Penilaian Kondisi Hidrologi dan Simulasi Debit Puncak di Daerah Aliran Sungai Cianten Menggunakan Model HEC-HMS

Abstract

Daerah Aliran Sungai (DAS) Cianten mengalami dinamika perubahan penggunaan lahan dan variabilitas curah hujan yang berpotensi mempengaruhi respon hidrologi DAS. Penelitian ini bertujuan untuk mengevaluasi perubahan respon hidrologi dan menilai kondisi DAS Cianten dalam kurun waktu 12 tahun terakhir serta memperkirakan debit banjir berdasarkan periode ulang melalui pendekatan pemodelan hidrologi. Pemodelan dilakukan menggunakan HEC-HMS dengan metode SCS Curve Number (CN), Clark Unit Hydrograph, recession untuk baseflow, dan metode lag untuk routing, sedangkan analisis curah hujan rancangan harian dan jam-jaman maksimum menggunakan distribusi Log Pearson Tipe III dan PSA 007. Hasil kalibrasi dan validasi menunjukkan kinerja model yang memadai dengan nilai Nash–Sutcliffe Efficiency (NSE) berkisar antara 0,54–0,66, koefisien determinasi (R²) 0,65–0,71, nilai RMSE sekitar 0,6–0,7, serta PBIAS dalam rentang ±10%, yang mengindikasikan bahwa model cukup andal dalam merepresentasikan respon hidrologi DAS Cianten. Berdasarkan hasil analisis simulasi respon hidrologi tersebut, peningkatan tutupan hutan lahan kering sekunder sebesar 9,59% berimplikasi pada penurunan debit puncak periode ulang hingga sekitar 150 m³/s, serta penurunan debit puncak pada kondisi curah hujan yang sama dari 70,8 m³/s menjadi 57,1 m³/s antara tahun 2011 dan 2022. Secara fisik, DAS Cianten didominasi oleh jenis tanah Hydrologic Soil Group (HSG) B dan C, dengan sebagian wilayah HSG A, yang menunjukkan kemampuan infiltrasi sedang hingga rendah. Selain perubahan tutupan lahan, faktor meteorologis seperti curah hujan dan debit menunjukkan tren peningkatan serta fluktuasi yang tinggi selama periode pengamatan. Evaluasi respon hidrologi menunjukkan bahwa kondisi hidrologi DAS Cianten pada tahun 2022 cenderung lebih teredam dibandingkan tahun 2011, meskipun masih dipengaruhi oleh variabilitas curah hujan dan karakteristik fisik wilayah.

The Cianten River Basin (DAS) experiences dynamic changes in land use and rainfall variability that have the potential to affect the hydrological response of the watershed. This study aims to evaluate changes in hydrological response and assess the condition of the Cianten Watershed over the past 12 years and estimate flood discharge based on the return period through a hydrological modeling approach. Modeling was carried out using HEC-HMS with the SCS Curve Number (CN) method, Clark Unit Hydrograph, recession for baseflow, and lag method for routing, while the analysis of maximum daily and hourly design rainfall used Log Pearson Type III and PSA 007 distributions. Calibration and validation results showed adequate model performance with Nash–Sutcliffe Efficiency (NSE) values ranging from 0,54–0.66, coefficient of determination (R²) of 0,65–0,71, RMSE values of around 0.6–0.7, and PBIAS in the range of ±10%, which indicates that the model is quite reliable in representing the hydrological response of the Cianten Watershed. Based on the results of the hydrological response simulation analysis, an increase in secondary dryland forest cover of 9.59% has implications for a decrease in peak discharge over the return period of approximately 150 m³/s, as well as a decrease in peak discharge under the same rainfall conditions from 70.8 m³/s to 57.1 m³/s between 2011 and 2022. Physically, the Cianten Watershed is dominated by Hydrologic Soil Group (HSG) B and C soil types, with some areas of HSG A, which show moderate to low infiltration capacity. In addition to changes in land cover, meteorological factors such as rainfall and discharge show an increasing trend and high fluctuations during the observation period. The evaluation of the hydrological response shows that the hydrological conditions of the Cianten Watershed in 2022 tend to be more damped than in 2011, although they are still influenced by rainfall variability and the physical characteristics of the region.