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Proceeding the 6th Civil Engineering Conference in Asia Region: Embracing the Future through Sustainability ISBN 978-602-8605-08-3
THE INFLUENCE OF THE SAND COLUMN DENSITY LEVEL TO THE GROUNDWATER RECHARGE IN RECHARGE RESERVOIR Akhmad Azis1 1
Civil Engineering Department, Polytechnic State of Ujung Pandang, Jl. Perintis Kemerdekaan Km 10 Makassar, E-mail:
[email protected]
ABSTRACT Recharge reservoir is one of artificial recharge methods constructed on area with more than 103 cm/sec permeability and directly connected to the aquifer layer. The problem occurs when it is to be built on area with less than 10-5 cm/sec permeability. Thus, it is required to study the recharge column model by using sand columns put into the recharge reservoir base and connected to the semi-confined aquifer layer within various parameters. The purpose of this research is to analyze the influence of the sand column density level to the amount of groundwater recharge. This research is carried out in laboratory for the tests of soil and sand permeability and for the making of recharge reservoir models either with or without sand column. The results were primary data of debit enters aquifer with various parameters were used, such as: the energy height differences ( , thick of soil layer/height of sand columns (z), diameter (d) and number of column (Nkp). Each parameter consists of 3 variables. Results of this study indicate increasing maximum debit due to the increasing density of the sand column from 0,0019 to 0,0157 for soil thickness of 30 cm, 32,5 cm and 35 cm, were 743,97%; 743,99% and 745,03%, respectively. It is expected that the development and application of this study will be useful to cope with the problem of groundwater crisis, especially for areas with small permeability. Keywords: Recharge Reservoir, Groundwater, Sand Column Density.
INTRODUCTION Excessive groundwater exploitation to fulfill the water demands for domestic, industrial, agricultural, and commercial activities have generated groundwater emptiness. This will also cause land subsidence, sea water intrusion, groundwater surface downgrading, and decreasing groundwater quality. To cope with these problems, various efforts have been taken such as having the recharge into the either natural or artificial reservoir, in order to accelerate groundwater recharge. One of the methods of artificial recharge is the making of recharge reservoir to dissipate surface flow instead of pond, which functions as water container. Recharge reservoir is designed to reach the aquifer or soil layer with high absorbance power (more than 10-3 cm/sec). However, when a recharge reservoir is built on an area with small permeability value and low absorbance power, water will be very slow in reaching the aquifer layer that it fails to fulfill its function as a recharge reservoir. Thus, it is required to study the use of sand column model put into the base of the recharge reservoir which directly connects to the semi-confined aquifer layer with various parameters. This is expected to cope with the problem of groundwater recharge at the particular condition. The purpose of this research was to identify the influence of sand column density to the debit enters aquifer.
LITERATURE STUDY Groundwater Crisis Issue Water is essential for humans to support their activities because the second most important natural element in human body is oxygen. About 70 % of human body consists of water. The body system demands so much amount of water intake (Pramono, 1999). Also, water is important for commercial activities such as industry, fishery and other urban businesses. To obtain water, man can find it from various sources, either on the surface or underground. Although the amount of water on earth is 1.360.000.000 km3 or covering almost 75% of the earth surface, but the 97,3 % is seawater with quite
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high level of salt, which makes it imposable for consumption. On the other hand, ground water is only 0,610 % (Sunjoto, 2012). This fact indicates that the groundwater percentage on earth is insignificant. The increasing population also increases the demand of groundwater. Groundwater crisis, especially in big cities in Indonesia, has entered the dangerous step. The development of high buildings with deep basements also reduces the ground capability to absorb rain water.
