PDF 2003 Erwin Ciremai Bul.geologi

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To be submitted to BULETIN GEOLOGIVol 35 No 1 Tahun 2003

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The Influence of Hydrogeological Factors on Variations of Volcanic SpringDistribution, Spring Discharge, and Groundwater Flow Pattern

Deny Juanda PURADIMAJAD. Erwin Irawan

Lambok M. Hutasoit

Hidrogeology LaboratoryDepartment of Geology, Institut Teknologi Bandung,

Abstract

This study has been conducted on east slope of Mt. Ciremai, a strato-type volcano with elevation of 3072 masl,in Kabupaten Kuningan, West Java, Indonesia.

Result of 20 observations had shown that spring discharge varies from 10 l/sec to 400 l/sec, consisted of deviated

and isolated groundwater flow patterns. Analysis on available data and facts also indicates that there are threehydrogeological factors which influence the variations of spring distribution, spring discharge and groundwaterflow pattern: distribution of lithology and morphology; intensity of macro fracture; thickness and finalinfiltration rate of residual soil.

The first factor, the change of rock distribution forms slope break at elevation range of 500 - 650 masl, slopeangle changes from 19 0 to 4 0. The change of slope angle controls the hydraulic of unconfined groundwater todevelops the largest spring distribution at Zone 2 (500 650 masl). The elevation range of 100 1250 masl isdischarge area, while the elevation range of 1250 3100 masl is recharge area. In detailed scale, volcanic depositdistribution forms morphological feature of ridges and valleys which controls the groundwater flow pattern. Thesecond factor, fracture zone controls the level of spring discharge in volcanic terrain. The fracture system occurson Laharic Breccia, the fractures stretch consecutively to rock distribution, which also controls the isolatedgroundwater flow; on Lava flow. The fractures are in form of cooling joints with unsystematic pattern, which

controls the deviated groundwater water flow. The third factor, the weathering processes in the study area is veryintensive, resulting in thick residual soil and high final infiltration rate, which is very potential to store and to beinfiltrated by rain water and surface water.

Keywords : Volcanic fracture spring, hydrogeological factors, groundwater flow pattern


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1. INTRODUCTION

The vast growing population and industrial activities had caused groundwater resource todecrease rapidly. Its depletion rate has raised concerns and urgent calls for conservation andimmediate spring management measures.

Identification of geological control is a pre-requisite in determining groundwater flow system.Mandel (1981) 1 explains that volcanic aquifer system shows a distinctive feature,characterized by rapid change of deposits, where pyroclastic and lava materials areinterchanging in close distance.

Studies on identification of recharge-discharge system of volcanic aquifer system have beencarried out previously by Asseggaf and Puradimaja (1998) 2, Irawan et.al. (2000) 3, Irawan andPuradimaja (2002) 4, using physical-chemical properties analysis, combined with surface andsubsurface geological observation. The general result indicates that groundwater flow involcanic area is controlled by distribution of volcanic aquifers.

This research study was carried out on the east slope of Mt. Ciremai, a strato-type volcanowith elevation of 3072 masl, situated 20 km south of Cirebon, in Kecamatan Cilimus Jalaksana, Kabupaten Kuningan, West Java Province (Figure 1). The diameter of Mt. Ciremaifrom the peak to the foot slope is about seven km. This location was selected because of theexistence of a groundwater system which forms spring belt with no less than 300 springs,discharging over 1500 l/sec of water (IWACO-WASECO, 1989) 5. The scientific interest of this study is to determine the geological control on spring distribution, spring discharge andgroundwater flow and spring discharge.

Figure 1. Location of study area

2. METHOD

Hydrogeological condition is a combination of two main aspects: the solid and the fluid. Thesolid aspect comprises the material and the geometry of an aquifer, and the hydraulicproperties of the aquifer; while the fluid aspect involves the hydraulic behaviour of thegroundwater. Therefore, two complementary methods have been carried out in this study:

Scale 1 : 1.500.000

Location ofStudy Area

A B

C D


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(1). Surface mapping of volcanic aquifer system with 1 : 25.000 scale, to identify thegeometry of the aquifer and the hydraulic properties of soil (unconfined aquifer). The datawere obtained from observation of 20 springs and volcanic rock exposures; and alsosupported by 10 field permeability measurements.

