SUBMARINE GROUNDWATER DISCHARGE (SGD) IN INDONESIA

ABSTRAK Mengikuti kontrol gayaMengikuti kontrol gaya gravitasi, airtanah akan mengalir menuju titik terendah dan pada beberapa lokasi akan mengalami kontak dengan air laut pada akhir sistem luaran aliran. Pada penelitian terdahulu, bentuk kontak ini telah seringkali dibahas berdasarkan hukum Ghyben-Herzberg. Mengikuti hukum fisika, airtanah dapat keluar di tepi pantai, lepas pantai atau didasar laut. Keluaran inilah yang secara terminologi dapat disebut sebagai keluaran airtanah di lepas pantai (SGD). Dari analisis keluaran airtanah di lepas pantai ini, terlihat bahwa keluaran ini memiliki beberapa bentuk seperti rembesan dekat pantai, rembesan aliran airtanah dan mataair lepas pantai. Keluaran inipun merupakan jalur penghubung yang penting antara interaksi airtanah dan air laut. Pemahaman keluaran airtanah di lepas pantai ini akan sangat membantu untuk permasalahan potensi pencemaran pantai, sumber nutrisi untuk wilayah lepas pantai dan alternatif kebutuhan akan air bersih. Makalah ini membahas tentang bukti ilmiah keberadaan keluaran airtanah di lepas pantai Indonesia. Hasil penelitian menunjukkan bahwa proses keluaran airtanah dilepas pantai tersebar di berbagai wilayah pesisir Indonesia. Penilaian karakteristik dan besarannya di masing-masing lokasi memerlukan berbagai teknik yang berbeda tergantung pada kondisi geologi dan hidrogeologi keluaran tersebut. Pengamatan secara detail telah dilakukan di 6 lokasi, dimana penelitian ini adalah pertama kalinya dilakukan di Indonesia

PERUBAHAN IKLIM DAN PEMANASAN GLOBAL DI INDONESIA; DAMPAKNYA TERHADAP KONDISI BAWAH PERMUKAAN Studi Kasus : DKI JAKARTA

Indonesia is exposed to climate change, especially with regard to the rising sea level, changes in precipitation and extreme events. This will particularly impact to many sectors in this country. In order to evaluate the impact on subsurface environment, groundwater temperatures in boreholes can be an important source of information on recent climatic changes. Subsurface temperatures in Jakarta city were analyzed to evaluate the effects. As a result the magnitude of surface warming was increase 1.4°C which agreed with the increase of air temperature meteorological data during the last 100 years. This is the preliminary results of significant increase in climate change during the last century in Jakarta. Still today, the information on vulnerability and adaptive measures is not sufficient in order to plan and design appropriate activities on the national level in Indonesia

PENENTUAN LOKASI IMBUHAN AIRTANAH DENGAN PELACAK ISOTOP STABIL 18O DAN 2H DI CEKUNGAN AIRTANAH DATARAN RENDAH SEMARANG, JAWA TENGAH

ABSTRAK Pengambilan airtanah di dataran rendah Semarang yang tidak terkendali menimbulkan dampak krisis airtanah yang ditandai dengan penurunan muka airtanah dari tahun ke tahun. Ketersediaan airtanah berkaitan erat dengan jumlah imbuhan (recharge) air ke dalam tanah dan jumlah yang diambil. Penentuan daerah imbuhan dilakukan dengan cara melakukan analisis isotop stabil 18O dan  2H dan membandingkannya dengan tipe air serta kondisi hidrologelogi. Untuk keperluan tersebut, telah dilakukan penelitian airtanah di 9 lokasi yang tersebar di wilayah Semarang, yang terdiri atas 7 conto airtanah tertekan dan 2 contoh airtanah tidak tertekan. Hasil yang didapat dari analisis tersebut adalah bahwa airtanah pada akifer yang berumur kuarter berasal dari air yang diresapkan ke dalam tanah di dalam cekungan tersebut, sementara air yang terdapat dalam akifer Formasi Damar berasal dari daerah di ketinggian di atas 400 m dpl yang terletak di selatan Semarang. Di samping itu sesar yang memisahkan sistem akuifer Formasi Damar dengan sistem akuifer kuarter berfungsi sebagai penghalang masuknya airtanah dari bagian selatan ke akuifer kuarter di dataran Semarang