Groundwater Recharge Recharge Based on the hydrology cycle, the main groundwater source comes from rain water and surface water. Having the tropical wet climate, areas in Indonesia receive relatively high water fall. This condition is favorable for natural underground recharge such as from woods in the forest, lakes and ponds, which occurs during the rainy season for filling and replacing. Groundwater Groundwater is one phase in hydrological cycle. It starts with an event where due to sun heat, water changes into steam from either evaporation of river, reservoirs, seawater and surface water or evapotranspiration from plants. Steam resulted from evaporation at particular height will become cloud. Then, due to various causes, cloud will condensed into precipitation, in the form of snow, ice rain, rain, and dew. Rainwater falls onto the ground partly flows to become surface water and enters the catchment area towards the river system, lake or reservoir and then finally to the sea. Some of it is absorbed into the ground in the form of infiltration and percolation that finally becomes either shallow or deep groundwater ( Kodoatie and Sjarief, 2008). Permeability Permeability is defined as the characteristic of pored substance that enables seepage flow of liquid substance or water or oil from the pores and connected to each other to enable water to flow from high energy point to low energy point. For ground, the permeability is described as the ground characteristic to flow water from soil pores (Hardiyatmo, 2010). Soil permeability coefficient Soil permeability coefficient is the amount of water flowed per time unit to pass through one width unit of aquifer section. To determine the soil permeability coefficient accurately, it is required to take the laboratory method by using head specimen for soil with coarse granule and high permeability and falling head specimen for soil with fine granule and small permeability coefficient. The Law of Darcy The Law of Darcy explains the ability of water to flow in the ground pores and the influencing characteristics. The speed of the flow and the debit/quantity of water per time unit is proportional to the hydraulic gradient (Soedarmo and Purnomo, 2001). Q = k.i.A .........................................................................(1) V = = k.i ......................................................................(2) With: q = water flow volume per time unit (cm3) A = the soil section width to be passed by water (cm2) k = permeability coefficient (cm/sec) i = hydraulic gradient v = flow velocity (cm/sec)
Recharge Reservoir The Function of Recharge Reservoir Recharge reservoir is one type of reservoir with main function as water absorbency media to have it easy and rapid entry to the aquifer layer. This type of reservoir is suitable for wide area with shallow groundwater surface (Kusnaedi, 2005). According to Sudinda (2004), the chairman of the development project of recharge reservoir of The Ministry of Research and Technology, the basic philosophy of the development of recharge reservoir is how to minimize the runoff on the surface to improve the soil ability to absorb the surface water. Recharge reservoir can be classified into single purpose reservoir, which is
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used as flood controller by using a working system to increase the filter function optimization, which improves the water storage capability in the aquifer layer. The use of recharge reservoir are: 1. to optimize the aquifer function and to improve the water storage capability in the aquifer 2. to control flood in the downstream or runoff area. 3. to store water during the dry season.
Sand column
Fig. 1: The concept of recharge reservoir with sand column Sand column is a media expected to have the ability to absorb the reservoir water into the aquifer layer. The traditional method in making the sand column is by drilling holes on the clay layer, which has small permeability, and refilling it with gradated sand. Sand should be able to be flown by water efficiently without bringing fine soil particles. Figure 1 shows the sketch of the use of column-sand column with water that comes from the surface water contained in the reservoir at particular height. Then water is flown through the column-sand column. It is hoped that sand with large permeability coefficient can accelerate and enlarge the occurrence of recharge, as well to be used as filtration to have water entering the aquifer layer is in clean condition. Sand Column Density Sand column density is the comparison between the surface area of sand column ( ) and the surface area of recharge reservoir (A), or written as the following equations : =
..................................................................................................(3)
................................................................................................................(4) where: = sand column density d = diameter of sand column Nkp = the numbers of sand column Based on the above equation, it is seen that the density of the sand column is proportional to the surface area of the sand column. While the surface area of the sand column, is a function of the diameter and the number of sand columns.
RESEARCH METHOD Time and Location This study was carried out in six months, started from the sample collecting up to the experiment in the Soil Mechanic Laboratory and Hydraulic laboratory of the Civil Engineering Department, Polytechnic State of Ujung Pandang. The sand sample was taken from Sungai Jeneberang Kabupaten Gowa, and the soil sample was taken from Tamalanrea Makassar.
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Procedures This study was grouped into two steps. 1. Data collecting During this step, soil and sand sampling was carried out together with equipment preparation in the laboratory. 2. Laboratory Experiment Experiment in the laboratory included the tests of water content, sieve analysis and permeability. The test of recharge reservoir model was carried out with and without using the sand column and with various parameters such as the energy height differences ( , thick of soil layer/height of sand columns (z), diameter (d) and number of column (Nkp). Each parameter consisted of 3 variables. 3. Data Analysis Based on the observation on the test of the recharge reservoir model with and without column-sand column, data was analyzed and plotted into correlation graphic of recharge (Qa) and the available parameters. Based on the physical model test results using the sand column, the debit of recharge equation was resulted as the function of the reservoir water height, sand column diameter, sand column height, numbers of sand column and the energy height differences. To obtain qualified results, the test of correlation strength between the parameters was taken as well as the validation of each result.
