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Setyawan Purnama
Faculty of Geography, Universitas Gadjah Mada, Yogyakarta
Earth & Planetary Sciences

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Dinamika Kedudukan Interface di Pesisir Kabupaten Kebumen, Jawa Tengah Setyawan Purnama
Majalah Geografi Indonesia Vol 31, No 2 (2017): Majalah Geografi Indonesia
Publisher : Fakultas Geografi, Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1818.05 KB) | DOI: 10.22146/mgi.25493

Abstract

Abstrak Interface adalah mintakat pertemuan antara air laut yang bersifat asin dan airtanah di daratan yang bersifat tawar. Interface tidak ditemukan dalam wilayah yang tegas, namun merupakan wilayah percampuran antara air tawar dan air asin, sehingga keberadaan interface tidak bersifat statis melainkan dinamis. Penelitian ini bertujuan untuk (1) mengetahui dan menganalisis kedudukan interface di Pesisir Kabupaten Kebumen dan (2) menganalisis dinamika kedudukan interface selama kurun waktu 21 tahun yaitu tahun 1993 dan 2014. Kedudukan interface diketahui berdasarkan pendugaan geolistrik rangkaian Schlumberger. Pendugaan dilakukan pada lokasi dan jalur yang sesuai dengan penelitian yang dilakukan oleh Simoen dkk. (1993), yaitu pada (1) jalur Salak-Petanahan-Munggu-Gadung-Pantai Petanahan, (2) jalur Tambakrejo-Jeblok-Prajuritan-Adikarto-Pantai Kebumen dan (3) jalur Sinungrejo-Sidoluhur-Bener-Kaibon-Ambal dan Pantai Kutowinangun. Perbandingan hasil pendugaan interface di kedua waktu tersebut akan diketahui perbedaan dan persamaan kedalaman interface pada masing-masing titik pengukuran dalam selang waktu 21 tahun dan selanjutnya dapat dianalisis faktor-faktor yang mempengaruhinya. Hasil penelitian  menemukan adanya lapisan airtanah tawar mulai kedalaman 2 hingga 10 meter dari permukaan tanah. Berbeda dengan di tahun 1993, hasil pendugaan di tahun 2014 tidak mendeteksi adanya interface di semua jalur pengukuran. Tidak terdeteksinya interface disebabkan kedudukan interface semakin dalam akibat desakan airtanah tawar yang semakin kuat. AbstractAn interface is a zone where seawater (salt) and inland groundwater (fresh) meet. It has no distinct boundaries because it is formed by a mixture of fresh and saltwater. Therefore, the presence of interface is not static or somewhat dynamic. This research aimed to (1) identify and analyze the position of salt-freshwater interface in the Coast of Kebuman Regency and (2) analyze the dynamics of the said interface at a timespan of 21 years, i.e., in 1993 and 2014. The position was estimated using geoelectrical sounding with Schlumberger arrangement. The estimation was conducted in the locations and along the lines that were determined based on the research performed by Simoen et al. (1993). The lines traversed the following areas (1) Salak-Petanahan-Munggu-Gadung-Petanahan Coast, (2) Tambakrejo-Jeblok-Prajuritan-Adikarto-Kebumen Coast, and (3) the Sinungrejo-Sidoluhur-Bener-Kaibon-Ambal-Kutowinangun Coast. The comparison of the estimated interfaces in two observation years yielded depth differences and similarities at every measurement point. This information, then, provided the underlying factors of the dynamic interface. The research found a freshwater layer at a depth of 2 to 10 m from the soil surface. Unlike the estimation results in 1993, the ones in 2014 did not detect any presence of interface in all of the measurement lines. The interface was undetected because it lowered as the pressure of fresh groundwater became stronger.   
Ketersediaan dan Kualitas Airtanah pada Akuifer Tidak Tertekan Di Kecamatan Jawilan dan Kopo, Kabupaten Serang Setyawan Purnama
Majalah Geografi Indonesia Vol 33, No 1 (2019): Majalah Geografi Indonesia
Publisher : Fakultas Geografi, Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (961.952 KB) | DOI: 10.22146/mgi.33250

