Case Study Storm Surge Produced by Tropical Cyclone Gavin in Fiji March

A fine illustration of the effects of storm surge on sea flooding is provided by the example of Vanua Levu island in Fiji during Tropical Cyclone Gavin in early March 1997 (Terry and Raj 1999). TC Gavin, lasting from 3 to 11 March, was the first cyclone to strike the Fiji Islands in the 1997 hot season (Fig. 5.23), and was the severest storm to affect the nation since the early

Spiralling Forces
Fig. 5.23. Satellite image of Tropical Cyclone Gavin, 8 a.m. local time on 7 March 1997. Note the well-developed structure of TC Gavin in its mature stage, especially the spiralling arms of cloud. Base image courtesy of the Fiji Meteorological Service.

1990s (Fiji Meteorological Service 1997b). Initially the depression formed north of Fiji waters and west of the atolls of Tuvalu, achieving tropical cyclone status with storm-force winds at a position approximately 10°S 173°E.

By the evening of 5 March, TC Gavin strengthened to hurricane intensity, with winds gusting to 130 knots (240 km h-1). The system approached the large island of Vanua Levu from the north on 6 March, but shortly after midnight it altered course to the southwest (Fig. 5.24). Continuing on this track, the storm traversed directly over the small islands of the Yasawa and Mamanuca groups in western Fiji on the following day. After 7 March, TC

Fig. 5.24. Track of Tropical Cyclone Gavin through Fiji waters, from 4 to 10 March 1997.

Gavin maintained a southerly track away from the Fiji archipelago, but stayed at hurricane strength until well after leaving Fiji waters.

A heavy storm surge from TC Gavin inundated many coastal areas in northern Fiji. On Vanua Levu island, almost the total length of the north coast was affected, with sea walls breached in at least ten places (Fig. 5.25). Labasa town, the largest urban area on Vanua Levu, sits on the banks of two major rivers, the Labasa River and the Qawa River. Surface water levels in the estuary of the Labasa River are measured continuously by the Hydrology Division of the Fiji Public Works Department. In Fig. 5.26 the water levels during TC Gavin are compared with barometric pressure measured at the Udu Point weather station, situated 75 km away on the northeastern peninsular of Vanua Levu.

For the period that TC Gavin was approaching from northern Fiji waters, Labasa was on the right side of the cyclone track, relative to its direction of movement. This means that winds were blowing offshore as the storm advanced, which had the effect of driving water out of the river estuary. This produced an exceptionally low tide at 10 p.m. on 6 March. Once the eye of the storm had passed the mouth of the Labasa River on the following morning, the winds then swung around to an onshore direction. These vigorous onshore winds effectively retarded the outflow of water during the next low tide at 1 p.m. on 7 March, giving a low tide that was barely lower than normal

Udu Point Fiji
Fig. 5.25. High seas spilling over the sea wall at Tabucola on the northern coast of Vanua Levu island in Fiji, pushed up by storm surge associated with Tropical Cyclone Gavin on the afternoon of 7 March 1997. Photo courtesy of the Land and Water Management Division, Fiji Ministry of Agriculture.

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Fig. 5.26. Water level in the Labasa River estuary, measured at Labasa town on the north coast of Vanua Levu island in Fiji, during Tropical Cyclone Gavin in March 1997. Water level is compared with corresponding low barometric pressure at Udu Point on the northeast peninsular of Vanua Levu island, 75 km distant. The maximum storm tide peaked around 7 p.m. local time on 7 March and caused widespread coastal flooding.

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Fig. 5.26. Water level in the Labasa River estuary, measured at Labasa town on the north coast of Vanua Levu island in Fiji, during Tropical Cyclone Gavin in March 1997. Water level is compared with corresponding low barometric pressure at Udu Point on the northeast peninsular of Vanua Levu island, 75 km distant. The maximum storm tide peaked around 7 p.m. local time on 7 March and caused widespread coastal flooding.

high tide. At the time of the next high tide at 7 p.m. in the evening, the storm tide caused comprehensive flooding of Labasa town and the surrounding flat coastal hinterlands.

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