Kadavu Island, Fiji: Fluvial Studies of a Volcanic Island in the Humid Tropical South Pacific

This paper examines features of drainage and stream channel form and process on the mountainous volcanic island of Kadavu in the humid tropical South Pacific, and interprets the findings in relation to island environmental characteristics such as geology, regolith soils, topography, vegetation and climate. At island and sub-island scales, drainage patterns are linked to the geographical arrangement and topography of the late Cenozoic volcanoes. Stream channel and bedload characteristics demonstrate the importance of both deep saprolite weathering profiles for supplying sediment into the fluvial system, and the high energy nature of the fluvial transport regimes. Landscape chemical denudation is estimated at 50-85 mm per 1,000 years from baseflow solute concentrations converted from water conductivity readings.
Relative tectonic and sea-level stability during the late Holocene and the largely undisturbed rainforest and savanna vegetation on the island suggest that climatic factors control rates of fluvial processes on Kadavu. Streamflow records show particularly that tropical storms can have a big impact. The effects of possible increasing numbers of cyclones in the South Pacific and human vegetation disturbance on Kadavu are considered.