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ScienceDirect Procedia Environmental Sciences 23 (2015) 110 – 115

International Conference on Tropical and Coastal Region Eco-Development 2014(ICTCRED 2014)

Seawater Intrusion Modeling On Groundwater Confined Aquifer In Semarang 1)

Edy Suhartono1,2,*), P. Purwanto1,3), S. Suripin1,4)

Doctorate Program Of Environmental Studies, Post Graduate Program, Diponegoro University* Jl. Imam Barjo, SH No. 5, Semarang-Indonesia-50000 2) Polytechnic State Of Semarang, Jl. Prof.Sudarto, SH, Semarang - Indonesia- 50000 3) Department Of Chemical Engineering, Faculty Of Engineering, Diponegoro University, Jl. Prof.Sudarto, SH, Semarang - Indonesia- 50000 4) Department Of Civil Engineering, Faculty Of Engineering, Diponegoro University, Jl. Prof.Sudarto, SH, Semarang - Indonesia- 50000

Abstract The focus of this study is to identify and describe of a seawater intrusion in confined aquifer modelling in Semarang with a descriptive quantitative analytical method. The results showed potentially experiencing seawater intrusion which increased of 0.575 km2/years. Seawater intrusion models divide to 3 models are the western route have a maximum error is 27.9%, then the middle route have the maximum error is 41.1% and the eastern route have the maximum error is 40%. In 2035, the seawater intrusion on western route is predicted about 3.0 km from the coastline, 4 km for middle route, and about 3.25 km for eastern route. This is one of the information that from right now, the management of a groundwater in the confined aquifer in Semarang is necessary to supervise and better and more optimal controlling © 2015 2014Published The Authors. Published by Elsevier B.V. © by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-reviewunder underresponsibility responsibility of scientific committee the ICTCRED Peer-review of scientific committee of theof ICTCRED 2014 2014.

Keywords: Coastal Areas; Groundwater; Chloride; Seawater Intrusions 1. Introduction The rapid pace of development in the city of Semarang in line with the high population growth is expected to require cleanwater to rise sharply. According to Bachtiar [1], the population of Indonesia in 2013 amounted to 250 millions peoples and about 60% of them live in coastal areas, these conditions resulted in marine environments burdens heavier, especially to meet the needs of clean water. According to Hadi [2], in environmental management, at first the human relationship with the environment running in a spirit of harmony that humans become an integral * Corresponding author. Tel.: 081575161357; fax: 024-8453635. E-mail address:[email protected]

1878-0296 © 2015 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of scientific committee of the ICTCRED 2014 doi:10.1016/j.proenv.2015.01.017

