Groundwater Vulnerability from Sea Water Intrusion in Coastal Area Cilacap, Indonesia
TL;DR: In this article, the authors performed an analysis of the groundwater vulnerability to the sea water intrusion using GALDIT, whereas the distance and depth of the interface was determined using the method of DupuitGhyben-Herzberg.
Abstract: The important issue relating to water resources is sea water intrusion (SWI) phenomena. Nowadays, the phenomena has become serious problem in the urban coastal area. Groundwater as main sources for domestic usage cannot be used again because of its salinity.Cilacap as one of urban coastal area also face the problem. In 1977 SWIwas detectedand experienced significant developmentsin 1996,This research was conducted to: (1) analyze agroundwater vulnerability to the SWI; (2) determine adistance and adepth theinterface; and (3) analyze relationship of the groundwater vulnerability to the interface depth.It was performed an analysis of the groundwater vulnerability to the SWI using the method of GALDIT, whereas the distance and depth of the interface was determined using the method of DupuitGhyben-Herzberg. The linkage analysis of the groundwater vulnerability to the depth of the actual interface was conducted by quantitative descriptively.The results showed that the distance from the shoreline was the most determined factor of the groundwater vulnerability to the SWI, the closer to the shoreline the more swallow the depth of the interface. It existed the relevance between the vulnerability level of groundwater to the SWI with the depth of actual interface. The regions with low level of vulnerability had deep interface depth, whereas the regions with moderate level of vulnerability had swallow interface depth. Nevertheless, the SWI has not yet affected the groundwater in people wells because of its depth that was not yet exceeded of 25 m.so that this depth can be used as a reference in digging wells in the research area++
Summary (2 min read)
Jump to: [Introduction] – [Determination of Groundwater Vulnerability] – [Determination of Distance and Interface Depth] – [Height Calculation of Groundwater Level from Mean Sea Level] – [Calculation of Freshwater Depth from Sea Level] and [Vulnerability Relationship to SWI with Interface Depth]
Introduction
- Because of this location, coastal areas are vulnerable to various problems such as SWI and tidal flooding.
- Partly citiesin Java, Indonesia are located incoastal area, such as:Jakarta, Cirebon, Pekalongan, Semarang, and Surabaya are some of cities located on the northern coast of Java, whereas Cilacap is located on the southern one of Java Island.
- With the GALDIT, it can be seen the environmental condition of a place related to its vulnerability including the distance from the shore line, whereas with the Dupuit Ghyben-Herzberg, the depth of the interface can be known at a certain distance on the shore line.
Determination of Groundwater Vulnerability
- It was conducted a research using GALDIT method to get the information about groundwater vulnerability fromSWI.
- GALDIT stands for parameters that can cause sea water intrusion.
- The basic principle of this method was determination of vulnerability based on numerical system in weight and rating.
- The weight was determined based on the significance of parameter influence to SWI, whereas rating was specified based on the significancy of variable effect of each parameter to the SWI.
Determination of Distance and Interface Depth
- For the aquifer type the weight was 1, the aquifer hydraulic conductivity was 3, height of groundwater level was 4, distance from the shore was 4, the ratio of Cl-/[HCO3-+ CO32-] was 1, and for the aquifer thickness was 2.
- It was estimated that the distance from the shoreline was dominant parameter in determining the groundwater vulnerability in the research area because its value was quite varied, and it was similar for the ratings.
- Based on the rating of GALDIT index, the value range was entered in one category and was valued by 2.5.
Height Calculation of Groundwater Level from Mean Sea Level
- The height of groundwater level from mean sea level is determined by the parameters i.e. specific discharge of groundwater, distance from shoreline, the density of freshwater and saline water, and the aquifer hydraulic conductivity.
- The groundwater specific discharge of each observed wells is based on the calculating results in Table 5, freshwater density that is appropriate with the Law Ghyben-Herzberg is determined by 1.000 g/ cm3, whereas the density of saline water is determined by 1.025 g/cm3 (Todd & Mays, 2005).
