Inlet Evolutionary Trends
Flood shoal and Aunt Lydia's Cove navigation
In the short term, the recommended dredging of a channel orientated from
northwest to southeast over the thinnest area of the west ebb spit of the flood shoal
will provide a serviceable navigation channel, with the least amount of dredging.
This dredged channel will connect the anchorage with the lower part of the west
flood channel and out to the inlet. In the near future, the apparent re-establishment
of the west flood channel through the spillover lob of the ebb shield of the flood
shoal will change the tidal circulation, navigation channel orientation, and flood
shoal growth. It appears that the west side of the present flood shoal will become
detached as the channel cuts through the shoal. The sand in this western part of
the present shoal will form a shoal similar to the former Tern Island south shoal.
The position and orientation of the entrance channel to the anchorage may have to
be re-evaluated as this shoal detachment takes place.
With the split of the flood shoal, the trend of shoal growth will probably be
located more to the east side of Chatham Harbor. The northward movement may
also continue until an equilibrium is established with the ebb and flood flow
dynamics. The growth in the flood shoal in both measured area and calculated
volume has continued since inlet formation and this influx of sand has interfered
with both the east and west flood channel position and depth. The re-established
west flood channel through the ebb shield area of the flood shoal may restore a
more stable tidal circulation to the upper reaches of the estuary.
Ebb shoal navigation
With the development of the north ebb channel since 1995, the ebb shoal has
undergone a switch from the once single main ebb channel that has migrated to
the south to a two-channel system. The north ebb channel appears to have begun
the process to become the dominant channel, and to abandon the south ebb chan-
nel. Southward and landward migration of the ebb shoal has all but pinched off
the elongated and hydraulically inefficient south ebb channel.
Future development of the more efficient north ebb channel will establish a
growth trend in the northern ebb shoal/swash platform, moving the north end
seaward. The north ebb channel will begin to migrate more to the south and repeat
the cycle of southward migration. The southern part of the ebb shoal and its large
swash platform will migrate south and landward following the South Beach
toward the mainland. Navigation over the ebb shoal will become more difficult, as
the north channel becomes the main ebb flow route and the south channel loses its
identity as the southern swash bars migrate randomly, bisecting the swash plat-
form into several small ebb channels.
Chapter 7 Conclusions