PENGARUH PENGGUNAAN LAHAN TERHADAP FUNGSI KONSERVASI AIR TANAH DI SUB DAS CIKAPUNDUNG

Cikapundung sub-watershed is a potential area that serves as the main drainage and supply of residents water need in Bandung. Increased developed land in this region resulted in the conversion of land that extends the number of impermeable surface, that reduces infiltration, decreasing supply and rising groundwater runoff. To determine the effect of landuse on the function of the groundwater conservation, conservation index analysis was conducted. The method is to give weight to the parameters of rock types, soil types, morphology, rainfall and landuse. Each parameter has a value of its effect on the ability to absorb rain water. From the analysis, it is known that changes in landuse during the period 2001 - 2008 has lowered the overall conservation function at Cikapundung sub watershed. Conservation value of the function started to decline as shown by the reduction of good conservation area of 5080,5 h. However, this condition was also followed by the increase of the normal conservation classes of 5093,3 ha and critical conservation area of 12,9 ha. ABSTRAKSub DAS Cikapundung merupakan kawasan potensial yang berfungsi sebagai drainase utama dan penyedia air baku untuk kebutuhan penduduk di Kota Bandung. Peningkatan lahan terbangun di wilayah ini mengakibatkan banyaknya konversi lahan yang memperluas permukaan kedap air yang menyebabkan berkurangnya infiltrasi, menurunnya pasokan airtanah dan meningkatnya limpasan permukaan. Untuk mengetahui pengaruh penggunaan lahan terhadap fungsi konservasi airtanah maka dilakukan analisis indeks konservasi. Metode yang dilakukan adalah memberikan bobot pada parameter jenis batuan, jenis tanah, morfologi, curah hujan dan penggunaan lahan yang masing-masing telah di nilai sesuai pengaruhnya pada kemampuan untuk menyerap air hujan. Dari analisis tersebut diketahui bahwa perubahan penggunaan lahan pada kurun waktu 2001 - 2008 telah menurunkan fungsi konservasi secara keseluruhan pada Sub DAS Cikapundung. Nilai fungsi konservasi mulai menurun ditunjukkan oleh pengurangan kelas yang bernilai konservasi baik seluas 5080,5 ha. Namun kondisi ini juga diikuti dengan kenaikan kelas konservasi normal seluas 5093,3 ha dan penurunan kelas konservasi kritis seluas 12,9 ha

KESESUAIAN LAHAN UNTUK KOMODITAS TEH DI WILAYAH SAGALAHERANG, SUBANG, JAWA BARAT

ABSTRAK Penurunan produksi komoditas teh di wilayah Sagalaherang, Kabupaten Subang, telah terjadi sejak tahun 2007. Penurunan produksi ini disebabkan oleh semakin berkurangnya ketersediaan lahan untuk budidaya teh akibat konversi lahan perkebunan menjadi pemukiman, diversifikasi komoditas menjadi kelapa sawit. Ketersediaan dan kualitas lahan merupakan salah aspek penting dalam pengembangan komoditas teh guna meningkatkan produksi teh di masa datang. Oleh karena itu diperlukan studi untuk menilai kondisi lahan sebagai bahan pertimbangan dalam penilaian kesesuaian lahan untuk komoditas teh di wilayah Sagalaherang. Kegiatan studi dimulai dengan penyusunan peta dasar, yaitu berupa peta-peta tanah, geomorfologi, topografi, dan geologi pada skala 1 : 100.000. Survei tanah dilakukan dengan pengambilan contoh tanah untuk analisa sifat kimia dan fisika tanah di laboratorium. Analisis kesesuaian lahan dilakukan dengan cara mencocokkan antara persyaratan tumbuh tanaman dengan karakteristik lahan dengan teknik tumpang tindih (overlay). Hasil studi didapatkan bahwa di wilayah studi memiliki 4 ordo tanah, yaitu Inceptisols, Andisols, Ultisols dan Entisols dengan 8 sub grup. Nilai kelas kesesuaian lahan untuk komoditas teh diperoleh kelas S1 dengan luas 6,44 km2, kelas S2 dengan faktor pembatas lereng seluas 45,94 km2, kelas S3 dengan faktor pembatas lereng dan ketersediaan air seluas 38,50 km2 dan kelas N dengan faktor pembatas ketersediaan air dan nutrisi, kondisi drainase dan lereng seluas 32,98 km2. Berdasarkan penilaian kondisi lingkungannya, wilayah Sagalaherang secara umum memiliki kondisi lahan yang sesuai untuk komoditas teh. Oleh karena itu kegiatan alih fungsi atau konversi lahan baik berubah ke lahan pemukiman maupun beralih komoditas ke sawit perlu dibatasi, sehingga produksi teh dapat kembali meningkat dan menjadi komoditas utama di wilayah Sagalaherang