- The groundwater level with the height of 0.59 m was founded southern Cilacap village, whereas the groundwater level with the height of 3.05 m is existed in Gumilir village.
- It could be said that the farther distance from the shoreline, the higher the groundwater level.
- This statement is proved by graphic that showed in Figure 3.,.
Calculation of Freshwater Depth from Sea Level
- The freshwater depth from saline water level is also determined by groundwater specific discharge, distance from the shoreline, density of freshwater and saline water, and aquifer hydraulic conductivity.
- The calculating results showed that the region of South Cilacap located 300 m from the shoreline, had the most shallow groundwater depth, 24.59 m, whereas the region of Gumilir located 2000 m from the shoreline had the largest groundwater depth, 125.93 m.
- This showed the tendency that the farther distance from the shoreline, the greater the depth of interface would be, and otherwise the closer distance from the shoreline, the swallower the depth of interface .
- The completely results related to the calculation of groundwater depth from sea water level could be regarded in Table 7.
Vulnerability Relationship to SWI with Interface Depth
- The results showed that in the research area had been detected interface with varied depths, ranging from 26.68 m in South Cilacap to 129.74 m in Gumilir.
- This could be understood because of the community well had the depths that was not greater than 25 m.
- There was a quite interesting phenomenon in the observed wells located in TegalKamulyan which had the distance of 500 m from the shoreline.
- Compared with other areas of research, the groundwater specific discharge in the area was low, that was 0.40 m3/day.
- Cases of deep well drilling that took place in Takome Village were a real example that the hydrological conditions of the northern part of Ternate Island were very vulnerable to SWI.
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Groundwater Vulnerability from Sea Water Intrusion in Coastal Area
Cilacap, Indonesia
Setyawan Purnama
Faculty of Geography, Universitas Gadjah Mada, Yogyakarta, Indonesia
Abstract e important issue relating to water resources is sea water intrusion (SWI) phenome-
na. Nowadays, the phenomena has become serious problem in the urban coastal area. Ground-
water as main sources for domestic usage cannot be used again because of its salinity.Cilacap
as one of urban coastal area also face the problem. In 1977 SWIwas detectedand experienced
signicant developmentsin 1996,is research was conducted to: (1) analyze agroundwater vul-
nerability to the SWI; (2) determine adistance and adepth theinterface; and (3) analyze relation-
ship of the groundwater vulnerability to the interface depth.It was performed an analysis of the
groundwater vulnerability to the SWI using the method of GALDIT, whereas the distance and
depth of the interface was determined using the method of DupuitGhyben-Herzberg. e link-
age analysis of the groundwater vulnerability to the depth of the actual interface was conducted
by quantitative descriptively.e results showed that the distance from the shoreline was the
most determined factor of the groundwater vulnerability to the SWI, the closer to the shoreline
the more swallow the depth of the interface. It existed the relevance between the vulnerability
level of groundwater to the SWI with the depth of actual interface. e regions with low level of
vulnerability had deep interface depth, whereas the regions with moderate level of vulnerability
had swallow interface depth. Nevertheless, the SWI has not yet aected the groundwater in
people wells because of its depth that was not yet exceeded of 25 m.so that this depth can be used
as a reference in digging wells in the research area++
Received: 2019-05-18
Accepted: 2019-07-29
Keywords:
groundwater vulnerability,
sea water intrusion,
coastal city,
Cilacap,
Indonesia
Corespondent Email:
Igiwan@ugm.ac.id
1.Introduction
Coastal is a contact area between land and sea.
Towards the land covers parts of the land, both dry and
submerged in water, which are still inuenced by the
characteristics of the sea such as tides, sea breezes, and
SWI, while towards the sea covers the part of the sea
which is still inuenced by natural processes. Because
of this location, coastal areas are vulnerable to various
problems such as SWI and tidal ooding.
Partly citiesin Java, Indonesia are located incoastal
area, such as:Jakarta, Cirebon, Pekalongan, Semarang,
and Surabaya are some of cities located on the northern
coast of Java, whereas Cilacap is located on the southern
one of Java Island. In general, coastal zone oen face
intensive pressures for development (Gwalema, 2011).
