Analisis Tren Jangka Panjang Curah Hujan dan Debit Daerah Aliran Sungai Bengawan Solo

Abstract

Bengawan Solo Watershed is classified as one of the most degraded watershed in Indonesia. The Watershed usually was utilized as water resource for irrigation, transportation and industry. The problems in the Bengawan Solo Watershed is deforestation, illegal logging and land conversion. This research aimed to find out trend of rainfall and streamflow in Bengawan Solo Watershed for period of 1980-2010. Twelve rainfall stations in the Watershed were chosen for rainfall trend analysis and calculating rainfall area. The trend analysis was divided into two parts that is before and after reformation era (year at 1998). Trend analysis was performed using Mann-Kendall test at 95% confidence interval (α= 5%). Research result showed that before reformation era we found there were no significantly trend for rainfall and annual streamflow. However, after reformation era we found that there was a significantly negative trend for rainfall at most stations, but significantly positive trend for average annual streamflow. Coefficient of runoff in Bengawan Solo Watershed range 0,4-0,81 and did not occur a significantly trend for this research.