OUTLINES ON THE HYDROGEOLOGYOF THE ISLE OF MADURA (INDONESIA)

H. FLATHE and D. PFEIFFERBundesanstalt für Bodenforschung Hannover

ABSTRACT

In 1961 a hydrogeological inventory survey by aid of geoelectrical investigationmethods was carried through on the Isle of Madura (Indonesia) northeast of Java. Theresults of these investigations are to constitute the fundamentals for an improvement ofthe present water supply; they have been summarized in a "Hydrogeological map of theIsle of Madura 1:250,000".

This map mediates a general view on the geological structure of the isle, thelithology, the groundwater quantities to be recovered from these rocks, the knownsprings (with indications as to their yield), the distribution of fresh and briny ground-water as well as the monthly average of precipitation.

The explanatory text pertinent to this map contains a description of the differentgroundwater provinces, of detail investigations in regions of special importance, and arepresentation of the combined hydrogeologic-gcophysical investigation methodapplied.

RÉSUMÉ

En 1961 on réalisait à l'aide de méthodes géoélectriqucs un bilan hydrogéologiquedans l'Ile de Madura (Indonésie), située au NE de Java. Les résultats de ces investig-tions constituent la base de l'amélioration de l'approvisionnement en eau et sontreprésentés sommairement sur une carte hydrogéologique ("Hydrogeological Map ofthe Isle of Madura 1:250,000").

Cette carte donne une vue générale de la structure géologique de l'île, de la litho-logie, des ressources en eau souterraine, des sources connues (en indiquant leur débit),de la répartition d'eau souterraine douce et salée, ainsi que des précipitations moyennesmensuelles.

La note explicative accompagnant cette carte donne une description des différentesnappes d'eau souterraine, des investigations détaillées dans des régions d'importancespéciale et une représentation de la méthode d'investigation hydrogéologique etgéophysique appliquée.

1. GEOGRAPHY

The Isle of Madura is situated north of East-Java. It comprizes an area of 4,382km2. Its maximum length is about 160 km, its maximal width about 40 km.

In the North, Madura is bordered by the Java Sea, in the South by the "Straitof Madura". Both seas are relatively shallow; the Strait of Madura, for instance, isnot deeper than 60 meters.

In wide spaces the Isle of Madura is a mountainous and hilly region, with thehighest elevations in the eastern part of Central Madura reaching heights of about450 m above sea level (s.l.).

Larger plains (delta regions), generally rising to about I 10 m s.l., are to befound E and NE of Bangkalan, between Baliga and Sampang, E and SE of Pamekasanand between Saronggi and Sumencp (see Hydrogeological Map 1 : 250,000).

2. GtOLOGY

Madura is, geologically, part of the Isle of Java. The underground is built up, asfar as known, of tertiary (miocène and pliocene) and quaternary (pleistocene andholocene) sediments. The table I indicates the rock series and their hydrogeologicalposition.

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TABLE IThe Stratification of Rocks oh the Isle of Madura

Origin, thickness, faciès and hydrogeological position

Designation Thickness

Holocene

3

a Pleistocene

Pliocene

Miocene

Kabuh- and Putjangani layers

Kalibeng layers (*)

I Upper Orbitoidlayers

_2 £• i Lower Orbitoid

on layers

• | « Base marlsID O

strongly alternating, butrelatively thin

50 — 300 m

3000 m (?)

Faciès Hydrogeological position

pebbles, sand, clay, marls aquifers to impermeable beds; theand compound of these latter prevailingrock types

primarily clays and marls,secondarily limestones

primarily strongly kar-sted limestone beds, secon-darily calcareous sand-stone

practically impermeable beds

primarily clay- or marl-stone beds with secon-darily limestone beds inalternation

mainly aquifers

aquifers to impermeable beds

. mainly clay- and marl- practically impermeable bedsstone layers

(•) see Fig. 1.

The tertiary beds are generally strongly folded. Besides, a far extended saddle-and trough structure is clearly evident.

The general trend of the layers is E-W; locally there occur strong deformations,also circulating strikes, overthrusts and breaks. The oldest rocks crop out, presumedlydue to a strong uplift, in the core of the isle.

The quaternay beds have a horizontal layering. The N-S profile of the Hydro-geological Map 1: 250,000 provides a concept of bedding conditions on the isle. Thismap was designed on the base of data at hand, of own field surveys and of aerialfotos.