Imbuhan Airtanah Buatan untuk Konservasi Cekungan Airtanah Bandung-Soreang

Airtanah saat ini telah menjadi isu di dunia dan Indonesia akibat terjadinya degradasi airtanah. Tingginya pertumbuhan penduduk dan industri di wilayah kota telah meningkatkan eksploitasi airtanah, sementara laju pengisian airtanah (infiltrasi) terus menurun. Penurunan laju infiltrasi diakibatkan oleh adanya perubahan tutupan lahan. Berdasarkan permasalahan ini maka konservasi airtanah harus dilakukan untuk menjaga ketahanan air. Cekungan Bandung-Soreang sebagai wilayah perkotaan telah mengalami penurunan muka airtanah sebagai akibat adanya pengambilan airtanah yang berlebih. Tulisan ini adalah telaah dari berbagai metode teknis yang telah diterapkan untuk mengatasi masalah tersebut di atas khususnya metode imbuhan buatan untuk konservasi airtanah di Cekungan Bandung. Berbagai teknik telah diterapkan baik oleh masyarakat, industri maupun pemerintah dengan sumber utama adalah air hujan. Namun penurunan muka airtanah masih terus terjadi meskipun upaya-upaya tersebut telah dilakukan. Hasil penelitian terakhir menunjukkan bahwa metode imbuhan buatan hanya mampu mengurangi penurunan muka airtanah. Jika hasil yang diharapkan adalah kembalinya muka airtanah ke kondisi awal maka diperlukan pengembangan metode dan atau penambahan jumlah imbuhan buatan yang sangat banyak. Groundwater becomes an issue globally due to groundwater degradation. The high population and industry growth in the cities had increased the exploitation of groundwater. On the other hand, the rate of infiltration is lower due to city development. Therefore, groundwater conservation is required to maintain water resistance. The Bandung-Soreang Basin, as an urban area, has experienced a decline in groundwater as a result of excessive groundwater extraction. This paper presented a review of various technical methods that have been applied to overcome the problem. Artificial recharge method for groundwater conservation in the Bandung-Soreang Basin has been used by the community, industry, and government, with rainwater as the main source. The most recent condition indicated that the groundwater level has been still decreasing despite these efforts. The results of the latest research suggested that artificial recharge has only  reduced the groundwater depletion. To restore the groundwater to its initial condition, we need to develop a new method or simply add a lot more artificial recharges

Lineament Extraction using Gravity Data in the Citarum Watershed

Lineament is one of the most important features showing subsurface elements or structural weakness such as faults. This study aims to identify subsurface lineament patterns using automatic lineament in Citarum watershed with gravity data. Satellite gravity data were used to generate a sub-surface lineament. Satellite gravity data corrected using Bouguer and terrain correction to obtain a complete Bouguer anomaly value. Butterworth filters were used to separate regional and residual anomaly from the complete Bouguer anomaly value. Residual anomaly gravity data used to analyze sub-surface lineament. Lineament generated using Line module in PCI Geomatica to obtain sub-surface lineament from gravity residual value. The orientations of lineaments and fault lines were created by using rose diagrams. The main trends observed in the lineament map could be recognized in these diagrams, showing a strongly major trend in NW-SE, and the subdominant directions were in N-S. Area with a high density of lineament located at the Southern part of the study area. High-density lineament might be correlated with fractured volcanic rock upstream of the Citarum watershed, meanwhile, low-density lineament is associated with low-density sediment. The high-density fracture might be associated with intensive tectonics and volcanism

GROUNDWATER CHARACTERISTICS IN JAKARTA AREA, INDONESIA

ABSTRACT In the Jakarta area (Indonesia), excessive groundwater pumping due to the rapidly increasing population has caused groundwater-related problems such as brackish water contamination in coastal areas and land subsidence. In this study, we adopted multiple hydrogeochemical techniques to understand groundwater characteristic in the Jakarta area. Although almost all groundwater existing in the Jakarta basin is recharged at similar elevations, the water quality and apparent residence time demonstrates a clear difference between the shallow and deep aquifers. Due to the rapid decrease in the groundwater potential in urban areas, we found that the seawater intrusion in shallow aquifer and the shallow and deep groundwaters are mixing, a conclusion confirmed by major ions, Br−:Cl− ratios and chlorofluorocarbon (CFC)-12 analysis