(2). Flow net analysis, to identify the groundwater flow system. The analyzed system were: a.Regional flow in Linggarjati and Cibulan areas; b. Detailed flow at Cibulan spring area.The flow net analysis was based on water table measurement at dug well and springelevation.

3. FIELD OBSERVATION

Observation has been done on 21 spring location, which is limited to large springs, dischargemore than 10 l/sec of groundwater. Based on the observations, all of the springs are fracture

spring.

3.1 Characteristics of Fracture Spring

All of the observed-aquifers are unconfined. Based on its elevation, springs in the east slopeof Mt. Ciremai (Cilimus-Jalaksana area) can be divided into two zones as follows: SpringZone 1: 100-650 masl; and Spring Zone 2: 650-1250 masl. The spring zonation is presented inFigure 2, while the hydrogeological condition and volcanic facies distribution is summarizedin Table 1.

Based on Table 1, there are three volcanic facies:

1)Volcanic core facies is distributed at 3050-3100 masl, consists of andesites to dacite rock.This facies is impermeable with no spring;2)Volcanic Proximal facies is distributed at 650-3050 masl, consist of:

2a)Proximal 1 at 1250 3050 masl, composed of impermeabel Pyroclastic flow and falldeposit with andesite boulder and tuff matrices;

2b)Proximal 2, composed of permeable andesite to dacite lava flow at 650 1250 masl.On Proximal 2 facies, there is Spring Zone 1 with three springs which are discharge atotal of 98 l/sec. The estimated thickness is at least 100 m (IWACO-WASECO,1989

6).

3)Volcanic Distal facies is distributed at 100 650 masl, consist of permeable laharic breccia,with small to large andesite to dacite boulders planted in tuff and volcanic sand matrices.The rock is fractured with unidentified dimension and geometry, which set up a goodpermeability. On this facies, there is Spring Zone 2 which consists of 18 springs with totaldischarge 1063 l/sec. The estimated thickness is at least 100 m (IWACO-WASECO,1989

6).


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Table 1 Summary of hydrogeological conditions

Volcanic facies(according to

McPhie, 1993 6)

Description Slope Spring Physical and hydraulic propertiesSymbol Lithology Zone Number Discharge

(L/s)Volcanic Core

(3050 masl-estimated

3100 masl)

Volcanic neck, consists of andesites to dacite

- 0 0 Impermeable rock with less, no otherdata is available

Volcanic Proximal(650 3050 masl)

Volcanic Proximal 1(1250 3050 masl)

Volcanic Proximal 2(650 1250 masl)

Pyroclastic fall and pyroclasticflow. Consists of andesiteboulder and tuff matrices

Lava flow. Consists of andesite to dacite lava

-

1

0

3

0

98(class 1-3)*

Impermeable rock, high infiltration rate of soil 1.5 cm/min, no other data is available

Permeable, secondary permeability:cooling/sheeting joint with unsystematicpattern, thick residual soil (2-5 m), finalinfiltration rate of 0.5 1.2 cm/min

Volcanic Distal(100 650 masl)

Laharic breccia. Consists of andesite to dacite boulderwith tuff and volcanic sandmatrices.

2 18 1063(class 1-3)*

Permeable, secondary permeability:fractured with isolated pattern, thick residual soil (2-5 m), final infiltrationrate of 1.26 2.53 cm/min

* according to Meinzer classification of spring discharge (op.cit Todd, 19847)

0o 45o 20 o 10o 30 o


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Figure 2 Volcanic Deposit Distribution. Laharic breccia is deposited at the lowest elevation (100 - 650 masl). At the upperpart, seriesof lava flow are deposited at 650 1250 masl of elevation, and series of pyroclastic (flow and fall) is deposited at 1250 3100 masl of elevation. The changing of rock type, from lava flows to pyroclastic breccia, forms a slope break. The slope changes from 4 to 19 0 at500 650 masl of elevation. Zone 1 consists of 3 spring observation with total discharge 98 l/sec. Zona 2 consists of 13 springobservation with total discharge 1063 l/sec.