Fig. 2: Density 0,0157
Fig. 3: The measurement of reservoir entry debit
RESULTS AND DISCUSSIONS Soil Type The test results on sand and soil sample of the four soil classification system indicated that the soil used in this study was silt with low plasticity and the sand material was coarse.
The Influence of Sand Column Density Soil layer thickness/sand column height of 30 cm
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Aquifer entry discharge (cm3/det)
70.00 60.00
Δh = 37,4
50.00
Δh = 34,9
40.00
Δh = 32,5
30.00
Δh = 30,2
20.00 10.00 0.00 0.0000 0.0050 0.0100 0.0150 0.0200 Density
Fig. 4: The correlation of debit enters aquifer and sand column density at z =30 cm Figure 4 shows that the debit enters aquifer increases in line to the increasing column density. This was because the larger the sand in column density, the wider the sand column surface would be. Therefore, it enables more water to enter the soil layer. The percentage of increasing debit enters aquifer (maximum) was 743,97% from density of (ᵹ) = 0,0019 to 0,0157. The minimum percentage was 48,66% from density of (ᵹ) = 0,0019 to 0,0028.
Aquifer entry discharge (cm3/det)
The Soil Layer Thickness/The Height of Sand Column of 32,5 cm The same thing occured as seen in Figure 5, that the use of sand column in each density at sand column height of 32,5 cm would increase the debit due to the increasing sand column density from the smallest of 0,0019 to the larger sand column density at all energy height differences. 70.00 60.00
Δh = 40,3
50.00
Δh = 37,5
40.00
Δh = 35,2
30.00
Δh = 32,4
20.00 10.00 0.00 0.0000
0.0050
0.0100
0.0150
0.0200
Density
Fig. 5: The correlation of debit enters aquifer to the sand column density at z =32,5cm The percentage of increasing debit enters aquifer (maximum) was 743,99% from density of (ᵹ) = 0,0019 to 0,0157. The minimum percentage was 48,9% from density of (ᵹ) = 0,0019 to 0,0028. The Soil Layer Thickness/The Height of Sand Column of 35 cm The same happened when the height was 35 cm, as seen in Figure 6. It can be seen that increasing debit due to the increasing sand column density from the smallest (0,0019) to the larger sand column density are all energy height differences. The increasing percentage of the debit enters aquifer (maximum) was
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745,03% from density of (ᵹ) = 0,0019 to 0,0157. The minimum percentage was 49,06% from density of (ᵹ) = 0,0019 to 0,0028.
Aquifer entry discharge (cm3/det)
70.00 60.00
Δh = 42,6 Δh = 38,9 Δh = 37 Δh = 34,6
50.00 40.00 30.00 20.00 10.00 0.00 0.0000 0.0050 0.0100 0.0150 0.0200 Density
Fig. 6: The correlation of debit enters aquifer and sand column density at z =35 cm Figure 4, 5, and 6 describe the correlation of debit enters aquifer and the sand column density on each energy height differences for three soil layer thickness of 30 cm, 32,5 cm and 35 cm. The gap between the three graphics are not too wide due to the insignificant influence of the soil layer thickness to the amount of debit enters aquifer. Similarly with the energy height differences, the gap between one another is not too wide. However, it can be seen that the greater the height difference of energy, the percentage increase of the debit entered the aquifer. This is due to the pressure that inhibits pizometrik water into the aquifer layer gets smaller. Based on the three graphics, it can provide indication that the debit enters aquifer would be higher due to the increasing sand column density at all energy height differences. This result is in accordance to the Law of Darcy that the correlation between the groundwater recharge is proportional to the width of sand column area, so that it can be stated that the surface area or the level of sand column density contributes to the magnitude of groundwater recharge.
CONCLUSIONS AND RECOMMENDATIONS Conclusion Based on the results of this study, several conclusions can be drawn as the followings: 1. The sand column in the recharge reservoir highly influences the increasing debit enters aquifer at the sand column density. 2. There was increasing debit due to the increasing density level of the sand column from 0,0019 to 0,0157 (maximum) at soil thickness of 30 cm, 32,5 cm and 235 cm in 743,97 %; 743,99 % and 745,03 %, respectively.
Recommendations It is recommended that his study is to be continued with the followings: 1. To positioned the sand column in serial, in order to identify its influence on the groundwater recharge. 2. To study the stoppage due to sedimentation both on the sand column surface and inside the sand column resulted from water flow from the soil layer entering the sand column which is assumed to bring fine material or the amount of intake debit through the sand column.
