Pemodelan Spasial untuk Pembuatan Peta Rawan Banjir dan Peta Tingkat Risiko Banjir Bengawan Solo di Kota Surakarta

Abstract

ABSTRAK Penelitian ini bertujuan untuk melakukan pemodelan spasial untuk menyusun Peta Bahaya Banjir dan Peta Tingkat Risiko Banjir akibat luapan Bengawan Solo di Kota Surakarta. Lokasi penelitian meliputi penggal alur Bengawan Solo di wilayah Kota Surakarta. Metode penelitian yaitu dengan analisis hidrograf, pemodelan banjir, analisis potensi bahaya banjir, analisis kerentanan banjir, dan analisis tingkat risiko banjir. Analisis hidrograf dilakukan dengan menghitung debit puncak rancangan, analisis geometrik sungai, dan analisis karakteristik banjir. Pemodelan spasial banjir menggunakan perangkat lunak ArcView dengan ekstensi HEC-GeoRAS dan perangkat lunak hidrologi HEC-RAS. Analisis potensi bahaya banjir dari peta genangan hasil pemodelan spasial dengan input debit puncak rancangan banjir periode ulang 60. Analisis kerentanan dengan identifikasi elemen yang berisiko pada peta penggunaan lahan daerah bahaya. Analisis tingkat risiko dilakukan dengan cara overlay peta bahaya dan peta kerentanan banjir. Perangkat lunak ArcView 3.3 dengan ekstensi HEC-GeoRAS mampu untuk melakukan pemodelan banjir dengan tingkat validasi yang tinggi. Validasi dilakukan dengan membandingkan kedalaman maksimum hasil pemodelan dengan hasil perhitungan debit puncak rancangan. Nilai  perbedaan antara 0,68% - 4,54%. Meskipun secara kuantitatif peta model bahaya banjir rancangan sesudah pelurusan lebih luas daripada sebelum pelurusan, tetapi berdasarkan uji statistik penambahan luas tersebut tidak berbeda signifikan. Dari peta tingkat risiko banjir diketahui Kelurahan Sewu, Semanggi, Sangkrah dan Gandekan mempunyai potensi risiko banjir tertinggi di Kota Surakarta.

ABSTRACT This research is intended to perform flood modelling in Bengawan Solo River in order to develop flood hazard map, flood vulnerability map, and flood risk map as a result of overflow of such river in Surakarta City. The research area covers cut-off channel of Bengawan Solo in Surakarta City. The research was conducted by applying hydrograph analysis, flood modelling, flood hazard analysis, flood susceptibility analysis, and flood risk analysis. Hydrograph analysis was executed by calculating peak discharge designed, analysis of river geometric, and analysis of flood characteristic. Flood spatial modelling was done by means of ArcView with HEC-GeoRAS extention and hydrological software HEC-RAS. Flood hazard analysis was obtained by spatial modelling of flood inundation map with returned period of peak discharge designed of 60. Flood vulnerability analysis was derived from land use map used to identify risk element which exists in prone area. Flood risk analysis was carried out by overlying flood hazard map and flood susceptibility map. ArcView with HEC-GeoRAS extention and HEC-RAS was able to perform high validation of flood modelling. The validation was done by comparing maximum depth of the model and estimated peak discharge with different percentage 0.86% – 4.54%. Even the estimated flood hazard after river streamlining was wider than before, statistical analysis proves that different width of it was not significance. It means of river streamlining didn’t influence the wide of flood hazard area. Sewu, Semanggi, Sangkrah,and Gandekan Sub District has the highest risk of flood in Surakarta City.