Results - data and trends
The beach profile data were collected from 1979 to 2013.
The graphs below show yearly horizontal shoreline changes at Coromandel east coast beaches since beach profile records began (1979 at most sites). The beach profile record shows that the position of the dune usually fluctuates by 10-15m and occasionally up to 25m. Shoreline fluctuations are greatest near estuary entrances, where the toe of dune can move by up to 100m. In some cases, hard materials underneath the sand limit the extent of erosion that can occur. Site specific influences on shoreline change are summarised in the figure captions below.
Sometimes one end of Whiritoa Beach erodes while the other end accretes. This is common at pocket beaches on the Coromandel Peninsula, and is sometimes called “beach rotation”, as it changes the orientation of the beach slightly. This indicates that the transport of sand along the beach often occurs in response to changing conditions. Other times erosion and accretion occurs along the whole beach. In general, the dune at Whiritoa has fluctuated by up to 10m over the period of the record.
This graph shows data from Whangamata Ocean beach (CCS56 - Surf Club) and Otahu Beach (CCS57 - Island View and CCS58 - South). The data shows shoreline fluctuations of 10-15 m at these beaches. Looking at the beach profile data, there appears to be a trend for accretion. However, old aerial photograph records show that this build-up is part of a longer term (multi-decadal) fluctuation. The longer term record also indicates that larger fluctuations in the shoreline can occur than those shown on the beach profile record.
This graph shows changes in the position of the dune at Onemana Beach since 1996. The data shows that the shoreline fluctuates by 10-15m.
At Opoutere, measurements are taken at four beach profile sites, from CCS41 (north) to CCS44 (south). There has been very little change since 1996.
The dune toe at Pauanui has fluctuated by up to 20 m since 1995. Profile site CCS38/1 is closest to the estuary entrance, and experiences greater shoreline fluctuations than elsewhere on the beach. There is no trend for long term erosion or accretion at Pauanui.
Tairua Ocean Beach
The shoreline has fluctuated by approximately 15m at the southern end of Tairua Beach (CCS36), but only 7m at the northern end (CCS37). Like many pocket beaches, Tairua Ocean Beach sometimes undergoes “beach rotation”, when one end of the beach erodes while the other end accretes. This occurs when sand is moved along the beach in response to changing conditions. The overall “average” beach change is relatively small.
At Hahei, the dune toe has fluctuated by 10-15m since 1979. There is no clear long term trend for shoreline change. Coastal erosion is limited in some areas at Hahei by underlying rock.
At Cooks Beach, shoreline fluctuations of up to 28m have occurred at CCS31 (opposite Hicks Place towards the eastern end of the beach) and 19m at CCS30 in the middle of the beach. Dune toe fluctuations at the eastern end of the beach (CCS31/1) have been largely prevented by shoreline armouring structures.
At Maramaratotara Beach, the dune toe has fluctuated by approximately 10 m over the last 30 years. Coastal hazard studies have identified hard, erosion resistant materials underneath the sandy beach, which will probably prevent erosion from occurring far beyond the current position.
Buffalo Beach (Whitianga)
The shoreline at Ohuka Beach (CCS24) has been influenced by human activities, including stormwater drainage and associated beach works. At the north end of Buffalo Beach (CCS25), severe erosion occurred in the winter of 2000, partly due to end effects from the adjacent seawall. The shoreline in this area was then artificially rebuilt and seawalls have prevented any significant erosion since. The shoreline has been able to fluctuate more naturally further south at CCS25/1, though this area has experienced erosion partly caused by effects of the seawall.
Wharekaho ("Simpsons") Beach
At Wharekaho (Simpson’s) Beach, the shoreline has typically fluctuated by up to 10m since 1981. At CCS22 (north) the dune toe has only fluctuated by approximately 4m since 1981.
At Opito Bay, hard materials are present underneath the sand in central areas of the beach, preventing significant change in shoreline position. The beach profile sites graphed here are the north-western and south-eastern ends of the Bay, where there are sand dunes. Away from the influence of stream erosion, the dune toe at Opito Bay has fluctuated by less than 10 m (usually less than 5 m).
At Kuaotunu East, shoreline change of up to 25 m has occurred in the last 20 years. Storms in 2006 and 2008 caused significant erosion, which is now gradually recovering; although sections of the beach are still relatively depleted compared to when monitoring began. Profile CCS21 is at the southeastern end of the beach, and has experienced significant erosion since records began. These changes are most likely linked to changes in the stream mouth.
The shoreline at Kuaotunu West has fluctuated by just 5-7 m over the last 36 years. The overall pattern has been for erosion; further monitoring will confirm if this trend will continue or if the observed changes are part of a longer cycle of shoreline change. Like Kuaotunu East, this beach was impacted quite severely by the 2006 and 2008 erosion events.
Rings Beach is very stable, and the dune toe has fluctuated by only about 2 m over the 38 year beach profile record.
There have been two periods of severe erosion at Matarangi Beach, in 1997 and in 2008. Steady beach building has occurred between these times. Overall, the dune toe has tended to fluctuate by up to 30 m.
The dune toe at Whangapoua has fluctuated by just over 10 m over the 36 yr beach profile record. The beach was most severely eroded in the late 1990s and again in 2008 (central and southern parts of the beach). Steady beach recovery occurs in between these erosion events.
The Excel spreadsheet below contains the source data for this indicator and its graphs.