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An examination of vertical accretion of floodplain sediments in the Labasa river sugarcane belt of northern Fiji: rates, influences and contributing processes

Terry, James P. and Lal, Radesh C. and Garimella, Sitaram (2008) An examination of vertical accretion of floodplain sediments in the Labasa river sugarcane belt of northern Fiji: rates, influences and contributing processes. Geographical Research, 46 (4). pp. 399-412. ISSN 1745-5863

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Abstract

The 137Cs (caesium-137) method was used to investigate medium-term rates of sediment deposition on the floodplain of the Labasa River, on Vanua Levu island in northern Fiji. The Labasa basin is commercially important for sugarcane farming, which provides much revenue and sustains the economy in the greater Labasa area. Alluvium was sampled at three riverbank sites in vertical increments of 30 mm. Measured net vertical accretion rates, based on analysis of depth-profiles of 137Cs activity, ranged from 10 mm yr−1 at a low-lying site near a tributary confluence with the main river, to 60 mm yr−1 on a levée that was elevated slightly above the adjacent floodplain. These rates of accretion are high, but in general agreement with rates recorded using similar methods in other tropical Pacific island river systems. Soil erosion under sugarcane on hilly parts of the lower Labasa basin is an important factor in rapid floodplain development. Observations made during Cyclone Ami, which traversed Vanua Levu island in early 2003, illustrate the major contribution of severe storm events to floodplain sediment supply, by triggering numerous landslides on catchment slopes and in-channel debris floods, and by generating large-magnitude overbank floods.

Item Type: Journal Article
Subjects: G Geography. Anthropology. Recreation > GB Physical geography
Q Science > QC Physics
Divisions: Faculty of Science, Technology and Environment (FSTE) > School of Engineering and Physics
Depositing User: Ms Neha Harakh
Date Deposited: 11 Jan 2008 11:14
Last Modified: 18 Jul 2012 19:50
URI: http://repository.usp.ac.fj/id/eprint/220
UNSPECIFIED

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