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part of nature, so that its behavior in tune and in harmony with the rhythms of nature and nature conservation in these conditions can be maintained. However, when the number of people more and more in line with advances in technology and increased demand, then the man is no longer a part of nature, human nature to want to handcuff antrophocentrism properties. This attitude fruitful in the destruction of nature that is often referred to as environmental disasters such as pollution that occurs in groundwater. Purwanto [3] asserts that the use of Natural Resources was massive and uncontrolled and ignore the environmental equilibrium will result in a variety of negative effects will be felt in a relatively quick time in both the acute and the condition of chronic conditions in the long term. Environmental damage in coastal areas according to Ding and Peng [4] triggered by ecological conditions of coastal areas that have the ability to meet the economic needs of human beings through some important activities such as industry, fisheries and services. According to Kjellen and McGranahan [5], the socio-cultural aspects of the population such as the number of people, lifestyle, culture and social organization needs can be met through economic aspects such as industrial activities, household, agriculture, transportation and services will have an impact on the quality and quantity Resources the water. Susanto [6], predicted that in 2030, the city of Semarang will experience a water crisis, it is because the need for freshwater of industry in 2010 about to 90% of water taken from the ground at 3.17 x 106 m 3, then the need for freshwater for residents amounted to 263,267 m3, assuming the need for freshwater for hotel guests alike with fresh water needs population of 150 liters per person per day and assuming the hotel charged 75%. If the freshwater needs of the 90% wear groundwater, the groundwater needs to hotels of 236,940 m3, the total ammount of groundwater use in the city of Semarang is predicted at 4.04 x 106 m3. In general, groundwater flow conditions are very complex. Groundwater contamination due to sea water intrusion by Riley and Skirrow [7] can be identified from the dissolved contaminants such as chloride (Cl), because the content of salt (NaCl) in sea water made p 39.3% of Sodium (Na) and 60.7% of Chloride (Cl). An understanding of groundwater contamination due to seawater intrusion needs to be improved, so as to get information and better knowledge about the intrusion of sea water to the groundwater in the aquifer Depressed in this study will be developed in a model. Zhou et al. [8] argue that the development model of seawater intrusion can help Water Resource management efforts primarily groundwater in aquifers Depressed by describing the research area more accurately in a relatively fast with an inexpensive cost. According to Zhang [9], A model of seawater intrusion can be done by using the equation of mass transport of contaminants by advectiondiffusion equation approach in the form of one-dimensional differential equation parsiil. Previous researchers such as Kumar, et., al [10], have examined the intrusion of sea water to ground water in shallow wells using the advection-diffusion equation in one dimension, New Delhi, Mohammadi and Manteghian [11] have examined the intrusion of seawater to river water by using advection-diffusion equation in one dimension Australia, and in Sweden, Gong and Nordstrom [12] also investigated the intrusion of seawater to river water by using the advectiondiffusion equation 1 dimensions. The originality of this research is the modeling of seawater intrusion to the advection-diffusion equation approach one-dimensional and using indicator Chloride concentrations in ground water contained in the confined aquifer in Semarang. The purpose of this study is to describe the condition of the sea water intrusion in groundwater or confined aquifer in Semarang, and then the seawater intrusion condition models into the advection equation in one dimensional diffusion, and predict the level of sea water intrusion of groundwater in the confined aquifer in Semarang. 2. Methods According to Sibanda [13] to answer the above problems, then this type of research is a quantitative with descriptive quantitative analytical approach. The study population was groundwater in Well Drilling In Semarang coastal area covers the majority of Semarang District of West, North Semarang, Semarang, Central, South Semarang, Gajahmungkur, East Semarang, Genuk, Gayamsari, and Pedurungan with a sample of 33 Well Drilling In the located on the 3 lines of research, namely the Western Line located in the District of West Semarang, Central Line, located in the District of North Semarang, Central District of Semarang, Semarang District of the South, and the District of Gajahmungkur, and East Line, located in the district of East Semarang, District Genuk , Gayamsari District, and District Pedurungan. Data collection techniques used observation and literature. Analysis using quantitative descriptive analytic techniques using GIS computer program to illustrate the condition of seawater intrusion on groundwater in aquifers Depressed, followed by the drafting of seawater intrusion models using the advection-diffusion equation approach one-dimensional finite difference numerical methods with a grid step forward for distance x by 0.1 units and the grid for time t of 0.08 units. Then, using the chosen model, the prediction is done

