Home Forum Coastal Erosion Forum Pocket Full Of Acorns East Anglia Coastal Erosion and Drought: Operation OASIS Phase 1 New Zealand coastal erosion case study, August 2006. 1 The Important Role of Trees in Combating Coastal Erosion, Wind and Salt Spray – A New Zealand Case Study Peter Berg, NZ Forestry Limited.
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TOPIC: New Zealand coastal erosion case study, August 2006. 1 The Important Role of Trees in Combating Coastal Erosion, Wind and Salt Spray – A New Zealand Case Study Peter Berg, NZ Forestry Limited.

New Zealand coastal erosion case study, August 2006. 1 The Important Role of Trees in Combating Coastal Erosion, Wind and Salt Spray – A New Zealand Case Study Peter Berg, NZ Forestry Limited. 2 years 3 months ago #223


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Summary
In their technical papers on aspects of tree development in coastal areas Prasetya (2006)
and Takle et al (2006) discuss a number of important factors that determine how best to
use trees and forests to combat coastal erosion, wind and the debilitating effects of salt
spray. The principles and techniques they describe can be used to determine not only the
most effective methods for establishing and using trees, but are also important pointers to
the species most likely to survive and do well in such situations.
This paper describes an example from New Zealand of severe coastal erosion arising
from inappropriate land use, leading to the wide-scale release of partially consolidated
coastal sand-dunes during settlement of the country. Adopting many of the principles
and techniques described by Takle and Prasetya has led to the problem largely being over
come.

Although in this case it is likely that careless landuse created much of the problem, it
could equally have arisen as a consequence of vegetation removal via extreme drought,
fire, tsunami, or earthquake and the consequences would have been the same.
An important feature of the New Zealand programme is that much of the erosion
involved tribally owned lands, and through direct involvement in the restoration and
subsequent commercial forest harvesting activities local people have gainful employment
and social and community development has occurred.

When European settlement commenced in the early 1800s most of these areas were
stabilized by native grasses and shrubs, although early journals of explorers such as the
naturalist Sir Joseph Banks (1769), who accompanied Captain James Cook in his great
voyage of discovery, reported seeing tall dunes of bare sand in the north of the country.
At this time the country had already been occupied for possibly 800 years by the
indigenous Polynesian people, the Maori, whose food gathering and cropping activities
included land clearance and use of fire and it is likely that at least some of the dunes had
been open up in this manner. However it is also clear that as European settlement
proceeded land clearance for agricultural purposes involving careless use of fire, other
inappropriate vegetation removal, and grazing of livestock led to even greater disturbance
of the sand areas and wide scale drifting soon recommenced.

Conclusions
In this New Zealand case study into the use of trees to combat the effects of coastal
erosion, wind and salt spray, the benefits of adopting soundly based techniques such as
are discussed by Takle and Prasetya (loc cite) are well demonstrated. Issues such as wind
speed and run and the use of permeable barriers to cause deposition of wind carried sand,
use of species with high inherent salt tolerance and development of shelter are addressed.
The product of the sand stabilization process has been development of a successful
commercial forestry enterprise providing permanent employment for local people, while
simultaneously high quality agricultural land has been returned to production and other
facilities including coastal settlements, railways and roads are also protected.

www.fao.org/forestry/11283-0f0bb329900ba...d3d31af07f337f85.pdf
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PROTECTION FROM COASTAL EROSION: The role of coastal forests and trees in protecting against coastal erosion Gegar Prasetya 2 years 3 months ago #227


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Development within coastal areas has increased interest in erosion problems; it has led to major efforts to manage coastal erosion problems and to restore coastal capacity to accommodate short and long-term changes induced by human activities, extreme events and sea level rise. The erosion problem becomes worse whenever the countermeasures (i.e. hard or soft structural options) applied are inappropriate, improperly designed, built, or maintained and if the effects on adjacent shores are not carefully evaluated. Often erosion is addressed locally at specific places or at regional or jurisdictional boundaries instead of at system boundaries that reflect natural processes. This anomaly is mostly attributable to insufficient knowledge of coastal processes and the protective function of coastal systems.
The costs of installing hard structures for coastal protection are very high; strong negative public reaction to rock emplacements along the coast often aggravate the problem (Bray et al., 1995; Black, 1999; Clark, 1995; van der Weide, 2001).