PENCEMARAN LIMBAH DOMESTIK DAN PERTANIAN TERHADAP AIRTANAH BEBAS DI KABUPATEN BANDUNG

Airtanah bebas merupakan salah satu sumber air bersih bagi penduduk di Kabupaten Bandung bagian selatan. Pemanfaatannya dilakukan dengan cara membuat sumur gali maupun sumur pantek. Lokasi sumur-sumur tersebut berdekatan dengan sumber pencemar domestik dan pertanian sehingga rentan terkontaminasi. Pencemar yang dapat timbul pada air sumur akibat limbah domestik adalah solid, ammonium, dan bakteri coliform. Sementara, pencemar nitrat umumnya bersumber dari kegiatan pertanian. Untuk mengetahui pencemaran airtanah di lokasi penelitian, dilakukan analisis kimia air dan kandungan bakteri coliform, pada 21 conto air dari sumur gali di Kabupaten Bandung bagian selatan. Pemilihan lokasi berdasarkan pada hasil pemantauan kepadatan pemukiman menggunakan citra satelit pada aplikasi Google Earth, kemudian selanjutnya disesuaikan dengan kondisi lapangan di wilayah penelitian. Hasil analisis menunjukkan telah terjadinya pencemaran solid, nitrat, ammonium, dan coliform di beberapa titik. Hasil pemantauan lapangan memperkirakan nitrat berasal dari kegiatan pertanian, sedangkan solid, ammonium, dan coliform berasal dari limbah domestik. Pergerakan pencemar sampai ke airtanah ini didukung oleh pola aliran airtanah di lokasi tersebut.Unconfined groundwater is the source of clean water to residents in the southern part of Bandung Regency. The need of water is fulfilled through shallow drilling of wells and panteks. The locations of the wells are close to domestic and agricultural pollution sources, so they are vulnerable to get contaminated. Pollutants that may arise in wells water due to domestic waste are solid, ammonium, and coliform bacteria. While, nitrate are generally derived from agricultural activities. To determine the contamination of groundwater at the study area, chemical analysis and coliform bacteria were conducted from 21 wells in southern part of Bandung Regency. The dug well locations were chosen based on the results of monitoring the residential density based on satellite images from the Google Earth application and adjusted to the field conditions in area of research. The result of analysis showed that contamination of solid, nitrate, ammonium, and coliform had occurred at some points. Result of field monitoring estimated that nitrate had derived from agricultural activities, while solid, ammonium, and coliform came from domestic waste. The movement of contaminants to groundwater was supported by the groundwaterflow pattern at the location

PROCJENA PODLOŽNOSTI NA KLIZIŠTA INICIRANA POTRESOM: POTRES OD 7,5 MW U 2018. GODINI U PALUU, SULAWESI, INDONEZIJA

A catastrophic Palu earthquake on September 28th, 2018 with Mw 7.5 triggered countless slope failures, generating numerous landslides. This paper presents a practical method for susceptibility assessment of earthquake-induced landslides in the Palu region and the surrounding area. The statistical weight of evidence (WoE) model was used to assess the relationship between landslides induced by seismic motion and its causative factors to determine the susceptibility level and derive an earthquake-induced landslide susceptibility map of this study area. The 1273 landslides were classified into two data series, training data for modelling (70%) and test data for validation (30%). The six selected thematic maps as landslide causative factors are lithology, land use, peak ground acceleration (PGA), and slope (gradient, aspect, elevation). The selection of causative factors considerably influences the frequency of landslides in the area. The result is satisfactory because the AUC value of the chosen model excelled the minimum limit, which is 0.6 (60%). The estimated success rate of the model is 85.7%, which shows that the relevancy of the model is good with the occurrence of landslides. The prediction rate of 84.6% indicates that the applied model is very good at predicting new landslides.Katastrofalni potres koji se dogodio u Paluu 28. rujna 2018. godine, magnitude 7,5 Mw, izazvao je brojne nestabilnosti na padinama, uključujući nastanak velikoga broja klizišta. Ovaj rad predstavlja praktičnu metodu za definiranje procjene podložnosti na klizišta izazvana potresom u regiji Palu i okolnom području. Metoda Weight of Evidence (WoE) korištena je za procjenu odnosa između klizišta izazvanih seizmičkim kretanjem i preduvjeta kako bi se odredila razina podložnosti i izradila karta podložnosti na klizišta izazvana potresom u istraživanom području. 1273 klizišta podijeljena su u dvije serije podataka: podatci za treniranje modela (70 %) i podatci za validaciju modela (30 %). Korišteno je šest odabranih tematskih karata kao faktora koji utječu na pojavu klizišta: litologija, korištenje zemljišta, vršno ubrzanje tla (PGA), nagib padine, orijentacija padine i nadmorska visina. Odabir uzročnih faktora znatno utječe na učestalost klizišta na tom području. Rezultat modela zadovoljavajući je jer je vrijednost AUC odabranoga modela premašila minimalnu granicu koja iznosi 0,6 (60 %). Procijenjena uspješnost modela iznosi 85,7 %, što pokazuje relevantnost modela kod pojave klizišta. Stopa predviđanja od 84,6 % upućuje na to da je primijenjeni model vrlo dobar u predviđanju novih klizišta

