KARAKTERISTIK PERSEBARAN GRANULOMETRIS SEDIMEN PERMUKAAN DASAR SUNGAI DI DAS PABELAN, PROVINSI JAWA TENGAH
WIDIYANTO, Prof. Dr. Sutikno
2013 | Disertasi | S3 GeografiPenelitian sedimen permukaan dasar sungai ini dilakukan di DAS Pabelan, Sub-DAS Progo, Provinsi Jawa Tengah. Sungai-sungai di DAS Pabelan sebagian terletak di Gunungapi Merbabu, sebagai gunungapi istirahat dan sebagian terletak di Gunungapi Merapi, sebagai gunungapi aktif. Sungai Apu, Sungai Tringsing dan Sungai Senowo mengalir dari Gunungapi Merapi bermuara di Sungai Pabelan. Pada sungai-sungai tersebut sering terjadi lahar yang selalu mengancam lahan pertanian, permukiman dan fasilitas umum. Oleh karena itu sejak tahun 1969 hingga 2009 telah dibangun pengendali sedimen. Aktivitas masyarakat pada sungai-sungai yang sering terjadi lahar antara lain: pertanian, penambangan pasir dan batu. Tujuan penelitian ini adalah: 1) mengkaji karakteristik persebaran granulometris sedimen permukaan dasar sungai di DAS Pabelan; 2) mengkaji karakteristik persebaran granulometris sedimen permukaan dasar sungai di bagian hulu dan bagian hilir terjunan atau dam pengendali sedimen; 3) menganalisis karakteristik persebaran granulometris sedimen permukaan dasar sungai akibat penambangan pasir dan batu; dan 4) menentukan pengelolaan alur sungai. Metode survei digunakan dalam penelitian ini dengan cara pengamatan dan pengukuran, baik di lapangan, maupun di laboratorium. Pengamatan dilakukan pada sungai-sungai di Gunungapi Merapi, sungai-sungai di Gunungapi Merbabu, dan di Sungai Pabelan. Pengambilan sampel dilakukan secara purposif, sedangkan analisis secara deskriptif. Hasil penelitian adalah: 1) Ada kesamaan karakteristik granulometris persebaran sedimen permukaan dasar sungai di Gunungapi Merbabu, Gunungapi Merapi, dan sedimen permukaan dasar Sungai Pabelan, yaitu; a) persentase besar butir sedimen tertinggi pada fraksi kerakal kecil, b) persentase kebulatan butir sedimen permukaan dasar sungai tertinggi pada klas bulat; dan c) persentase kebundaran butir sedimen permukaan dasar sungai tertinggi pada klas bundar. 2) Pengaruh dam pengendali sedimen terhadap karakteristik sedimen permukaan dasar sungai adalah: a) besar butir sedimen permukaan dasar sungai di bagian hulu dam lebih kecil dibanding dengan besar butir sedimen permukaan dasar sungai pada bagian hilir dam, kecuali jika terjadi perbedaan proses; b) dam pengendali sedimen kurang berpengaruh terhadap persebaran kebulatan dan kebundaran butir sedimen permukaan dasar sungai. 3) Penambangan pasir dan batu pada bagian hulu sungai menyebabkan kelangkaan pasir di bagian hilir sungai. 4) Pengelolaan alur sungai dapat dilakukan dengan cara: a) peningkatan inovasi tehnologi untuk meningkatkan nilai jual pasir dan batu; b) penegakan peraturan perundang–undangan yang berkaitan dengan sungai; c) peningkatan pendidikan non formal bagi keluarga penambang agar dapat bekerja di luar bidang penambangan; d) pelestarian pengendali sedimen dan penataan penambangan agar tidak menimbulkan kerusakan alur sungai; e) penempatan petugas pengawas penambangan yang berdedikasi tinggi, jujur dan mampu sebagai negosiator.
Research for riverbed sediment was conducted in the Pabelan River Basin, Progo Sub-basin, Central Java Province. The rivers in Pabelan River Basin partially located in Merbabu Volcano, as a dormant volcano, and partly located in Merapi Volcano, as an active volcano. Apu River, Tringsing River, and Senowo River flows from Merapi Volcano and empties into the Pabelan River. In these rivers, lahar frequently happens and always threatens farmland, settlements, and public facilities. Therefore, since 1969 to 2009 has been constructed sediment control. Community activities on the rivers that frequently happens lahar flow include: agriculture, and sediment mining. The aims of this research are: (1) to study the characteristics of granulometris distribution of the riverbed sediments in Pabelan River Basin, (2) to study the characteristics of granulometris distribution of the riverbed sediments in the upstream and downstream waterfall or Sabo Dam, (3) to analysis the characteristics of granulometris distribution of the riverbed sediments due to sediment mining, and (4) to determine riverbed sediments management. This research was done by using survey method with observation and measurement, either in field and in laboratory. Observations were made on the rivers at Merapi Volcano, rivers at Merbabu Volcano, and Pabelan River. The sampling method was purposive sampling, while the analysis was performed with descriptive statistical analysis. The results are: (1) There is similar characteristics on distribution of granulometris riverbed sediment in Merbabu Volcano, Merapi Volcano and Pabelan River, i.e.: a) percentage of grain sediment size was highest in fractions of small pebble, b) percentage of grain riverbed sediment sphericity was highest in spherical class, and c) percentage of grain riverbed sediment roundness was highest in round class. (2) The effect of Sabo Dam on the riverbed sediment characteristics are: a) grain size riverbed sediment in the upstream is smaller than downstream, except if there is any process differences, b) Sabo Dam have less influence for distribution of grain riverbed sediment sphericity and grain riverbed sediment roundness. (3) The sand mining on the upstream led to the scarcity of sand in the downstream. (4) River management can be done by: a) a) Using innovation technology for increasing of sand and stone value. b) Enforcement of laws and regulations related to the river. c) Improving education for miner families, so they can work outside the field of mining. d) Preservation of sediment control and structuring of mining so did not cause rivers damage. e) Placement of supervisors mining officer, who highly dedicated, honest and capable as a negotiator.
Kata Kunci : karakteristik; granulometris; persebaran sedimen; penambangan; pengendali sedimen; pengelolaan alur sungai.
