Perubahan Tutupan Lahan, Indeks Baseflow (IBF), dan Debit Andalan Pemeliharaan Sungai Cisadane Hulu

Abstract

Perubahan tutupan lahan di Daerah Aliran Sungai (DAS) Cisadane Hulu menjadi perhatian karena dampaknya terhadap ketersediaan air. Penelitian ini menganalisis pengaruh perubahan tutupan lahan terhadap Indeks Baseflow (IBF) dan debit andalan pemeliharaan sungai DAS Cisadane Hulu tahun 2000-2020. Data tutupan lahan dianalisis secara overlay menggunakan QGIS, sementara data debit sungai diperoleh dari Pos Duga Batubeulah. Metode pemisahan baseflow dilakukan secara digital menggunakan fixed interval method untuk menghitung Indeks Baseflow (IBF) dan analisis probabilitas debit dilakukan untuk menentukan debit andalan pemeliharaan sungai. Hasil overlay tutupan lahan menunjukkan perubahan signifikan dalam tutupan lahan, termasuk peningkatan area pemukiman dan penurunan area hutan serta pertanian lahan kering. Urbanisasi dan pengurangan hutan dapat berdampak pada stabilitas aliran dasar sungai, penurunan nilai rata-rata IBF terjadi dari periode 2000-2010 (0,75) ke periode 2010-2020 (0,71) menunjukkan presentase aliran dasar terhadap aliran total menurun. Nilai Koefisien Regim Aliran (KAT) terklasifikasi sedang dan nilai Koefisien Regim Aliran (KRA) terklasifikasi kategori sangat rendah. Debit andalan pemeliharaan sungai (probabilitas 95%) tertinggi sebesar 45,98 m3/detik pada bulan Februari dan terendah sebesar 5,18 m3/detik pada bulan September. Hasil analisis pada DAS Cisadane Hulu menunjukkan perubahan tutupan lahan berpengaruh pada rata-rata nilai Indeks Baseflow (IBF), sedangkan nilai debit andalan pemeliharaan sungai berfluktuasi dipengaruhi musim.

Land cover changes in the Upper Cisadane Watershed have garnered attention due to their impact on water availability. This study analyzes the effects of land cover changes on the Baseflow Index (BFI) and the reliable discharge for river maintenance in the Upper Cisadane Watershed over the period from 2000 to 2020. Land cover data was analyzed through overlay techniques using QGIS, while river discharge data was obtained from the Batubeulah gauging station. The baseflow separation process was conducted digitally using the fixed interval method to calculate the Baseflow Index (BFI), and discharge probability analysis was performed to determine the reliable discharge for river maintenance. The land cover overlay results revealed significant changes, including an increase in settlement areas and a decrease in forest and dryland farming areas. Urbanization and forest reduction may impact the stability of river baseflow. A decline in the average BFI value was observed from the 2000–2010 period (0.75) to the 2010– 2020 period (0.71), indicating a decrease in the proportion of baseflow to total discharge. The Annual Runoff Coefficient (ARC) value is classified as moderate, and the Flow Regime Coefficient (FRC) value is classified in the very low category. The highest reliable discharge for river maintenance (95% probability) was recorded at 45.98 m³/s in February, while the lowest was 5.18 m³/s in September. The analysis of the Upper Cisadane River Basin shows that land cover changes affect the decline in the average Baseflow Index (BFI) value, and reliable discharge values fluctuate due to seasonal variations.