Geomorphological mapping has been done at the upstream part of Progo Drainage Area by measuring some geomorphological indexes and level of shallow groundwater level at 196 stations, to investigate connections between geomorphological characteristics and groundwater system in the area. These indexes are valley floorheight ratio (V f), valley cross section (V ratio o rV r), stream gradient index (S L), and drainage density (Dd). Based on the linear regression analysis, the four indexes show none to very weak correlation to water table at most locations. It means that all width, height, and width of the river valley do not control shallow groundwater level. However, some locations indicate a strong control of elevation to shallow groundwater level. The first case indicates that there is another controlling factor to the shallow groundwater system. Most likely, a deeper aquifer exists at those locations, which does not show up in the second case. All results give a preliminary indication that morphometry can be used to predict groundwater system in the area.

Salah satu parameter yang perlu dipertimbangkan dalam menentukan karakteristik hidrolik akuifer adalah petrofisik batuan. Potensi airtanah di suatu daerah sangat tergantung dari petrofisik batuan setempat. Karakterisik hidraulik yang penting diketahui antara lain adalah porositas dan permeabilitas batuan. Daerah Sub DAS Code disusun oleh batuan dari Formasi Yogyakarta dan Sleman yang merupakan batuan vulkanik Merapi Muda. Batuan akifer di daerah ini antara lain adalah batupasir tufan dan breksi andesit. Batupasir tufan memiliki tekstur klastik, ukuran butir pasir halus-kasar, kadang-kadang kerikilan, berstruktur gradasi, masif atau berlapis. Breksi andesit bertekstur piroklastik ataupun epiklastik, dengan ukuran butir fragmen kerikil hingga kerakal-berangkal, sortasi buruk -sedang, kemas terbuka, struktur masif atau berlapis tebal. Dari beberapa sampel yang dianalisis diketahui bahwa batuan akifer memiliki porositas 31,29 -50,254% dan permeabilitas 1,48.10 -6 hingga 8,45.10 -4 cm/dtk. Hubungan antara porositas dan permeabilitas batuan tidak menunjukkan hubungan yang kuat, namun masing-masing parameter tersebut dipengaruhi oleh tekstur dan struktur batuan serta komposisinya, khususnya dalam hal kehadiran mineral lempung. Kata-kata kunci: airtanah, petrofisik, porositas, permeabilitas PENDAHULUANStudi ini merupakan kajian terhadap batuan di wilayah Sub DAS Code untuk mengetahui petrofisik serta parameter hidrolik khususnya porositas/permeabilitas batuan yang menyusun akifer. Sifat-sifat fisik batuan, utamanya tekstur dan struktur batuan yang dijumpai di daerah penelitian dideskripsi untuk selanjutnya dikaji agar dapat melihat hubungannya dengan porositas /permeabilitas batuan. Pemahaman tentang petrofisik batuan maupun karakteristik hidrauliknya merupakan bagian penting dalam studi potensi airtanah di suatu daerah. Dengan penelitian ini diharapkan kajian petrofisik batuan dapat dipahami lebih baik sebagai pendukung parameter hidraulik akifer khususnya pada cekungan airtanah di Yogyakarta. Lokasi PenelitianDaerah penelitian termasuk dalam wilayah Sub DAS Code (Gambar 1). Sub DAS ini merupakan bagian dari DAS Opak. Sungai Code mengalir dari lereng atas G. Merapi di Kabupaten Sleman melewati Kota Yogyakarta hingga bermuara di sungai induknya (S. Opak) di wiayah Kabupaten Bantul.

Groundwater in the Banjararum area is found in various rocks that build  the West Progo Hills, including the Nanggulan and the Andesite Breccia Formations. Groundwater can be found in dug wells and springs. Field surveys show that the groundwater is generally clear, tasteless and odorless, except for the well at Ngipikrejo. Chemical test results from four samples showed that groundwater in limestone has Ca, Mg - HCO3 type, whereas in volcanic rocks of type Ca - HCO3 and Ca, Na - HCO3. Groundwater chemistry type is generated from the soil, mineral dissolution in sedimentary rocks and igneous rocks as well as the atmosphere through rainwater. The considerable content of NO3 in the Ngipikrejo area indicates pollution from human activities, plants or animal dung. In general, groundwater in the study area is suitable for use as clean water or drinking water, characterized by a measurable pH in the field of 6.6 - 7.2 and TDS 54 - 155 ppm. Nevertheless, laboratory test results show that groundwater samples are water-filled, with a hardness of 135,866 - 778,048 (moderately hard - very hard), so special treatment is required before drinking.

Hydrogeological surveys have been carried out in the Borobudur area and its surroundings, the northern part of the West Progo Hills to the Magelang intermountain plains. The purpose of this study is to determine the variations in groundwater’s chemical types in the study area and to interpret the hydrochemical processes. Primary data was taken in the field, including groundwater data and rock petrology. Physical / chemical data of groundwater were obtained from laboratory test results. Data analysis includes hydrochemical analysis using the Stiff, Piper, and Durov diagrams. The result shows that groundwater in the study area has a wide variety of chemical types, namely Ca, Mg - bicarbonate; Ca, Mg, alkaline – bicarbonate; Alkaline, Ca – chloride, and Alkaline - chloride. Groundwater in the study area is fresh (type Va) to brackish (type Vc), with low -moderate TDS content (119 - 6,810 ppm), and soft calcium carbonate hardness (6.0 - 16.6 ppm). Hydrochemical processes occur in groundwater are simple dissolution and cation exchange caused by clay materials originating from Quaternary deposits or weathering of Old Andesite Formation volcanic breccia. In addition, the presence of brackish water in Karangrejo and Candirejo may be triggered by mixing with fossil water.

This research is a hydrogeological survey activity with the aim to determine the quality and pattern of groundwater flow in the Degan and surrounding areas, Banjararum Village, Kalibawang, West Progo District. The research method is carried out by hydrogeological surveys to collect groundwater data and groundwater quality in the form of pH, TDS and EC. The research area is included in the Dome of the Kulon Progo physiography, where this area is a non CAT area. The geomorphology of the study area in the north and west is dominated by relatively coarse landscapes forming hills, while in the central, eastern and southern parts it is a weak wavy landscape to the plains. The results showed that shallow groundwater depth of 1.2 - 10.8 m (under surface). The pattern of groundwater flow is to the east / southeast, with boundary conditions H5 and V1. Groundwater aquifers are composed of colluvium deposits and weathered  - medium weathered rock. The pH value of water in the study area ranges from 6.7 -7.1; TDS is 165 - 901 ppm, while EC ranges from 187 - 1240 µS / cm. Thus, groundwater in the Degan area is neutral and tasteless.