Wind + waves + sand = a potent combination
By Roger Childs
“… starkly simplistic (coastal hazards lines on maps) … have the potential to seriously affect the value and marketability of coast properties”. Judge Joe Williams
Whatever the final outcome of the debate over coastal hazard lines and what goes on LIM (Land Information Memorandum) property reports, the threat of the sea to Kapiti beachfront areas remains a reality.
A Christmas Day walk on the Raumati South revetment provided dramatic evidence. The combination of a high tide and moderate north-easterly winds had the surf pounding over the rocks and on to the walkway.
Without the combination of seawall, rocks and concrete pathway, The Esplanade overlooking the beach would have been history long ago and several houses would have succumbed to the power of the sea.
A history of battling the elements on the Kapiti Coast
When we came to live in Raumati Beach in the mid 1960s, there was
- no full length Raumati seawall
- no Raumati South revetment
- no rock and bank protection for Marine Parade
- no housing in Paraparaumu North Beach.
The photo below shows well known Raumati Beach identity, Sally Ashley, playing in the Raumati sand dunes with her family in the 1950s.
However for home owners further on towards Raumati South, coastal erosion was a worry. Housing had been built along the entire foredune in Raumati, which meant that the natural processes of sand removal and replenishment were disrupted.
Some home owners did their best to protect their land from the stormy seas. The early seawalls protecting individual properties were built in the 1950s and often consisted of rails with logs of wood and branches in behind. The Hutt County Council constructed a basic seawall in the 1970’s.
Nevertheless, for many beachfront residents it was a losing battle. A friend recently recalled that a relative living in Raumati South lost 10-15 metres from the front of his property in the late 1950s.
In the absence of consistent, durable protection along the whole beachfront, based on sound engineering and knowledge of marine processes, waves would just go around or under poorly constructed walls.
House destruction leads to more protection
The spring tides of 1976 made a ferocious assault on the flimsy seawall and the foredune along Rosetta Road in Raumati Beach. Many properties lost metres of beachfront land and one house collapsed into the sea and sand. (See alongside: photographer unknown.) A seawall in Paekakariki was also destroyed.
The Council followed up this disaster with the building of a more substantial seawall, but a lack of understanding of the natural processes at work meant that this construction was undermined, leading to further expense for ratepayers.
Whereas the original walls were built 1.2 meters in height and 600mm below the beach surface level, nowadays the heights are less than 1.5 meters high and a fully 2.7 meters below the surface of the beach. That is deeper than the average house ceiling is high. John Mills, Mills Building Co. (The company built the recently erected Paekakariki seawall and walkway.)
Another mistake had been made at Raumati South where the wall ended just beyond the last property. Nothing was done to deal with the obvious: the sea sweeping in beyond the end of the seawall and eating away at the dune behind. Eventually rocks and wall protection were added.
A changing scene in Paraparaumu North Beach
While coastal erosion was occurring in the Raumati area in the 1950s-1980s, sand accretion was occurring further north. What is known as a cuspate foreland, was building out south of the Waikanae River.
Housing was expanding at the north end of Manly Street and the new homes closest to the beach had a buffer of over 30 metres of sand dunes. At that time there was definitely no threat to these properties from the sea. People strolling or running on the beach could not see these houses.
But that’s all gone now. In 2013, these houses are within 10 metres of the high tide. Passersby can look into their diminishing front yards and sixty large concrete blocks, buried deep in the sand for years, are now clearly visible from the beach. The sea is now encroaching north and south of these blocks.
Coastal processes are very unpredictable and today’s beach nourishment can be tomorrow’s sand erosion. Tides are variable throughout the year and the impact of the sea on coasts worldwide is affected by
- phases of the moon
- the earth’s rotation round the sun
- inconsistencies in the force and direction of winds
- global warming.
The early 21st century has seen further major concerns for residents and the Council as the sea has pounded the Kapiti Coast.
Marine Parade, Paraparaumu Beach This is one of the most scenic drives on the coast, but severe storms and peak tides in the early 2000s threatened to undermine the road. Furthermore, sand blowing up from the beach was a nuisance for residents and traffic. To deal with the problem KCDC in 2005
- developed a 15 metre dune slope
- added over 1000 cubic metres of sand
- planted pingao and spinifex
- fenced off and grassed the land on the seaward side of the road.
To solve the underlying problem, over 1200 tonnes of rocks were placed on the lower part of the dune in 2006. This seems to have stabilised the dunes and helped dissipate the force of the waves during the highest tides and stormy conditions.
The Esplanade, Raumati South As part of the Raumati Beach seawall development, rocks were deposited along the base to help reduce the power of the waves. However, on The Esplanade, which is the only place south of Marine Parade where a major coastal road is adjacent to the beach, the sea threatened.
A storm in 2008 saw waves throw debris right onto the road above and the steep bank below was seriously damaged. So in 2009-2010 KCDC had a rock revetment built to protect the road and prevent further erosion.
The resulting rock accumulation, stone path and concrete wall afford protection for The Esplanade and provide an attractive walkway which is reminiscent, on a small scale, of the famous Coastal Walkway in New Plymouth.
The ongoing battle with the sea
The tens of kilometres of safe sandy beaches are one of the Kapiti Coast’s greatest attractions. Coastal properties fetch high prices because of their ready access to the sand and the sea views. However, as local geographer, Gordon Dickson, recalls: House prices seaward of Rosetta Road plummeted after this event ( the 1976 storm) and took some years to recover.
From 2008 to 2010, Paula Lynch lost 5 metres of her land, as did other residents south of where the protection for Marine Parade finished. As with Raumati South, the sea washed around the end of the protected area and cut into the sandy sections beyond.
In 2010 the KCDC set aside $100,000 for sand replenishment and many residents began building barriers to the sea. However there is still much work to be done in this vulnerable area.
The Council is ‘making changes to coastal hazard information included in Land Information Memoranda (LIMs) to take into account new information… received as part of the recent expert coastal panel process.’
This is, no doubt, good news for beachfront owners. However the reality of the history and continuing threat of coastal erosion to the Kapiti Coast is apparent to any beach walker, from Paekakariki to the Waikanae River.
It might be some comfort for readers to know, that over the last thirty years senior geography students at Kapiti and Paraparaumu Colleges, have studied the reality of coastal processes along the Kapiti coastline as part of their curriculum.
Photographs by Pam Childs, December 2013.
Double click on the photos to enlarge.