International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 23 (2016) pp. 11358-11362
© Research India Publications. http://www.ripublication.com
Seepage Saltwater Reduction by Physical Barrier at Coastal Aquifer
Nurnawaty1, M. Selintung2, M.A. Thaha3 and F. Maricar4
1
Doctoral Student of Civil Engineering Department, Hasanuddin University Of Makassar, The 2nd Campus FT Unhas,
Poros Malino Street Km 6, Gowa Regency, South Sulawesi Indonesia.
2
Department of Civil Engineering, Hasanuddin University, The 2nd Campus FT Unhas. Poros Malino Street Km 6,
South Sulawesi Indonesia.
3
Department of Civil Engineering, Hasanuddin University, 2nd Campus FT Unhas. Poros Malino Street Km 6,
South Sulawesi Indonesia.
4
Department of Civil Engineering, Hasanuddin University,2nd Campus FT Unhas. Poros Malino Street Km 6,
South Sulawesi Indonesia.
Abstract
Unconfined aquifers in coastal areas, generally in the form of
sand and rock will cause seawater more easily get into the
groundwater.One way that can be used to minimize seawater
seepage into groundwater in coastal areas was creating a
physical barrier in the subsurface by injecting water and cement
ratio into the sand. This study is a purely experimental
laboratory and performed once time. The purpose of the study
was to determine the pattern of saltwater seepage into coastal
aquifers in static conditions, application of the Darcy formula
for water flow and Ghyben-Herzberg equation in the soil
provides evidence of significant the positive effect of the
addition of subsurface physical barriers that intersect directly
with seawater. Testing is done by seepage flow test on the
channel model using grouting bulkhead can be successfully
used to estimate the decrease of saltwater seepage discharge on
unconfined aquifer at coastal area. The results showed the
effect of adding insulation barrier to ingredient water-cement
ratio 0.42 by injecting into the subsurface can change the nature
of the sand permeability levels, seepage of salt water in
constant height 20cm with a depth of bulkhead 1 cm, 3cm and
5 cm may be reduced length seepage respectively by 27% ,42%
and 94% . It’s reduce the velocity of the entry of seawater
compared with those without physical barriers.
Keywords: Coastal aquifer, physical barrier, saltwater,
seepage,
INTRODUCTION
The aquifer layer boundary between freshwater and seawater
constitute the fundamental problems in the seawater intrusion
system. In coastal areas there are generally extensive
unconfined aquifers. Characteristics sands and rocks in the
coastal area consist of sand and rock will cause seawater more
easily get into the groundwater, making up one of the causes of
sea water easily seepage into the groundwater area. this flow
occurs due to seepage through the pores, the value of seepage
on the beach sand can be reduced by changing the size of the
pores so that the volume of water passing through will be
reduced by physical barrier sub surface soil making the
artificial material that is a mixture of water and cement are
injected into the sand (grouting) so as to form the new structure
of the soil layers with different permeability values.
Design of subsurface environmental barrier not only serves to
inhibit the saltwater seepage further inland, but also functions
as a soil reinforcement base at the waterfront building that can
serve to protect freshwater reserves. This is necessary as a
preventive measure to prevent contamination of ground water
levels as a result of the excessive intrusion of sea water, which
can lead to changes in salinity and water crisis. One way that
can be used to minimize the seepage of saltwater is to create a
physical barrier in the subsurface (Bear, et.al, 1999; Bear and
Chang, 2010) by injecting a mixture of water - cement into the
sand to lower the value of the seepage velocity. By planning to
conduct laboratory-scale research to find out; materials, and
grouting dimensions of effective bulkhead to reveal the
condition of the drainage interpretation and reduce seepage of
salt water into fresh groundwater in the subsurface soil.
LITERATURE REVIEW
The relationship between sea water with underground fresh
water in coastal aquifers in a static state can be explained by the
laws Ghyben – Herzberg. Given differences in seawater density
between the underground fresh water, then the boundary
(interface ) depends on a balance of both, Relationships
between salt water with fresh water in aquifers underground
freely in coastal areas as shown in fig 1[3].
Figure 1: Relationship saltwater with freshwater underground
in unconfined aquifers of coastal areas
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 23 (2016) pp. 11358-11362
© Research India Publications. http://www.ripublication.com
The coastal boundary condition is depicted for the case
unconfined aquifer flow
The depth of the interface beneath shoreline (Z0) taking place
where x is zero can be defined by :
𝜌 𝑞
Z0 = 𝑓
(4)
∆𝜌𝐾
The freshwater above the sea level at Z = 0 is
1
2∆𝜌𝑞𝑥 2
h𝑓 = (
𝜌𝑓 𝐾
)
(5)
The above equation will be used in this study to determine the
location and depth of the interface obtained from the scale
down model simulation under the natural condition.
