were computed for
each zone, and the mean hydraulic conductivity value was
assigned to the entire zone. The size of zones was initially
estimated, but then adjusted during model calibration. The
hydraulic conductivity of the sandy layers was determined
to be approximately 10 m day-1 (layers 1, 3, and 5) and
clay layers approximately 1 m day-1 (layers 2, 4, and 6).
The vertical hydraulic conductivity was assumed to be
10 % of the horizontal hydraulic conductivity. The distri-
bution of conductivity values from top to bottom is shown
in Fig.4. The average water level rise in the post-monsoon
of 2006 was 1.07 m. The study area is mostly covered bysandy clay; hence, the specific yield was taken as *0.07
(Sastri et al. 1973; Seetaramaswamy and Poornachandra
Rao 1975). The estimated recharge was 73 mm year-1,
and it is applied only to the upper most active layer. There
is no significant withdrawal of groundwater in the delta
region except from the Cairn Energy India Ltd. pumping
wells in Ravva On-shore Terminal area. The net ground-
water pumping inside the Ravva On-shore Terminal has
been simulated through 5 pumping wells (C30 to C34 in
Table 1 Statistical analysis of
major ions in groundwater,
central Godavari delta, 2006
All values are mg/l except pH
Pre-monsoon 2006 Post-monsoon 2006
Mean Minimum Maximum Mean Minimum Maximum
pH 7.9 7.3 8.9 7.9 7.4 8.8
TDS 8,266 274 27,856 6,307 248 27,771
HCO3-
109 37 220 238 61 1,037
Cl- 1,606 57 6,308 1,665 64 6,996
F- 0.7 0.25 0.95 0.7 0.32 1.02
NO3-N 11 2.2 79.2 3.1 1.1 22
SO42- 88 20 285 97 30 350
Na?
3,753 24 14,260 2,164 32 12,906
K? 247 2 803 163 2 789
Ca2?
156 12 952 210 24 1,864
Mg2?
136 10 596 93 5 803
Table 2 Statistical analysis of
major ions in groundwater,
central Godavari delta, 2007
All values are mg/l except pH
Pre-monsoon 2007 Post-monsoon 2007
Mean Minimum Maximum Mean Minimum Maximum
pH 8.2 7.4 8.9 7.6 6.9 8.2
TDS 5,149 256 25,088 6,486 141 28,536
HCO3- 290 85 610 442 70 2,008
Cl- 2,104 43 13,490 2,943 19 16,221
F- 0.72 0.37 1.06 0.30 0.05 0.74
NO3-N 3 1 18 6 2 47
SO42- 109 30 365 364 11 1,870
Na?
1,276 12 7,898 1,507 6 8,019
K? 67 2 275 61 5 336
Ca2? 254 16 1,224 147 30 1,408
Mg2?
110 5 684 342 4 2,159
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Fig.1) each with a pumping rate of 3,500 m3 day-1 in four
wells. These waters are directly injected into the oil
exploratory wells to realize higher production, while the
water from the fifth well is used for domestic use and
drawing about 4,700 m3 day-1. However, the water from
fifth well has been subjected to reverse osmosis for the use
of drinking and cooking.
Boundary and initial conditions
Because the model is set up to simulate saltwater intrusion
in coastal aquifers, boundary conditions are required for
both groundwater flow and solute transport. Streams and
rivers are specified with the river boundary conditions in
the flow model using the MODFLOW package. Width,
depth, and elevation of the river/drains in the study area
were determined from topographic maps and also from
field observations. Constant-head boundary conditions
were assigned in the model to allow for lateral inflow
across the western boundary near the Amalapuram area and
lateral outflow to the Bay of Bengal with zero head in the
East. The groundwater salinity at different depths was
analyzed by CGWB (1999) and reported as 35,000 mgL-1
below 122 m depth. Therefore, in the bottom-most layer of
the density-dependant solute, transport model starts at an
elevation of-120 m (amsl) with groundwater salinity of
35,000 mgL-1. The zone between -120 and -90 m (amsl)
was given a salt concentration of 30,000 mgL-1 and the
overlying zone a concentration of 20,000 mgL-1 up to an
elevation of-10 m (amsl) near the coast. The intervening
layer with a salt concentration of 10,000 mgL-1 has been
assumed between -60 and -10 m (amsl) for the interior
region of the study area. Along the coast, it has been
assumed with a slightly elevated concentration up to
20,000 mgL-1 for the same layer as per quality analysis.
Up to -10 m (msl) elevation, the salt concentration of
1,000 mgL-1 has been given for interior areas away from
coast based on analytical results of the groundwater sam-
ples at different depths in the study area provided by
CGWB and Cairn Energy India Ltd. as shown in Fig. 5. A
boundary condition constant concentration was specified to
simulate the potential mass flux transport through upconing
phenomena to facilitate the dispersion processes along the
vertical section of the model. The values specified for the
constant concentration boundaries are consistent with the
reported values of initial concentrations of each layer by
CGWB and from the pumping wells of Ravva On-shore
Terminal.
