ABSTRACT. The population in Yogyakarta City, Indonesia has increased since 1970, resulting in high groundwater utilization. This normally results in a decline of groundwater level in shallow aquifer beneath the city. However, expansion of the city and urbanization effects can also have the opposite effect and lead to a rise of groundwater levels due to urban recharge. This study investigates groundwater level changes in Yogyakarta City during a time period of 30 years between 1985 and 2015. Collected data in this research are groundwater level, rainfall, population density, sewer system, and land use. Overlaying various spatial information reveals a pattern of groundwater level rise in some areas of the city by 0-12 m, whilst in other areas a decline of 0-9 m is discovered. Rising groundwater levels are mainly found in areas moderate to high population density where sewer system networks have been installed. The rising of groundwater levels is thus expected to be caused by urban recharge and sewers leakage.
Bayat is located in the south of central Java, Indonesia. In the quaternary deposit area, groundwater on some dug wells taste salty and previous studies discovered salty-tasted water with electrical conductivity (EC) >5000 μS/cm and chloride concentration >1000 mg/l. Local information reported that the number of wells containing salty-tasted water increased after the 6.2 Mw earthquake on May 27th, 2006 in Yogyakarta. This research aims to determine the distribution of salty-tasted groundwater and its relation with the geological condition by conducting a hydrogeological investigation. On the hydrogeological investigation, dug wells were observed for physical-chemical characteristics such as total dissolved solid (TDS) and EC; additionally, groundwater samples were collected for chloride ion analysis. Geology of the study area is mapped based on previous studies. The result showed that the high TDS/EC groundwater correlated with salty-tasted water which found in three different areas, including in the west, middle and east part of the study area. The occurrence of salty-tasted water strongly aligns with faults zone. In conclusion, deep salty-tasted water emerges not only locally near the fault zone but also associated with trapped groundwater and buried anticline. In regard to those sources, it can be predicted that in the near future more dug wells water may turn into salty-tasted water, especially in the area closed to the fault zone.
Kebutuhan perumahan di daerah perkotaan semakin tinggi, tidak sebanding dengan ketersediaan lahan untuk perumahan. Upaya pembukaan lahan yang murah tersedia pada daerah bentang alam ekstrim seperti perbukitan, seperti di Godean, Yogyakarta, yang memiliki potensi bahaya gerakan massa. Kajian ini bertujuan untuk memetakan zona bahaya gerakan massa dan mengevaluasi keamanan site-plan perumahan. Metodologi peneltian berupa pemetaan aspek geologi teknik yaitu kelerengan, kekuatan batuan, dan densitas struktur geologi yang kemudian diolah dengan metode overlay pada perangkat lunak Sistem Informasi Geografis. Aplikasi analisis multi kriteria (AMK) spasial menghasilkan zonasi kerentanan/potensi bahaya gerakan massa detil di lokasi penelitian, dimana zona ekstrim bahaya gerakan massa berasosisasi dengan lereng yang curam-terjal, kekuatan batuan lemah dan densitas struktur geologi yang rapat-sangat rapat. Penampalan peta bahaya tersebut dengan site-plan memungkinkan perencana dan pemangku kepentingan melakukan perencanaan ulang pada beberapa blok perumahan untuk memastikan pengembangan perumahan yang aman.
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