Beside it, urban areas in the coastal area have faster rate
of growth than the rural ones, marked by higher level
of population growth and the expansion of residential
areas.A greater growing number of people needs more
facilities and infrastructure, one of them is water
resources availability. It would aect to the greater
number of groundwater extraction, whereas in another
side it would be decreased the groundwater inow
because of the larger open land used for recharge area
was converted into residential area (Tillman & Leake,
2010; Fenta & Kie, 2014; Waikar & Nilawar, 2014).
e decreased number of groundwater would
eect to the decreased number of water pressure that
could cause penetration of saline water from sea into
the mainland (Pousa, et al., 2007; Marandi & Vallner,
2010). is phenomenon is called sea water intrusion
(SWI), whereas border between freshwater and saline
water is called interface (Young Kim, Suk Park, & Pyo
Kim, 2009; Basack, Bhattacharya, Sahana, & Maity,
2010; Rotzoll, et al., 2010). Beside that, recently SWI
was also driven by future sea level rise which result
to the increase of the fresh water front forward move
(Rahmawati, Vullaume, & Purnama, 2013). It could
be said that the SWI is problematic issue in the cities
located on the coastal regions, because it could make
quality changes of groundwater that could not be use
more as drinking water resource (Obikoya, 2010; Dayal
& Chauhan, 2010).
Some researchresults showed that it has been
detected an interface in Cilacap City. It turned out over
time the depth of interface in some places of the city
was changed. In 1996 it was found the existence of SWI
in some places that were not detected with it in 1977
(Simoen, Darmanto, & Darsomartoyo, 1977; Purnama,
Perkembangan intrusi air laut di Kota Administratif
Cilacap., 1996). Nevertheless, some places with
interface in 1977 and 1996 were not detected anymore
with it in 2013 (Purnama, et al., 2013). Related to this
Indonesian Journal of Geography Vol. 51 No. 2, August 2019 (206 - 216)
DOI: http://dx.doi.org/10.22146/ijg.44914
© 2019 by the authors.is article is an open access article distributed under the terms and conditions of the Creative
Commons Attribution(CC BY NC) licensehttps://creativecommons.org/licenses/by-nc/4.0
RESEARCH ARTICLE
Indonesian Journal of Geography, Vol. 51 No. 2, August 2019 : 206 - 216
207
problem, it has been continued the research of SWI in
the coastal area of Cilacap to get actual information
about the eects of distance from the shoreline to the
depth of interface in the researcharea.
Base on the background, the objectives of the
research are (1) analyze the groundwater vulnerability
to the SWI in the research area, (2) determine the
distance and the depth of the interface in the research
area, and (3) analyze the relationship of the groundwater
vulnerability to the interface depth.
2.e Methods
To nd out the relationship between groundwater
vulnerability fromSWI and distance from shoreline and
interface depth two method were used, namely GALDIT
method and Dupuit Ghyben-Herzberg principle
With the GALDIT, it can be seen the environmental
condition of a place related to its vulnerability including
the distance from the shore line, whereas with the
Dupuit Ghyben-Herzberg, the depth of the interface
can be known at a certain distance on the shore line.
e GALDIT method has been successfully uses to
asses groundwater vulnerability from SWI in the
Portuguese aquifer system of Monte Gardo (Lobo-
Ferreira, Chachadi, Diamantino, & Henriques, 2005)
and the Bardez aquifer in Goa India (Chachadi & Lobo-
Ferreira, 2005).
Determination of Groundwater Vulnerability
It was conducted a research using GALDIT method
to get the information about groundwater vulnerability
fromSWI. GALDIT stands for parameters that can
cause sea water intrusion. G is dened as groundwater
occurrence, A is dened as aquifer hydraulic
conductivity, L is dened as level of groundwater above
mean sea level, D is distance from the shore, I as impact
of existing status of SWI and T is thickness of aquifer
being mapped (Chachadi & Lobo-Ferreira, 2005).
e basic principle of this method was
determination of vulnerability based on numerical
system in weight and rating. e weight was determined
based on the signicance of parameter inuence to SWI,
whereas rating was specied based on the signicancy
of variable eect of each parameter to the SWI. Weight
and rating of each GALDIT parameter and variable is
shown in Tables 1 and 2.