This has led to uncertainty among managers and local government authorities on how to treat shoreline erosion. It has become an issue for serious debate for politicians, coastal managers, land- and property owners, lawyers, bankers, insurers and fisherfolk, especially in areas of intensive use and rapidly rising coastal land value. Many of these stakeholders are resorting to planned retreat where houses or hotels are simply removed and the coast is left to erode. However, planned retreat can be expensive, unnecessary and sometimes impossible, especially in highly modified environments.
Increased interest in soft structures for coastal protection (including increased forest cover) and a combination of hard and soft structures is predominating and is consonant with advanced knowledge on coastal processes and natural protective functions. There is evidence that coastal 1 Agency for the Assessment and Application of Technology, Indonesia.
104 forests and trees provide some coastal protection and that the clearing of coastal forests and trees has increased the vulnerability of coasts to erosion (Figure 4.1) — such as in Viet Nam (Mazda et al., 1997; Cat et al., 2006), Malaysia (Othman, 1994), Indonesia (Bird and Ongkosongo, 1980; Nurkin, 1994; Tjardana, 1995), Sri Lanka (Samarayanke, 2003), India (Malini and Rao, 2004; Gopinath and Seralathan, 2005) China (Bilan, 1993) and Thailand (Thampanya et al., 2006).

This paper will elaborate on and discuss the causes of coastal erosion induced by human activities; erosion management options; and the role of coastal forests and trees in protecting coastal areas against coastal erosion, as well as their socio-economic and environmental considerations.

4.2.3 Coastal re-vegetation
Based on studies and scientific results, the presence of vegetation in coastal areas improves slope stability, consolidates sediment and reduces wave energy moving onshore; therefore, it protects the shoreline from erosion. However, its site-specificity means that it may be successful in estuarine conditions (low energy environment), but not on the open coast (high energy environment). In some cases, re-vegetation fails because environmental conditions do not favour the growth of species at the particular site or there is ignorance as to how to plant properly given the same conditions. It is also possible that anthropogenic influences have completely altered the natural processes in the area. The most obvious indicator of site suitability is the presence of vegetation already growing. This can be extended by other factors such as the slope, elevation, tidal range,salinity, substrate and hydrology (Clark, 1995; French, 2001).

4.2.3.2 Coastal re-vegetation on other coastal types Sandy coast. Beaches composed of fine sand are usually broad and have a gentle seaward slope representing a low energy environment; beaches with coarse sand, gravel, shells, or broken coral branches have relatively steep slopes representing a high energy environment. Short-term fluctuations on these coasts (if there is no human intervention) do not mean that an erosion problem exists; variations on
the beach face are the natural response of the beach to wave form and energy and also strong
winds. After extreme conditions, a naturally eroded beach, with features such as a lowered beach face slope, the absence of berms and erosional scarps along the backshore/foredune will return to normal during lower wave energy seasons when waves return sand to the beach and wind
transports it landwards to rebuild the upper beach and foredune. Therefore, long-term observations are needed before deciding that the beach is being seriously eroded.
Severe erosion problems on these types of beaches are usually due to human activities such as dam building that decreases the river sediment supply to the coast, vegetation clearance on dunes and in beach woodlands, offshore mining, and building inappropriate coastal structures. In terms of erosion generated by vegetation clearance, re-vegetation of the area using indigenous vegetation is the only option. Other coastal protection options should be considered in combination with re-vegetation if the erosion problem is attributable to multiple factors.

Cliff and platform structures

Erosion of cliff and platform structures where there is no beach during high tide is due to complex processes and no single process predominates. These include gradual changes to cliff morphology owing to weathering and wave action at the base of the cliff, and slope instability due to episodic failure of the cliff. Planting shrubs and trees will improve slope stability, for example with belukar (dense thickets possibly dominated by isolated trees tangled with lianas); however, other coastal protection options should be considered in combination with re-vegetation.

4.3 Combinations of options

As mentioned already, combining hard and soft solutions is sometimes necessary to improve the efficiency of the options and provide an environmentally and economically acceptable coastal protection system.