PODRIJETLO I KVALITETA PODZEMNIH VODA BAZENA RAWADANAU, SERANG BANTEN, INDONEZIJA

Rawadanau is a tropical mountain swamp located in Serang, Banten, Indonesia. Rawadanau groundwater is the main source of supply for the Cilegon Banten industrial area. Knowing the origin and quality of the groundwater can help preserve existing resources. This paper aims to clarify the origin of Rawadanau groundwater with new evidence of stable isotopes (18O and 2H) and hydrochemical data. Field measurements included pH, temperature, EC, HCO3ˉ, while the analyses of cations, anions and stable isotopes were carried out in the laboratory. The existing water supplies include springs, excavated wells, and river water. Cluster hierarchy analysis based on water chemistry and stable isotopes can be grouped into two clusters, cluster K (K1 and K2) and cluster L. Data δ18O and δ2H springs in Rawadanau indicate that they are of meteoric origin and that there has been evaporation from several springs. Water comes from meteoric water with a stable isotope content of δ18O between -6.39 to -4.82 ‰ and δ2H between -41.35 to -31.30 ‰, which are controlled by two main mechanisms, namely rock dissolution and evaporation dominance. Aquifers are composed of volcanic rocks with a dominant composition of porphyritic andesite, basaltic andesite, and andesite. According to the multivariate statistical analyses results other than pH and SO4 2-, all parameters (cations and anions) showed a significant correlation. There are four hydrochemical facies of groundwater, namely Ca-HCO3, Ca-Mg-HCO3, Mg-Ca-HCO3, and Na-Cl.Rawadanau je područje tropske, planinske močvare u Serangu (Banten), Indonezija. Tamošnje podzemne vode glavni su izvor opskrbe industrijskoga područja Cilegon, Banten. Poznavanje njihova podrijetla i kvalitete može pomoći u očuvanju toga resursa. Cilj je ovoga rada objasniti podrijetlo tih voda s novim podatcima o stabilnim izotopima (18O i 2H) te hidrokemijskim podatcima. Terenska mjerenja uključila su pH, temperaturu, EC, HCO3ˉ, a analiza kationa, aniona i stabilnih izotopa napravljena je u laboratoriju. Postojeći izvori vode uključuju izvore, bušotine i rijeke. Načinjena je hijerarhijska analiza klastera na temelju kemije vode i stabilnih izotopa. Izdvojena su dva klastera: K (K1 i K2) te L. Podatci δ18O i δ2H iz izvora upućuju na meteorsko podrijetlo vode te na evaporaciju iz nekoliko njih. Meteorska voda sa sadržajem stabilnih izotopa δ18O između –6,39 i –4,82 ‰ te δ2H od –41,35 do –31,30 ‰ određena je dvama procesima, tj. otapanjem stijena i evaporacijom. Vodonosnici su sastavljeni od vulkanskih stijena pretežito od porfiritskoga i bazaltnoga andezita te andezita. Multivarijantna statistička analiza svih varijabli (osim pH i SO4 2-), tj. većine kationa i aniona, pokazala je znatnu korelaciju. Izdvojena su 4 hidrokemijska facijesa podzemne vode, redom: Ca-HCO3, Ca-Mg-HCO3, Mg-Ca-HCO3 i Na-Cl