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

HIDROGEOLOGI DAN POTENSI CADANGAN AIRTANAH DI DATARAN RENDAH INDRAMAYU

Potensi airtanah pada suatu cekungan tidak terlepas dari kondisi hidrogeologi di wilayah itu sendiri. Cekungan airtanah Indramayu, yang berada di pesisir utara Jawa Barat, hingga kini belum diketahui secara pasti potensi cadangannya. Penelitian ini bertujuan untuk mengetahui potensi cadangan  air tanah berdasarkan rekonstruksi hidrogeologi data bor. Hasil interpretasi hidrogeologi menunjukkan bahwa litologi akuifer didominasi oleh endapan lempung dengan sisipan lanau, sedikit pasir halus di bagian atas, endapan lempung marin dengan sisipan lanau, dan pasir halus di bagian bawah. Hasil perhitungan menunjukkan prediksi cadangan airtanah yang cukup potensial. Nilai rata – rata potensi airtanah bebas adalah 65.213,8 m3/hari atau 0,754 m3/det. Nilai rata – rata potensi airtanah tertekan adalah 79.557,1 m3/hari atau 0,920 m3/det. Tetapi kualitas airtanah di wilayah Losarang – Lobener – Pasekan – Sindang sebagian besar payau dan memiliki nilai DHL yang tinggi, berkisar antara 4710 – 11400 µs/cm.The groundwater potential of a basin depends on the hydrogeology of the area. Indramayu groundwater basin is located at the north coast of Java Island. Its reserves potential was not identified despite its importance. The objective of this research was to understand the potential of groundwater reserves based on hydrogeological reconstruction from drilling data analysis. The results of the hydrogeology interpretation had indicated that the aquifers lithology are dominated by clay deposits with silt layering, slightly fine sand at the top, marine clay deposits with silt inserts, and fine sand at the bottom. The calculation results had indicated a good potential of groundwater reserves. The mean value of the unconfined groundwater is 65,213.8 m3/day or 0.754 m3/sec. The mean value of the confined groundwater is 79,557.1 m3/day or 0.920 m3/sec. However, groundwater supply potential is not supported by the quality. The groundwater in Losarang - Lobener – Pasekan-Sindang area is brackish and has a high DHL value (4710 – 11400 µs/cm)

THE GREAT SUMATRAN FAULT DEPRESSION AT WEST LAMPUNG DISTRICT, SUMATRA, INDONESIA AS GEOMORPHOSITE FOR GEOHAZARD TOURISM

Two approaches can be taken to understand geotourism, namely the geological approach and the geographical approach. This approach will lead to the creation of new geotourism products, initiatives, and experiences, one of which is geohazard tourism involving faults and earthquakes. To identify geomorphosites, the researchers examined rocks, outcrops, and geomorphology. Then various thematic maps are created using mapping software and other drawing applications to simplify textual material and aid synthesis. A synthesis of all that is then carried out to reconstruct the geological and geomorphological history of the study area. Furthermore, the West Lampung geomorphosite candidate was compared to the worldwide fault and earthquake geomorphosite theme. The Great Sumatran Fault depression landscape can be found in Balak Pekon, Batubrak Regency, and Pekon Padang Dalom, Balik Bukit District, West Lampung Regency. This depression is caused by both endogenous and exogenous factors. The endogenous activity takes the form of sediment from volcanism and fault movement, whereas exogenous activity takes the form of river water erosion. The valley's sediments are ignimbrite tuffs/sandy tuffs that form a cliff morphology with a height of + 75 meters and a trend of Southeast-Northwest. In the case of geotourism, initiatives have grown over time around two complementary approaches (geological and geographic) and the result is a geomorphosite in the geohazard area. One of the areas is the Sumatran Great Fault depression geomorphosite, this area was formed due to the movement of the Sumatran fault which caused the 1908, 1933, and 1994 earthquakes. Situations like these can be used as opportunities to enhance learning about the relationships between people, land use, natural processes, and large-scale events by providing real-life examples, this can be packaged into the form of geohazard tourism

