Analisis Indeks Baseflow Daerah Aliran Sungai Bengawan Solo

Abstract

Study about baseflow characteristics in Java Island remains research challenge especially to correlate biophysical characteristics of watershed with long term streamflow observation. This study aimed to know baseflow characteristic of Bengawan Solo watershed which physically grouped as one of critical watersheds in Java Island. We analysed daily streamflow data 1980-2010 to calculate baseflow index (BFI) based on smoothed minima method. We compared non-overlapping 3 days, 5 days, and 7 days of streamflow to calculate BFI. The results showed that higher N days would generate lower BFI. Lower BFI meant less baseflow contributing on streamflow. We found that average BFI3d, BFI5d and BFI7d in period 1980-2010 were 0.67, 0.56 and 0.49. It showed that Bengawan Solo watershed has permeability of fissure with low storage. We also found that trend BFI, BFa, and Qann rise significantly (α = 5%) in period 1998-2010, while annual precipitaion indicated negatif trend