Sitaram Garimella

Rates of floodplain accretion in a tropical island river system impacted by cyclones and large floods

Abstract Fluvial processes, especially rates of floodplain accretion, are less well understood in the wet tropics than in other environments. In this study, the caesium-137 (137Cs) method was used to examine the recent historical sedimentation rate on the floodplain of the Wainimala River, in the basin of the Rewa River, the largest fluvial system in Fiji and the tropical South Pacific Islands. 137Cs activity in the floodplain stratigraphy showed a well-defined profile, with a clear peak at 115 cm depth. Our measured accretion rate of 3.2 cm year−1 over the last ca. 45 years exceeds rates recorded in humid regions elsewhere. This is explained by the high frequency of tropical cyclones near Fiji (40 since 1970) which can produce extreme rainfalls and large magnitude floods. Since the beginning of hydrological records, large overbank floods have occurred every 2 years on average at the study site. The biggest floods attained peak flows over 7000 m3 s−1, or six times the bankfull discharge. Concentrations of suspended sediments are very high (max. 200–500 g l−1), delivered mainly by channel bank erosion. In the future, climatic change in the tropical South Pacific region may be associated with greater tropical cyclone intensities, which will probably increase the size of floods in the Rewa Basin and rates of floodplain sedimentation.

Characterization of aerosols generated in a steel processing factory

The levels of total suspended particulates (TSP) within the complex of a steel factory (Fletcher Pacific Steel Fiji) have been investigated through high volume air sampling. The levels of TSP inside and outside (in the ambient environment) the factory has been found to be in the range of 121-339 and 33-80 μg m-3 respectively. The levels inside the factory exceed the WHO guideline by a factor of 2-4. The management of the factory was very proactive to determine the air quality for records and to safeguard the health and safety of all the employees, contractors, and visitors. At the request of the factory, the exposed filters were analysed by neutron activation and gamma-ray spectroscopy techniques and the results are presented.

Concentration of 7Be in surface air at Suva, Fiji

A high-volume air sampler and a high-resolution gamma-ray spectrometer have been used during the period 1999-2000 at the University of the South Pacific to measure the activity of 7Be in the surface air at Suva, the capital city of Fiji. The measurements indicate that the average concentration of 7Be in surface air is about 1.6 mBq m-3, which agrees closely with the corresponding values reported for other Pacific islands in the region. 7Be shows a significant correlation with nitrate in the atmosphere. This could imply long-range transport of anthropogenically-derived continental material to Fiji or the intrusion of nitrogen species from the stratosphere to surface air.

Trace element concentrations in sediments from Kadavu passage, Fiji

Grab sediments, collected from 11 locations from the Pacific Ocean floor in the region between Suva Peninsula and Kadavu Island, Fiji, were investigated for concentrations of 20 elements using neutron activation and high-resolution gamma ray spectroscopy techniques. The sediments were collected at distances between 5-35 km from the mainland and at ocean depths ranging from 500 to 2000 m. A comparison of the elemental abundances of these sediments with those of the Suva lagoon and other nearby locations indicates that the ocean sediments are likely to be derived from sediments washed out to sea from the mainland. The sediments also show no evidence of any metal contamination from the industrial activity in the Suva metropolitan area.