Impact of Landslides Induced by the 2018 Palu Earthquake on Flash Flood in Bangga River Basin, Sulawesi, Indonesia

Abstract

High magnitude flash flood has occurred several times in some areas in Central Sulawesi Province after the 2018 Palu Earthquake, one of them is in the Bangga River, Sigi Regency, Indonesia. It has caused massive impacts such as damaging agricultural and plantation areas and submerging public facilities and infrastructure and even causing fatalities. The flood carries a variety of materials, especially high concentration sediments which are thought to originate from eroded soils due to landslides induced by a 7.5 magnitude earthquake. These materials are eroded and transported by the flow at the upstream watershed due to heavy rainfall. This study intends to investigate the potential of landslides, factors that trigger floods and increased flooding after the earthquake. This research was conducted by investigating the landslides potency based on field surveys and interpretation of the latest satellite imagery, analyzing the characteristics of rainfall as a trigger for flooding, and predicting the flood potency as the primary impact of these two factors. Rainfall-flood transformation was simulated with the HEC-HMS Model, one of the freeware semi-distributed models commonly used in hydrological analysis. The model input is the configuration of river networks generated from the National DEM (DEMNAS), hourly rainfall during floods and other watershed parameters such as land cover, soil types and river slope. The similar simulation was also carried out on the condition of the watershed before the earthquake. Based on the results of the analysis, It can be inferred that flash floods in the Bangga River are mainly caused by heavy rainfall with long duration and landslide areas in the upper watershed triggered by the 2018 Palu Earthquake with an area of approximately 10.8 km 2 . The greatest depth of rainfall as a trigger for flooding is 30.4 mm with a duration of 8 hours. The results of the study also showed that landslides in the upper watershed could increase the peak flood by 33.33% from 118.56 m 3 /s to 158.08 m 3 /s for conditions before and after the earthquake.

Increased Nonstationarity of Stormflow Threshold Behaviors in a Forested Watershed Due to Abrupt Earthquake Disturbance

“…Peak discharges and the time to peak were increased by 22.58%~367.42% and 25 min, respectively. This is consistent with Tunas et al (2020) in Bangga River Basin affected by the 2018 Palu Earthquake in Indonesia. The large physical disturbances triggered by earthquake-induced landslides can efficiently reflect the reduced water storage of shallow soil and vegetation canopy.…”

“…The unstable disturbances from endogenous (earthquake) and exogenous (rainstorms and concomitant hydro-geohazards) origins remarkably increase the uncertainty in the assessment of the hydrological regime from disturbance to recovery and flood risk management (Seidl et al, 2017). Previous studies have suffered from over-calibrated hydrological models (Chiang et al, 2019;Maina and Siirila-Woodburn, 2019;Tunas et al, 2020) and lack of understanding of runoff generation mechanisms in exploiting the effects of natural disturbance events on streamflow response. The efficient identification of nonlinear hydrologic behaviors in an earthquake-affected watershed as well as the understanding of post-earthquake long-term dynamics of hydrologic thresholds patterns is still urgently needed.…”

Bantuan Kemanusiaan Civitas Akademika Poltekkes Kemenkes Palu untuk Korban Banjir Bandang Rogo, Sigi - Sulawesi Tengah

“…Menurut analisis Tunas dkk menyatakan bahwa banjir bandang juga terkait dengan gempa, sebagai contoh salah satunya di Bangga, Kabupaten Sigi. Banjir membawa berbagai material, terutama sedimen konsentrasi tinggi yang diperkirakan berasal dari tanah yang terkikis akibat longsor yang disebabkan oleh gempa berkekuatan 7,5 SR. Material ini terkikis dan terangkut oleh aliran di hulu DAS akibat curah hujan yang tinggi (Tunas, Tanga, & Oktavia, 2020).…”

Designing and building earthquake warning system with Arduino and web-based SES60 SLP sensor

“…Padang is a city located in the Western Indonesian archipelago, the city closes to three earthquake resources. Based on the seismicity data, 4000 earthquakes occurred from 1779 to 2020 with magnitude Mw>4 as shown in Figure 1(a) and some of them created tsunami in Indonesia shows in Figure 1(b) [1]- [3], and similar to Palu city [4], [5]. Earthquakes are disasters that often occur in areas located in plate regions.…”