This study aims to simulate the sea water intrusion into
unconfined aquifers and to assess to determine the effects of
controlling methods by subsurface barrier techniques steady
state flow test in physical model for reducing the rate of
seawater intrusion in laboratory scale. The results can assess
the performance of these generally practiced controlling
methods. Figure 3 shows the length seepage of seawater into
coastal aquifers (a) without barrier/ natural condition, (b) with
the barrier and (c) the physical model laboratory
20
20
10
Muka Air Tanah
?h = 10 cm
Air Tawar
0
Figure 2. Setting the fresh and saline groundwater at coastal
area in unconfined aquifers
0
k
Q
- 10
Int
erfa
ce
Air Asin
k
- 10
Elevation (cm)
10
- 20
150
140
130
120
110
100
90
80
70
60
Hydrostatic pressure at point
50
40
30
20
10
0
- 10
- 20
- 30
- 40
- 50
(a)
A =B
Profil Memanjang
PA=PB
Skala 1 : 100
s. g . hs = f . g . hf + s. g . hs
hs =
𝑟𝑓
+ ℎ𝑓
𝑟𝑠 − 𝑟𝑓
hs = 40 hf
(b)
Figure 3. Profile of groundwater and saltwater on natural
condition and with Physical Barrier
(1)
Where : s is density saltwater (1,025 gr/cm3), f is
density freshwater (1 gr/cm3), hs is the seawater level from
point A depth, hf = depths underground water table
The corresponding shape of the water table is given by
2∆𝜌𝑞
𝑥
h𝑓 = ((𝜌+∆𝜌)𝐾
)
1
2
(2)
Where  is the difference between the density
freshwater (f) and saltwater (s) K is the hydraulic
conductivity of the unconfined aquifer and q is the freshwater
flow per unit length of shoreline
The width Xo of sub marine zone through which freshwater
discharges into the sea can obtained from equation 2 by setting
equal to 0 yielding:
x0 =
𝜌𝑓 𝑞
2∆𝜌𝐾
(3)
Previous research [3] has been conducting research extraction
of fresh water injection wells/ artificial impregnation and
barrier under land or subsurface[9]. simulates sea water
intrusion into the aquifer free near the shoreline and to assess
the effectiveness of control methods using a physical model of
a scaled-down, controlling intrusion of the injection of fresh
water, extraction of salt water and create artificial barrier below
the ground surface in the coastal area in [5] investigated the
changes in the permeability using long columns of 25 cm of
sediment coastal aquifers in China [2], using gypsum as the
artificial barrier design is supported by laboratory experiments
and by the mathematical model simulating seawater intrusion
in coastal aquifers, Southern Italy. As well as research
conducted [5] concerning grouting; estimate the amount of
fluid injection is needed, as well as determining the graduation
rate of water in the soil and the large number permeability
coefficients[10], examined the effect of variations in the mix
and the time of immersion species in seawater to a depth of
11359
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 23 (2016) pp. 11358-11362
© Research India Publications. http://www.ripublication.com
intrusion, effect cement-water factor to the strength of concrete
[4], examined the effect of water and cement ratio on
compressive strength and abrasion of micro silica concrete.
MATERIALS AND METHODS
This study is an experimental method that is carried out in the
laboratory followed by a model aquifer sand beach in on 50 cm
long, 50 cm wide and 40 cm depth are mounted with the
upstream position and downstream slope of 1: 1 (slope 45O) in
the mid-section of the models channel test. The test model was
used long seepage channel represent a vertical cross section
unconfined aquifer across the shoreline by creating a
transparent acrylic with length 250 cm, wide 50 cm height 50
cm, In the channel model upstream is filled with freshwater and
downstream in the content of saltwater, and then observed
seepage that occurs statically (Fig 4)
Sand materials used for the laboratory test were collected white
sand from a field beach site. Coarse sand containing organic
material is a local material. All sand samples were taken from
the top soil layer at thickness of 0.1 – 4.0 m. Table 1 display
key properties of the soils used in the study. The research was
conducted on laboratory testing of samples for examination of
the characteristics of sand sample used. Value of hydraulic
conductivity (K) is about 0,034 (m/sec)
right side of reservoir used saltwater is simulate the seawater
can be maintained constant at any level. Saltwater is saturated
brine (100% salinity) collected seawater from a field beach site.
The simulated physical barriers used bulkhead cement was
used to created injected (grout) a mixture of water - cement into
the sand, water cement ratio used 0,42. The simulated bulkhead
soil cement is 20 cm height 50 cm wide and 2 cm thick are
mounted in upright position between sand particles and
saltwater.