Determination of Distance and Interface Depth
eoritically, the groundwater ow in the coastal
aquifer could be explained through the combination of
Dupuit equation and Ghyben-Herzberg principle such
as the following (Fetter, 2001) :
z=Gq/K+√(2Gqx/K) ..…………................................(2)
by q is the specic discharge of groundwater per unit of
wide in m3/day/m, x is shoreline distance to the point
of the determined land and K is hydraulic conductivity
that determined by Morris and Johnson criteria (Todd
& Mays, 2005). e specic discharge of groundwater
could be calculated by using the method of Darcy
(Rushton, 2003; Davie, 2008):
q=K.A.dh/dl ……………......................................(3)
by dh/dl is hydraulic gradient.
e heigh of freatic level from sea water level in
each distance of x and the depth of z interface could be
determined using the following equation (Fetter, 2001) :
h=√(2qx/GK) ....….………...........................(4)
To validate the calculated results, it could be
conducted a measurement of electrical conductance in
the observed well. If the electrical conductance is less
than 1500 µmhos/cm, it could be said that the observed
well is not yet inuenced by the saline water. Likewise,
if the level of chloride is less than 150 mg/l, it could be
said for the same condition of the observed well.
3.Result and Discussion
Groundwater Vulnerability
As explained before, therewere six types of
parameters used to calculate the index of GALDIT i.e.
aquifer hydraulic conductivity, height of groundwater
level, distance from the shoreline, ratio of Cl-/ [HCO3-
+ CO32-], and thickness of aquifer. Because of the
dierent inuence of each parameters in saline water
intrusion, the weight was also dierent. For the aquifer
type the weight was 1, the aquifer hydraulic conductivity
was 3, height of groundwater level was 4, distance from
the shore was 4, the ratio of Cl-/[HCO3-+ CO32-] was
1, and for the aquifer thickness was 2.
Result determinant of rating of each parameter
indicated that based on the composition of rock
layering of the data drilling, there was only one types of
aquifers in the research area that is unconned aquifer,
so that the same value of the rating was 7.5. Related
to the aquifer constituent rocks, all of them have sand
textured so that the aquifer hydraulic conductivity was
also 7.5.
It was quite varied for the height of groundwater
level in the sea level. Nevertheless, almost all had
categories of more than 2 meters of mean sea level, so
that it valued of 2.5. Only one observed wells which
had the groundwater level between 1.5-2 m of mean sea
level and 5 in value.
It was estimated that the distance from the
shoreline was dominant parameter in determining the
groundwater vulnerability in the research area because
its value was quite varied, and it was similar for the
ratings. e results of rating determination showed
that the parameter of distance from the shoreline varied
from 2.5 to 10.
Giving attention to the ratio value of Cl-/[HCO3-
+ CO32-], it was known that the groundwater in
observed wells had value between 0.13 to 0.33. Based
on the rating of GALDIT index, the value range was
entered in one category and was valued by 2.5. It was
also existed for the parameters of the aquifer thickness
that ranged from 11.39 to 17.55 m. Based on the ratings
GROUNDWATER VULNERABILITY FROMSEA Setyawan Purnama
208
of GALDIT index, the range value was entered in one
category thickness level with the value of 10.
Furthermore, based on the ratings of each
parameter it could be calculated the GALDIT index
for each observed well. e calculations showed that
there were eight observed wells with the GALDIT index
of 4.8, two observed wells with the GALDIT index
of 5.5, and seven observed wells with the GALDIT
index of 6.8. Viewed from the vulnerability level,
eight observed wells were belonged to the level of low
vulnerability and nine observed wells were belonged
to the moderate vulnerability. It is regarded from
the spreading, generally the observed wells with the
moderate vulnerability level were located at the closer
distance from the shoreline, whereas the observed wells
with the low level of vulnerability were located further
away from the shoreline. Based on this data (Table 4),
it could be created a Groundwater Vulnerability Map of
saline water intrusion in the research area as shown in
Figure 1.
