Vol:5 Issue:12 December 2012 ISSN:0974-6846
Indian Journal of Science and Technology
Salinity and seawater intrusion into the ground water Funda Dökmen
The University of Kocaeli, The Vocational School of Ihsaniye, Campus of Arslanbey, 41285 Arslanbey, Kartepe/Kocaeli-Türkiye.
[email protected] & [email protected]
Abstract
Many shallow and deep wells were dug on the coastal plains to meet drinking water needs, and to satisfy industrial and irrigation
requirements of private establishments. The excess water drawn for drinking and irrigating purposes affects the water reservoir resulting
in a lowering of the “water table”. Consequently, there is intrusion of seawater into the reservoir, which results in salinity problems. The
negative effects of using salt water on agricultural crops and seawater intrusion occurred because of excessive abstraction of water from
the bore-holes located in the coastal plains of Hersek, Taşköprü, and Altınova in Yalova region, Turkey. Previous studies have shown
that the depth of shallow wells ranged from 5 m to 20 m in depth and deep wells ranged between 16 m and 243 m. Seawater intrusion
was found within a 1 km radius of the coastal line of the research area.
Keywords: Borehole and pumping, Catchments management, Ecohydrology, reservoir, water quality
1. Introduction
A geological formation that contains water and transmits it
from one point to another is called an aquifer. Note that although
clay has a high porosity, it has a very low specific yield. Almost all
groundwater is meteoric water derived from precipitation. Water
from precipitation reaches groundwater by infiltration and percolation. Direct percolation is most effective in recharging groundwater where the soil is highly permeable or the water table is close
to the surface. Sand and gravel, which make up most of the more
productive aquifers, yield about 80% of their total water content
(Linsley et al. 2000).
A basic problem in engineering groundwater studies is the
question of the amount of water permitted to be withdrawn from a groundwater basin. This quantity, defined by (Meinzer 1923), is
commonly called the safe yield. The safe yield of an aquifer system is not static. (Stedinger
1980) suggests that safe yield must be recognized as a quantity
determined for a specific set of controlling conditions and subject
to change as a result of changing economic or physical conditions.
The possible withdrawal from a single well or group of wells in
a field is affected by a variety of factors such as size, construction, and spacing of wells as well as by any control on the flow of
groundwater toward the particular field. Excessive lowering of the water table may result in contamination of the groundwater by inflow of undesirable waters. This
risk is increased near coastal areas, where seawater intrusion may
occur. A similar problem may occur wherever an aquifer is adjacent to a source of saline groundwater.
Seawater intrusion occurs near a coastline when a freshwater
aquifer is depleted faster than it can be recharged. Seawater generally intrudes upward and landward into an aquifer and around a
well, though it can occur “passively” with any general lowering of
the water table near a coastline (Graham 1994).
Groundwater beneath a uniformly permeable circular island
would appear as shown in Fig.1. About 1/40 unit of freshwater
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72
is required above sea level for each unit of freshwater below sea
level to maintain hydrostatic equilibrium. True hydrostatic equilibrium does not exist with a sloping water table since flow must
occur. Thus, there is likely to be a seepage face for freshwater flow
to the ocean and a zone of mixing along the saltwater-freshwater
interface (Cooper 1959 & Todd 1980).
When a cone of depression is formed around a pumping well
in the freshwater, an inverted cone of salt water will rise into the
fresh water (Fig.1 and 2).
Fig.1. Natural e quilibrium
Fig.2. Effect of pumping
Since the early 1960’s, the coastal aquifers of China have been
studied for salt-water intrusion. With a transition zone of 1.5 to 6.0
km, and an aquifer more than 850 km2, the increasing salt-water
intrusion is a major concern in this area (Xue et al. 1993).
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Indian Journal of Science and Technology
Vol:5 Issue:12 December 2012 ISSN:0974-6846
A study contacted in the City of Laizhou in 1971, and in the City
of Longkou in 1979 illustrated that salt-water intrusion had been
caused by excessive abstraction of the groundwater in these areas.
In the 1970’s, the salt-water intrusion in the southwestern part
of the study area increased by 4 km2 each year. In 1979, the area
of salt-water intrusion covered 16 km2 , increasing to 39 km2 in
1982 and 71 km2 in 1984. By 1989, the salt-water intrusion area
became a continuous zone covering an area of 238 km2 in Laizhou
(Xue et al. 1993).
