Accretion, Depletion, Erosion- what does it all mean?



CCRU recently questioned the CCC regarding the erosion line on page 22 of Item 7 of the recent Coastal Hazards adaption plan programme report presented at a round of 3 Public meetings in November 2020.


Download the report here.

establishment-coastal-hazards-adaption-p
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Download • 11.92MB

CCRU asked why an Erosion line was indicated along the Southshore portion of this diagram and inquired as to the evidential Base for this erosion line. CCC indicated it had used 2017 information.


CCRU raised concerns that this recently released CCC report stated it was using the most current information available. CCRU view the most current report for this beach area as being the NIWA Sand Budget Report 2018, which indicated that this beach area was in fact an accreting beach.


CCC indicated to CCRU that this new information would be included in a new update along with other relevant data in a Tonkin and Taylor technical update report later in 2021. In discussion with Staff at the 'after the public meeting' in New Brighton, it was stated that, even if the new information was included there would still be an erosion line on the Southshore beach.


CCRU posed the question of whether erosion was the correct or appropriate term to give the line that extends along the South Shore Beach. Given that erosion, as a term, may have negative connotations for both planning and insurance, and is the word erosion appropriate or erroneous? Should it in fact be more correct to term this area a Dynamic Beach Environment rather than an erosion zone?


CCRU recognise that there will be accretion and degradation over time but our understanding from the NIWA report is that degradation will not put the sand budget into the negative territory for the foreseeable future and that the process is more one of beach dynamics than that of erosion.


As this is not our area of expertise, CCRU commissioned BOEE (Brighton Observatory of Environment and Economics) to assist in increasing of our understanding of this issue.


We asked BOEE the following “Would it be possible for you to clarify and define the word erosion in this context and the appropriate and correct use of erosion to describe a process, again in this context."


Here is the link to the Definition.

BOEE-Coastal Erosion and Accretion-Jan-2
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Download • 218KB


While the BOEE definition in no way provides an opinion on the appropriateness of the use of the word 'Erosion', it does indicate there is a need for pause. We need to carefully consider the words and definitions used in these reports. They will become policy and inform actions!


Words have power, history, and stigma. Best practice would seem to indicate words used about a process should be neutral and describe that process- nothing less nothing more. If this is the case then should the line not be titled accreting beach, as the science indicates, this is factually the process that is occurring?


We need to be sure we get this correct from the start.





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