Table2. Ratingsfor parameteraquifer hydraulic conductivity, height of groundwater level above sea level,
distance from the shoreline, ratio of Cl-/[HCO3-+CO32-], and thickness of aquifer
Indicator Variable
Indicator Weights Vulnerability
Class Range Rating
Aquifer hydraulic conductivity (m/day) 3 High >40 10
Medium 10-40 7.5
Low 5-10 5
Very low <5 2.5
Height of groundwater level above sea
level(m)
4 High <1 10
Medium 1-1.5 7.5
Low 1.5-2 5
Very low >2 2.5
Distance from the shoreline(m) 4 Very small <500 10
Small 500-750 7.5
Medium 750-1000 5
Far >1000 2.5
Ratio of Cl-/[HCO3-+CO32-] (epm) 1 High >2 10
Medium 1.5-2 7.5
Low 1-1.5 5
Very low <1 2.5
ickness of aquifer (m) 2 Large >10 10
Medium 7.5-10 7.5
Small 5-7.5 5
Very small <5 2.5
Source : Chachadi A.G. & Lobo-Ferreira, J.P. 2005
Table 1. Rating forparameter aquifer type
Indicator Weight Indicator Variable Vulnerability Rating
Aquifer Type 1 Conned Aquifer 10
Unconned Aquifer 7.5
Semi-Conned Aquifer 5
Bounded Aquifer 2.5
Source : Chachadi A.G. & Lobo-Ferreira, J.P. 2005
Table3. GALDIT vulnerability classes
Index Range of GALDIT Vulnerability Classes
>7.5 High vulnerability
5-7.5 Moderate vulnerability
<5 Low vulnerability
Source : (Chachadi & Lobo-Ferreira, 2005)
Indonesian Journal of Geography, Vol. 51 No. 2, August 2019 : 206 - 216
209
Table 4. Calculation of GALDIT index and vulnerability classes
Number of
Observed
Well
Aquifer Type
Hydraulic Conductivity Height of Groundwater
Level
Distance from the Shore Ratio of Cl-/[HCO3-
+CO32-]
Aquifer ick-
ness
Index of
GALDIT
Vulner-
ability
Classes
Rating Weight Value Rating Weight Value Rating Weight Value Rating Weight Value Rating Weight Value Rating Weight Value
1 7.5 1 7.5 7.5 3 22.5 2.5 4 10 10 4 40 2.5 1 2.5 10 2 20 6.8 Moderate
2 7.5 1 7.5 7.5 3 22.5 2.5 4 10 10 4 40 2.5 1 2.5 10 2 20 6.8 Moderate
3 7.5 1 7.5 7.5 3 22.5 2.5 4 10 10 4 40 2.5 1 2.5 10 2 20 6.8 Moderate
4 7.5 1 7.5 7.5 3 22.5 2.5 4 10 10 4 40 2.5 1 2.5 10 2 20 6.8 Moderate
5 7.5 1 7.5 7.5 3 22.5 2.5 4 10 10 4 40 2.5 1 2.5 10 2 20 6.8 Moderate
6 7.5 1 7.5 7.5 3 22.5 2.5 4 10 10 4 40 2.5 1 2.5 10 2 20 6.8 Moderate
7 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
8 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
9 7.5 1 7.5 7.5 3 22.5 5.0 4 20 7,5 4 30 2.5 1 2.5 10 2 20 6.8 Moderate
10 7.5 1 7.5 7.5 3 22.5 2.5 4 10 5,0 4 20 2.5 1 2.5 10 2 20 5.5 Moderate
11 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
12 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
13 7.5 1 7.5 7.5 3 22.5 2.5 4 10 5,0 4 20 2.5 1 2.5 10 2 20 5.5 Moderate
14 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
15 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
16 75 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
17 7.5 1 7.5 7.5 3 22.5 2.5 4 10 2,5 4 10 2.5 1 2.5 10 2 20 4.8 Low
GROUNDWATER VULNERABILITY FROMSEA Setyawan Purnama
210
Regarding to the Groundwater Vulnerability Map
of saline water intrusion that is shown in Figure 1, it
could be said that the distance from the shoreline
was the most determined factor of the groundwater
vulnerability to the saline water intrusion in Cilacap
coastal area. e closer area to the shoreline has a
higher vulnerability to the saline water intrusion than
the farther area.