Abstract

Tujuan dari penelitian ini adalah (1) mengetahui sistem akuifer di daerah penelitian, (2) menghitung ketersediaan airtanah pada akuifer tidak tertekan dan (3) menganalisis kualitas airtanahnya. Sistem akuifer diketahui dengan melakukan interpretasi data geolistrik. Potensi akuifer tidak tertekan dihitung secara kualitatif melalui skoring dan tumpang susun antara Peta Kedalaman Muka Airtanah, Peta Fluktuasi Airtanah dan Peta Kualitas Airtanah. Volume akuifer ditentukan berdasarkan perkalian antara luas wilayah masing-masing potensi dan tebal akuifer. Ketersediaan airtanah dihitung berdasarkan asumsi aliran airtanah statik, sedangkan hasil aman pengambilan airtanah ditentukan berdasarkan parameter fluktuasi airtanah, luas akuifer dan spesifik yield. Kualitas air dianalisis berdasarkan pengambilan sampel air pada sumur gali. Hasil penelitian menunjukkan bahwa di daerah penelitian ditemukan adanya akuifer semi tertekan dan akuifer tidak tertekan. Ditinjau dari potensinya, ketersediaan airtanah pada akuifer tidak tertekan sebesar 1.205.967.345 m3, dengan hasil aman pengambilan airtanah sebesar  54.585.307 m3/tahun. Untuk kualitas air, secara umum baik, meskipun beberapa parameter seperti kalsium, magnesium, mangan dan COD kadarnya telah melampaui baku mutu  di beberapa sampel.ABSTRACT The objectives of the research are (1) knowing the aquifer system in research area, (2) calculate groundwater availability in unconfined aquifer and (3) analysis the groundwater quality. Aquifer system is known by interpretation of geoelectric data. Groundwater potency is calculated qualitatively by scoring and overlay of Groundwater Depth Map, Groundwater Fluctuation Map and Groundwater Quality Map. Aquifer volume is calculated by multiplied area width of each potency and aquifer thickness. Amount of groundwater is calculated base on static groundwater flow assumption, whereas safe yield of groundwater exploitation is determined base on parametre groundwater fluctuation, aquifer width and specific yield. Groundwater quality are analized by groundwater samples that taken from dug well. Result of research show that there are two aquifer type in research area i.e. semi confined aquifer and unconfined aquifer. The potency of unconfined aquifer is 1.205.967.345 m3, with safe yield 54.585.307 m3/year. For groundwater quality, generally good, although some parameters have concentration exceeded the standard in some samples such as calcium, magnesium, manganese and COD.
Groundwater Vulnerability from Sea Water Intrusion in Coastal Area Cilacap, Indonesia Setyawan Purnama
Indonesian Journal of Geography Vol 51, No 2 (2019): Indonesian Journal of Geography
Publisher : Faculty of Geography, Universitas Gadjah Mada

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (635.627 KB) | DOI: 10.22146/ijg.18229

Abstract

The important issue relating to water resources is sea water intrusion (SWI) phenomena. Nowadays, the phenomena has become serious problem in the urban coastal area. Groundwater as main sources for domestic usage cannot be used again because of its salinity.Cilacap as one of urban coastal area also face the problem. In 1977 SWIwas detectedand experienced significant developmentsin 1996,This research was conducted to: (1) analyze agroundwater vulnerability to the SWI; (2) determine adistance and adepth theinterface; and (3) analyze relationship of the groundwater vulnerability to the interface depth.It was performed an analysis of the groundwater vulnerability to the SWI using the method of GALDIT, whereas the distance and depth of the interface was determined using the method of DupuitGhyben-Herzberg. The linkage analysis of the groundwater vulnerability to the depth of the actual interface was conducted by quantitative descriptively.The results showed that the distance from the shoreline was the most determined factor of the groundwater vulnerability to the SWI, the closer to the shoreline the more swallow the depth of the interface.  It existed the relevance between the vulnerability level of groundwater to the SWI with the depth of actual interface. The regions with low level of vulnerability had deep interface depth, whereas the regions with moderate level of vulnerability had swallow interface depth.  Nevertheless, the SWI has not yet affected the groundwater in people wells because of its depth that was not yet exceeded of 25 m.so that this depth can be used as a reference in digging wells in the research area++
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