Analisis Skenario Bahaya Banjir Berbasis Model Hidrodinamika 2D pada Kawasan Banyakan, Kabupaten Kediri
DOI:
https://doi.org/10.58344/locus.v5i8.6310Keywords:
Zonasi Bahaya Banjir, HEC-RAS 2D, AIDR Guideline 7-3, DAS Tanpa Data Debit, Kala UlangAbstract
Kawasan Banyakan dan Grogol di Kabupaten Kediri berulang kali tergenang akibat luapan Sungai Bendo Krosok dan Bondo Mongal. Kedua DAS tidak memiliki stasiun ukur debit, sehingga penilaian bahaya banjirnya bergantung sepenuhnya pada pemodelan. Penelitian ini menyusun zonasi bahaya banjir pada kala ulang 20, 50, dan 100 tahun sekaligus menelusuri bagaimana kenaikan debit rancangan terkonversi menjadi bahaya di dataran hilir. Limpasan wilayah hulu dihitung menggunakan HEC-HMS dengan metode SCS Curve Number, hidrograf satuan SCS, dan Lag Routing, lalu dimasukkan sebagai hidrograf ke model HEC-RAS 2D bersolver Diffusion Wave pada domain hilir seluas 27,01 km² yang terdiri atas 230.205 sel komputasi. Model dikalibrasi terhadap kejadian banjir 23-24 Desember 2024 dan menghasilkan RMSE 0,0176 m serta NSE 0,9854 pada tujuh titik observasi. Tingkat bahaya diklasifikasikan menurut AIDR Guideline 7-3 berdasarkan hasil kali kedalaman dan kecepatan aliran. Dari T20 ke T100, debit puncak gabungan naik 40,7% dari 171,8 menjadi 241,8 m³/s, luas genangan bertambah 21,90% dari 618,08 menjadi 753,45 ha, kedalaman maksimum naik 16,20% dari 1,42 menjadi 1,65 m, sedangkan luas area berbahaya hanya bertambah 11,61% dari 1.199,31 menjadi 1.338,53 ha. Setiap indikator pada rantai tersebut tumbuh lebih lambat daripada indikator sebelumnya. Meskipun demikian, kelas bahaya menengah tumbuh paling cepat, yaitu H2 sebesar 32,13% dan H3 sebesar 39,98%, sedangkan luas kelas kedalaman 0,5 sampai 1,5 m bertambah 41,20%. Unit bangunan terdampak naik 8,38% dengan kelas H3 bertambah 45,24%. Ancaman utama pada kala ulang ekstrem berupa penguatan bahaya pada wilayah yang telah tergenang, bukan perluasan wilayah terdampak, sehingga mitigasi yang sesuai berbentuk intervensi titik pada lokasi prioritas.
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