Calculation of Specic Discharge
In this research, it was conducted the calculation
of specic discharge at all observed wells in accordance
with the path of groundwater ow in the ownet. Such
as explained in research methods, the equations used in
the calculation was the general equation of groundwater
ow from Darcy.
In accordance with this equation, calculation of
groundwater specic discharge needed some data i.e.
aquifer hydraulic conductivity, aquifer cross-sectional
area, and hydraulic gradient. e value of aquifer
hydraulic conductivity is determined based on drilling
data, which are located closest to the observed wells.
In the area of research there are three data drillings
i.e. villages of Cilacap, Sidanegara, and Tambakreja.
Considering to the constituent material of the aquifer,
the three sites of drilling are composed of sand with
varied colors i.e. brown and yellow sand at the top,
and black and gray sand on the bottom. Based on the
Morris and Johnson criteria (Todd & Mays, 2005), the
hydraulic conductivity value of sand is 12 m/day.
Figure 1. Groundwater Vulnerability Map fromSWI in the research area
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TL;DR: In this article , a quantitative descriptive study of subsurface resistivity data was used to identify the potential of groundwater as a source of raw water for the community in Holimombo Village, Wabula District, Buton Regency.
Abstract: Holimombo Village is an area with a karst landscape, where the problems in the area are the absence of surface water sources. Based on these problems, the research objective is to identify the potential of groundwater as a source of raw water for the community in Holimombo Village, Wabula District, Buton Regency. The research is a quantitative descriptive study, where the subsurface resistivity data was used. The Field observation techniques were used for data collecting in this study, where the measurement of the subsurface resistivity value uses a set of geoelectrical resistivity meters. The results of the geoelectric measurements will then be processed using the Res2DinV application. The subsurface resistivity measurements were carried out in four different paths. Based on the measurement results, the subsurface resistivity values at the research site in Holimombo Village, Wabula District, Buton Regency vary, ranging from 6.64 Ωm to above 1000 Ωm. Areas that have ground water potential are on the line 4 with coordinates 5°33,751' S and 122°53,112' E. The layer at this point is weathered limestone in the form of sand and gravel which has groundwater potential because it has a resistivity value of 50-500 Ωm. The potential for groundwater at that point is quite a lot with a thickness of 27.7 m. Therefore, this potential can be utilized by the Holimombo Village community as a source of daily raw water. AbstrakDesa Holimombo merupakan daerah dengan bentang alam kars, dimana permasalahan di daerah tersebut adalah tidak adanya sumber air permukaan. Berdasarkan permasalahan tersebut, maka tujuan penelitian ini adalah untuk mengidentifikasi potensi air tanah sebagai sumber air baku masyarakat di Desa Holimombo, Kecamatan Wabula, Kabupaten Buton. Penelitian ini merupakan penelitian deskriptif kuantitatif, dimana data yang digunakan berupa nilai resistivitas bawah permukaan. Teknik observasi lapang digunakan untuk pengumpulan data dalam penelitian ini, dimana pengukuran nilai resistivitas bawah permukaan menggunakan satu set alat geolistrik resistivitymeter. Hasil pengukuran geolistrik tersebut selanjutnya akan diolah dengan menggunakan aplikasi Res2DinV. Pengukuran resistivitas bawah permukaan dilakukan di empat lintasan berbeda. Berdasarkan hasil pengukuran diperoleh nilai resistivitas bawah permukaan di lokasi penelitian di Desa Holimombo Kecamatan Wabula Kabupaten Buton bervariasi, mulai dari 6,64 Ωm sampai dengan di atas 1000 Ωm. Wilayah yang memiliki potensi air bawah tanah yaitu pada lintasan 4 pada titik koordinat 5°33.751' LS dan 122°53.112' BT. Lapisan di titik ini merupakan lapukan batu gamping yang berupa pasir dan kerikil yang memiliki potensi air tanah karena memiliki nilai resistivitas 50-500 Ωm. Potensi air tanah di titik tersebut cukup banyak dengan ketebalan 27,7 m. Oleh sebab itu, potensi ini dapat dimanfaatkan oleh masyarakat Desa Holimombo sebagai sumber air baku sehari-hari.
