The evolution of Jumpinpin Inlet - OzCoasts

The evolution of Jumpinpin Inlet
(a) domination of tidal flow outward of the inlet, sufficient to counteract wave-induced
onshore sediment movement; and/or (b) that efficient natural sand bypassing is
occurring.
The ebb-tidal delta at Jumpinpin is offset, protruding farther seaward on the downdrift
side than the updrift side of the inlet. Along wave-dominated coasts the longshore
currents dominate the sediment dispersal pattern. Consequently, the barrier islands
flanking Jumpinpin have become long and continuous while the ebb delta remains
small because of rapid dispersal of its sediment by waves.
Three major forms of sediment accumulation are associated with the ebb-tidal delta at
Jumpinpin: (1) Asymmetrical swash bars oriented landward and forming a broken
semicircle around the perimeter of the delta; (2) channel margin linear sand bars that
trend perpendicular to shore and parallel to the main channel; and (3) a subaqueous
terminal lobe deposited seaward of the main channel ebb currents. These
characteristics are shown in the diagram below (Figure 5.2) and are best seen in the
1965 aerial photograph (see Appendix B, Figure B.3).
Figure 5.2. Typical ebb-tidal delta morphology
(Source: Adapted from Hayes, 1991)
A common feature of ebb-tidal deltas shown in the 1965 aerial is the segregation of
ebb and flood flow. The primary channel at Jumpinpin has a main channel oriented
perpendicular to the shoreline which carries a large portion of the ebb flow. The flood
flow tends to be distributed as a sheet, with a number of flood channels. These
channels hug both beaches.
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