Geomorphological characteristics of slope failures in northeast Viti Levu island, Fiji, triggered by Tropical Cyclone Winston in February 2016

Abstract

The highways circumnavigating Viti Levu play a pivotal role in Fiji's socioeconomic development, and are a crucial link to transport aid during disasters. Slope failures triggered by heavy rainfall and tropical cyclones have led to considerable damage and fatalities along Viti Levu's main roads in the past. Knowledge of slope instability mechanisms is key for the successful identification and management of slope failure hazards, however, there is a paucity of such information for Fiji's main roads. Severe Tropical Cyclone (STC) Winston was the strongest cyclone on record to make landfall in Fiji and affected the Fiji Islands from the early hours of 20 February until 3 am, 21 February, 2016. We present a field reconnaissance examining the characteristics and mechanisms of slope failures induced by STC Winston along a 35 km stretch of the northern part of the Viti Levu's ring road, “Kings Road”. Approximately 61 distinct shallow, small‐scale slope failures were identified most of which were of a complex type and included earth and debris slides (planar and rotational) with a minor flow component. The trigger for the slope failures was the ~258 mm of rainfall in 24 hours after 30‐days of antecedent rainfall totalling 482 mm. This caused rapid increases in porewater pressures, especially at the contact of residual soils and the underlying weathered basement rock. Evidence of recurring slips along Kings Road indicates that contemporary slope instability is likely caused by elevated porewater pressure during high intensity rainfall events in clay‐dominated soils.

Engineering geomorphological investigation of the Kasavu landslide, Viti Levu, Fiji

“…8a, b). The 24-h rainfall values are much lower than the values (> 258 mm) reported in Ram et al (2018) for TC Winston-induced landslides along Kings Road, but the 30-day antecedent rainfall totals are similar (482 mm in TC Winston). Focussing on the 3-day antecedent rainfall may be a more useful approach for landslide hazard forecasting in the study area.…”

“…The landslide on 17-18 December 2016 was triggered by prolonged rainfall from tropical depression (TD) 04 (12-20 December 2016) (Fiji Meteorological Service 2017). The event occurred 10 months after the equally damaging TC Winston, the strongest cyclone to date in the Southern Hemisphere (Esler 2016;Ram et al 2018). Several significant landslides were triggered on main roads by TD04, including Veisari along the Queens Road in southern Viti Levu, and in Qamea Island in northern Fiji, but the Kasavu landslide caused the most damage.…”

Landslide Hazard Zonation from a GIS Perspective and Urban Planning Solutions in Central –Division of Fiji Islands

“…Peak water discharge rates measured near the mouths of the Navua and Rewa rivers apparently correlated with the triggering of landslides. The great majority of the slides involved only regolith material; in only one instance was the removal of bedrock observed.Ram et al [19] revealeda landslide pushed a bus with six people totheir deaths into the Wainibuka River along the King roads northeast of Korovou town. Table 2illustrates the data collected and prepared for this particular study.…”

“…This study is essential because it adds knowledge and provide an understanding of the usefulness of ArcGIS and remote sensing analysis in Fiji Islands in solving complex issues of disaster risk reduction. Thus, several experts carried out research on landslide in Vitilevu Island, Fiji such Lawson [14], Howorth et al [15], Ram et al [16,19] and Greenbaum et al [17] revealed that rainfallinduced landslides are lethal for humanity.…”

Addressing unavoidable climate change loss and damage: A case study from Fiji’s sugar industry

“…Recent cyclones in Fiji, such as tropical cyclone (TC) Evan, TC Winston, and TC Yasa brought destructive winds and ash oods that caused massive L&D to the agricultural sector and associated communities (Government of Fiji 2012; UNOCHA 2003; Esler 2016). On 20th February 2016, TC Winston, a category ve cyclone, and one of the strongest recorded in the Southern Hemisphere, made landfall in Fiji (Ram et al 2018). Sugarcane production was severely impacted as TC Winston struck during the planting season (Esler 2016).…”