1 citations
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TL;DR: For example, the thickness of the longest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments.
Abstract: Freshwater-lens thickness and long-term changes in freshwater volume in coastal aquifers are commonly assessed through repeated measurement of salinity profiles from monitor wells that penetrate into underlying salt water. In Hawaii, the thickest measured freshwater lens is currently 262 m in dike-free, volcanic-rock aquifers that are overlain by thick coastal sediments. The midpoint depth (depth where salinity is 50% salt water) between freshwater and salt water can serve as an indicator for freshwater thickness. Most measured midpoints have risen over the past 40 years, indicating a shrinking lens. The mean rate of rise of the midpoint from 1999–2009 varied locally, with faster rates in highly developed areas (1.0 m/year) and slower rates in less developed areas (0.5 m/year). The thinning of the freshwater lenses is the result of long-term groundwater withdrawal and reduced recharge. Freshwater/salt-water interface locations predicted from measured water levels and the Ghyben-Herzberg principle may be deeper than measured midpoints during some periods and shallower during other periods, although depths may differ up to 100 m in some cases. Moreover, changes in the midpoint are slower than changes in water level. Thus, water levels may not be a reliable indicator of the amount of freshwater in a coastal aquifer.
18 citations
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TL;DR: In this paper, a ground water flow and transport model of the Kopli Peninsula was built to investigate the upconing of saline water from an underlying layer, due to overexploitation of groundwater.
Abstract: The Cambrian-Vendian aquifer system is the most exploited groundwater resource in northern Estonia. As a result, the extensive use of groundwater has caused changes in the direction and velocity of groundwater flow in the Tallinn area. A ground- water flow and transport model of the Kopli Peninsula was built to investigate the upconing of saline water from an underlying layer, due to overexploitation of groundwater. A transient flow model was run in different flow regimes, using the pumping and water head data from the years 1946-2007. The vertical conductivity of crystalline rocks and the lower portion of Cambrian- Vendian rocks was found to be of the greatest importance for the range and shape of upconing phenomena. The results of the current study show that the range of the upconing process is dependent on the depth of the well screen interval. Therefore the results of many previous studies can be biased by the leaking of water from the underlying crystalline basement. The results also suggest that leakage from an underlying layer can be minimized by changing the screen depth of production wells.
13 citations
"Groundwater Vulnerability from Sea ..." refers background in this paper
...The decreased number of groundwater would effect to the decreased number of water pressure that could cause penetration of saline water from sea into the mainland (Pousa, et al., 2007; Marandi & Vallner, 2010)....
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01 Jan 2010
TL;DR: In this paper, the characteristics and flow pattern of saline water intrusion into natural porous medium followed by subsequent fresh water recharge are investigated. But the paper is based on experimental laboratory model study with relevant mathematical analysis followed by field investigation.
Abstract: The paper is based on experimental laboratory model study with relevant mathematical analysis followed by field investigation so as to understand the characteristics and flow pattern of saline water intrusion into natural porous medium followed by subsequent fresh water recharge.
6 citations
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11 Jul 2016TL;DR: In this article, the authors measured the electrical conductivity (EC) and salinity of groundwater measurement in the northern coastal area of Ternate island, in order to know the depth of interface and to analyze the aquifers and to avoid seawater intrusion caused of groundwater extraction.
