Analisis Risiko Banjir di Wilayah Sungai Citarum Hulu

Abstract

Perubahan iklim meningkatkan risiko bencana hidrometeorologi khususnya banjir di DAS Citarum Hulu yang berdampak infrastruktur sumber daya air. Penelitian ini bertujuan untuk mengidentifikasi tingkat risiko banjir serta mengevaluasi infrastruktur pengendali banjir sebagai bentuk adaptasi. Analisis risiko dilakukan menggunakan metode scoring dan overlay berbasis Sistem Informasi Geografis (SIG) dengan menggabungkan parameter bahaya, kerentanan, dan kapasitas adapatasi. Selanjutnya, dilakukan inventarisasi infrastruktur pengendali banjir yang eksisting sebagai aksi adaptasi di wilayah dengan risiko banjir tinggi. Infrastruktur kemudian dievaluasi dengan analisis curah hujan rencana menggunakan metode Gumbel dan debit banjir rencana menggunakan metode HSS Nakayasu. Hasil penelitian menunjukkan bahwa 85,86% wilayah Cekungan Bandung yang mencakup 73 dari 85 kecamatan memiliki tingkat risiko banjir tinggi yang dipengaruhi oleh kombinasi bahaya, kerentanan, dan kapasitas adaptasi. Tingkat bahaya tinggi dipengaruhi oleh tingginya lahan terbangun, topografi datar, tanah aluvial, dan aliran utama Sungai Citarum Hulu yang melewati wilayah ini. Analisis kerentanan menunjukkan 76 kecamatan termasuk kategori kerentanan sedang dan 30 kecamatan kategori rendah, sedangkan kapasitas adaptasi secara umum berada pada kategori sedang di keseluruhan wilayah. Analisis curah hujan rencana terus mengalami kenaikan mulai dari 87,69 mm pada periode ulang 2 tahun hingga 213,81 mm pada periode ulang 100 tahun yang diikuti dengan peningkatan debit banjir rencana. Berdasarkan hasil evaluasi, kapasitas tampung Kolam Retensi Andir diperkirakan telah terlampaui oleh debit banjir rencana pada periode ulang 5 tahun. Sementara itu, batas kapasitas tampung Kolam Retensi Cieunteung diperkirakan tercapai pada periode ulang 10 tahun, sedangkan Embung Gedebage pada periode ulang 20 tahun. Hasil tersebut menunjukkan bahwa infrastruktur pengendali banjir eksisting seperti embung dan kolam retensi dapat mereduksi banjir, tetapi kapasitas tampungan beberapa infrastruktur belum sepenuhnya mampu menampung debit banjir pada periode ulang tertentu.

Climate change has increased the risk of hydrometeorological disasters, particularly flooding, in the Upper Citarum River Basin, affecting water resources infrastructure. This study aims to identify flood risk levels and evaluate existing flood control infrastructure as an adaptation measure. Flood risk analysis was conducted using a Geographic Information System (GIS) based scoring and overlay approach by integrating hazard, vulnerability, and adaptive capacity parameters. Furthermore, an inventory of existing flood control infrastructure was carried out as an adaptation measure in areas with high flood risk. The infrastructure was then evaluated using design rainfall analysis based on the Gumbel distribution and design flood discharge analysis using the Nakayasu Synthetic Unit Hydrograph (SUH) method. The results showed that 85,86% of the Bandung Basin area, covering 73 of the 85 sub districts, was classified as having high flood risk, influenced by the combination of hazard, vulnerability, and adaptive capacity. High hazard levels were primarily associated with extensive built up land, flat topography, alluvial soils, and the presence of the main channel of the Upper Citarum River. Vulnerability analysis indicated that 76 sub districts were categorized as having moderate vulnerability, while 30 sub districts were classified as low vulnerability. In contrast, adaptive capacity was generally categorized as moderate across the entire study area. The design rainfall increased from 87,69 mm for the 2 year return period to 213, 81 mm for the 100 year return period, resulting in a corresponding increase in design flood discharge. The evaluation revealed that the storage capacity of Andir Retention Pond is expected to be exceeded by the design flood discharge at the 5 year return period. Meanwhile, the storage capacity of Cieunteung Retention Pond is projected to be reached at the 10 year return period, whereas Gedebage Detention Pond is expected to reach its capacity at the 20 year return period. These findings indicate that existing flood control infrastructure, such as detention ponds and retention ponds, contributes to flood reduction, however the storage capacity of several infrastructures is insufficient to accommodate design flood discharge under certain return periods.