Bankfull capacity analysis on the downstream Pekalen River due to the latest design flood

Abstract

Conditions in the upper reaches of the Pekalen River Basin have experienced changes in land cover, causing an increase in flood discharge, overflowing of the river body, and sedimentation. Flash floods in several villages in the Tiris sub-district in 2018 and 2019 made it clear that it was essential to control the cross-section of the river in several sections to anticipate similar events downstream. Then harvesting sengon (Albizia chinensis) trees simultaneously on community forest lands impacts the wide opening of the land, resulting in land degradation and lowering environmental quality. The purpose of this study is to determine the cross-sectional capacity of the river based on the latest rain data and to provide alternative solutions to the problem of handling the Pekalen River. Based on the results of hydrology and hydraulics calculations simulated in HEC-RAS, it was found that the existing capacity of the Pekalen River section could not accept the Q50 year of 484,090 m3/s. In the upstream section, 163 stake sections from upstream, middle, and downstream river sections experienced runoff, with a total length of 18,847 km of the river section that experienced runoff. One effective alternative solution to the flooding problem is to install Concrete Sheet Pile (CCSP) embankments at each stake segment that experiences runoff. Besides that, efforts are being made to handle non-structural measures such as erosion control using vegetation, socialization of flood plains, and a flood early warning system.