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on the condition of sea water intrusion in groundwater aquifers in coastal areas Depressed Semarang on the conditions in 2015, 2020, 2025, 2030, and 2035. The scope of this research model is restricted to arrange mass transport equation Chloride (Cl) which is of contaminants dissolved in the groundwater in the aquifer Depressed through advection-diffusion model approach one dimension. Dependent variables of the model equation is C ie Chloride concentration, and x is the independent variable is the distance Well Drilling In the shoreline and t is the time of measurement. Parameters that affect the value of C is the retardation factor R that is ground, then Dx is the diffusion coefficient of chloride and vx is the flow velocity of the ground in aquifers Depressed, and W as other factors that affect the rate of seawater intrusion. Furthermore, the model chosen, made a prediction of the concentration of chloride in Well Drilling in Semarang in excess of 250 mg/L by Permenkes RI [14], as an indicator that the ground water has been contaminated by seawater and this shows the level condition seawater intrusion that occurs in the future. 3. Results And Discussion According to Bappeda and BPS Semarang [15], in 2005 the population in Semarang as much as 1,419,478 peoples and the soul rising to 1,544,358 peoples in 2011. This trend of increasing population density, followed by the growth of population and activity. In the research area of Semarang with an area of 115.84 km 2s is 31% of the entire area of Semarang city has a total area of 373.67 km 2s, has a population density of 7,457 peoples per km2 consisting of the population density for the District of West Semarang of 7,365 peoples per km2, North Semarang for 11,615 peoples per km2, Central Semarang of 11,812 peoples per km2, Gajah Mungkur of 6,966 peoples per km2, South Semarang of 4,183 peoples per km2, East Semarang of 10,340 peoples per km2, Genuk of 3,248 peoples per km2, Gayamsari of 11,821 peoples per km2, and Pedurungan of 8,404 peoples per km2. In 2011, the population in the nine districts have as many as 863,808 peoples or about 56% of the total population, it is show that the coastal area of Semarang has a high potential for population activities to the development of Semarang consists of 16 districts have the average population growth of 1.36% per years. Measuring the quality of groundwater, including concentrations of chloride (Cl) in the coastal area of Semarang is done by the Department of Energy and Mineral Resources of Central Java Province each period of two years, this is because the Department of Energy and Mineral Resources of Central Java Province is entitled to provide recommendations for the management of licensing throughout Drilling Well In Central Java and every two years the manager of groundwater in need of updating its permit to include the results of groundwater samples in the confined aquifers. Given some of the conditions in the coastal area of Semarang is dominated by the rate of population growth resulting in increased population density and condition of groundwater, the study conducted in the confined aquifers that lie in the three paths position of the Well Drilling in sample from the coastline to landward. Three strings of West Line that crosses the District of West Semarang, Central Line across the District of North Semarang, District of Central Semarang, District of South Semarang, and District of Gajah Mungkur, and East Line that crosses the District of Genuk, District of Gayamsari and District of Pedurungan. Conditions of seawater intrusion in coastal areas of Semarang is illustrated through three channels are Western route is located in the district of West Semarang, then the middle route is located in the District of North Semarang, District of Central Semarang, District of South Semarang and District of Gajahmungkur, and further Eastern route is located in District of East Semarang, District of Genuk, District of Gayamsari, and District of Pedurungan showed a trend of seawater intrusion could potentially occur in groundwater in confined aquifer increasing from 41,1 km 2, or about 35.5% in 2009, to 43.4 km2, or about 37.5% in 2013. it can be concluded that the level of seawater intrusion in Semarang has increased at a intrusion rate about 0.575 km2 per year (see figure 1).

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JAVA SEA

Fig.1. Condition of Seawater Intrusion in Semarang Models of seawater intrusion in an unsteady condition in Semarang has met the requirements of the stability of the model are :

1. Western route :

2. Middle route :

3. Eastern route :

wC wt

0, 064

wC w 2C  0, 74  0, 016t 2 wx wx .............(1),

wC wt

0, 064

wC w 2C  0,87  0, 016t 2 wx wx …… …..(2),

wC wt

0, 064

wC w 2C  0,58  0, 016t wx 2 wx …….… …(3),

20

15

25

Further models of seawater intrusion in steady conditions in Semarang are :

1. Western route :

2. Middle route :

3. Eastern route :

17

13

wC wt

wC wt

35

wC wt

0, 064

0, 064

w 2C wC  0, 74 wx 2 wx .................................(4),

w 2C wC  0,87 wx 2 wx ………………… …. .(5),

0, 064

w 2C wC  0,58 wx 2 wx ………………..… (6),

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The error value of models of seawater intrusion in unsteady conditions on western route models about 22.4% to 24.1%, then the middle route models about 33.3 % to 36.0%, and Eastern route models about 24.0% to 33.1%. and the error value of models of seawater intrusion in steady conditions on western route models about 12.5% to 27.9%, then the middle route models about 37.8% to 41,1%,, and Eastern route models about 31.9% to 40.0%. In 2035, it is predicted that the chloride concentrations exceeding 250 mgs per litre in confined aquifers in western route distributed up to 3.0 kms from the coastline, and in middle route distributed up to 4 kms, and in eastern route distributed up to 3.25 kms from the coastline (see figure 2).