Abstract: ABSTRAK Penelitian ini dilakukan di wilayah pesisir bagian utara Pulau Ternate, dengan tujuan mengetahui kedalaman batas kontak airtanah dengan air laut dan menganalisis akuifer serta cara pengambilan airtanah sehingga tidak terjadi penyusupan air laut ke dalam tubuh airtanah. Sampel air sumur diukur untuk mengetahui kadar salinitas dan daya hantar listrik (DHL). Kedalaman batas kontak airtanah dengan air laut dukur dengan menggunakan metode geolistrik. Hasil pengukuran DHL dan salinitas airtanah di wilayah pesisir utara menunjukkan, terdapat penyusupan air laut di Desa Tobolo dan Sulamadaha, dengan rentang nilai masing-masing antara 0,5-3,3 mS/cm dan 0,2-1,7 ppt. Hasil pengukuran geolistrik menunjukkan batas kontak airtanah dengan air laut rata-rata antara 12-15 m dari permukaan. Nilai resistivitas air laut berkisar antara 0,01-20 Ωm. Hasil penelitian ini memberikan peringatan untuk tidak melakukan pengeboran sumur di wilayah pesisir. Sebagai contoh kasus, pengeboran sumur hingga 80 m dengan jarak sekitar 250 m dari garis pantai di Desa Takome, di mana batas kontak airtanah dengan air laut pada kedalaman 15 m. Pengukuran nilai DHL dan salinatas air dari sumur ini menunjukkan masing-masing 6,1 mS/cm dan 3,3 ppt. Nilai ini menunjukkan kedalaman sumur bor telah melewati zona pencampuran antara airtanah dengan air laut ( interface ). ABSTRACT This research was conducted in the coastal areas of northern part of Ternate island, in order to know the depth of interface and to analyze the aquifers and to avoid seawater intrusion caused of groundwater extraction. Well water samples were measured to determine levels of salinity and DHL. The depth of interface was measured using geoelectric method. The results of electrical conductivity (EC ) and salinity of groundwater measurement in the northern coastal area showed that, there is infiltration of sea water in Tobolo and Sulamadaha. The EC and salinity values ranging between 0.5-3.3 mS/cm and 0.2-1.7 ppt respectively. The geoelectric measurement results showed that the depth of interface ranging between 12-15 m from the surface. The resistivity of saline water values ranging between 0.01-20 Ωm. This research provides a warning for not drilling well in coastal areas . For example case, a drilled well with a depth 80 m, located about 250 m from the shoreline in village Takome, where the depth of the interface is 15 m. The value of EC and saline water were measured from this drilled well showed 6.1 mS/cm and 3.3 ppt respectively. This value indicates the depth of the drilled well has exceeded the interface zone .
4 citations
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TL;DR: In this paper, the authors examined the socioeconomic and cultural impacts of urban development pressure on the lives of coastal local communities in Tanzania, in linewith the implementation of basic Human Rights, and the National Land and HumanSettlement Development Policy.
Abstract: The study examined the socio-economic and cultural impacts of urbandevelopment pressure on the lives of coastal local communities in Tanzania, in linewith the implementation of basic Human Rights, and the National Land and HumanSettlement Development Policy. It has suggested measures to manage or preventthe adverse impacts and enhance beneficial impacts. Social Impact Assessment(SIA) principles were employed to study the social, economic and cultural impactsof urban development pressure on coastal local communities of Kaole, Ununio andKilwa-Masoko. Qualitative data was collected from 12 informants and 6 focusgroups, while quantitative data was collected from 150 heads of household andtheir spouses using a semi-structured questionnaire. Data analysis was done usingthe SPSS computer software. It was found out that there were more negativeimpacts than positive ones. Positive impacts included; expanded market for goods,water supply, electric supply, presence of schools, and cultural harmonization.Negative impacts included: insecurity over land, depeasantisation, low incomes dueto lack of integration into respective urban areas, food insecurity, poor access tosea resources, unfair compensation for loss of land, discrimination in urbanplanning and poor access to social services. These could be regarded as short termimpacts. The vulnerability of local coastal people to poverty was the long termimpact. It is recommended that land allocation processes should implement HumanRights and the National Land and Human Settlement Development Policy properlyso as to bring more positive impacts. Key words: development pressure, urban development, implementing human rightsin Tanzania, poverty alleviation in Tanzania, policies and development
3 citations