EVALUASI TITIK KUMPUL EVAKUASI (TKE) BANJIR LAHAR HUJAN BERBASIS TESELASI SPASIAL DAN ANALISIS PERGERAKAN EVAKUASI

ISNAINI ANNURIAH M, Trias Aditya KM, S.T., M.Sc., Ph.D.

2013 | Skripsi | TEKNIK GEODESI

Bencana letusan Gunung Merapi tahun 2010 menimbulkan ancaman primer berupa lava dan awan panas serta ancaman sekunder berupa abu vulkanik dan banjir lahar hujan. Empat sungai yang membawa material Gunung Merapi meluap sebagai banjir lahar hujan di 13 desa di Kabupaten Magelang. Kali Putih merupakan sungai yang menimbulkan korban dan kerugian terbesar. Banjir lahar hujan Kali Putih meluap di Desa Gulon, Desa Seloboro, Desa Sirahan, dan Desa Blongkeng mengakibatkan kerusakan bagi permukiman warga, lahan pertanian, perkebunan, dan infrastruktur. Banjir lahar juga mengharuskan sejumlah warga mengungsi dalam rentang waktu yang cukup lama. Titik Kumpul Evakuasi (TKE) sebagai tempat pengungsian banjir lahar hujan merupakan salah satu fasilitas yang harus disiapkan dalam penyelenggaraan penanggulangan bencana sesuai dengan amanat UU No. 24 tahun 2007 tentang Penanggulangan Bencana. Lembaga Rehabilitasi dan Rekonstruksi Masyarakat dan Permukiman berbasis Komunitas (REKOMPAK) bersama pemerintah daerah dan masyarakat telah merencanakan TKE banjir lahar hujan. Sayangnya, perencanaan TKE tersebut dilakukan berdasarkan atas asumsi dan belum dievaluasi bagaimana kemampuannya dalam mengakomodasi pengungsi. Pada penelitian ini dilakukan pencarian TKE tambahan melalui survei lapangan, evaluasi terhadap TKE yang telah direncanakan dan TKE tambahan, serta penentuan cakupan setiap TKE dalam mengakomodasi pengungsi. TKE yang dianalisis adalah TKE yang telah direncanakan REKOMPAK dan perangkat desa terancam banjir lahar hujan Kali Putih ditambah dengan TKE hasil survei lapangan. Jumlah pengungsi dari data penduduk setiap desa didistribusikan dalam teselasi segi enam beraturan dan dihitung menggunakan basisdata spasial. Kapasitas setiap TKE dalam mengakomodasi pengungsi dihitung dengan rumus berdasarkan luas dan jenis penggunaan bangunan. Cakupan setiap TKE dianalisis pada tiga skenario menggunakan dua metode Catchment Area Analysis pada software Flowmap. Skenario tersebut terdiri atas skenario waktu aktif (siang hari), skenario waktu pasif (malam hari), dan skenario final. Metode yang digunakan adalah metode Second Best Catchment Distance untuk analisis dengan prioritas waktu tempuh menuju TKE serta metode Catchment Area Anlysis with Linear Optimization untuk analisis dengan prioritas kapasitas setiap TKE. Berdasarkan analisis, diperoleh hasil bahwa TKE yang tersedia belum mampu mengakomodasi seluruh pengungsi banjir lahar hujan Kali Putih baik pada skenario waktu aktif, skenario waktu pasif, maupun skenario final. Metode Second Best Catchment Distance mampu mengakomodasi hampir seluruh pengungsi namun terjadi penumpukan pengungsi secara besar-besaran di beberapa TKE sedangkan metode Catchment Area Anlysis with Linear Optimization mampu menghasilkan distribusi alokasi pengungsi yang merata dan mendekati nilai kapasitas setiap TKE namun metode tersebut hanya mampu mengakomodasi tidak sampai setengah dari jumlah pengungsi secara keseluruhan.

Mount Merapi eruption in 2010 caused primary and secondary hazards. Primary hazard consist of lava and pyroclastic flow, locally known as wedhus gembel. The secondary hazard, which was also very dangerous, included volcanic ash and lahar flood. Four rivers drained off the volcanic materials of Mount Merapi and overflowed as lahar flood to 13 villages in Kabupaten Magelang. Kali Putih had the most victims and losses among the other rivers. Lahar flood of Kali Putih caused damages in Desa Gulon, Seloboro, Sirahan, and Blongkeng. It was not only harmed people and their houses, but also ruined agricultural land and critical infrastructures. It also forced a mount of people to evacuate in a long period of time. Titik Kumpul Evakuasi (TKE) as evacuation place for lahar flood’s evacuees is one facility that must have been prepared in disaster management according to the Law 24 in 2007 on Disaster Management. REKOMPAK together with the local goverment and the community had planned the TKE in case of lahar flood ever come back in the future as Mount Merapi eruption’s cycle. They had planned the TKE based on assumptions and local agreements. The TKE had not been evaluated whether it could accommodate lahar flood’s evacuees entirely or not. This research was done to find new buildings for TKE, evaluate the TKE, and define the catchment area of each TKE for accommodating the evacuees. Analysis was done to the TKE planned by REKOMPAK and the village goverment threatened by Kali Putih’s lahar flood and the TKE from field survey. The number of inhabitants was distributed to regular hexagonal tessellation calculated in spatial database. The capacity of each TKE for accommodating the evacuees was calculated by formulas based on building areas and building uses. The catchment area of each TKE was analysed in three scenarios using two Catchment Area Analysis methods in Flowmap software. The scenarios were active scenario (day time), passive scenario (night time), and final (combined) scenario. The methods were Second Best Catchment Area Analysis for time evacuation priority and Catchment Area Analysis with Linear Optimization for TKE capacity priority. The result of this research shows that the current proposed TKE are not capable to accommodate all of the Kali Putih lahar flood’s evacuees in active scenario, passive scenario, and final scenario. Second Best Catchment Distance method resulted the catchment area for almost all of the evacuees but it accumulated a huge number of evacuees in some TKEs. Catchment Area Analysis with Linear Optimization method could distributed the evacuees appropriately to fulfill the capacity of each TKE depend on its evacuation capacity, but its catchment area was only accommodating under half of all the evacuees.

Kata Kunci : Titik Kumpul Evakuasi, basisdata spasial, teselasi, lahar hujan, Gunung Merapi, Flowmap