INFLUENCE OF BAMBOO DEBRIS ACCUMULATION FORMED BY CULVERT BRIDGES ON BACKWATER RISE DURING FLASH FLOOD

Abstract

Bambooplants appear to cover the sorrounding environment on the edge of River in Lombok
to alleviate many environmentalproblems such as river bank erosion. Despite its usefull, side erosion along
the upstream river during a heavy rain 2017 in Lombok island, West Nusa Tenggara. This phenomenon was
drifted a significant amount of sediment and bamboo. Unfortunately, there are many culvert bridges installed
in the river. The transported bamboo accumulated at thebridges and then overflowed the banks at several
sections. The accumulation or jam also caused backwater rise. There are two types of culvert bridges in the
river. One is a pipe culvert bridge and the other is box culvert bridge. This condition due to the accumulation
at a bridge from the view of river engineering becomes a vital factor in flood problems. A series of
experimental study was performedin Hydraulic Laboratory of University of Muhammadiyah Mataram in
order to investigate the formation of bamboo debris accumulation formed by the two different types of
culvert bridges. The small size of bamboo and model of culvert bridges were tested. The released of bamboo
pieces were trapped by the model bridges and formed bamboo debris accumulation. These experimental
results reveal that the bamboo debris accumulations contribute to backwater rise. The backwater rise and loss
coefficients increase slowly with the volume of bamboo pieces trapped by a culvert bridge. A procedure of
predicting backwater rise was proposed.