Results and discussions
In this study, groundwater flow model calibration has been
achieved through a trial and error method by adjusting the
two key parameters (i.e., hydraulic conductivity and
recharge rates) until head values as calculated by SEA-
WAT match the observed hydraulic head values to a sat-
isfactory degree. During the model calibration, 42 observed
hydraulic head values measured in 2006 were used. The
aquifer hydraulic conductivity decreased with depth due to
the effect of increased weight of overburden on the aquifer
material (Davis and Deweist1966; De Marsily1986). The
conductivity of the aquiclude (2, 4, and 6 layers) was
reduced to 0.72, 0.61, and 0.55 m day-1 from top to bot-
tom from the initial value of 1 m day-1, whereas con-
ductivity of the aquitard was increased to 11.1, 10.9, and
10.2 m day-1 from 10 m day-1 from top to bottom (1, 3,
and 5 layers). The groundwater recharge was marginally
reduced from 73 to 70 mm year-1. Calibration results
show an overall correlation coefficient of 0.91, root-mean-
square (RMS) error of 1.389 m, standard error of 0.258 m,
and normalized RMS of 8.71 % indicating a reasonable
match between observed and calculated heads (Fig. 6). The
80000 84000 87000 90000 93000 96000 99000 103000
0.5
-30
-60
-90
-120
-150
-180
-200
(m)
(m) (m)
Fig. 4 A typical vertical cross
section of the multilayer aquifer
system and permeability
distribution
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calibrated model also was compared against the 2007 post-
monsoon data. The results did not reflect any significant
change in the root-mean-square or standard errors.
The regional groundwater budget was estimated by
assigning different zones in the study area using a zonebudget package (Harbaugh and McDonald1996; Harbaugh
2005). Results derived from the zone budget indicate that
lateral inflow into the study area was about
5,229 m3 day-1; recharge was about 36,856 m3 day-1, and
groundwater discharge to the Bay of Bengal was about
13,843 m3 day-1. While streams and rivers were receiving
a base flow of 9,146 m3 day-1, the total groundwater dis-
charge through pumping wells that included for oil
exploration and domestic needs was 18,700 m3 day-1. The
difference between total inflow and outflow in the central
Godavari alluvial aquifer was -396 m3 which is the model
mass balance error or model discrepancy that was 0.9 %.
The computed regional groundwater budget clearly showsthat there is a significant groundwater outflow
(13,843 m3 day-1) toward the Bay of Bengal, and hence,
there was no possibility of lateral inflow of sea water into
the delta or the coastal aquifers from the Bay of Bengal.
Further modeling was performed to simulate density-
dependent solute transport modeling using SEAWAT with
2006 pre-monsoon hydrogeological parameters including
TDS values in mgL-1. The computed concentration values
were correlated with observed TDS values, obtained from
35000
30000
20000
10000
Salt (TDS) = 1000 mg/l
(m)80000 84000 87000 90000 93000 96000 99000
0.5
-30
-60
-90
-120
-150
-180
-200
(m)
103000
InactiveFlow
InactiveFlow
Fig. 5 Salt concentrations
(mgL-1) of groundwater at
different depths in the
SEAWAT model, along the
profile AB in Fig.1
Fig. 6 Observed versus calculated heads in the SEAWAT model
Observed Concentration (mgL-1)
CalculatedConcentration(mgL-1)
No. Of Data Points : 28Normalized RMS : 10.2%Correlation Coefficient : 0.914
Fig. 7 Observed versus calculated salt concentrations in the SEA-
WAT model
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the analytical results. During the initial simulations, the
correlation levels were unacceptable. Therefore, greater
effort was made to improve the match by modifying the
magnitude and distribution of the background salt con-
centration closer to the analyzed values. However, the
situation could not be improved much. An attempt was
then made to change the transport parameters: dispersivity
and effective porosity. The dispersivity was changed to
95 m (from 100 m) and effective porosity to 0.17 (from
0.15). With these changes, a good match between observed
and computed TDS concentrations was obtained with acorrelation coefficient of 0.914 and normalized error of
10.28 %. For the concentration calibration, 28 observation
wells were utilized to represent the study area including
four wells in Ravva On-shore Terminal (Fig. 7).
The calculated model was then simulated for the next
50 years using the same hydrological parameters for future
prediction and to assess the extent of saltwater intrusion
due to pumping wells in the deltaic region. Upconing
phenomena were predicted for the years 2011, 2016, 2026,
2036, 2046, and 2056. The simulations indicated that the
phenomena of upconing can extend up to 500 m2 around
the Ravva On-shore Terminal in the year 2056. The cone ofdepression is mainly due to point groundwater withdrawal,
and the groundwater velocity vectors do not show any
lateral flow from Bay of Bengal entering the On-shore
Terminal. Variable density-dependent groundwater flow is
responsible for upconing of salt concentration around the
area due to groundwater withdrawals. The SEAWAT
model shows that the upconing of salt up to a concentration
of about 20,000 mgL-1 has been confined to the layers just
below the Ravva On-shore Terminal. The mixing process
and upconing phenomena in and around pumping wells for
2016 were shown in (Fig. 8).
