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

1.2.1 Topography:
The floor of the harbour rises with an averags
gradiant of 1:100 (Map N.Z. 6321 Lyttelton Harbour).
The deepest part is at Godley Head from where the depth
decreases steadily to Governo~s
Bay which is largely
uncovered at low tide, (Fig 2). Over a large area
surrounding Quail Island, Charteris Bay and Purau Bay
the depth is constant at 3.5 - 5.5 metres. Only at. two
places are rocks exposed on the harbour floor. These are
Parsons Rock, north of Ripapa Island, and Shag Reef,
north~east
and the mooring basin.
of Quail Island, midway between Quail Island
Most of the harbour shore is fringed by cliffs
that have been cut into the solidified lava.
Alternating
with this, and particularly around Quail Island, similar
cliffs have been cut in the deep loess deposits.
The harbour is surrounded.by hills, averaging about
400 metres in height, formed by the lip of the Lyttelton
Harbour volcano crater. This topography tends to
restrict the inflow of freshwater from the local catchment
(Maps NoZ.M.Se 2 S 84/4 and S 84/5)
Hydrology:
Wave action is generally small.
of low amplitude and long wavelength.
It usually is
Normally the swell
is 100 metres long and 1 to 1.5 metres high. ~he wave
; j'
base from this extends to about seven metres and disturbs
a great deal of mud in the upper harbour.
While this type of swell generally results from
oceanic disturbances, it may be accentuated by winds from
the north-east and south~west.
These are locally strong
due to the funnelling effect of the surrounding hills.