TINJAUAN PENURUNAN MUKA TANAH AKIBAT PEMANFAATAN UNTUK IRIGASI DI DAERAH JOGONALAN-KLATEN JAWA TENGAH
T 551.49 SUD
T1NJAUAN PENURUNAN MUKA AIR TAN AR DALAM AKIBAT PEMANFAATAN UNTUK IRIGASI DI DAERAH JOGONALAN KLATEN (Kingkasan) Penelitian dilakukan pada daerah pengembangan lahan sawah yang berlokasi di Jogonalan, Kabupaten Klaten, Propinsi Jawa Tengah. Daerah tersebut termasuk dalam area Sub Das Dengkeng. Secara topografi daerah penelitian relatif datar (kelerengan 0-3%). Kondisi agroklimatnya termasuk dalam kategori C2 (5-6 bulan basah dan 2,3-4 butan kering), Curah hujan rata-rata bulanan tertinggi terjadi pada Bulan Januari (360, tmm) dan terendah pada Bulan Agustus (16,8mm). Curah hujan rata-rata tahunan berkisar 2300mm, Daerah penelitian secara fisiografi merupakan dataran Merapi- Merbabu, Secara geologi daerah penelitian didomosasi oleh produk vulkanik Merapi (pasir, tufa, breksi dan pumice). Batuan Unit Vulkanik Merpi dan Unit Vulkanik Merapi diidentifikasikan terletak di atas Formasi Kalibeng Atas. Secara hidrogeologi terdapat dua sistem akuifer, yaitu akuifer bebas dari Unit Pasir Tufa Merapi dan akuifer tertekan dari Unit Vulkanik Merapi. Karakteristik akuifer diinterprestasikan ketebalannya berkisar antara 57 s/d 75m, nilai transnusisitas antara 97,22 slid 456,77 m2/hari. Nilai storativitas berkisar antara 6,789x 10 - ' s/d 1,3610 x 10 "3. Ditakukan ekploitasi dengan 23 sumur debit 21 sit 38 lt/dt (total debit 713 lt/dt), luas daerah oncoran 604 Ha. Datam kurun waktu MT Oktober 1995 std MT April 1997 terjadi penurunan muka air tanah dalam, 2,05 std 7,88 m. Debit ct k imam perrompeae berkisar 31,20 sit 49,341tt/ct Debit petnompaan (Op) yaag dilaukan masih dibanwah debit maksimumnya ( Qmak). Debit pemompaan berkisar 76% debit maksimum (Qmak). Seteiatt dilakukan anatisis debit maksimum a berkisar 71,(17 s'd 31,44tu'dt.Debit pemompaan (Qp) melampoui Qmakya. berkisar 6% (rata-rant Qp = 1,06 Qmak). Berdasarkan hasil analisis disarankan debit pemornpaan diturunkan, berkisar 25% terhadap debit pemompaan sekarang (Qp). Kegiatan awal tanam ice-1 dilakukan Awal Oktober, sehingga penurunan muka air tanah path setiap akhir musim tanam (MT) tetah mengalami pemulihan (recovery). iii
DRAW DOWN OF PIZOMETRIC GROUNDWATER LEVELS DUE TO THE IMPLEMENTATION OF IRRIGATION IN JOGONALAN-KLATEN-CENTRAL JAVA PROVINCE (Abstract) The study was carried out in ricefield development area located in Jogonalan, Kiaten, Central Java Province. It is section area of Dengkeng River cathment areas. Topographically, this area is relatively fiat (0-3%), with agroclimatic type C2 (5-6 wet mounth and 2.34 dry mounth per years). Total precipitation for the mounth with highest rainfall in January (360. 1mm) and the lowest in August (16.8mm). The average annual precipitation was 2300mm. The physiographic area study were dominated by Merapi- Merbabu plain. The geology in this area consists of young Merapi vulcanic materials products (sand, tuff, breccia and pumicce). The unit sand and tuff Merapi and unit vulcanic Merapi were Quartenary age underlaying the tertiery formation Upper Kalibeng. There has two-layered aquifer systems; an upper unconfined aquifer by the unit sand and tuff Merapi, and lower confined aquifer by the unit vulcanic Merapi. Base on intrepretation of pumping test data have caracteristic akuifers are thickness aquifer 57-75m, transmissivity 97.2-456.7m 2 /day, storativity 6.789-1.361 x 10-3. In implementation of groundwater pumping with 23 wells for irrigation on 604 Ha areas during wet season ( October 1995) to dry season (April 1997) would cause water levels drawdown about 2.05-7.88m decrease. The result on analyses fo: hidrogeokgical parameters by simulation model indicated that aktual pumping rate discharges greater than recommanded maximum discharge, abaut 6 percent. For this reason to reducing drawdown water levels must reduce the aktual pumping rates. abaut 25 percent. The water requirement fo: irrigation this areas will be complete if the ajusting initial cropping date.