8722-7 Tamboon Inlet

This information has been developed from the publications:

• Sites of Geological and Geomorphological Significance in Central Gippsland (1981) by Neville Rosengren, M.S McRae-Williams and S.M Kraemers.
• Sites of Geological and Geomorphological Significance in the Gippsland Lakes Catchment (1984) by Neville Rosengren.
• Sites of Geological and Geomorphological Significance in East Gippsland, Victoria (1981) by Neville Rosengren, M.S McRae-Williams

A small enclave of weathered Ordovician sedimentary rock occurs in the Cann Valley above Lake Furnell. Tertiary sands overly the granitic rocks east of Tamboon inlet and to the west are the sands for the barrier formations that extend to Sydenham Inlet. Other Quaternary materials include extensive alluvium and swamp deposits between lake Furnell and Reedy Crrek, silt, sand and gravel in the Cann River delta, an beach and dune sands.

1) The river channel and delta.

The Cann River is tidal for several kilometres upstream from Furnell and salt water probably penetrates as fas as the rapids above the junction of reedy Creek. The narrow and deep channel is here fringed by reedswamp which is most extensive at Lake Furnell and in the backswamp and cut-off meander forming O’Meara Lagoon. The delta consists of coarse sand overlying silts and clays and there is one small deltaic island that accumulates sediment during river floods.

2) The northern basin.

The main body of the Tamboon Inlet consists of two basins which are separated by a sand bar and a long tapering spit that extends from the western shoreline. The northern basin is saucer-shaped and slopes gradually to a maximum depth of eight metres. This basin. Being relatively isolated from river and tidal inflow, contains the finest sediment material in the inlet.

3) The southern basin.

This slopes steeply to a maximum depth of 12 metres. Being more open to river and tidal inflow, the sediments here are coarser and there is a smaller clay fraction than in the northern basin.

4) The eastern channel.

A well defined channel lies along the eastern margin of the inlet and may be traced from the river mouth south towards the entrance. The channel is of variable depth averaging two to three metres. The deepest point (8 metres) is in the south where it is constricted between granitic rocks to the east and the active dune mass to the west of the entrance.

5) The entrance.

The entrance and the coastline immediately to the east and west are areas of considerable geomorphological interest. The entrance is periodically closed by a sand barrier and after opening it becomes constricted by spit growth from both eastern and western sides that coalesce to re-form the barrier. The height of the barrier is increase by sand deposition from wave to wind action and the water level in the inlet rises until the barrier is breached. Local residents occasionally artificially open an entrance through this barrier.

Bluffs and freshwater lagoons now partly filled by sand dunes indicate a former entrance channel that extended two kilometres east to Clinton Rocks Creek. The size of these dunes and the degree of vegetation cover suggests that this channel has not been active for perhaps several hundred years.

On the south west of the entrance is a massive active dune formed in part from the re-activation of older vegetated parabolic dune ridges. The dune has an active slip face on the northern and eastern sides and develops a steep sliding face when undercut by tidal flow through the entrance channel. Estimates of forward movement made from aerial photographic interpretation indicate an average rate of 1.2 metres per year for the period 1940 to 1973. It is apparent from the configuration of the entrance that the channel, when open, is deflected to the west and thus undercuts the dune. Some sand eroded in this way washed into the inlet but much is carried out by ebb tide flow and moved back onshore by wave action and blown once more into the dune system.