Yaqoob and Dökmen (2005) studied salinity in water management and its effects. According to this study, where salinity accumulated or salinity was present in underground water discussed
by whichever method: quantity of salt is raised by means of water
leaching, level of salinity from water, and soil systems. Dökmen and Kurtuluş (2008a & 2009) investigated salinity and pumping in relation to water quality about usability of
drilled wells. This study suggested that the quality and quantity of
groundwater varies from place to place. The relationship between
water wells and salinity can be quite complex. And also, some
water quality parameters’ temporal variation reflect changes in precipitation that depend on water quality parameters and salinity.
Dökmen and Kurtuluş (2008b) examined movement and flow
velocity of groundwater in wells and its relation to salinity problems, pumping and level of water by using Darcy’s Law. According to this research, the filtration of the aquifer and the hydraulic
slope affected the flow of the groundwater strongly. The presence
and state of groundwater depend on the geology of the area.
The salinity increases as a result of more pumping from
groundwater in the vicinity of Yalova. Even though irrigation
water used in cultivation is of good quality, crops still absorb a
certain quantity of salt, depending on the properties of the water
source. Salts transmitted into the soil by water affects the growing
plants. The osmotic pressure of the soil solution increases because
of accumulation of salts in the soil. For this reason, physiological
drought occurs because plant roots take in water with difficulty.
Salt accumulation within the root zone negatively affects yield and
quality of plants over the time.
mean temperature is 14.1 0C. Annual mean real evapotranspiration is 415.7 mm. Annual mean defective water is 152.2 mm and
excessive water is 341.3 mm. The annual mean for defective water
according to rainfall stream is 415.7 mm (Anonymous 1978a). The
climatic data in the research area are given in (Table 1) (Anonymous 1984).
Table.1 Climatic data of research area (average of over 44 years of
Goverment Meteorology Station)
Months
Daily
Mean
amount of
Max.
Min.
Mean
amount
max.
temp. 0C temp. 0C temp. 0C of rainfall
rainfall
(mm)
(mm)
January
5.1
19.4
-12.6
87.52
February
5.3
21.0
-9.5
65.29
54.7
March
6.6
25.6
-9.6
62.24
49.7
April
10.8
27.7
-0.4
45.89
50.5
May
15.5
31.6
2.6
29.96
48.8
June
20.0
35.3
8.4
21.61
31.7
July
23.2
36.7
12.0
19.37
57.9
August
23.1
39.4
11.4
29.11
76.5
September 19.3
36.6
6.7
39.77
81.0
October
43.8
15.1
30.2
1.8
63.85
112.5
November 11.7
25.7
-4.6
86.12
86.0
December 7.9
20.0
-11.5
100.44
64.8
Annual
mean
39.4
-12.6
651.17
112.5
13.6
The government meteorological station reports that distribution
of precipitation is as follows: 22% in spring, 11% in summer,
28% in autumn, and 39% in winter (Anonymous 1998).
Agriculture is the most important economic activity in Yalova, consisting mainly of growing flowers, fruits, and vegetables
in greenhouses. Other commercial crops within the study area
include beans, peas, gumbo, cucumber and lettuce. Also, many
kinds of flowers and fruits are produced in this area. The climate
in Yalova and its vicinity is well suited to many types of agricul-
2. Materials and methods
tural activities. Agriculture continues to be negatively affected by competing
2.1 Materials
demand for water from the nearby urban and industrial areas.
The research area is located in Turkey, east of the Marmara
The geological formations in the research area are Paleozoic,
Sea, expanding along the shores south of the Gulf of İzmit and the
Trias,
Top Kretase, Eosen, Neojen, and Quaternar. Alluvions that
North side of the Armutlu Peninsula, situated at 400 28’- 400 44’
take place in the coastal plain at the sea side are in the Quaternar
north latitude and 290 02’- 290 43’ east longitude. The research
formation. The Top Kretase formation is a moving sedimentation
area covers the coastal palins of Yalova-Hersek-Taşköprü and
of sea. Volcanism of submarine is in excess here. Volcanism and
Altınova. Yalova is situated at 280 45’- 290 35’ north latitude and
sedimentation interact with each other (Anonymous 1978b).
400 28’- 400 45’ east longitude. The total area is 832 km2, of which
Conform the correct usage of “Alluvion”: An area of land cre70 km2 is plain area. Beginning with the coastal plains at the seaated by riverine deposition. The accreted alluvion extends from the
ward side in the northern portion, the area rises toward the south. existing coastline. The formations bearing the underground water
The research area exhibits a typical “Marmara” climate: are generally alluvions. These alluvial plains at the coastal area are
Summer is hot and arid; winter is cooler, with more rain. Annual appropriate for operating and utilizing underground water.