PEMANFAATAN BAND TERMAL CITRA LANDSAT UNTUK IDENTIFIKASI KELUARAN AIRTANAH LEPAS PANTAI (KALP) DI PANTAI UTARA LOMBOK

This paper examines the use of Landsat 7 and 8 thermal band as an indirect method of identifying submarine groundwater discharge (SGD) in the northern coast of Lombok Island. Image processing steps include atmospheric correction, the acquisition value of the effective temperature, effective temperature anomalies and effective standardised temperature anomalies, as well as image enhancement. Effective standardised temperature anomaly map has more varied pattern than the effective temperature map. But both of them have not been able to demonstrate the extreme temperatures that indicate the location of SGD. Parameter of effective standardised temperature anomaly could not be used as a single variable. SGD identification in tropical area needs more detailed spatial resolution. The acquisition time has also to be considered i.e. when low tidal and for low temperature SGD, when the water temperature is warmer. AbstrakMakalah ini mengkaji penggunaan band termal citra Landsat 7 dan 8 sebagai metode tidak langsung dalam mengidentifikasi kehadiran keluaran airtanah lepas pantai (KALP) di perairanutara Pulau Lombok. Langkah pengolahan citra meliputi koreksi atmosferik, pemerolehan nilai suhu efektif, anomali suhu efektif, dan anomali suhu efektif standar serta penajaman citra. Petaanomali suhu efektif standar memiliki pola yang lebih bervariatif dibandingkan peta suhu efektif. Namun keduanya belum dapat menunjukkan suhu ekstrim yang mengindikasikan lokasi KALP. Parameter anomali suhu efektif standar tidak dapat dipergunakan sebagai variabel tunggal. Identifikasi lokasi KALP di daerah tropis membutuhkan data citra dengan resolusi spasial yang lebih detail. Pemanfaatan data citra juga perlu memperhatikan waktu perekaman citra yaitu pada saat kondisi perairan hangat untuk kasus KALP bersuhu rendah dan pada saat air surut

Basement Characteristics of Jakarta Groundwater Basin Based on Satellite Gravimetry Data

Jakarta groundwater basin is one of the most developed basins in Indonesia as Jakarta city is located within the basin, with an elevation ranging from 0 to 1000 m above sea level. The study of the basement characteristics of groundwater basins still needs further study in the Jakarta Groundwater Basin. The objective of this study is to examine the basement characteristics of Jakarta Groundwater Basin by satellite gravimetry. Gravity forward models were constructed using Oasis Montaj and 2-D GM-SYS software for two north-south sections, A and B, and west-east section C-D. Regional anomalies in the study area with a value range of 36.7 to 53.2 mGal, while the residual anomaly values in the study area were in the range of -7.0 - 10.0 mGal. There are four rock formations based on forwarding modeling. Holocene Beach Ridge Deposit formation has a density of 2.0 gr/cc. The thickness of this formation is estimated to be around 10-20 meters. Late Pleistocene Alluvial fan has a density of about 2.2 gr/cc. The depth of this layer ranges from 10-50 meters. Early Pleistocene Formation, has a density of 2.35 gr/cc. The thickness of this formation is at a depth of 50-200 meters in the cross-section. The Tertiary Marine Sediment Formation is a basement of the Jakarta Groundwater Basin. This formation has a rock density of 2.45 gr/cc.

PENENTUAN INDEKS KERENTANAN AIRTANAH PESISIR JAWA DI WILAYAH SELAT SUNDA DENGAN MENGGUNAKAN METODE GALDIT

Kerentanan airtanah pesisir merupakan salah satu isu yang sangat penting dalam perkembangan pembangunan saat ini. Antisipasi dan upaya mengurangi dampak negatif kualitas airtanah wilayah pesisir akibat faktor antropogenik dan perubahan iklim, memerlukan upaya penentuan indikasi daerah yang memiliki kerentanan tinggi. Upaya pembobotan diperlukan berdasarkan faktor-faktor yang paling penting dalam memahami kerentanan airtanah wilayah pesisir. Metode GALDIT merupakan salahsatu sistem peringkat numerik untuk menilainya. Tiga komponen penting dari sistem ini adalah kriteria bobot, rentang data dan peringkatnya. Fokus dari penelitian ini adalah pada penerapan dan metode GALDIT untuk mengakses kerentanan airtanah pesisir di wilayah Pulau Jawa sepanjang Selat Sunda. Kesimpulannya, metode ini perlu diintegrasikan dengan faktor kerentanan lokal dan dibandingkan dengan metode lainnya agar dapat diaplikasikan dengan lebih akurat.Groundwater coastal vulnerability is one of the most important issues in the human development today. Anticipation to mitigate negative impacts of groundwater coastal quality due to climate change impacts and anthropogenic activities, required to indicate the zonation with high vulnerability index. The GALDIT method is a one of numerical rating system for assessing the susceptibility of groundwater coastal vulnerability. Three important parts of this system were weighting criteria, range of data and ratings. The focus of this research is to applied GALDIT method to access groundwater coastal vulnerability in Jawa Island along the Sunda Strait. In conclusion, this method needs to be integrated with local vulnerability factors and compared with other methods to be applied more accurately