The evolution of Jumpinpin Inlet - OzCoasts

The evolution of Jumpinpin Inlet
must have been in abundant supply as despite severe weather in the early 1950s
closure was complete in 1955.
During the period of closure of the southern channel, the northern channel widened in
response to increasing tidal prism. Once closure was complete, littoral transport
conditions returned to normal. The channel then began to slowly migrate and
continued to do so until a second channel was again created. Migration of the
northern channel was slow due to the presence of coffee rock on Kalinga banks and
probably on the other deltaic islands. Efficient sand bypassing by stable inlet and tidal
current processes is witnessed in deposits of sand to the downdrift side causing a
slight offset in coastal alignment.
Cyclones in the early 1950s severely eroded South Stradbroke spit from the east.
Flooding in 1967, 1972 and 1974 exaggerated erosion in the bend of Tipplers
Passage where flows attempt to move along a straight path. By 1970 the spit was
dangerously narrow. It is of little surprise that the catastrophic weather of 1974 forged
a second channel through this spit, thus denoting another cycle in the evolution of
Jumpinpin.
The force of the 1974 storms was sufficient to further widen the northern channel, and
with two channels active, Jumpinpin was capturing more tidal prism than before. By
1978 rebuilding of the updrift spit had begun, thus consuming littoral drift which in turn
restricted migration of the northern channel and caused a recession in the downdrift
offset.
Between 1978 and 1981, when the northern channel came dangerously close to
closing, more tidal flow than ever before was directed through the southern channel.
The northern channel may still have been conducting significant volumes of water and
as such it is possible the two channels were beginning to behave as separate inlets. If
the northern channel had closed, the cycle of inlet migration and spit breaching as
experienced early in the century may have again taken place. However, severe
cyclones in the early 1980s prevented this from happening. The channel was forced
to expand to accommodate the 0.7m storm surge associated with the cyclone of
1981. By 1983 it had returned to critical width by scouring the sand mass separating
the two channels rather than scouring the downdrift bank. The southern channel also
widened implying more tidal prism was moving through Jumpinpin than before.
Prior to the 1981 cyclone, North Stradbroke developed an east–west square
foreshore at Jumpinpin. This implies that although the channel had narrowed
significantly, the volume of water moving through the channel was still high. The high
flow rates jetted water directly eastward out to sea and prevented erosion of North
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