The Analysis of Backwater Impact on the Increasing of Floodwater Level in Palu River.

Talise Beach as the estuary of Palu River, Indonesia, is dissociated from any potential factors that may decelerate the river's stream flow and cause flooding in the surrounding area. There are some major issues that cause the overflow of Palu River, such as high rainfall, sedimentation that has formed a delta in the estuary due to deforestation at the upper area, the capacity of the river which is no longer able to accommodate the flood discharge, and the effect of backwater that occurs during high tide and inhibits the flow of water from upstream thus brings the impact of the rise in river water level. Because of the reason, the current research is conducted to find out the relationship between the increase in floodwaters at the cross section of Palu River and the rise in tidal flooding that occur simultaneously as the result of backwater. HEC-RAS software with unsteady flow model was used to investigate the stream flow using flood discharge of 2, 5, 10, 25 and 50 years return period as boundary condition at the upstream side and the highest of high tide of tidal surface as boundary condition at the downstream side. The results indicate that the increase in floodwaters of Palu River is caused by the rise and fall of the tides between 0.01 - 2.84 meters where the farthest cross section of Palu River impacted by backwater is the cross section at the station 183, 8.8 km from the estuary or lower part of Palu River. [ABSTRACT FROM AUTHOR]