Modelling Debris Flow Runout: A Case Study on the Mesilau Watershed, Kundasang, Sabah

Muhammad Iylia Rosli,Khamarrul Azahari Razak,Tetsuo Tobita,Faizah Che Ros,Aznah Nor Anuar,Samira Albati Kamaruddin,Yusuke Ono,Sumiaty Ambran,Aminaton Marto

doi:10.3390/w13192667

Muhammad Iylia Rosli, Khamarrul Azahari Razak + Show 7 more

Open Access

https://doi.org/10.3390/w13192667

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Abstract

Debris flows are among the fatal geological hazards in Malaysia, with 23 incidents recorded in the last two decades. To date, very few studies have been carried out to understand the debris flow processes, causes, and runouts nationwide. This study simulated the debris flow at the Mesilau watershed of Kundasang Sabah caused by the prolonged rainfall after the 2015 Ranau earthquake. Several interrelated processing platforms, such as ArcGIS, HEC-HMS, and HyperKANAKO, were used to extract the parameters, model the debris flow, and perform a sensitivity analysis to achieve the best-fit debris flow runout. The debris flow travelled at least 18.6 km to the Liwagu Dam. The best-fit runout suggested that the average velocity was 12.5 m/s and the lead time to arrive at the Mesilau village was 4.5 min. This high debris flow velocity was probably due to the high-water content from the watershed baseflow with a discharge rate of 563.8 m3/s. The flow depth and depositional thickness were both lower than 5.0 m. This study could provide crucial inputs for designing an early warning system, improving risk communication, and strengthening the local disaster risk reduction and resilience strategy in a tectonically active area in Malaysia.

Highlights

Debris flows are among the disastrous geological hazards that occur in both developed and developing countries
This study modelled the past debris flow in the Mesilau watershed by applying several interrelated processing platforms, including ArcGIS (ArcHydro and HEC-GeoHMS), HECHMS, QGIS, and HyperKANAKO
On the basis of the observation data and the best-fit simulation result, it can be concluded that: (1) The debris flow happened on 15 June 2015, i.e., ten days after the 2015 Ranau earthquake (Mw 6.0) with a seven-day cumulative rainfall of 66.3 mm

Summary

Introduction

Debris flows are among the disastrous geological hazards that occur in both developed and developing countries. This sediment-related disaster strikes quickly without warning, and results in severe consequences, including human and economic losses [1]. In Malaysia, approximately 23 debris flow incidents were recorded nationwide between 1995 and 2015 (Table 1). These events were mostly induced by rainfall and very few were triggered by the cascading earthquake. In Sabah, the vicinity of Mount Kinabalu, the first UNESCO World Heritage Site in Malaysia has recorded two recent debris flows at the Mesilau watershed of Kundasang (the southeast flank of Mount Kinabalu) and the Kedamaian watershed of Kota Belud (the northwest flank of Mount Kinabalu), respectively [7,8]

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