The center part of the isle is prcponderately built up by the Orbitoid layers. Thebasic marls within the distribution area of these beds are to be found in few places inthe center of the isle, so for instance about 10 km N of Baliga. The Kalibeng layersare surrounding this core; they form the surface almost everywhere till to the coast,except for the lowlands. In the basin of Gulukguluk, an E-W directed stretch ofthese limestones, of 5 km width, penetrates the mainly clayey rock series of the Rem-bang beds.

The pleistocene Kabuh- and Putjangan layers of mostly clayey consistence areto be encountered prediminantly in the large delta districts at the coast.

Holocene sediments are to be found everywhere on the isle. They prevail, however,in the just mentioned delta districts and in the remaining coastal area.

The limestones have a content of 85% to 99% of carbonate. The percentage ofMgO always remains below 1%. The insoluble residue of the limestones consistsmainly of chlorite, muscovite, illite, coalinite and quartz. The carbonate content of"terra rossa" is 1-10%. Claystones and marls contain 1-50% of carbonates.

3. CLIMATE

3.1 Rainfall

In Central Madura, the main annual rainfall lies between 1000 and 1500 mm, inEast Madura between 1500 and 2000 mm and in West Madura between 1500 and2500 mm.

The Hydrogeological Map 1: 250,000 gives detailed information about the rain-fall during the whole year and during the single months.

The air temperature on Madura lies between 25,9"C(July) and 27,9üC(November).

4. HYDROLOGY

The main hydrostatic base level for the Isle of Madura in the North is, after all,the Java Sea. in the South the "Strait of Madura".

The surficial watershed proceeds in about the northern third of the isle. Its exactcourse may be derived from the Hydrogeological Map 1: 250,000. Also to be takenfrom this map is the fact that the rivers running north have only a short course, whereasthose running south have a longer one.

Only few of the multitude of rivers carry water the whole year through.

5. HYOROGEOLOGY

The hydrogeological position of the different layers is described in the table I.Layer sequence, inclined stratification and morphology have caused the develop-

ment of several groundwater storeys in the layer complexes and also a series of source

545

Kalibeng layers

Fig. 1 — Clear morphological break at the junction Upper Orbitoid layers/Kalibenglayers.

lines. One important source line, for instance, is the interface Upper Orbitoid layers/Kalibeng layers. (Fig. 1).

The quantities of waters to be developed may locally be very different, in equalstratifications; this depends among other things, on expansion, bedding, altitudeabove sea level, tectonical stress. In the Gunung Waru, e.g., which is situated highabove the corresponding hydrostatic base level and is built up of limestone beds, —this outlier is present in a great altitude level on top of clayey beds (shallow karst,Fig. 2) — practically only very little groundwatcr quantities arc exploitable. In com-parative limestone layers, on the other hand, — for instance near Sumenep — there

r

Fig. 2 — The western margin of the Gunung Waru.

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may be a yield of large water quantities under the corresponding hydrostatic baselevel (deep karst) and with an expansive catchment area.

Wide parts of the isle can be considered as being groundwater prospective; thecentral and the western part of the isle, however, must be regarded as rather short ofgroundwater. The chances for groundwater development are outlined in detail in theHydrogeological Map 1 : 250,000.

6. GROUNDWATER PROVINCES

According to morphological, hydrological, geological and hydrogeological facts,ihe Isle of Madura can be classified into a series of different groundwater provinces(Fig. 3).

Fig. 3 — Groundwater provinces.

1. The lowlands of Bangkalan,2. the highly situated limestone region in the South between Kamal and Baliga,3. the plain of Tanahmcrah,4. the limestone region in the North from Bulukagung till Djurangan and from

there to the South till Sumenep,5. the marly region in the center of the isle,6. the lowlands of Baliga,7. the limestone region between Saronggi and Pamekasan and Tordjun/Sampang,8. the lowlands of Pamekasan,9. the limestone trough of Gulukguluk (Pajudan-Plateau),

10. The lowlands of Saronggi-Sumencp.

6.1. The lowlands of Bankalan

They form a plain gently sloping westwards, with elevations hardly surpassing10 m. In the East, this area joins the higher situated plain of Tanahmerah, in the Northand South the elevated limestone regions of the isle.

The layer sequence and the stratification is schematically illustrated by the sketchin figure 4.

Among these layers, practically only the porous limestones of the Kalibeng layers,on account of their clefted and karsted structure, may generally be considered as beingaquifers, whereas the younger rock layers superposing them are to be regarded aslittle to nonpermeable.