Hard solutions are known to:
• cause erosion and unnecessary accretion;
• be expensive and often further aggravate the problem; and
• spoil the aesthetic aspect of the beaches or coastlines they seek to protect, hence decreasing their economic value, especially for tourism purposes.

Meanwhile, many soft solutions can:

• take time to become effective (not overnight or quick-fix solutions), which generates
negative public response; and
• be effective solutions only in medium- to long-term perspectives (five to ten years).

A planned retreat where the coast is left to erode can be expensive, unnecessary and sometimes impossible, especially in highly modified environments such as tourism areas and waterfront cities. To optimize the long-term positive impact of soft solutions, many combinations with hard solutions can be selected; combining beach nourishment and artificial headlands/groynes and re-vegetation and temporary offshore breakwaters/artificial reefs that act as interim hard structures is the most common approach.
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Practical Measures To Tackle Climate Change: Coastal Forest Buffer Zones in Zanzibar 2 years 3 months ago #228


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Author(s):
Mustelin, J et al.
Available for download at:
www.unesco.org/csi/climate-frontlines/Pr...esZanzibar_Ebook.pdf

A joint research project of the Department of Geography (University of Turku) and the Department of Commercial Crops, Fruits and Forestry (Zanzibar)

2009 Mustelin, J et al, 'Practical measures to tackle climate change: coastal forest buffer zones and shoreline change in Zanzibar, Tanzania', Turku University Department of Geography Publications, B Nr 13, Turku, Finland.


www.unesco.org/csi/climate-frontlines/Pr...esZanzibar_Ebook.pdf
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PROTECTION FROM WIND AND SALT SPRAY Thematic paper: Protective functions of coastal forests and trees against wind and salt spray Eugene S. Takle, T.-C. Chen and Xiaoqing Wu1 2 years 2 months ago #244


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www.fao.org/forestry/13190-096ac883cae10e56957927f1e0b2b331.pdf

Intense rainfall can reduce salt accumulation problems by washing salt from vegetation and
leaching salt from the soil. Regions receiving in excess of 50 centimetres of rain per year have fewer problems with salt accumulation in the soil (Appleton et al., 2003).

2 Use of forests and trees for suppressing damage Research on the characteristics and sheltering effectiveness of coastal shelterbelts and forests is quite limited. Recent review papers on shelterbelt modelling (Wang et al., 2001) and worldwide applications of shelterbelts (Brandle et al., 2000) make no mention of coastal applications. Zhu et al. (2003) provide a model for winds within a coastal forest canopy, but do not address the
sheltering function beyond the confines of the forest.
However, the fluid dynamics of flow through vegetation barriers are based on universal laws of
physics, so simulating flow through a coastal shelterbelt is no different than simulating flow
through agricultural shelterbelts, provided that the characteristics of the coastal vegetation (see Section 2.1 below) are specified. Windbreaks consisting of shelterbelts (one or two rows of trees) and forest belts (multiple rows) are commonly used at inland locations as natural barriers to reduce windspeed, modify the microclimates of small regions and suppress the movement of snow, pollen, dust, sand and odours. They are most widely used in agriculture in regions of high windspeed such as Australia, New Zealand, the Russian Federation, China and the Great Plains of the United States. Therefore, the methods used and results derived from studies of agricultural shelterbelts can be applied to coastal shelterbelts and forests as well. In this section we discuss the knowledge base 77
on shelterbelt design and application as it has been established through research on agricultural shelterbelts. In Section 3 we apply the qualitative results of these agricultural applications to the design of coastal shelterbelts and forests.
Windbreaks substantially reduce windspeed on the windward side for a horizontal distance of 2–5 H, where H is the height of the barrier (Figure 3.8). A much larger region of reduced windspeed, typically extending from approximately 10 H downwind to 30 H downwind, is created in the lee of the barrier, with the sheltering effectiveness near the barrier being determined by the incident angle of the wind to the shelterbelt (Wang and Takle, 1996a). Some very limited windspeed reduction as far as 60 H downwind has been reported (Caborn, 1957; 1971), but the biological or practical significance is considered to be quite limited (Brandle et al., 2000). However, as will be shown in Section 2.3, the impact of even minor wind reduction can have a disproportionately high impact on particle deposition, even though windspeed reduction might be considered minor.

