In this contribution first published in the NZ Property Investor Magazine, Director Mason Reed explains that developers of coastal properties are advised to engage suitably qualified expertise from the outset.<\/p>\n\n\n\n
New Zealand is blessed with stunning natural beauty.\u00a0 In particular, being an island, a large proportion of our country is coastal.\u00a0 Some of the prime sites in the major centres, and other holiday areas, are sites which are close to the sea.\u00a0 This coastal land, because of its location, is typically very sought after (and therefore expensive).<\/p>\n\n\n\n
However,\nthere are geotechnical hazards which are normally associated with coastal land,\nwhich purchasers need to be aware of. <\/p>\n\n\n\n
The land\nis continually being battered by erosional forces, such as wind, rain and ice. These forces have been eroding the land for\nmillions of years, and have resulted in the formation of many of the soils in\nNew Zealand. The erosion process, for\nsteep sites, is often accelerated by land slippage, typically caused by extreme\nweather events (and large earthquake events).<\/p>\n\n\n\n
Steep\ncoastal cliff sites, which are popular sites for expensive houses, are also\nsubjected to an additional force, that being coastal erosion by wave action.<\/p>\n\n\n\n
The\ncliff toes adjacent to coastal sites are typically exposed to wave action from\nthe sea. The wave forces have the effect\nof eroding the toe of the clifflines, which results in oversteepening of the\ncliffline, which can result in subsequent cliffline instability and regression\nof the cliffline. <\/p>\n\n\n\n
Coastal cliff\nlines will be slowly and relentlessly retreating under the influences of\ncontinuing geological processes. The\nlikely rate of retreat of seaward exposed cliff lines ranges between\napproximately 3 m and 10 m per century.<\/p>\n\n\n\n
The main\nfactors affecting stability along the cliff line are the water content, slope\nangle, and in situ undrained shear strength of the veneer soils, and the\nerosion of the cliff line toe and subsequent regression of the cliff face.<\/p>\n\n\n\n
Factors\ninfluencing the stability of the cliff line slopes at the site include\nvariations in lithologies, their hardness, extent, thickness and orientation,\nvegetative cover, groundwater seepage, stormwater or surface water\ninfiltration, and the presence of subsurface discontinuities, such as\nsubsurface erosion tunnels, and the influence of coastal processes.<\/p>\n\n\n\n
Properties\nlocated on coastal cliff lines are subject to a greater risk of slope\ninstability than properties located elsewhere, due to the risk of cliff line\nregression occurring. The increased risk\nto any building can however be mitigated by appropriate foundation design,\ntaking into account the various factors affecting cliff line regression.<\/p>\n\n\n\n
Given\nthat the erosion of the toe of the cliffline is a critical factor to cliffline\nregression, an obvious remedial measure would be to protect the toe of the\ncliffline from wave force action. \nHowever, this is often easier said than done. The cliffline toe is often\nlocated outside the property boundary in the \u201cQueen\u2019s chain\u201d. Works to protect the toe of the cliffline\noften involve civil engineering building works and the use of machine excavators\non the beach. It is very difficult to obtain the necessary consents to\nundertake building and earthworks on beaches (which are sensitive receiving\nenvironments).<\/p>\n\n\n\n
That\nbeing said, there are ways to prevent the regression of land adjacent to\nclifflines. A common method is to construct\nwhat is called a \u201cburied palisade wall\u201d at the crest of the cliffline. This structure is essentially a large\n\u201cburied\u201d retaining wall, which has the structural capacity to provide permanent\nretention to a theoretical height of soil, located upslope of the wall, which\nis determined by assuming the ground to the seaward side of the wall, has been\nremoved i.e. has slipped away.<\/p>\n\n\n\n
These\nwalls are expensive to design and construct, but, if appropriately designed,\ncan prevent the loss of land into the sea, as a result of coastal cliffline\nregression. Given the value of coastal\nland, these types of measures are sometimes justified to protect the land and\nthe structures on it.<\/p>\n\n\n\n
My advice\nto anyone considering purchasing coastal land, is to engage a suitably\nqualified and experienced geotechnical engineer to undertake a pre-purchase\nassessment, in order to determine the risk of the land being adversely affected\nby cliffline regression. Buyers should\nbe aware that coastal properties are subject to a greater risk of slope\ninstability than properties located elsewhere.<\/p>\n","protected":false},"excerpt":{"rendered":"
In this contribution first published in the NZ Property Investor Magazine, Director Mason Reed explains that developers of coastal properties are advised to engage suitably qualified expertise from the outset.<\/p>\n","protected":false},"author":3,"featured_media":4955,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[38],"tags":[75,76,74],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/posts\/4957"}],"collection":[{"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/comments?post=4957"}],"version-history":[{"count":0,"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/posts\/4957\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/fraserthomas.co.nz\/wp-json\/"}],"wp:attachment":[{"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/media?parent=4957"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/categories?post=4957"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fraserthomas.co.nz\/wp-json\/wp\/v2\/tags?post=4957"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}