The Subaerial Volume Index (SVI) is a simple
measure of the overall (i.e., for the five
cross-shore profile lines) accreted/eroded state
of the beach relative to the long-term (1976-2006)
average. A positive SVI indicates that the
subaerial beach (the section of the beach system
situated above mean sea level) has a greater
amount of sand volume relative to the long-term
average, whereas a negative SVI means that the
subaerial beach has less sand volume and hence in
a more eroded state.
Beach Orientation Index (BOI)
The Beach Orientation Index (BOI) is a gauge of
the average orientation of the beach, as measured by
the mean sea level contour, relative to the long-term
(1976-2006) average. A positive BOI means that the
beach has a more clockwise orientation relative to the
long-term average, whereas as a negative BOI
highlights a more anti-clockwise orientation. The BOI
is an important indicator of beach rotation, where
sand within the embayment alternates between the two
extremities and can expose one end of the embayment to
erosion.
Southern Oscillation Index (SOI)
The Southern Oscillation Index (SOI) records the monthly
difference in surface air pressure between Tahiti and Darwin
as a measure of El Niño and La Niña events in the Pacific
Ocean. Consistent SOI values less than -7 generally indicate
El Niño events, while consistent SOI values greater than +7
generally indicate La Niña events.