Understanding the Sediment System
Lifuka, Ha'apai, Kingdom of Tonga
Zulfikar Begg,, Jens Kruger1 & Susaane Pholer2
Applied Geoscience and Technology Division, the Secretariat of the Pacific Community, Private Mail Bag
Suva, Fiji Islands
2
Faculty of Science Technology and Environment, the University of the South Pacific, Private Mail Bag
Suva, Fiji Islands
Emails: zulfikar@sopac.org ;jens@sopac.org; pohler_s@usp.ac.fj;
1
Low lying islands and their reefal system formations are largely dependent on carbonate
derived sediments for sustainability. Acceleration of sea level rise over the century has
affected the mechanisms distributing sediments and the relative sedimentary processes that
zone our coastal regions. Sediment analysis in terms of grain size distribution and grain
composition is essential for monitoring coastal zones.
Two techniques were adopted to understand and describe the sediment systems in Lifuka.
Sieve analysis of the samples were done and an excel based macro (Gradistat) was used to
calculated the statistics for grain size distribution. This incorporated the methods of Folk and
Ward (1956) and the method of moments to produce statistical parameters arithmetically
and logarithmically.
Sorting and texture of sediments were used to suggest the possible transport medium.
Majority of the samples collected from the beach were coarse to medium whereas most
lagoon samples were medium to fine grained. General trend of sediment migration were
seem to be southwards from the courseway, north of Lifuka, which seemed to be halting at
the wharf and the old Jetty in Pangai.
Point Count analysis was completed using the Gazzi-Dickinson method and components of
sediment samples were noted. Majority of the composition in the samples were made up of
Foraminifera followed by corals, mollusk and coralline algae.
Wave and current dynamics were the major drivers of sediments. Lighter materials such as
forams are carried by tides in suspension and get deposited on the beaches. In addition to
that, long shore currents carry and deposit these sediments along the coasts. Denser
components such as corals resulted from adjacent reef colonies and probably disintegrated
by wave actions.
The presence of reefal components on the beach depicts a positive sign as it acts as a
reservoir for these sediments. Contrarily, sea level rise and wave events affect the sediment
budget on the beaches which has resulted in high erosion rates along the coast of Lifuka.