Comparison of upconing characteristics of the year 2006
with 2016 in the Ravva On-shore Terminal indicates that
200 m2 around the wells could be affected with elevated
salt concentrations. The upconing of salt occurs only in a
very small area confined to in and around the Ravva On-
shore Terminal wells. The pumping wells are tapping
groundwater from a depth [67 m. Further, the aquifer
system separated with insulating clay layer (the second
layer in the model) significantly isolates the vertical flowduring pumping. As a result, the shallow aquifer zone (the
first layer in the model) does not contribute to groundwater
being pumped. Therefore, there was no significant impact
of groundwater pumping on the shallow aquifers around
the pumping wells. This could be seen in typical three-
dimensional cut-away section for the year 2056 (Fig. 9).
The upconing phenomenon is observed to be highly
localized due to excess groundwater pumping at point
locations.
Limitations
The numerical model developed in this study represents the
interpretation of a simplified hydrogeological model
observed in the field. The model synthesizes the current
hydrogeological knowledge prevailing in the region. The
regional aquifer formations are simulated as equivalent
porous media, which is considered reasonable at the given
scale. This knowledge, often qualitative, was translated
into numerical model parameters by a process that involves
various assumptions and simplifications. The vertical
Fig. 8 Upconing phenomena
around groundwater pumping
wells at Ravva On-shore
Terminal after 10 years of
pumping (2016) along the
profile AB in Fig.1
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distribution of aquifer parameters and subsurface concep-
tualization of model have the potential to cause large
errors. These sources of uncertainty have to be suitably
considered when interpreting the modeling results. The
model results should only be used to address questions
pertaining to groundwater flow and its management at a
regional scale. Moreover, the model was calibrated for
steady-state conditions, ignoring transient conditions that
occurred preceding the 50-year simulation period, seasonal
variations, or other density-driven changes in the flow
conditions.
Conclusions
In the Godavari delta, there was no considerable change in
groundwater elevations over the 2 years of observation
period between 2006 and 2007. The groundwater contours
indicate that the groundwater flow is directed toward the
Bay of Bengal with a steep groundwater gradient. The high
salinity in the shallow groundwater is assumed to be theresult of interaction with marine clays and dissolution of
evaporates of early Holocene period. The major ion
chemistry indicates that coastal wells are highly vulnerable
to saltwater intrusion associated with upconing of brines
and mixing of marine waters. The estimated regional
groundwater budget from the model studies indicates that a
significant amount of groundwater discharges as outfall to
the Bay of Bengal. The computed and observed salt con-
centrations from the SEAWAT model do not show
elevated concentrations exceeding 25,000 mgL-1 around
pumping wells in Ravva On-shore Terminal. The presence
of thick impermeable subsurface clay layers regulates the
lateral and vertical flow pattern in the region that can avoid
sea water intrusion during heavy pumping from the deep
aquifer. The large-scale groundwater pumping at point
location was insulated by clay layer and restricted the
upconing of elevated salt concentrations to the close sur-
roundings of the Ravva On-shore Terminal only. The steep
groundwater hydraulic gradients, high hydraulic conduc-
tivity, and the upconing characteristics of the coastal
aquifer system do not permit seawater intrusion despite the
large-scale groundwater withdrawals taking place from
deep aquifers in the region, and the salt concentration was
stable at 25,00028,000 mgL-1 since the beginning of
pumping in 1991. Assuming present hydrological condi-
tions and groundwater pumping, no considerable advance
of saltwater would be expected in the coastal aquifer sys-
tem of the central Godavari delta. Continued groundwater
level and quality monitoring on a regular basis are needed
to verify the efficacy of the models developed and also lead
to a better understanding on process-response characteris-
tics of saltwater mixing in coastal aquifers under heavy
pumping conditions.
Acknowledgments The authors are grateful to the Director, CSIR
National Geophysical Research Institute, Hyderabad, for his kind
permission to publish the paper. We are also thankful to Dr. Paul
Pavelic, International Water Management Institute (IWMI), Hydera-
bad, for his critical inputs and editing the manuscript. The time
provide by IWMI to write this paper is highly appreciated. We thank
Fig. 9 A typical three-dimensional cut-away section of upconing of salt concentration (mgL-1) around Ravva On-shore Terminal wells (NW
SE direction) after 50 years of pumping
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Dr. Virginia Burkett, United States Geological Survey (USGS) for her
useful suggestions and language editing to improve quality of the
paper.
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