Coastal Hazard Data and Development Setbacks for Coromandel Peninsula Beaches

The close proximity of development to the sea and the degradation of natural dune systems have resulted in coastal hazard problems at many Coromandel coastal settlements (eastern and western). There is also potential for hazard problems to be considerably aggravated over the next 50-100 years as a consequence of predicted sea level rise and intensification of existing near-shore development. The Development Setback Lines have therefore been designed to identify the areas at risk from coastal hazards (erosion and flooding) and provide for maintenance of a protective buffer zone even with worst likely erosion. Purpose: To predict hazard zones and determine safe development setbacks.

Coring and radiocarbon dating of Holocene dunes Historic shorelines Beach profiling Historical coastal flooding Development setbacks Primary Development Setback (PDS): includes the worst probable erosion likely to be associated with existing coastal processes plus an allowance of 10 m to ensure a protective buffer is maintained even under conditions of worst erosion. Secondary Development Setback (SDS): the second setback incorporates an allowance for the effects that may accompany predicted global warming over the next 100 years. Along the eastern Coromandel coast, the PDS is either 35 m or 40 m, while the total SDS varies from 50-60 m. The equivalent setbacks along the western Coromandel are typically 25 m and 50 m, though a lesser setback (15 m) is recommended for Otautu Bay. Toe of Dune: the shoreline mapped from 1995/96 aerial photography (Coastal Toe of Vegetation) provided a baseline for the PDS and SDS to be mapped from. This line represents the toe, or base of the most seaward dune at the time of the 1995/6 photography. This line was mapped from the photos and ground truthed with field visits. Considerable care was taken to keep this line reasonably smooth. This was necessary to minimise irregularities in location of the setback boundary, which could potentially disadvantage some properties in relation to adjacent areas. Setback for Undeveloped Areas (SUA): in areas that have not yet been developed, a third setback has been mapped. On the eastern and western Coromandel coast, this setback is 100 m and 50 m respectively. This larger setback (same as SDS on western Coromandel) is to allow for coastal hazard risk and other values such as natural character and public amenity. In some specific locations, a different setback has been proposed and reasons for this are recorded in the technical report and as comments in the attributes of the GIS database.

Coastal areas of the Thames Coromandel District Council and Hauraki District Council Administrative boundaries.

Coastal areas of the TCDC and HDC boundaries -

The dataset has varying currency of data ranging from the early 1990s to the present day.

Data has been assessed from aerial mapping, oblique photography, recollections from local residents, radiocarbon dating of dune sediments and other coastal deposits, beach surveys, and applied science (e.g. using the Brunn Rule). These have been used to determine the long-term trend of each shoreline and the effect of predicted sea level rise. Holocene beach development investigations involve drilling and dating Holocene dunes and limited investigations of the surface morphology of the dune systems. This work was undertaken at Whiritoa, Whangamata, Opoutere, Tairua, Cooks Beach, Buffalo Beach, Matarangi and Whangapoua. Shoreline change is determined from limited mapping of historical shoreline change, beach profile monitoring, and historical aerial maps. Coastal flooding work includes the compilation of historic newspaper reports and analysis of the Tararu tide gauge records. Frequency of collection: It is envisaged that the data will be updated every 10 years. Updating and maintenance of the data will not be on a continuous basis.

The dating of barrier development relies heavily on the radiocarbon dating of shell. Shells provide an indication of the maximum age of the ridge immediately seaward, be it cannot be assumed that they necessarily provide a useful indication of the age of the ridge immediately landward. Gaps in collection: Infrequent mapping of shoreline change and beach profiling and aerial maps. Data quality: Peer reviewed by Dr Terry Hume (NIWA) and Associate Professor Patrick Hesp (Massey University), both concluding that the proposed setbacks were not overly conservative on the basis of present scientific data. Shell radiocarbon dating was repeated to provide some crosscheck on dates. Identification of where samples were taken is important for dune dating. Positions of drill holes were identified on large scale, vertical aerial photographs (typically 1:5000). Attribute accuracy: Unknown Completeness: 100%, although site specific strategies are required at some locations.

report, tables, maps. The data can be provided in hard or soft copies of customised GIS map outputs at a range of scales. Digital Format: MS Word, MS Excel, GIS (ArcView)

Determine which properties are prone to coastal hazards as shown by the position of the proposed development setbacks Locate the position of the 1995/96 vegetated toe of dune, and hence monitor future changes in the position of the beach Determine areas requiring site specific strategies

Environment Waikato makes the dataset available to TLA's on the basis that no modification of the dataset is to take place (as this could reduce its validity). The following disclaimer applies to this dataset; DISCLAIMER: While Environment Waikato has exercised all reasonable skill and care in controlling the contents of this information, Environment Waikato accepts no liability in contract, tort or otherwise howsoever, for any loss, damage, injury or expense (whether direct, indirect or consequential) arising out of the provision of this information or its use by you. Sensitivity/Confidentiality: None

The proposed development setbacks were developed from scientific data collected up until July 2000. If required, the dataset will be updated in 10 years time as new research and information comes to hand.

Additional comments: Currently going through community consultation to be adopted into local council planning.