Characteristics of Internal Solitary Waves near Its Generation Site in the Lombok Strait, Indonesia

Evidence of internal solitary waves (ISWs) formation through the Lee wave mechanism in the Lombok Strait was revealed from the echosounder measurements conducted in November 2017. This study is aimed to characterize the property of ISW packet formed around ~30 km away from the generation site, in the southern part of the strait above the Nusa Penida Sill (NPS), by employing Korteweg-de Vries (KdV) solution. The packet can be categorized as the early stage of ISW formation, consisting of two waves of depression, with typical amplitude of 30 m and 10 m, for the first and second wave, respectively. The waves propagated northward with a typical phase speed of ~1.2 m∙s -1. The waves drive a maximum horizontal velocity anomaly of ~0.8 m∙s - 1 and a vertical velocity anomaly of ~10 cm∙s -1. The amplitude of the ISW packet will be potentially amplified during their propagation away from the strait. This study provides an observational based understanding on the early stage of internal tides evolution in the Lombok Strait, particularly highlights the energy transfer of internal tides through the propagation of internal solitary waves

SUSCEPTIBILITY ASSESSMENT OF EARTHQUAKE-INDUCED LANDSLIDES: THE 2018 PALU, SULAWESI MW 7.5 EARTHQUAKE, INDONESIA

A catastrophic Palu earthquake on September 28th, 2018 with Mw 7.5 triggered countless slope failures, generating numerous landslides. This paper presents a practical method for susceptibility assessment of earthquake-induced landslides in the Palu region and the surrounding area. The statistical weight of evidence (WoE) model was used to assess the relationship between landslides induced by seismic motion and its causative factors to determine the susceptibility level and derive an earthquake-induced landslide susceptibility map of this study area. The 1273 landslides were classified into two data series, training data for modelling (70%) and test data for validation (30%). The six selected thematic maps as landslide causative factors are lithology, land use, peak ground acceleration (PGA), and slope (gradient, aspect, elevation). The selection of causative factors considerably influences the frequency of landslides in the area. The result is satisfactory because the AUC value of the chosen model excelled the minimum limit, which is 0.6 (60%). The estimated success rate of the model is 85.7%, which shows that the relevancy of the model is good with the occurrence of landslides. The prediction rate of 84.6% indicates that the applied model is very good at predicting new landslides

Seasonal Driven Mechanism of the Surface Chlorophyll-A Distribution along the Western Coast of Sumatra

The chlorophyll-a (chl) abundances on the Fisheries Management Area of Indonesia Republic (WPP-RI 572), as fishery resources over the western coast of Sumatera (WSC) and Sunda Strait, were examined in this study. The extensive investigation on the mechanism ocean dynamics on chl variability along WSC was observed by using remotely sensed data on the surface. The spatial analysis was conducted using the Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua Ocean colour data for a period of January 2003 to December 2015. On seasonal time scale, the surface chlorophyll-a (schl) concentration in the southern tip of Sumatra is higher than the schl in the northern tip of Sumatra. The obtained results showed that the schl concentration in the southern tip of Sumatra increases (decreases) during the southeast (northwest) monsoons. Interestingly, its interactions with the southeast monsoon wind result in intensified coastal upwelling along the monsoon trough in July – August. It triggered a large bloom of the schl concentration from the upwelling region of southern tip Sumatra. Moreover, the schl in the center region followed the peak of the equatorial wind during the period transition in the Indian Ocean which is controlling the dynamics ocean such as upwelling event. Meanwhile, the opposite situation of the schl concentration observed low along the western coast of Sumatra during the northwest monsoon. At the same time, strong upwelling observed at the northern tip of Sumatra was associated with intense cooling on the sea surface temperature. It triggered a large bloom of high schl water from the upwelling region of northern Sumatra Island