REFERENCES Broto, S and Susanto, H. (2008). Perancangan Model Pendugaan Efektifitas Waduk Resapan Kota Bogor terhadap Optimalisasi Aquifer Groundwater. Jurnal Teknik, 29 : 220 – 227. Darrundono (2009). Krisis Groundwater Jakarta Berbahaya. Tempo Interaktif, Jakarta
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Djudi (2006). Kajian Recharge reservoir Tambakboyo, Kecamatan Ngemplak, Kabupaten Sleman, Propinsi DI Yogyakarta. Tesis tidak diterbitkan. Bandung : Program Magister Teknik Sipil ITB Hadian, S. (2006). Sebaran Aquifer and Pola Aliran Groundwater di Kecamatan Batu ceper and Kecamatan Benda KotaTangerang, Propinsi Banten. Jurnal Geologi Indonesia, 1 : 115 – 128 Hardiyatmo, H,C. (2010). Mekanika Tanah 1. Gajah Mada University Press, Yogyakarta Hargono, B. (2011). Belajar Dari Embung Tambakboyo Di Yogyakarta Untuk Mengatasi Masalah Sumber Daya Air Di Pulau-Pulau Kecil and Pantai. Prosiding PIT XXVII HATHI, Ambon Herlambang,A., Indriatmoko,R,H. (2005). Pengelolaan Groundwater and Intrusi Air Laut. Jurnal Air Indonesia, 2 : 211-225 Joleha (2001). Analisa Drainase Vertikal Untuk Mempercepat Konsolidasi Pada Tanah Lunak. Jurnal Natur Indonesia. Vol. 4 No. 1 Kodoatie, R.J., Sjarief, R. (2008).Pengelolaan Sumberdaya Air Terpadu. Andi, Yogyakarta Koosdaryani (2009). Penggunaan Modifikasi Desain Sumur Resapan Sebagai Pengisian Kembali Groundwater and Pengendalian Banjir di Kel.Sewu Surakarta. Media Teknik Sipil, 9: 136 – 139 Kusnaedi (2011). Sumur Resapan Untuk Pemukiman and Perkotaan. Swadaya. Jakarta. Media Indonesia, Digilib. 17 Maret 2004. Recharge reservoir Atasi Banjir and Kekeringan, (Online), (Ztp://www.mediaindonesia.com, diakses 20 Juli 2011) Pramono, R., (1999). Permasalahan Air di Perkotaan and Perilaku Masyarakat. Jurnal Studi Pembangunan, Kemasyarakatan and lingkungan, 3 : 39-45 Putranto, T., Kusuma (2009). Permasalahan Groundwater di Daerah Urban. Jurnal Teknik, 30:48 – 56 Puradimaja, D. (1997). Permasalahan Groundwater and Peluang Risetnya. Buletin Geologi Tata Lingkungan, 21 : 22 – 30 Setiadi,B,D. (2011). Analisis Dimensi Bangunan Resapan Air Hujan Untuk Lahan Pekarangan.Tesis tidak diterbitkan, Yogyakarta : Program Pascasarjana Fakultas Teknik UGM Soenarto, B. (2007). Teknik Sumur Injeksi untuk Pengendalian Banjir and Keperluan Lain serta Berbagai Teknik Ekivalen Lainnya. Jurnal Sumberdaya Air, 3 : 49 – 62 Sudinda, T, W. (2004). Simulasi Potensi Recharge reservoir Pada Akifer Tertekan Dengan Metoda Finite Difference. Jurusan Teknik Sipil FTSP Trisakti, Jakarta Sunjoto (2011). Teknik Drainase Pro-Air. Proceeding Seminar Nasional-1 BMPTTSSI - KoNTekS 5, Medan Sunjoto (2012). Subsurface Hydrology. Post Graduate Program Department of Civil and Environmental Engineering Faculty of Engineering Gadjah Mada University, Yogyakarta Tresnadi, H. (2007). Dampak Kerusakan yang Ditimbulkan Akibat Pengambilan Groundwater yang Berlebihan. Jurnal Alami, 12 : 76 – 81 Wahyudi, H. (2009). Kondisi and Potensi Dampak Pemanfaatan Groundwater di Kabupaten Bangkalan. Jurnal Aplikasi, 7 : 14 - 19
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