Research article
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Vol:5 Issue:12 December 2012 ISSN:0974-6846
Indian Journal of Science and Technology
2.2 Methods
All of the hydrogeological information about the research area was collected by the DSİ (Government Water Works). Observation
wells were established by DSI to determine the level of underground water in the plains. Other research wells and those built by the
public were also been used for observations. The map of the research area showing the location of the wells is given in Fig.3 & 4.
Fig.3. The research area and places of wells on the map of Marmara region
Fig.4. The research area and water table depth contour in Turkey’s Yalova-Hersek coastal plains
A geophysical receptivity survey was carried out to determine
the geology and lithology of formations in the plains. The mean
depth measurement was 120 m and the measurement points varied
between 0.5 and 1.5 km.
Problems in using underground water were discussed with
farmers residing within the study area. Irrigation water was analyzed at selected underground sites and the classification of irrigation water was determined based on these sources. Standard
methods were used in analyzing the water (APHA 1985). Besides
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74
focusing on the problem of unauthorised bore-holes, and looking
at problems involved in the process, the study tried to identify areas suitable for underground water operation and utilization.
3. Results and discussions
The geological formations present in the research area were
in the following stratigraphical order: Paleozoic (şist, marble−no
underground water); Trias (gre-konglomera−no underground water); Top Kretase (limestone, konglomera−no underground water);
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Research article
Indian Journal of Science and Technology
Vol:5 Issue:12 December 2012 ISSN:0974-6846
Eosen (fliş, volcano tufa−little underground water); Neojen (marn,
clay layer, silt layer, konglomera−little underground water); and
Quaternar (clay, sand, gravel−more underground water). The alluvion formation sustains water in the research area. The levels of
sand, gravel, and a mixture of these, sustain the underground water
in the alluvion.
There were many shallow and deep wells for domestic, industrial, and irrigation uses in the research area. The depth of shallow wells ranged from 5 m to 20 m; the level of static water was
between 0 and 6 m. Shallow wells were constructed as source of
irrigation water. The depth of deep wells were between 16 and 243
m; static water levels were between +1.00 m and -5.35 m of that
surface. The coefficient of conductivity of wells in alluvial soils
varied from 12 to 632 m3/d/m. The general characteristics of the
wells are given in (Table 2).
Table .2 General chracteristics of wells in the research area
Shallow wells Bore
Aquifer
(water-bearing)
1.46-14.43
16-243
94-166
0.20-5.50
0.20-5.35
+1.00 and -5.35
3-4
3-4
3-4
80
80
80
Flow (L/s/m)
0.2-5
2.5
0.2-0.16
Conductivity
(m3/day/m)
12-632
12-632
12-632
0.3-1.4
0.37-1.6
0.3-1.5
C2S1 and C3S2
C2S1 and
C 5S 4
C2S1 and C3S2
Depth (m)
Static level
(m)
Diameter (m)
Alluvium
thickness (m)
EC (dS/m)
Classification
of irrigation
water
Feeding
Rainfall and
surface flow
Drinking,
Drinking and
industry and
industry
irrigation
Rainfall and Rainfall and
surface flow surface flow
Discharge
Drinking,
\irrigation
and industrial
using
Drinking,
Drinking,
irrigation and
irrigation and indusindustrial
trial using
using
Using purpose Irrigation
C2S1
C3S2
C5S4
: medium salty-less sodium
: high salty-medium sodium
: very high salty-very high sodium
Table.3 Amount of admissible efficiency and variation of water level of wells
Admissible efficien- Variation of waName of plains
cy (m3/year)
ter level (m)
6
Hersek
1
7.0 x 10
Taşköprü
Yalova
Research article
3.5 x 106
1-2
6
1-2
4.9 x 10
The general surface topography gradient was to the north
from the south in Hersek plain, which is east of the research area.
The water table was highest in the south part of the plain. It decreased toward the sea and approached sea levels at some locations. For this reason, there were salinity problems in the northern
part of the plain, close to the sea. The water table was highest in
the south portion of Taşköprü plain. Underground water flowed toward the north and the sea. Seawater intrusion occurred originally
due to excess pumping in that part close to the sea.
Generally, the levels of underground water were highest during the spring season, in April and May. After these months, the
levels decreased due to excess pumping. The level of water was
lowest in autumn. Variations in water level of between 1 m and 2 m were recorded. The degree of admissible efficiency and variation
in water level of the wells are shown in (Table 3).