Tamate (1956) discussed Japanese use of shelterbelts to reduce airborne salt movement in the coastal zone. He reported that airborne salt concentrations in the lee of shelterbelts were measured to be 12 percent lower than on the windward side.

2.4 Establishing shelterbelts as a part of dune restoration Sand dunes lacking vegetation provide an opportunity to develop protective barriers. Because drifting sand creates a hostile environment for developing plantings of woody vegetation, use of grasses for holding the dune intact and preventing saltation (launching of sand particles from the dune by wind action) is the first goal of such restoration. Low levels of organic matter (and hence
water-holding capacity) and nutrients (particularly phosphorus and nitrogen) limit the types of grasses that can be used. Soil amendments in the form of manures, leaves, detritus and so forth provide both nutrients for recycling and a means of enhancing plant-available water. Groundnuts provide crop residues rich in nitrogen, and residues from crops in close proximity have proved to be successful sources of such materials (Jerve et al., 2003). Local climate considerations must be addressed to cope with the possible loss of nutrients (particularly nitrogen due to leaching) if heavy rains are a frequent occurrence, and drought-tolerant species if a prolonged dry season is a natural part of the local climate. Reclaiming such sandy areas has been proved difficult but successful, and may take a few years to accomplish.

As soon as the dune is stabilized and moving sand is suppressed, seedlings of woody perennials
such as shrubs and trees may be introduced. Establishing the shelterbelt on dunes or protective dykes serves multiple purposes. The additional elevation allows better inception of high winds and a deeper layer of the atmospheric boundary layer for the capture of sea spray and salt particles (see Figure 3.7). The presence of woody vegetation also helps to protect the dune or dyke from erosion or from being a source of dust or sand moving inland


2.5 Use of rigid (non-vegetative) barriers for protection against wind and sea spray
Very little research has been done on the combined use of rigid and vegetative barriers for
protection against wind and sea spray. Such combinations may, however, provide alternatives that protect newly planted trees from excessive damage, increase the density of a shelterbelt in places where available tree species do not provide sufficient vegetative mass, and reduce the area needed to achieve a particular sheltering objective
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Dune restoration takes root in the Bay of Plenty. Bay of Plenty, North Island, New Zealand 2 years 2 months ago #262


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www.scottsasiapacific.com/case_studies/p...ay%20of%20plenty.pdf

“What we are finding is that this dune restoration is really
working as far as protecting the coastal dunes of the Bay
of Plenty and other areas. So much so that we’ve just been
in discussion with coastal scientists who are saying that the
dune restoration may be all that we need to do to counter
the effects of the predicted sea level rises for the next 100
years. It really is a very powerful response we are getting on
these plants. A lot is due to the fertiliser treatment that we are
giving them. They just don’t grow very successfully without a
decent dose of fertiliser.”
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Drawing the line at coastal erosion New Zealand Dune Management With Vegetation 2 years 2 months ago #263


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resources.ccc.govt.nz/files/AssetManagem...istchurchbeaches.pdf

WE Need to work with – not against – nature

The inexorable assault of the sea along our shorelines
has forced a rethink on how best to cope with its
impact on properties and the environment.

Study the first picture carefully from the document. It clearly shows how coastal forest has arrested coastal erosion and how exposed un-vegetated sand has done little to prevent erosion. The trees in the distance clearly illustrate how we should address the problem and the planting of grasses to stabilise the dunes can be used as a pioneering species.
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The causes, effects and mitigation strategies relating to coastal landslides at Highcliffe and Naish Farm on the Dorset – Hampshire border. 2 years 2 months ago #264


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www.dorsetforyou.com/media.jsp?mediaid=123278&filetype=pdf

