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Collapse Issue 442 - 09 Apr 2018Issue 442 - 09 Apr 2018
Collapse  NEWS NEWS
Popular cruise is cancelled as channel silts up
Auditing firm backflip clears Gosford accounts
Anzac Day services
Comments sought on flying fox strategy
Items of local heritage significance identified
Traffic lights at school unlikely before 2020
Rogers Park sandstone cost $31,790
Library refurbishment starts
Lightning stopped trains, caused fire and blackouts
Council maintains dredging position after legal advice
RMS clarifies its role with Ettalong Channel
Ferry services cancelled
Chamber fears ferry service may have to stop
A chance to reminisce about simpler times
Information provided for Seniors Festival
Technology sessions for seniors
Hotel owner seeks approval for 'urgent' works
Proposal to replace single dwelling with three
Proposal 'does not comply' with setbacks or length
Construction certificate issued for non-complying units
Wicks expects speedy response from ACCC
Street tree group praised by council
Rotary seeks exchange student
Chicken shop closes as administrator is appointed
Collapse  FORUM FORUM
Why is the channel not a Government priority?
Erosion study in 1977 described sand dynamics
Government should not approve unsafe ferry service
Council is not facing our infrastructure needs
Why don't we have our own Peninsula Council?
Making the area accessible
Residents could have made events viable
Unaware of planning regulations?
Collapse  HEALTH HEALTH
Cheque presented to hospital
New rehabilitation clinic opens
Collapse  ARTS ARTS
Pop-up paella at The Bays
Songwriters' conference planned for June
Troubadour hosts Canadian performers
Collapse  EDUCATION EDUCATION
Anzac service held early
Cross country carnival on Friday
Mariners learn dance moves with students
School leaders invested before Easter
Parents body positions announced
School receives grant for sensory garden
Supplies collected for Tathra community
Collapse  SPORT SPORT
Umina boxer makes Commonwealth Games
Umina rower takes schoolboy coxed four title
Youngest surf patrol praised for their actions
Ettalong prepares for pennant season
Umina bowls' major singles

Erosion study in 1977 described sand dynamics

In the article "Channel needs science, not amateur ideas, says CEN" (Peninsula News edition 441), the chairman of the Community Environment Network, Mr John Asquith, stated: "CEN could find no credible studies to support a strategy of pumping sand out of the clogged channel into Brisbane Water at Half Tide Rocks and onto Ocean Beach."

In the same article he claimed dredging needs science engineering and common sense and not ill-considered amateur ideas, opinions and dogma.

The problems of erosion at Ettalong and Ocean Beach go back well before the construction of the Diggers Building in 2004.

In fact, the problems are well documented back to 1948.

Dredging and renourishment of the beach is part of the highly credible 1977 Ettalong Beach Erosion Study and Management Program conducted by the Department of Public Works, Coastal Engineering Department.

Summary inter alia: The object of this study was to gain an understanding of the processes governing erosion of Ettalong Beach and to formulate a remedial Beach Management Programme for the area based on this understanding.

An appreciation of sand movements in the region and the controlling physical processes was developed progressively.

A geological survey was undertaken to define the boundaries of sediment movement within the Ettalong estuary.

A conceptual model was developed to describe the sediment dynamics within these boundaries prior to human intervention.

The model was verified by interpretation of historical data, aerial photographs and examination of the impact of human intervention.

Data on currents, tides, waves, shoal mobility and so on, was collected in the field and used to evaluate the time scales of erosion processes and rates of sand movements.

From this investigation a number of significant conclusions were reached.

Erosion events in the Ettalong area were inter-related and therefore not soluble in the long term by means of isolated remedial works.

Erosion is not primarily caused by the natural loss of sand from the estuary as the quantity of sand contained between the Rip Bridge and the outer edge of the Ettalong Point shoal in Broken Bay remains essentially constant.

Sand contained within this estuary system is quite mobile, moving from the outer shoal to the beach and thence back to the outer shoal via the tidal channels.

Erosion is attributable to the fact that this circulatory pattern is variable in time, rate and location, resulting in beach fluctuations.

These fluctuations can be increased by variation in channel alignment within the estuary.

Past works have interfered with this natural sand movement and/or removed sand from the system.

Hence Ettalong Beach is more sensitive to erosion cycles which are also more severe in degree.

In addition, these works have encouraged the development of a deep channel close to Ettalong Beach which further accelerates the removal of sand from the beach.

To retain an estuary beach amenity at Ettalong, a more natural pattern of sand circulation should be restored and the nearshore channel development against the Ettalong shoreline should be curtailed.

"Soft" management techniques such as dredging, beach nourishment and dune construction are more suited to achieving this objective than "hard" structures such as rock groynes.

In view of these conclusions, a beach management program was been formulated, based on the zoning of the beach according to its sensitivity, to the various identified modes of erosion and the implementation of "soft" management techniques.

The programme provided a flexible framework upon which to base future works, maintenance and long-term planning for Ettalong Beach.

It is stressed that there should be continuing management of this fragile beach in the future.

The beach management program recommended the inter-related activities of continued monitoring of the system and three stages of works.

The recommendations are detailed in Section 8 and summarised below.

1. Institute an ongoing monitoring program.

2. Establish a more natural sand circulation system by nourishment of the beach and nearshore channel, dredging, partial removal of Ettalong Point groyne, modification of Ettalong Beach groynes etc.

3. Consolidate the preceding works by construction and stabilisation of dunes in light of an assessment of the establishment phase.

4. Maintain the sand system with possible periodic nourishment as indicated by the monitoring program.

As part of the 1977 Department of Public Works survey, sampling was carried out over the entire area of Broken Bay.

The Hawkesbury River as far as Patonga Beach and into Brisbane Waters as far as Pelican Island.

To examine the dynamics of sand movements on the shoal at the entrance to Brisbane Waters, samples were collected at specified locations in Broken Bay and on the shoal at monthly intervals.

Beach erosion has been the subject of many studies since the 1977 report.

Beach erosion is not unique to Ettalong.

It is a worldwide problem.

If a study came up with an answer to natures' fury which causes the erosion, it would create world headlines.

In the meantime, dredging of the Ettalong channel is necessary in keeping with the recommendations of various studies and to help save lives as the dangerous channel at little Box Head has claimed many lives over the years.





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