Groundwater assessment for irrigation in Bantul regency, Yogyakarta special province Indonesia

SAMBO, Lun, Dr. Wahyu Wilopo, ST.,M.Eng

2010 | Tesis | S2 Teknik Geologi

Dibatasi oleh Sungai Opak dan Winongo, Daerah penelitian terletak di selatan Kabupaten Bantul meliputi dua desa di Jetis dan dua desa di Pundong.Total populasi 44.691 orang (2008), luas wilayahnya 26 km², 66% wilayahnya merupakan area pertanian, 29% pemukiman, dan 5% lahan dimanfaat kan untuk hal lainnya. Pada musim kemarau, masalah yang terjadi di daerah ini berkaitan dengan irigasi air untuk pertanian.Penelitian ini bertujuan untuk menilai kuantitas dan kualitas air tanah sebagai sumber alternatif untuk irigasi. Penelitian dan pengumpulan sampel dilakukan untuk mengumpulkan data utama. Dengan demikian, air permukaan secara kuantitatif dan kualitatif dianalisis menanggapi permintaan di bidang pertanian. Selain itu, tiga jenis tanaman perkebunan yang ditanam 3 kali setahun (padi, kacang tanah dan jagung) juga dianalisis berdasarkan periode mereka tumbuh dan kebutuhan air irigasi. Sementara itu, air tanah itu diukur kuantitasnya dalam hal penyimpanan statis dan dinamis dan kualitasnya digolongkan berdasarkan kriteria air irigasi.Air permukaan hanya dapat digunakan selama setahun untuk menyediakan suplai air bagi satu desa yang terletak di bagian atas area penelitian, namun demikian kualitasnya cukup baik untuk keperluan irigasi. Penipisan pasokan air permukaan terjadi ketika sistem rotasi padi-padi-padi dipraktikkan. Oleh karena itu, air tanah adalah satu-satunya sumber alternatif yang mengandung 227 juta m³dalam penyimpanan statis, 1,495,196 m³/tahun discharge dinamis dan 3,248,517 m³/tahun sebagai resapan tahunan; yang mana kualitasnya diklasifikasikan sebagai sumber yang baik untuk irigasi.Air permukaan adalah sumber yang baik untuk irigasi, namun kuantitasnya menipis di beberapa desa. Oleh karena itu, air tanah dapat dipompa keluar untuk irigasi selama musim kemarau agar dapat menerapkan konsep safe yield selama lahan tersebut diolah. Disarankan agar air tanah dapat dikelola untuk menjaga kualitas dan untuk dapat menyediakan supply atas kebutuhan sosial ekonomi dari segi kuantitasnya.

Bordered by Opak and Winongo River, research area is located in southern Bantul Regency covering two villages in Jetis and two villages in Pundong. It has total population of 44,691 persons (2008) and total area of 26 km² distributing in 66% of agriculture, 29% of settlement and 5% of other landuse. In the dry season,it has problem relating to water irrigation for agriculture.This research is aimed to assess groundwater in term of quantity and quality as alternative source for irrigation. Field investigation and sample collections were conducted to collect the main data. Accordingly, surface water was quantitatively and qualitatively analyzed responding to agricultural demand. Additionally, three types of crops with plantation of 3 times a year (rice, peanut and maize) were also analyzed based on their growing periods and irrigation water need. Meanwhile,the groundwater was quantified in term of static and dynamic storage and its quality was classified following the criteria of irrigation water.Surface water could be used in whole year to supply only one village located in the upper part of research area; however its quality was quite good for irrigation uses. The depletion of surface water supply had occurred when the rotation of rice-rice-rice was practiced. Hence, groundwater is the only one alternative source which had 227 million m³ as static storage, 1,495,196 m³/year as dynamic discharge and 3,248,517 m³/year as annual recharge. Therefore the optimum resources are 4,743,714 m³/year in which 198,925m³/year can be recommended for abstracting to supply the depletion; meanwhile its quality was classified as good source for irrigation as well.Surface water is good source for irrigation, though its quantity is depleted in some villages. Subsequently, groundwater can be pumped out for irrigation during the depletion period respecting to the safe yield concept during exploitation. It is recommended that groundwater should be well managed in order to conserve its quality while its quantity is able to supply for socioeconomic demand.

Kata Kunci : Air tanah,Air permukaan,Pertanian,Irigasi,Konsep safe yield, groundwater, surface water, agriculture, irrigation, safe yield concept