The benthic ecology and community structure in Lyttelton Harbour ...

17.
is particularly apparent ar6und Governors Bay, Head of
the Bay, and Charteris Bay where large mud flats are
e~ppsed
at low tide (Fig.S).
In the middle harbour, extending from Ripapa
Island to the tip of Quail Island, there is a region of
coarse sand which appears to be maintained by current
action since this lies in the path of incoming tidal
currents. This is fringed on the western side by an area
of sandy mud which slowly grades into the pure muddy
arease
The sandy regions also contain a large 'proportion
of crushed shell which adds to their coarse character.
This is particularly true of the region opposite Purau
Bay.
Reference was made in Section 2.2 to sediment
derived from loess and alluvial action. These sediments,
which are initially deposited unsorted are subjected to
current action and are grad~ally so~ted and redeposited.
Mention was made in Section 1.2.3 of dredging.
This has disturbed the natural sedimentation, raised the
bed of several eastern Bays, and there is also a constant
drift back up the harbour of the dumped material.
2.6 Hydrodynamic Processes
The distribution and character of sediments
is controlled by three factors. These are:
1. The supply of raw materials:
2. Turbulence through wave action;
3. Current sorting.
The factor that is of greatest importance in the
4
case of Lyttelton Harbour is current action.