1600

Chloride Consentrations(mg/L)

1200 1000 800 600 400 200 0

1600

year 2015 year 2020 year 2025 year 2030 year 2035

1400

Chloride Consentrations(mg/L)

year 2015 year 2020 year 2025 year 2030 year 2035

1400

1200 1000 800 600 400

1

2

3 4 range(km)

(Western route)

5

6

7

0

1200 1000 800 600 400 200

200

0

year 2015 year 2020 year 2025 year 2030 year 2035

1400

Chloride Consentrations(mg/L)

1600

0

0

1

2

3 range(km)

4

(Middle route)

5

6

0

1

2

3

4

5 6 range(km)

7

8

9

10

(Eastern route)

Fig. 2. Prediction of Seawater Intrusion in Semarang

4. Conclusions The condition of seawater intrusion in Semarang has increased rate of 0.575 km 2/years. The model of seawater intrusion in Semarang presented in two models are unsteady and steady models, on western route have error about 27.9%, then the middle route have error about 41.1% and the eastern route have error about 40.0%. In 2035, the seawater intrusion on western route is predicted about 3.0 kms from the coastline, 4 kms for middle route, and about 3.25 kms for eastern route. The management of groundwater in Semarang is necessary to supervise and control is better and more optimal. To determine the concentration of chlorides in confined aquifers, this model can be directly applied. 5. References 1. Bachtiar, T.(2002), Koprostanol sebagai indicator kontaminasi dan perunut alamiah limbah domestik di perairan pantai Banjir Kanal Timur, Semarang, Jawa Tengah, Ph.D Thesis, Universitas Diponegoro,Semarang. 2. Hadi, S.P.(2013), Manusia dan Lingkungan (Human and Environmental). Text Books Semarang : Badan Penerbit Universitas Diponegoro, 979-9156-69-6. 3. Purwanto (2005), Permodelan Rekayasa Proses dan Lingkungan, Text Books, Badan Penerbit Universitas Diponegoro, ISBN : 979.704.319.3 4. Ding,Y., Peng, Y.(2009), Contaminant transport in coastal aquifers, Journal Department of Civil and Environmental Engineering New Jersey Institute of Technology Newark, NJ. 5. Kjellén, M., McGranahan, G.(1997), Urban Water - Towards Health and Sustainability. Journal of (Commissioned for Comprehensive Assessment of the Freshwater Resources of the World.) Stockholm Environment Institute. 6. Susanto A.(2010), Strategi Konservasi Pemanfaatan Air tanahSebagai Sumber Air Bersih Di Kota Semarang Yang Berkelanjutan, Journal of FMIPA UT.Semarang.

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7. Riley, J. P., Skirrow. G.(1975), Chemical Oceanography. Vol. 2, 2nd Edition. Journal of Academic Press. New York. 8. Zhou, Q., Bear, J., Bensabat, J.(2005), Saltwater upconing and decay beneath a well pumping above an interface zone. Journal of Transport in Porous Media. 9. Zhang, Y.(2011), Groundwater Flow and Solute Transport Modeling. Dept. of Geology & Geophysics University of Wyoming 10. Kumar, A., Jaiswal, D.K., Kumar, N.(2009), Analytical solutions of one-dimensional advection–diffusion equation with variable coefficients in a finite domain, Journal of Earth System, No. 5, pp. 539–549. 11. Mohammadi, A., Manteghian, M.(2011), Numerical Solution of One-dimensional advection-diffusion Equation Using Simultaneously Temporal and Spatial Weighted Parameter, Australian Journal of Basic and Applied Sciences, 5(6): 1536-1543,ISSN 1991-8178 12. Gong, J., Nordstrom, J.(2011), Interface Procedures for Finite Difference Approximations of the AdvectionDiffusion Equation, Journal, Swedden. 13. Sibanda, N.(2009), Quantitative Research, Report, Lecturer in Statistics School of Mathematics, Statistics & Operations Research Victoria University Wellington 14. Peraturan Menteri Kesehatan Republik Indonesia No. 492.(2010), Tentang Baku Mutu Air Minum, Tambahan Lembaran Negara Republik Indonesia. 15. Bappeda Kota Semarang dan BPS Kota Semarang (2012), Semarang Dalam Angka 2011. Pemerintah Kota Semarang