547

w

Fig. 4 — Stratification in the Bangkalan lowlands (schematically). 1 = holocene,loose sediments (clayey silt prevailing) 2 — pleistocene claystones 3 — pliocenelimestones (Kalibeng layers).

Drillings for the purpose of opening groundwater may have a fair chance to belocally successful in the eastern part of the basin, i.e. in tectonically predestined places,with a larger catchment area, where the Kalibeng layers reach till under the corres-ponding hydrostatic base level. In the pleistocene and holocene marl- and clay layers,only very little water quantities will be procurable.

6.2. The high-lying limestone formation in the South between Kamal and Baliga

This province is preponderately built up of calcareous Kalibeng layers whichform here flatly to steeply sloped saddle- and trough zones generally striking E-W.In the South they submerge below the Strait of Madura. The region is strongly karstcd.Locally it shows formations similar to tower- and cone-shaped karst.

In the coastal area and in the valleys the limestones are locally superposed bypleistocene clays and marls — here of unknown preserved thicknesses. Moreover,the limestone beds arc covered with their weathering products, the terra rossa, whichlocally may attain thicknesses of several meters.

In places with clcfted limestone beds of adequate thickness reaching till underthe corresponding hydrostatic base level, it can be expected that locally moderatewater quantities may be recovered. Particularly promising seem tectonically predestinedplaces in a strech of 1 to 2 km width along the coast (The fresh water/saltwater limitlies relatively near the coast).

In the mostly N-S directed valleys within this region there occur locally springsof a moderate output.

6.3. The plain of Tanahmerah

The plain of Tanahmerah adjoins the lowland of Bangkalan in the East. It slopesgently towards W. The plain is crossed by the generally E-W flowing Kali Pantjoranwith its numerous tributaries.

A thin quaternary surface formation is here underlain by pliocene beds, consistingmainly of massive limestones, calcareous sandstones and sandy marls, which in someparts are superposed by thick marly beds. The layers constitute here an E-W strikingtrough, the axis of which proceeds directly north of Tanahmerah.

548

The chances for water procurement in the plain of Tanahmerah are, in places,partly good, on other parts very unfavourable. Moderate to average prospects forwater development by means of wells are given in the place Tanahmerah and also inregions situated about 5 km north and south of Tanahmerah. In these latter regionsthere are locally to be found springs with relatively large yield.

By aid of a geoelectrical measurement according to the four-point method (l) adetail investigation has been carried t h rough near Tanahmerah. 16 geoelectrical soundinggraphs have been recorded on a SSW-NNE-profite of 6,6 km length across the localarea of Tanahmerah. The result of these measurements is shown in Fig. 5. The verticalsection below shows the distribution of the specific electric resistivities in the under-ground at the individual measuring stations in 8-fold exaggeration. The section on topof it reflects (in 4-fold exaggeration) the geological concept as it is achieved by corre-lating the electrical resistivities to the geology of the underground. Rock layers to be

• tpec. rttisnviif of tht H

Tanahmtroh-Fanohmeroh ^ s V n c l i n e

isggerated bu 6)

~ 5

•O-2O

impermeable bed

, clayey-loamy çove^ ^ ™ 4 partly Ttrra rossa

— -~ _A marijtonf, cléytto

r,ng teas,Sim

-Ti ma/islone, tmnOy marl.~.'!1 marly limestone

Siryj

aquifer

i l h j limestone

T—^—| limestone

ZISE2^ g owe/- //m«

. lirvesandstone

stone

10 {with .nd.C»Von Of

rock rtysiivttits)

Fig. 5 — Geoelectrical investigation near Tanahmerah. The section below shows thedistribution of the spec, electrical resistivities calculated from the sounding graphs;the section on top of it reflects the geological and hydrogeological conceptachieved by correlating the electrical resistivities to the underground structure.

(*) A description of this method is given in f13), (u), (15) sec bibliography.

549

considered as aquifers (resistivities > lOOßm) will be encountered in view of thissituation, apart from the local area of Tanahmerah (sandy limestone) only at thenorthern and southern end of the profile.