Laharic depositLava flowsPyroclastic flowsPyroclastic fall

Pyroclastic flows

Pyroclastic fallRecharge area Discharge area

Laharic depositZone 1 and zone 2

Lava flowsZone 3

A B


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1. Fractures on lava flowThe fractures are constituted of cooling joints which form narrow openings in rock.The observed dimension of the joints ranges from few cm to 20 cm. The pattern of the

joints is not known, but seemingly to be unsystematic, showed by many orientations asfollows: N63 0E, N90 0E, N117 0E (Figure 3).

2. Fractures on laharic brecciaThe observed dimension of the fracture ranges from 10 cm to 60 cm. The fracturesstretch continuously to rock distribution. At Cibulan spring, the orientation of fractureis N93 0E, which is in the same direction as the ridge (Figure 3).

Figure 3 Fractures on lava flows and laharic breccia. There are 2 spring systemsat this location. The upper spring occurs in lava flows aquifer and emergesfrom cooling joints. The lower spring occurs in laharic breccia and emergesfrom fractures between large boulders.

3.2 Characteristics of Groundwater Flow Pattern

Regional isophreatic map covers 2 spring areas, 1) Linggarjati and 2) Cibulan. TheLinggarjati spring areas emerges from lava flow, discharging 80 l/sec of groundwater; whilethe Cibulan spring area is located at the edge of a ridge, and discharging overall 400 l/sec of groundwater (Figure 4A).

The groundwater flow pattern in Linggarjati Area is SW-NE with 0.4 of hydraulic gradientand 0.6 of slope. The groundwater flow appears to be in deviated, controlled by theunsystematic fractures orientation.

The groundwater flow pattern in Cibulan Spring Area shows NW-SE direction with 0.3 and0.4 of slope. The isophreatic contour shows an straight pattern.


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4. ANALYSIS AND INTERPRETATION

Based on the observations, there are three hydrogeological factors which controls springdistribution, spring discharge, and groundwater flow pattern as follows: the distribution of lithology and morphology; the intensity of macro fracture; the thickness and final infiltrationrate of residual soil. The details of each factors are described below.

4.1 Distribution of lithology and morphology

According to Freeze and Cherry 8, morphology and geology controls the distribution of potentiometric condition. Many variation os potentiometric pattern produces varied input-output system of groundwater flow. Another view from Purbohadiwijoyo 9 indicates thatspring distribution is strongly controlled by three types of geological condition: Type one).atthe slope break of volcano. Groundwater moves from recharge area to discharge area at slopebreak, form spring belt; Type two)at contact between aquifer and intrusion as boundary.

Groundwater emerges in form of contact spring at contact between aquifer and intrusion;Type three)at volcanic rock coastal zone, which only occurs at near-sea volcano. Groundwatermoves from recharge area to the coastal zone. Spring can emerge either above sea level orbelow sea level, known as under water spring.

At Mt Ciremai, morphology is controlled by change of rock distribution. Such conditionforms slope break at elevation range of 500 - 650 masl. The measured slope angle changesfrom 19 0 to 4 0. The change of slope angle controls the hydraulic of unconfined groundwater todevelops spring belt in the area, with the largest spring amount at Zone 2 (500 650 masl). On the other hand, at the upper slope (1250 3100 masl), there are no spring occurrences.Therefore, it can be concluded that the elevation range of 100 1250 masl is discharge area,

while the elevation range of 1250 3100 masl is recharge area.

In more detailed scale, the volcanic deposit distribution forms morphological feature of ridgesand valleys. Such features functions as passageway of groundwater (Figure 4A). The analysisis proven by some springs discharge from ridge edges. The groundwater flow matches thetopographical contour, as shown in Figure 4B. The ridge consists of 10 m thick of Laharicbreccia deposit (Figure 4C). The thick Laharic breccia deposit functions as productive aquifer.

4.2 The intensity of macro fracture

Fracture zone controls the level of spring discharge. There are two genetics type of fractures:a) Fractures on lava flow

The fractures are constituted of cooling joints which form narrow openings in rock.The pattern of the joints is unsystematic, with many orientations as follows: N63 0E,N90 0E, N117 0E. The orientation of the fracture controls the deviated groundwaterflow pattern.

b) Fractures on laharic brecciaThe fractures stretch continuously to rock distribution with. At Cibulan spring, theorientation of fracture is N93 0E, which is in the same direction as the ridge. Theunidirection fracture controls isolated groundwater flow pattern.


