Analisis Dampak Normalisasi dan Rekomendasi Nbs untuk Penanganan Banjir di Sungai Ciliwung

Figo Fabian Ahmad, Ir. Neil Andika, S.T., M.Sc., Ph.D.

2026 | Skripsi | TEKNIK SIPIL

Sungai Ciliwung kerap mengalami banjir akibat meningkatnya curah hujan dan keterbatasan kapasitas aliran. Program normalisasi dapat meningkatkan kapasitas sungai dalam mengurangi risiko banjir. Namun, efektivitas normalisasi dapat dipengaruhi oleh peningkatan curah hujan akibat perubahan iklim serta perubahan kapasitas sungai akibat sedimentasi. Oleh karena itu, pendekatan Nature-based Solutions (NbS) berpotensi diintegrasikan sebagai pendukung normalisasi untuk meningkatkan retensi air dan mengurangi limpasan permukaan. Penelitian ini bertujuan mengidentifikasi lokasi kritis genangan banjir pada DAS Ciliwung, mengetahui kapasitas sungai setelah normalisasi, serta menentukan rekomendasi NbS yang efektif menurunkan dampak banjir.

Penelitian dilakukan melalui empat tahapan. Pertama, analisis curah hujan meliputi pengujian data secara statistik, hujan kawasan, analisis frekuensi, kurva IDF, dan hujan rancangan. Kedua, pemodelan debit banjir dengan HEC-HMS menggunakan metode SCS-CN, SCS Unit Hydrograph, dan Lag routing yang dikalibrasi dan divalidasi terhadap data AWLR. Ketiga,  pemodelan hidraulika untuk skenario eksisting, normalisasi dan dampak perubahan iklim dengan HEC-RAS pada segmen PA Manggarai– sta 3+249.038, dikalibrasi dengan data muka air terukur. Keempat, eksplorasi dan penyusunan rekomendasi NbS berupa kolam retensi/detensi dan  restorasi hutan di Ciliwung Hulu, yang diuji kembali dengan HEC-HMS dan HEC-RAS.

Hasil penelitian menunjukkan bahwa Sungai Ciliwung pada kondisi alami tidak mampu mengalirkan debit kala ulang 25 tahun (sebesar 460.7 m³/s). Limpasan terjadi pada  61 cross section dari 66 pada kala ulang tersebut. Sementara itu, sungai setelah kondisi normalisasi mampu mengalirkan debit hingga kala ulang 100 tahun (sebesar 563.6 m³/s) dengan freeboard memadai. Namun, apabila terjadi peningkatan curah hujan akibat perubahan iklim sebesar 20% sesuai proyeksi BMKG, terjadi limpasan pada sungai normalisasi di banyak titik dengan ketinggian tertinggi sebesar 0.52 m. Untuk mengatasi hal ini, disusun rekomendasi NbS untuk mengurangi limpasan tersebut. Adapun, kombinasi NbS berupa restorasi hutan 40 km² dan kolam detensi seluas 2.25% luas sub-DAS pada S3, S4 dan S16 terbukti berhasil mengatasi peningkatan debit banjir akibat perubahan iklim tersebut, dengan menurunkan debit puncak 12.1% menjadi 646.9 m³/s dan mengurangi limpasan menjadi hanya 0.03 m pada satu titik.

The Ciliwung River frequently experiences flooding due to increasing rainfall and limited river flow capacity. The normalization program can improve river capacity to reduce flood risk. However, the effectiveness of normalization may be influenced by increased rainfall due to climate change and changes in river capacity caused by sedimentation. Therefore, the Nature-based Solutions (NbS) approach has the potential to be integrated as a supporting measure for normalization to enhance water retention and reduce surface runoff. This study aims to identify critical flood-prone locations within the Ciliwung watershed, determine the river's capacity following normalization, and formulate effective NbS recommendations to reduce flood impacts.

The research was conducted through four stages. First, hydrological analysis comprising areal rainfall calculation, statistical testing, frequency analysis, IDF curves, and design rainfall. Second, flood discharge modeling using HEC-HMS with the SCS-CN, SCS Unit Hydrograph, and Lag routing methods, calibrated and validated against AWLR data. Third, hydraulic modeling for the existing, normalization, and climate change impact scenarios using HEC-RAS on the PA Manggarai–sta 3+249.038 segment, calibrated against measured water level data. Fourth, exploration and formulation of NbS recommendations in the form of retention ponds in sub-catchments S3, S4, and S16, along with forest restoration in the upper Ciliwung, which were re-tested using HEC-HMS and HEC-RAS.

The 100-year return period peak discharge (PSA-007) was 563.6 m³/s. Under existing conditions, overflow occurred starting from the 25-year return period across nearly the entire cross-section. Following normalization, the river was able to convey discharge up to the 100-year return period with adequate freeboard. Normalization increased flow velocity by up to twofold (2–3.3 m/s), yet unexpectedly reduced average bed shear stress by 30% due to the more uniform channel geometry. Climate change (a 20% rainfall increase) raised the peak discharge to 735.9 m³/s and reintroduced overflow. The combined NbS intervention consists of 40 km² of forest restoration and detention ponds (2.25% of the area of sub-catchments S3, S4, and S16)  successfully mitigated the increased peak discharge caused by climate change, reducing it by 12.1% to 646.9 m³/s and limiting overflow to just 0.03 m at a single point.

Kata Kunci : Sungai Ciliwung, Normalisasi, Nature-based Solutions (NbS), HEC-HMS, HEC-RAS