Of hydrogeological interest are, in the first place, the rocklaycrs with resistivitiesaround 200 Q m, which were determined at the soundings 13, 12, 11 and 6. Quiteobviously they offer an aquifer with good preconditions for water recovery by meansof wells. Further to the North, however, a decrease of permeability is to be expected.In Bandjar, where also layers with resistivities of 150 to 200 Q m were encountered, adevelopment of water in larger quantities from these layers seems questionable (becauseof the high position of the terrain and the restricted chances for regeneration). Thebeds thereunder with 30 to 50 Q m, which doubtless posses a clayey/marly componentstrongly diminishing permeability, can be considered for water extraction to a limitedextent at the utmost.

The terrain with the thick marly beds south of Tanahmerah is decidedly to beexcluded from any waterprospecting plans. Only the limestones superposing the marlsat the southern end of the section represent an aquifer; but in view,of the total hydro-geological situation, groundwater drillings can only be effected in the South of themeasured profile, near about point 9.

6.4. The limestone region in the North from Bulukagung till Djurangan and from thereto the South till Sumenep

The area under regard predominantly consists of the calcareous Kalibeng layerswith intercalations of sandy lime- and marl-stones. The Kalibeng layers stretch fromthe coast into the inner part of the isle in a width of 5-10 km. Towards the coast theygenerally dip with about 5° to 25° (in the region of the Java Sea northwards, in theregion of the Strait of Madura southwards). This rock sequence is underlain by aninterbedding of clay and lime-stone (Uppar Orbitoid layers), which crop out in the"marly region in the center of the isle".

Here and there, the limestone layers reach the coast ending locally in steep banks(Fig. 6).

Fig. 6 — Waterfall at the steep bank of the Java Sea with calcareous sinter (approx.3 km E of Ketapang). Yield in August 1961 about 20 1/s.

In parts far ofT the coast there is developed a shallow karst. Towards the coast,where the limestones submerge below level of the sea, there begins the deep karst.

550

In the valleys frequently occur springs with locally remarkable yields (Sec Hydro-geological Map 1 : 250,000).

It seems possible — in particular in a range between 300 m and 3 km off thecoast — to open moderate water quantities by drillings. The course of the freshwater/salt-water limit, which in this area often runs very near the coast, is to be taken intoaccount. Its position is locally influenced by seawater penetrating the riverbeds duringthe tides.

A detail investigation near Sokabana is intended to clarify the hydrogeologicalsituation at the northern coast. Preliminary geoelectrical depth soundings accordingto the four-point method substantially contributed mainly towards an elucidationof the distribution of fresh/briny groundwater. The result of geoelectrical prospectingis illustrated in figure 7 in two vertical sections normal to the coast. Outgoing from

Profile 1

I ? - J I KlSlrr

\h-it*lt water Surface of•nterfac» "W"'/ * * " *

region 1

T geoelectrical soundingISO (with indication of

v»cHrc electricalrock rtsufrvtt.es)

r*bst,vttyof the wa'f

well (with groundwatmr table)

Fig. 7 — Vertical sections near Sokabana at the northern coast, based on geoelec-trical investigations.

the sea, the saltwater penetrates towards inland the limestone beds dipping north.This salt-water intrusion is superposed by fresh water. Naturally the differences in thespecific electric resistivity are particularly significant in this region. This fact can betaken from Fig. 8 which shows the geoelectrical sounding garphs as they are plottedin the customary way in log-log scale (so-called "apparent" resistivity oo as a functionof half the electrode distance L/2).

551

5000:

Fig. 8 — Geoelectrical sounding graphs, recovered near Sokabana (so-called "appa-rent" restivity o a (L/2) platted in log-log-scale).

6.5. The marly region in the center of the isle

This groundwater province extends from the region of Geger in the West east-wards in an N-S width of approximately 17 km. Near Pegantenan it branches into anorthern and a southern part; both branches are divided by the Pajudan-Plateau.

Perennial rivers do not exist in this area.The region is built up by Rembang layers of a clayey consistence especially in

their deeper parts. The '"base marls" were so far encountered only between Geger andTambelangan. The remaining part is occupies by the Lower and Upper Orbitoidlayers. They occur locally in a calcareous faciès.

The tectonics of this region is characterised by a complicated fold system.Springs occur only very isolated in this region: their yield is small and there arc

only few perennial springs.The chances for groundwater recovery in the distribution area of the base marls

and the Lower Orbitoid layers arc generally to be considered as very small, in thedistribution area of the Upper Orbitoid layers as only a little more favourable.

6.6. The lowlands of Baliga

The region is gradually dewatercd by the Kali Baliga, a small part in the East bythe Kali Kemuning.

