Analysis of Changes in Bathymetry of the Palu River Estuary and Its Effect on Flow Characteristics

Abstract

The tsunami triggered by the 7.4 magnitude Palu earthquake has caused a change in the shape of the Palu Bay coast. The results of field investigations have proven the existence of changes in the bottom waters around of the Palu River estuary. This has the potential to cause changes in the characteristics of the flow pattern of ocean currents that lead to and leave of the Palu River estuary. This study aims to determine and identify the impact of these coastal changes on the pattern of current flow to and leaving of the Palu River estuary by conducting hydrodynamic simulations using the Surface water Modeling System (SMS) software. obtain a bathymetry map, the results of which illustrate that the 2018 earthquake and tsunami caused a decrease in the elevation base at the Palu River estuary. From the results of the hydrodynamic SMS simulation before the earthquake and tsunami of 2018, the maximum value obtained for Point 1 is in step 11^th with a flow velocity value of 0.11 m/s, in Point 2 there is in step 24^th with a flow velocity value of 0.03 m/s . The minimum value for Point 1 is in step 17^th with a flow velocity value of 0.08 m/s, in Point 2 there is a step 17^th with a flow velocity value of 0.02 m/s. Simulation results after the earthquake and tsunami in 2018, the maximum value obtained for the simulation model is for Point 1 found in step 1^st with a flow velocity value of 0.14 m/s. For Point 2, found in step 1^st with a flow velocity value of 0.05 m/s. The minimum value for Point 1 is in step 19^th with a flow velocity value of 0.08 m/s. Whereas for Point 2 found in step 19^th with a value of flow velocity = 0.03 m/s. As for the direction of current flow, before the earthquake and tsunami of 2018, the flow of current to the estuary is mostly from the west and east direction, then when it reaches the estuary, turn left the estuary perpendicular to the river toward the north. Whereas after the earthquake and tsunami of 2018, from step 1^st to step 11^th, the flow of the current from the sea towards the estuary is perpendicular to the river through the north, when it reaches the estuary, the current flow is divided by turning west and east leaving the estuary, then in step 12^th to step 24^th there was no change in direction between before and after the earthquake and tsunami in 2018.

Keywords: Tsunami, bathymetry, hydrodynamic simulation, coastal current.