Attention given to vegetation on the slopes and terraces meant that salt tolerant
grass mixes had to be developed. The obvious benefits resulting from maintaining a
vegetation cover being that root systems hold together potentially unstable soils with
plants taking up a certain amount of moisture during their biological processes.
SXG 390 M. Hinton. R0416915
16
Additionally, dense evergreen foliage on the upper slopes was encouraged to provide
an umbrella cover to disperse the concentrated effects of wind and rain during winter
storm conditions. Tyhursts (1993) description with accompanying simplified diagram
(Figure 3) clearly sets out the mitigation strategy of engineering works that by 1985
had been applied to the complete Highcliffe frontage and his undated study, Tyhurst
(undated) describes the attention given to the vegetation at the site with salt tolerant
grasses sown on the lower slopes and selective use of small trees and shrubbery to
protect, drain and assist in stabilising the upper slopes.
Subsequently the 11 sheet piled groynes were progressively converted to substantial
random rubble moles to deflect direct wave action and the high maintenance timber
revetment was buried beneath many thousands of tonnes of imported gravel leaving
a mixed sand and gravel beach which formed a pleasant summer recreational
amenity. By the early 1990s a total of £2.5 M had been invested in the Highcliffe
frontage (Hooke, 1998), probably amounting to around £4 M at late 1990s prices.
This amounts to about £3 k per m run. As a measure of the effectiveness of the
stabilisation techniques, apart from some minor soil creep on steep slopes there has
been no major movement on this cliff section for at least 10 years and during summer
months the stabilised coastal slope forms a pleasant vegetated south facing
recreational amenity with a view of the approaches to the Solent, The Isle of Wight
and The Needles.
Figure 4 is reproduced from Halcrow Maritime (1999) and indicates the forecast cliff
recession at Naish Farm by 2049 based on a broad estimate of a 1 m/yr recession
rate. The mitigation proposal from Halcrow, if mitigation is appropriate, is to stabilise
both ends of the site allowing the large central section to reach an equilibrium
situation. It is unlikely that similar stabilisation techniques to those applied at
Highcliffe will ever be applied to the Naish Farm section of the cliff due to
conservation issues combined with negative cost benefit analysis results. However,
both Lee (2002) and Barton in Hooke (1998) discuss ‘ compromise solutions’ which
may be suitable for application to Earth Science Conservation Sites where it might
be appropriate to slow rather than prevent cliff degradation. The construction of
offshore reefs or nourishment of beaches are two techniques that are mentioned as
possible solutions as they do not directly interfere with exposed geology but give a
degree of protection to the cliff toe. (892 words)
SXG 390 M. Hinton. R0416915
17
6. Conclusions
Hopefully this report has given the reader a basic understanding of the causes,
effects and mitigation strategies that apply to landslides on this stretch of the coast of
Christchurch Bay spanning the Dorset – Hampshire border. The large chapter
devoted to the geology of the site is felt to be prerequisite to an investigation of
causes and this is stressed by all sources. Because of the early geological interest in
the coastal cliff there was a substantial literature base prior to more recent
engineering investigations which preceded mitigation schemes. Whether or not
coastal landslides require mitigation depends on ones point of view, whether or not
the landslide is viewed as a ‘geohazard’ and whether or not the expense of mitigation
can be justified. The techniques used at the Highcliffe segment of the site would be
eminently suitable for use at Naish Farm because of the geological similarity but the
expense combined with environmental considerations preclude this at present.
Compromise solutions such as offshore reefs or beach nourishment, or allowing
erosion and degradation to occur between strong points may be a way forward for
mitigation at Naish Farm. In any case this report has attempted to show that at the
location in question causes and processes are well understood, that the perception of
effects is somewhat related to ones point of view and that successful mitigation
strategies are available should they be needed and the expense justifiable. It is
commonly understood that sea level rise resulting from climate change will
accelerate coastal landsliding worldwide and sooner or later policy makers will need
to make difficult decisions as to whether to simply allow this to occur or make partial
efforts to slow down the process rather than halt it. (322 words)
Word total :- 4696
SXG 390 M. Hinton. R0416915
18
Cliff section showing the Highcliffe to Milford SSSI, the Highcliffe and Naish Farm sectors
occupy the left hand third of the section.
Cliff profile showing the degradation processes of the Barton Clay cliffs.
Aerial photograph showing the Hampshire – Dorset border, the stabilised Highcliffe sector is
on the left, the unstabilised Naish Farm sector is on the right. All pictures from the Ian West
geological website. Figure1
SXG 390 M. Hinton. R0416915
19
Cliff
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