Backflow characteristics at Palu estuary as the impact of bed subsidence after the 2018 earthquake and Tsunami

• Main Authors: Tunas, I. Gede, Ishak, Muh. Galib, Herman, Rudi, Setiyawan, Arafat, Yassir
• Format: Conference Proceeding
• Language: English
• Subjects: Discharge; Earthquakes; Estuaries; Flooding; Floods; Flow characteristics; Flow velocity; High tide; Return flow; Rivers; Simulation; Subsidence; Tidal flooding; Tsunamis; Upstream; Water levels
• ISSN: 0094-243X; 1551-7616
• DOI: 10.1063/5.0110409

The Palu River in Central Sulawesi is one of the rivers prone to flooding in Indonesia, especially in the middle and downstream segments. The intensity of flooding has also increased after the 2018 Earthquake and Tsunami due to bed subsidence around Palu Bay triggered by the earthquake. This paper intends to investigate the impact of configuration changes and bed subsidence on flow characteristics, particularly the upstream return flow associated with high tide. Hydrodynamic simulations have been performed for tracing the water level profile upstream using the HEC-RAS Package. The simulation was applied for three conditions: minimum discharge, average discharge and maximum discharge, and it established high tide levels as a condition of the downstream boundary. The high tide level is defined as the simulation boundary because high tides generally cause inundation in the estuary due to backflow during both low and high flows. The simulation results based on the geometry of the river after the 2018 earthquake and tsunami show that the backflow to the upstream of the Palu River due to high tides has been seen in all three simulation conditions. High tide has triggered the longest return flow at minimum discharge reaching nearly 3 km upstream with varying heights along the water level profile. This backflow has the potential to cause bottom silting due to reduced flow velocity.