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Figure 4 The 3 figures show the situation of Cibulan spring area,the isophreatic map, and the section of groundwater flow. 4A.Location of Cibulan spring; 4B. The isophreatic and groundwaterflow at the ridge; 4C. The cross section of Cibulan spring (400l/sec).

A

B

C

Mt. Ciremai


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4.3 Thickness and Final Infiltration Rate of Residual Soil

The intensity of weathering processes in the study area is very high, resulting in thick residualsoil. The thickness of residual soil is ranging from 2 m to nearly 10 m. Such thick residual soilis very potential to store and to infiltrate rain and surface water in to the aquifer.

Infiltration test (according to Chow et.al., 1964 10; Miyazaki, 1993 11) is carried out to verifythe final infiltration rate of residual soils. Residual soil from lahar shows the largest values of 1.26 2.53 cm/min, followed by residual soil from pyroclastic breccias 1.5 cm/min, and fromlava flow 0.5 1.2 cm/min. High final infiltration rate (Linsley & Franzini, 1978 12) indicatesthe high capacity of residual soil to be infiltrated by rain water and surface water.

5. CONCLUSIONS

Results from 21 observations had shown that spring distribution, spring discharge, andgroundwater flow pattern are controlled by three hydrogeological factors as follows:distribution of lithology and morphology; intensity of macro fracture; thickness and finalinfiltration rate of residual soil.

The first factor, the change of rock distribution forms slope break at elevation range of 500 -650 masl, slope angle changes from 19 0 to 4 0. The change of slope angle controls thehydraulic of unconfined groundwater to develops the largest spring distribution at Zone 2

(500 650 masl). The elevation range of 100 1250 masl is discharge area, while theelevation range of 1250 3100 masl is recharge area. In detailed scale, volcanic depositdistribution forms morphological feature of ridges and valleys which controls the groundwaterflow pattern. The second factor, fracture zone controls the level of spring discharge involcanic terrain. The fracture system occurs on Laharic Breccia, the fractures stretchconsecutively to rock distribution, which also controls the isolated groundwater flow; on Lavaflow. The fractures are in form of cooling joints with unsystematic pattern, which controls thedeviated groundwater water flow. The third factor, the weathering processes in the study areais very intensive, resulting in thick residual soil and high final infiltration rate, which is verypotential to store and to be infiltrated by rain water and surface water.


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References

1 Mandel S. (1981). Groundwater Resources: Investigation and Development. Academic Press, pp. 217

2 Asseggaf, A. & Puradimaja, D.J. (1998). Identifikasi Kawasan G. Salak G. Gedesebagai Zona Resapan dan Luahan Daerah Ciawi Bogor Kabupaten Bogor JawaBarat . Prosiding PIT IAGI XXVII, pp. 4-136 - 4-142

3 Irawan, D.E., Puradimaja, D.E., Yuwono, S. & Syaifullah, T.A. (2000)., PemetaanEndapan Bahan Volkanik dalam Upaya Identifikasi Akifer pada Sistem Gunungapi.Studi Kasus: Daerah Pasir Jambu-Situwangi Soreang, Kabupaten Bandung, JawaBarat , Jurnal Buletin Geologi, Vol 3, Tahun 2000

4 Irawan, D.E., Puradimaja, D.J. (2002). Geological Mapping and Groundwater Physical-Chemical Properties Characterization. An Approach to Spring Recharge AreaConservation , Proceeding of International Conference on Urban Hydrology, KualaLumpur, pp.

5 IWACO- WASECO. (1989). West Java Provincial Water Sources Master Plan forWater Supply: Kabupaten Kuningan. Vol A, Directorate of Water Supply, Ministry of Public Works

6 McPhie. (1993), Volcanic Textures ,

7 Todd, DK. , 1984, Groundwater Hydrology, John Wiley & Sons

8 Freeze & Cherry , 1979, Groundwater, Prentice-Hall

9 Purbo Hadiwijoyo (1965), Hydrogeology of Stratovolcanoes , International Association of Hydrogeologists, Memoires Congress of Hannover

10 Chow, VT (ed). (1964). Handbook of Applied Hydrology. McGraw-Hill, pp. 12.1-12.30

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Miyazaki, T. (1993). Water Flow in Soils. Dekker, pp. 29 4512 Linsley, R.K. & Franzini, J.B. (1978). Water Resources Engineering. McGraw Hill

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