The lowlands of Baliga are composed of holocene and thereunder of pleistoceneclays and marls (Kabuh- and Putjangan layers). The latter are underlain by the plio-

S

strongly clayey sedimentspartly salty

75 geoelectrical soundingI (with indication of

specific electricelrock resistivities)

Ikn

Fig. 9 — Vertical section £ of Baliga, based on geoelectrical investigations. Themeasured profile is situated N of the road Baliga-Tordjun. The section shows thestrata dipping southward. Layers with higher spec, electrical resistivities may beconsidered as aquifers.

553

cene, mainly calcareous Kalibeng layers, which crop out at the margin of the basin,but lie relatively deep in its center.

The fact that the saltwater/freshwater interface lies relatively far away from thecoast is due — apart from other natural phenomena — to the farreaching tide effectsof the Kali Baliga and the Kali Bahtatah and to salt pans.

In the limestone layers north of the road Baliga-Tordjun, which here dip towardsS, moderate groundwater quantities may be recoverable provided appropriate drillingpoints are selected (Fig. 9). In some places there occur partly relatively strong springs.

6.7. The limestone region in the South between Saronggi and Pamekasun and Tordjun)Sampang

This area is predominantly built up by pliocene limestone layers, with interbeddingof claystone. In general, the layers slightly incidc towards S and plunge below sealevel at the coast. In the northern part of this area there exists a shallow-formed trough,and in the South a little-developed saddle striking generally E-W.

In the East and in the West of the lowlands of Pamekasan and Baliga the limestonelayers plunge below quaternary sediments.

In the valleys there are locally relatively strong springs especially near the coast.It seems to be possible in these regions near the coast, which are developed as

deep karst, to gain moderate to large quantities of groundwater from boreholes.

6.8. The lowlands of Pamekasan

The lowlands of Pamekasan are embedded in the limestone region describedbefore. They are crossed by the numerous delta-arms of the Kali Bunder. Locally thelow lands rise up to + 10 m s.l.

The geological structure logically corresponds to that of the basin of Baliga;that means: the lowlands are filled with quaternary mostly clayey sediments whichare underlain by predominantly limy rocks in relatively large depth. These limy rocksare cropping out at the margins of the basins in the North and in the West. Here anumber of relatively strong springs exist, which are partly utilized for the water supplyof Pamekasan.

Possibilities for the opening of water are primarily given where — in the borderregions of the lowlands — these limestones have changed from shallow karst intodeep karst. In the basin itself, the possibilities — in particular in the East where thesaltwater/freshwater interface lies very far inland — are to be regarded as unfavourable.

6.9. The limestone through of Gulukgulitk (Pajudan-Plateau)

This district blessed with great fertility, is embedded in the central marly regionof the isle. The Pajudan-Plateau extends E-W in a width of approx. 5 km. In the East,this area changes over into the lowlands of Saronggi-Sumenep.

The Kali-Sumber-Padjung flows through the Pajudan-Plateau from WtoE, furthereast, this river is named Kali Soksok. Even in the dry season, the Kali Sumber Padjungstill carries a good amount of water; at the end of August 1961, for instance, approx.100 1/s near Gulukguluk.

In the E-W striking basin limestone layers (Kalibeng layers) are forming the sur-face and, because of their thickness, are building up the basin as well as adjacent moun-

, tains. These limestone strata are underlain by a sequence of clay- and marlstonc layerswith interbeddings of limestone (Upper Orbitoid layers). The preserved thickness ofthe limestone (above the underlying claystone) differs locally very much in the Pajudanvalley within the region of Gulukguluk.

554

In the limestone layers a groundwater body is developed the substratum of whichis formed by the underlying clay- and marlstones. It may be taken for granted that thegroundwater table lies relatively shallow in the lower part of the basin and is adjustedto the level of the Kali Sumber Padjung. As represented on the HydrogeologicalMap 1 : 250,000, good prospects for water opening are given in the lower part of thelimestone trough. At the morphologically elevated margins of the basin, the watertable lies in larger depths; the waterquantities to be raised there are small.

A greater number of partly relatively strong perennial springs (strata springsand valley springs) egress directly in the basin, whereas at the margins, springs (depres-sion springs) of smaller output are evident. Most of the latter exhaust during the dryseason.

6.10. The lowlands of Saronggi-Sumenep

These lowlands represent morphologically as well as geologically the easterncontinuation of the elevated trough region of Gulukguluk.