The test specimen is then inserted into the appropriate depth
subsurface sand that was planned and carried out testing
seepage. For the saltwater constant level remains 20 cm
seepage saltwater observed
RESULT AND DISCUSSION
Barrier’s Performance to Reduction Seawater Intrusion
Performance Bulkhead soil cement as modelling barrier
construction below ground by salt water seepage obtained from
laboratory tests on the conditions static using the channel
models with depth barrier 3 cm from saltwater level and using
white sand as media seepage of salt water with of coarse sand
texture acording to the depth of the sample location. Laboratory
test results follow in fig 5
Figure 5. Seepage Model with and without physical barrier
Table 2. Result of Seepage Saltwater Test / Water Level
Seepage Test(cm) without (before) and with (After) Physical
Barrier
Figure 4. Experimental Model Seawater Intrusion [6]
Table 1: Value of water content, specific gravity and porosity
in laboratory test
Properties
specific gravity
water content
void ratio
Notation
Gs
W
Eo
Unit
%
%
Fine Sand
1,215
3.158
0,793
Tap water materials in the laboratory used the left side of
reservoir used freshwater at constant level by continuously
supply with distilled water. It is used to simulate the far-field
groundwater table to supply freshwater to the sand aquifer. The
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Length
(cm)
Height Saltwater (hf)
Before
After
0
20
20
-4
18.1
3.6
-8
15.6
1.0
-12
11.9
0.6
-14
8.9
0.1
-16
4.8
0.0
-18
0.1
0.0
International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 23 (2016) pp. 11358-11362
© Research India Publications. http://www.ripublication.com
Laboratory tests seepage of salt water to the texture of coarse
sand conditions, constant water level saltwater conditions,
respectively 20cm with Darcy methods accordance, the theory
that the seepage of salt water into the aquifer will be reduced
by the bulkhead physical barrier created by injecting / grouting
cement-water into the sand in table 2 shows that face saltwater
will be reduced after the insulation barrier, barrier created with
the aim to keep the pressure underground water near or parallel
to the coast remain above the sea level, so there is no
displacement under fresh ground water by salt water. Model
subsurface barrier is needed in order to inhibit the intrusion of
seawater further inland and protect freshwater reserves that are
expected to slow the flow of salt water flow in the soil. The
depth value insulation and seepage distance based on
measurements taken at three different depth model bulkhead at
the same water level, depth measurement results bulkhead and
distance seepage in next Figure
Figure 7: Graph saltwater Seepage into the sand with barrier
(depth) = 0 cm, 1 cm, 3 cm and 5 cm
Figure 7 graph seepage of salt water with a depth of bulkhead
0 cm, 1 cm, 3 cm and 5 cm showing the relationship between
constant saltwater level of 20 cm in height surface fresh water
20 cm, this shows that the addition of a barrier with grouting
method into the sand it will extend the seepage path follows the
depth bulkhead. water levels salted different figures show
reduction seepage at distance 2 cm to the left namely the value
of (5,3%, 8,4% and 9,3%) 4 cm (10,5%, 8,4% and 9,3%), 6 cm
(1,5%, 1,2% and 0,3%), 8 cm 1,5%, 1,3% and 0,4%) this graph
shows a decrease in the water level seepage highest at a
distance of 4 cm than without insulation by 79 % , 84 % and 94
%.
Figure 6: Saltwater seepage to sand aquifer Model’s on (a)
Natural condition and (b) with physical barrier
EFFECT OF DEPTH BARRIERS TO REDUCE
SEEPAGE
Figure 7 graph seepage of salt water showing the relationship
between depth of bulkhead 1 cm, 3 cm and 5 cm from saltwater
level 20cm, figures show seepage highest at a distance of 4 cm
to the left is on value of 0.90 cm, 1.20 cm and 3.00 cm, but at a
greater distance is 8 cm until 12 cm to the left with three
different water levels declining numbers are obtained; 0.32;
0.20 and 0.0 cm.
CONCLUSION
To inhibit seepage of salt water in inland areas created
subsurface construction of environmentally sound barrier that
can serve as the basis of soil reinforcement in the building by
the beach and also protect freshwater reserves. Method of
Grouting injects water - cement mixture into the sand can
reduce or minimize the value of saltwater seepage velocity. The
amount of seepage discharge to the bulkhead grouting method
can be concluded that the permeability of the soil will change
the value of seepage that occurs in the flow of salt water into
the ground also changed. The depth of the insulation barrier
effect on the reduction of seepage that occurs within each
increment of 1 cm , 3 cm and 5 cm depth bulkhead , it can
reduce the distance seepage at 10,4 cm , 8,3 cm and 9,4 cm. at
distance 4 cm the left from shoreline
ACKNOWLEDGEMENT
Closing brief discussion of this study, the authors express
gratitude to all colleagues who provided input and discussions
for the complement of this article
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