User:Kingytom/Beach erosion

Beach Erosion - Gold Coast and Tweed shire
Vanishing Beaches - Perception or Reality. After observing shoreline developments and changes to Gold Coast and Tweed Shire beaches for some 70 years in conjunction with studies of Coastal Engineer’s reports including this Professorial Lecture, I too have come to the same conclusion as Sam Smith (1994) that University graduates exhibit a limited understanding of the forces that control our coast’s behaviour. Their published studies report only information that supports their computer based models ignoring information from observations, history, earlier reports and technical presentations so their conclusions fits in with their clients requested outcome feeling secure no one will challenge their conclusions.

Unfortunately an example of this pre-agreed agenda, from the tutorial side, is this June 2001 Professorial Lecture presented by the Director of the Griffith Centre for Coastal Management which details two forms of erosion that impact on beaches. The first is described as “Short Term Natural Variability – Submersion or Claytons Erosion, the erosion you are having when you are not having erosion”, which includes “Perceived” erosion observed during elevated storm surges (cyclones).

The second is “Shoreline Recession” resulting from ‘our’ interference with the natural supply of sand that sustains our beaches, a form that came into existence after European settlement. It occurs when sand is trapped by man made structures that have altered the coastal profile with the extension of the Tweed River training walls in 1962-5, being quoted in this lecture as the classic example of this form of erosion, when a large volume of sand was with-held from Gold Coast beaches creating shoreline recession to the beaches to the north for some 20 years with a corresponding build-up of sand to Letitia Spit.

While this information can be verified from the Tweed River Entrance Sand Bypassing Project June 1997 (TRESBP) the question to be answered is the non disclosure that this form of “Recession” also occurred after the construction in 1891-1904 of the first set of training walls at the Tweed River entrance when an even greater volume of sand was with-held from these same Gold Coast beaches with similar shoreline recession lasting into the early 1920s before Kirra beach rebuilt “naturally” to the ideal conditions depicted in the lecture’s 1936 photo.

Of further interest is the fact that these two occurrences of “shoreline recession” as a result of a training wall being built and then extended at a later date are not unique events there being a history in NSW dating back to 1862 where since then some 20 “profile changes” have been constructed, repaired and extended from the Hunter to the Tweed Rivers (Manly Hydraulics Laboratory Report 1994). However in the 139 year period up to 2001 no academic studies have ever been undertaken to reconcile the timing of these “erosion” (recession) events to when these “profile changes” were put in place which, in many instances, required protective seawalls constructions to mitigate recessions.

Consequently it is not surprising that Consulting Engineers, questioned along these lines, refuse to discuss this issue and instead refer to “inherent” difficulties they have to work under in understanding coastal behaviour recording them in correspondence as: “Generally incomplete understanding of the dynamic and complex interactions of physical coastal processes and sediment transport mechanisms”; “Limited comprehensive data sets upon which to determine underlying definitive trends in the movement of coastal features and shorelines”; “The influence of man induced impacts such as sand mining, dune restoration works, shore protection structures, river mouth breakwaters, etc”.

Further to this matter there is a reference in this lecture to a PWD Report (1978) covering a 20 year erosive period, mid 1950s to 70s, when both the Tweed and Gold Coast beaches recorded significant “recessions”. However it is also of interest to note that this period includes sand mining, and when already constructed walls were extended at the Richmond and Tweed rivers with new training walls constructed at the Brunswick River, Mooball and Cudgen Creeks all of which had impacts by interrupting the natural sand movement over adjacent lengths of related coastlines necessitating in some places sea wall constructions before a recovery, as a result of the completion of infill against their southern constructions, resulted in predicted recessions never eventuating.

On these matters the author of this lecture had a considerable input into data collection for the TRESBP (1997), as listed in references for a WBM Oceanics (2001 Study), and would consequently be expected to be conversant with the history of past events that affected adjacent Letitia Spit and the Gold Coast shorelines. However, to support the claim that the “ultimate” condition for Kirra Beach would be achieved as a result of effective management and long term planning, in this case the projected outcome from the TRSBP, it is evident that it was convenient to omit any reference to the earlier recession and subsequent recovery for Kirra Beach.

However the condition of Kirra Beach is now under fire with the TRESBP being accused of turning the beach into a desert, noted in a paper article in the Gold Coast Bulletin (September 27-28 2008) and published under the auspicious of this same Professor, where when the visual background of a supporting photo of the “Kirra Desert” is taken into account, there is a possibility that this “desert” photo was taken before the Tweed Sand Bypassing System came into operation in May 2001. Similarly the “perception” by another senior University Lecturer that by some mechanical intervention Nature can be directed to maintain Kirra Beach in a previous eroded state (Readers Digest 1983) defies logic, and is an undertaking fraught with unforeseen dangers.

With Nature now reluctant to move this accumulated sand north after several coastal erosion periods, the latest being 18-21 May 09 and 19-23 June 09 (Severe East Coast Lows), when previously built Gold Coast retaining walls were re-exposed, suggests this section of shoreline has yet to achieve its optimum alignment as determined by the naturally occurring headlands, and just maybe the lost Currumbin beachfront property, mentioned in the lecture, was an outcome from the 1891-1904 Tweed River training walls and that Kirra, Currumbin and beaches to the north may have continued to rebuilt had the extension to the Tweed Walls in 1962-5 not been undertaken. This exercise in conjunction with the bypass system has proved to be a failure in one of its aim that of achieving a safe navigational entrance to the Tweed River without recourse to river entrance dredging. (News Letter No 15 July 2006)

Consequently if Graduate Engineers are lacking an understanding of these coastal processes this reflects on the institutions involved in their teaching and highlights a need for academics to undertake a review of tuition methods by belatedly coordinating the history of recessions from man made profile changes with actual erosion outcomes. That is in the words of Sam Smith, deal in “Reality” (observations) to a greater extent as against the problems created by relying on the “Perception” from computer based models.

Kingytom

References; Tomlinson, Roger 2001 ‘Vanishing beaches – perception or reality, Research report 7, Griffith Centre for Coastal Management, Griffith University, Southport’.

Smith, A.W. Sam, 1994, ‘the coastal engineering literature and field engineer (editorial): Journal of    Coastal Research, v. 10, p iii-viii’.

NSW Public Works Department, 1978, Byron Bay – Hastings Point Erosion Study. Report No. PWD 78026, November.

Tweed River Entrance Sand Bypassing Project. ‘DLWC H.O./51/97, DLWC Report No. CFR 97/9, June, 1997. Report No.9706236-4D’.

Manly Hydraulics Laboratory Report. ‘NSW Breakwaters Asset Appraisal Part 1 Project Summary, May 1994, MHL Report No. 645,ISBN 0 7310 0985 1’.

WBM Oceanics Australia 2001. Tweed Shire Coastline Hazard Definition Study.

Gold Coast Bulletin; ‘September 27-28, 2008’.

Readers Digest, 1983. Guide to the Australian Coast, pages 54-55 Kirra Beach 1960s to 1970s.

Google Earth. Kirra Beach QLD Australia (30th April 2009)

News Letter No. 15 2006. www.tweedsandbypass.nsw.gov.au