They are built up by holocene and pleistocene, preponderatcly clayey rocks,which — in relatively great depth — are underlain by the Kalibeng layers. These arechiefly developed as limestones and crop out at the northern and southern margin ofthe basin.

As water-prospective can be regarded first of all the marginal zone of the basin,where the limestones are plunging below the clays and marls. Here a greater numberof relatively very strong springs emerge. It seems to be possible to raise greater quanti-ties of water by drillings in these marginal areas and in the limestones in the deeperunderground west of the saltwater/freshwater interface

The groundwater directly in the basin is of high grade salinity up to W of theroad Saronggi-Sumenep. The natural and artificial (salt pans) causes for this fact arethe same as in the basin of Baliga. West of this area with briny groundwater, onlysmall quantities of water are to be raised in the clays and marls of the lowlands.

A comprehensive prospection performed near Saronggi at the southern borderof the lowland o[ the Kali Saroka yielded results which are characteristic for tropickarst regions. For this reason they are briefly described here.

The vertical section shown in figure 11 results from the hydrogeological inventorysurvey. Geoelectrical measurements produced a detailed picture of the transitionalzones freshwater/saltwater near Saronggi (Figs. 10 and 12). According to this thehydrogeological situation can be outlined as follows:

The main hydrostatic base level for the region under regard is the Kali Sarokowhich, flowing from the region of Gulukguluk, discharges its water into the Strait ofMadura, about 5 km E of Saronggi.

The dry-weather runoff of the Kali Saroko amounts to about 2,500 1/s.Among the rocks the limestones in particular are generally well fissured and

karsted and therefore permeable for water, whereas the argillaceous rocks are unessen-tially to little fissured and have consequently a minor permeability.

Regions with bare cropping out let expect a very great coefficient of infiltration.Coverings of terra rossa, again, make it decrease.

The percolated precipitation feeds a karstic water body which intersperses theKalibeng layers. The groundwater's direction of flow is here from SSW to NNE. Thepressure gradient is unknown, but it is assumed to be about 4-7 m per km. There is ahydraulic connection between this groundwater and that present in the quaternaryloose sediments of the Saroko plain (pore water); seen in a large scale one can practi-cally speak of one groundwatcr-body which changes over from the heights S of Saronggito the low ground adjoining in NNE.

According to the geological structure and the given terrain- and hydraulic baselevel conditions we have to deal here with a pressure gradient from the crevice water

555

geoclsctiiCHl soun.itng

I ^.g ) rock sample (r. s ) 150-75,,,

I more than 75 m

Fig. 10 — Exploration area Saronggi.

SSWm

+200 r- Se\a\

NNESoronggi VvSavoVo Sumenep V>.?Q\ear\

c/ay nr///? sa/7oy intercalations (Quaternary)

limestone (Pliocene)

marly limestone (Miocene)

^ fresh-/salt water interface

—s- sea water table

.. .T.. groundwater table

o spring

kkm

Fig. 11 — Schcmatical hydrogeological profile across the basin of Saronggi-Sumenep.

table in the solid rocks to the pore water table in the loose sediments. The groundwaterlevel is generally adjusted to the Kali Saroko as hydrostatic base level.

In this section of the river plain of the Kali Saroko, the saltwater is submergingbelow the freshwater, and the saltwater/freshwater interface dips from the Sarokoplain in SSW direction.

SSW•so

I »

-too

NNE

•so

0

-50

-100

Qm

2- 6 F^T:

high grade

rich claysor strongly

sally sediments

10- X

20- 35

40- 60

IX-160

h z : -_J clayey-marly sediments (with + saltwater)

r-=^ -] weathered overburden (clayey-marly): ~ ^ H or limestone with salt water

ijJ=7J c'*yey-marly

geoclectrical sounding(with indication ofspecific electricalrock resistivities)

Fig. 12 — Vertical sections near Saronggi, bassd on g;o;le;trical investigations.

In the boundary between salt- and freshwater it comes to the issue of springs.(.Fig. 13; yield of this spring in dry season about 100 1/s). The freshwater not comingto the surface in springs possibly flows off into the plain in a relatively shallow layeron top of the saltwater, until it finally enters the Kali Saroko.

Proposals for water development :

Water may be developed by capturing the springs near Saronggi, constructing areservoir basin near Lenteng and establishing a well gallery NE of the main roadPanggulan-Saronggi-Djuluk, but W of the saltwater/freshwater limit. The depths ofthe wells should be estimated to about 50-70 m.