The length of the salt water wedge changed from 150-225 m
in the Hersek plain to 250-306 m in the Taşköprü plain during
underground water operation. Water samples taken from the wells
were observed to be saline. This situation occurs in the conglomerate of wells due to excessive pumping in these regions.
Most boreholes studied were affected by saltwater intrusion,
containing water with a moderate to high salt content. Salinity
increased in nearby coastal regions. If boreholes are deepended,
this can affect the problems of salinity within the bore.
The quality of water changed, depending on the pumping of
wells that were located near the sea. This situation must be considered important. Water from wells located inland was of better
quality due to displayed lower salinity. The results of the analysis showed that shallow wells, which
are near the sea, were affected by seawater. The irrigation water
was classified as C3S1, with sodium and chlorine as dominant
ions. Water samples taken from wells close to the sea had their EC
values increasing to 4 dS/m. Water from wells positioned further
inland from the sea was of a much better quality. Generally, these
waters were in the C2S1 category of irrigation water. The dominating ions were calcium, magnesium, and carbonate. The results of
chemical analysis of bore and shallow wells are given in (Table 4).
Generally, water from deep wells had a moderate to high degree of salinity. Most of these were affected by seawater intrusion.
Within deep wells located close to the sea, salinity increased at
the same depth. EC ranged from 3 to 1.2 dS/m. The water of these
wells cannot be used for irrigation. Water quality changed over
time, depending on the pumping of those wells which were affected by seawater.
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Vol:5 Issue:12 December 2012 ISSN:0974-6846
Indian Journal of Science and Technology
To control saline intrusion, a seaward hydraulic gradient
should be maintained and a proportion of the natural fresh-water
recharge allowed to flow into the sea.
Proper groundwater monitoring techniques, groundwater
management, combined with groundwater conservation are needed to keep salt-water intrusion under control.
In agriculture, salinity causes substantial yield losses. As a
precaution, before any saline underground water is used for irrigation, an analysis and classification of irrigation water must be
carried out in order to identify the most appropriate crop species. Table.4 Results of chemical analysis of bore and shallow wells (over mean valuable)
Chemical
parameters
+
Na (me/L)
+
K (me/L)
2+
Shallow wells
Bore
3.53
19.79
0.53
0.32
2+
Ca + Mg (me/L) 6.3
2-
5.64
CO3 (me/L)
0.45
0.96
HCO3 (me/L)
4.42
8.2
5. References
Cl (me/L)
2.05
14.5
SO4 (me/L)
2-
3.24
2.0
1. Anonymous.(1978a) Yalova Meteoroloji İstasyonu Kayıtları
(Recorders of Yalova Meteorological Station), Yalova-Turkey.
SAR
1.83
10.05
RSC
0
4.3
pH
8.1
8.2
0.96
1.53
Severity (Fs )
31.8
28.2
Classification of
irrigation water
C3S1 and C2S1
C3S1 and C2S1
-
-
EC ( dS/m)
0
2. Anonymous.(1978b) Yalova-Taşköprü-Hersek Kıyı Ovaları
Hidrojeolojik Etüt Raporu (Hydrogeological Survey of
Coastal Plains of Yalova-Taşköprü-Hersek), T.C. Enerji ve
Tabii Kaynaklar Bakanlığı Devlet Su İşleri Genel Müdürlüğü
(Government Water Working), Jeoteknik Hizmetler ve Yeraltı
Suları Dairesi Başkanlığı, Ankara-Turkey, p:1-32.
3. Anonymous.(1984) Meteoroloji Bülteni (Government Report
of Meteorologic), DMİ Yayınları, Başbakanlık Basımevi, Ankara-Turkey. 4. Conclusions
The areas suitable for obtaining underground water are in the
alluvial plains at the shore. There are risks of salinity and seawater intrusion in the Taşköprü plain. Seawater intrusion occurred
because of excessive water abstraction from the coastal plains
between Yalova and Hersek. For this reason, wells must not be
located within a 1 km radius of the coastline at Altınova. The total
quantity of water abstracted from wells located in the Taşköprü
plain exceeded the safe yield. This necessitates the controlled
operation of wells in the Taşköprü plain.
The water management strategy/abstraction licensing strategy
for wells and boreholes must be based upon maintaining appropriate hydraulic equilibrium, in order to minimise transfer of saline
water within the aquifer. The flow of pumped water must be regu-
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American Public Health Association, Washington, D.C.,
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Indian Journal of Science and Technology
Vol:5 Issue:12 December 2012 ISSN:0974-6846
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