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 Port Phillip Bay Heads

 

Due to the restriction of the tidal range within Port Phillip caused by the relatively narrow entrance, the tidal stream in the vicinity of the Heads does not turn at high and low water.

The force of the tidal streams depends upon the relative water levels inside and outside Port Phillip. The greatest difference in levels occurs at about the time of high and low water at Port Phillip Heads. This is when the inward and outward streams run at their strongest, up to six knots under normal conditions and may exceed nine knots in extreme conditions.

Slack water at Port Phillip Heads occurs at about three hours before and three hours after high water, which is when the levels inside and outside are the same. The ingoing stream runs from about three hours before to about three hours after high water and the outgoing stream at other times. On the average, it is high water at the Port Phillip Heads three and a quarter hours before that at Williamstown and slack water at the Heads when it is high or low water at Williamstown.

Tide Stream Signals

Tide stream signals are shown by night at the Point Lonsdale Lighthouse below the main light. Flood stream is denoted by one fixed green light for the first half of the flood and two fixed green lights vertically aligned for the second half of the flood. For the ebb stream, the first half of the ebb is denoted by one fixed red and the second half by two red lights vertically aligned.

Note: Tidal height information can be obtained by contacting Point Lonsdale Signal Station.

Southern Port Phillip

As shoal water extends some distance from the shore at Port Phillip Heads, the tide, due to friction, rises and falls over the shallows more slowly than in the channels. Consequently, during the rising tide, the water level in the fairway is higher than inshore and causes an onshore set, whilst, during the falling tide, when water level in the fairway is lower than inshore, there is an offshore set.

The main body of the ingoing stream from the southward and eastward sets at about 038? (T) directly through the entrance fairway, with drifts of considerable force across and through the reefs, spreading towards Shortland Bluff (Queenscliff) and the southern shore; thence directly through the channels of the Great Sand Bar.

In the South Channel, particularly in the western half, the incoming tidal stream generally sets in a direction of 108? (T) along the channel. At the same time, there is a north easterly and south easterly flow over the northern and southern banks of the Great Sands respectively. At the eastern end of the channel near Hovell Pile Light, the incoming stream sets at 045? (T) whereas the outgoing stream sets at 180? (T). The outgoing tidal stream has a rate of 2 knots and sets along the channel in a 288? (T) direction. Concurrently the flow over the northern and southern banks of the Great Sands is southerly and north westerly respectively.

The outgoing stream coming directly through the channels sets towards Lonsdale Bight, and from there out through the Entrance with great force partly athwart the channel at 200? (T) thence away south eastward along the land towards Cape Schanck.

The Victorian Tide Tables give the times of slack water at Point Lonsdale (Port Phillip Heads), i.e. when the tidal flow at the entrance to Port Phillip Bay changes direction. The timing of the tidal streams is such that slack water occurs at almost the same time throughout the south of the Bay, e.g. the time of slack water at Hovell Pile Light will be the same as that at Port Phillip Heads.

As at times the ebb stream attains a speed of nine knots the navigation of low powered vessels through the Heads will be rendered easiest at about the times tabulated for the start of tide stream. 

Geelong Approaches

The tidal stream in the Western Arm, i.e. Geelong Outer Harbour and Corio Bay is not appreciable. The exception is where the stream crosses the bar between Point Henry and Point Lillias; the outgoing stream at this point is 1 knot during the second quarter.

Tide and Stream Predictions

Tide and stream predictions are published annually by the Victorian Channels Authority (VCA) in the Victorian Tide Tables. The booklet is available in each October for the next calendar year and can be purchased Sport Phillip Marine. 

                                     

Chart Datum

Chart Datum used in Victoria is the Lowest Astronomical Tide (LAT). Extremes in meteorological conditions influence tidal levels and on some occasions, the tide level falls below LAT though this is infrequent.

Chart Datum are referenced to the Australian Height Datum (AHD), which is constant and based on a 1971 adoption of mean sea level at thirty tide gauge stations around the coast of the Australian continent.

Tides at Port Phillip Heads

Chart Datum at Port Phillip Heads (Point Lonsdale) is 0.86m below AHD and at Rip Bank it is 1.46m below AHD. The mean higher high water on Nepean Bank is 2.Om whereas on Rip Bank it is 2.5m.

Tides for Rip Bank and Port Phillip Heads (Point Lonsdale) may be obtained from Point Lonsdale Signal Station by VHF Channel 12.

 

Tides at Melbourne (Williamstown)

Chart Datum is 0.524m below AHD. The average tidal range is 0.7 metres.

The height of the tide at Williamstown may be obtained from Harbour Control by VHF Channel 12.

Tides at Geelong

Chart Datum for the Inner Harbour is 0.580m below AHD while Chart Datum for the Outer Harbour is 0.524m below AHD. The average tidal Range is 0.8 metres.

The height of the tide at Geelong may be obtained from the duty Marine Controller by VHF Channel 12.

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