558

Fig. 13 — Spring Kermata near Saronggi.

7. G ROUND WATER CHEMISM

The hydrogeological reconnaissance survey was accompanied by a chemicalfield laboratory. This facility rendered possible to analyse water samples in situ andto get a general view over the chemical quality of numerous kinds of waters.

The groundwater to be found in calcareous and marly rocklayers generally meetsthe requirements to be placed to drinking water. Water from calcareous beds showan average p// value of 7.0, choride contents (Cl ') between 5 and 35 mg/1, and totalhardnesses between 8° d.H. and 18° d.H. Those from marlstone beds show, underequal chemical conditions, total hardnesses between 4" d.H. and 12° d.H., whereaswaters from terra rossa beds only exclusively have hardnesses exceeding 5°.

Near the coast the groundwater is usually brackish; it gradually changes over tohighly saliferous water when approaching the sea.

8. CONCLUSION

The preceding parts of this treatise comprize a description of the outlines of hydro-geological conditions of a tropic island. It was proved that it is possible, by applyingappropriate working methods, to give a general view over the possibilities for waterrecovery in such an isle, in a relatively short time. It also was found practical to com-prehend the results obtained in a hydrogeological map. This map gives indicationsrespecting starting points for further investigations and constitutes, additionally, avaluable basis for economic development.

BIBLIOGRAPHY

f1) BEHRMANN, W. : Die Oberflächenformen in den feuchtwarmen Tropen.—Z. GesErdkd. Berlin, S. 44-60, Berlin 1921.

(2) BEMMELEN, R.W. VAN : The geology of Indonesia. — Vol. 1A : General geologyof Indonesia and adjacent archipelagos. Vol. IB : General geology : portfolio.Literature references. The Hague (Gov. Print. Off.) 1949.

559

(3) BEMMELEN, R.W. VAN : The geology of Indonesia. — Vol. 2 : Economic geology,265 S., The Hague (NijhofT) 1949.

(4) BOEREMA, J : Regenval in Nederlandsch-Indie. D. 1 : Gcmiddelden van den regenval... 1879-1922. D.2 : Kaarten. — Verhandelingen Kon. Magn. en Meteor. Observa-torium te Batavia, 14, Weltevreden 1925.

(5) BRAAK, C. : Klimakunde von Hinterindien und Insulinde. — Handbuch Klimatol.,4, T.R., 125 S., 29 Kt., 2 Diagr., Berlin 1931.

(°) BROUWER, H.A. : Geologische Overzichtskaart van den Nederlansch-Oost-Indischen Archipel. (Schaal 1:1.000.000). Toelichting bij blad XVII (Oost-Java,Madoera, Bali, Lombok, Soembawa). — Jaarb. Mijnwezen Nederl.-Oost-Indie,44 (1915), Verh. ged. 2, Batavia 1917.

(7) DUYFJES, J. : Zur Geologie und Stratigraphie des KendenggcbieteszwischenTrinilund Soerabaja (Java). — De Ingenieur in Nederl.-lndie, 3, Abt. 4, S. 136-149,Bandoeng 1936.

(R) DUYFJES, J. : Geologische kaart van Java, schaal 1:100.000. Toelichting bij blad109 (Lamongan). — Batavia (Dienst van de Mijnbouw in Nedcrlandsch-Indic)

1938.(9) GERTH, H. : Der geologische Bau Javas. — Geol. Rdsch., 22, S. 188-200, Berlin

1931.(10) HAAN, J .H. DE : Boschhydrologischc Problemen en onderzoekingen op Java. —

Bo.se/ibouwkundig Tijdschrift Tectona, 26, S. 932-988, Buitenzorg 1933.( n ) KUENEN, Ph. H. : Geology of coral reefs.—The Snellius — Expedition in the

eastern part of the Netherlands East-Indies 1929-1930, 5, p. 2., 125 S., 11 Taf.,Utrecht 1933.

(12) VERBEEK, R.D. M. & FENNEMA, R. : Description géologique de Java et Madoura.— T.I.2., Amsterdam (Stemler) 1896.

(13) BENTZ, A. : Lehrbuch der Angewandten Geologie I. — p. 718 ff., Stuttgart (Enke)1961.

(14) LASFARGNES, P. : Prospection électrique par convants continnes. — Paris 1957.(15) PARASNIS, D.S. : Principles of Applied Geophysics. — London 1962.

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