by Dr J Floor Anthoni (2000)
Because beaches and dunes change very slowly,
humans do not notice what is happening. Because they also poorly understand
how dunes and beaches behave, they often do the wrong things. Here you
can learn how to detect if a beach is healthy or sick, what causes it and
what you can do about it. But not all beaches can be saved.
Symptoms of a sick beach As
we have set out extensively before, the health of a dune/beach system has
little to do with the amount of sand either in the sea or on the land.
So one does not need to spend decades of laborious monitoring of the sand
budget in order to qualify the health of a given beach. (In fact sand mass
monitoring does not say anything about beach health at all). But some knowledge
of a beach's history could serve to advantage, much like a physician takes
clues from a patient's history.
Just like patients, no beach is alike. They are physically different,
and are affected in different ways by the same causes. So a bit of detective
work is needed before embarking on a course of action or before drawing
a final conclusion. But in the main, almost anyone can now assess the health
of one's own stretch of beach.
Dunes and beaches grow and shrink cyclically, depending on climate cycles
and other cycles. Although the amount of sand in the dune/beach system
can vary considerably, our health indicators remain valid whether the beach
is growing or shrinking.
Contrary to rocky and sandy cliffs that cannot repair themselves and
therefore can only shrink, beaches can hold their own over many thousands
The picture shows a short-hand checklist which
we will examine in detail below.
no dry beach: The dry beach, the beach above spring high tide, extending
to the fore dune is present only in very healthy beaches. Observe how much
of it is present. The amount of dry beach is an indication of how much
sand is freely moving along the beach.
ripples in the sand: ripples tell you which way the sand is moving.
Are they perpendicular (square) to the beach? In that case, the sand moves
along the beach and not into the dunes. The wind may be blocked by a steep
scarp or trees or houses. You may have to come back a few times because
winds do change direction and change the lay of the ripples. Ripples are
a health symptom, particularly when they run parallel with the beach.
crusting of dried sand: Along the high tide line, particularly where
the tide has been, the sand should have dried. Where it has not been crushed
by visitors, check whether the sand has formed a hard crust. Crusted sand
cannot be moved by the wind. It is a serious condition.
top of wet beach not drying out: When the tide is half-way in, 9
hours after high tide, the top of the wet beach should have dried completely
on a windy sunny day. Check how large the area is that has actually dried.
You may return for another visual check and compare the beach with other
beaches on the same day. In general, the top of the beach should dry, even
during an overcast day. If it doesn't dry, the sand can't be moved. Look
for green scum or foam, an indication of dense plankton blooms. Is the
beach too flat for drying out?
dirty looking sand: The sand needs to look clean, particularly when
dried (except for our black iron sand beaches and grey beaches with rock
sand). If it looks muddy, it is probably polluted by either mud or algae.
Polluted sand won't dry well. Take a sample in an air-tight container like
a photo film cartridge. Store it at room temperature for two weeks. If
it stinks, the beach is heavily polluted organically by sewage, algae or
kick the sand or winnow it in the wind: If a dust cloud forms, the
sand is severely polluted with silt and clay.
hard sand: the beach, both dry and wet, should always feel soft
to tread on. Only just above the tide line will the sand feel firm. Hard
sand is an indication of pollution by mud.
flat, wide beach: A flat, wide beach is a strong symptom that the
beach is on its way out and perhaps impossible to salvage. Note that sheltered
beaches are always flatter than exposed beaches. Beaches inside harbours
fall a bit outside the scope of this analysis. A bit of knowledge of how
the beach was some fifty years ago may back your observations.
bared base rock: Some beaches drop off steeply into a current channel
and their bases consist of hard rock. Only clean, coarse sand can be kept
on these beaches by the motion of the waves. When the sand is polluted
by fine particles, the beach lays flatter and loses its sand over the ledge
into the currents.
steep scarp in fore dune: A steep bank in the fore dune is a definite
symptom of ill health. It shows that the sea is eating into the dune. Sand
can not saltate up the bank. There is usually no dry beach and other symptoms
are generally present too.
no rolling dunes: Rolling dunes are characterised by a distinct
low fore dune with hardly any vegetation and behind it a second dune with
some vegetation, followed by one or more taller dunes. There is evidence
of the fore dune shifting and new fore dunes being formed. These beaches
are able to transport excess sand inland by means of their self repair
walls, reinforcements: Walls and reinforcements are a sure sign
that property owners feel threatened. The shoreline must have been eroding
recently. Listen to what the locals can tell about the beach.
high buildings close to beach: Tall buildings or any obstruction
close to the beach will influence the wind as far away as 30 times its
height. Watch for erosion signs that occur near obstacles, compared to
unaffected areas of the beach.
shelter belt close to beach: Shelter belts have a major influence
on the health of the beach.
sand banks: Sand banks occur immediately past the low tide line
and further out to sea. They can accommodate enormous quantities of sand.
Wherever a sand bank occurs, it will hinder the waves and shelter the beach.
As a result the beach lays flatter, which adversely affects its health.
Sand banks are usually a sure indication that the beach is ill.
Threats to our beaches Not
surprisingly, the main threats to our beaches arise from human activity.
The drawing shows the most important ones, which we will summarise here
from right to left:
Global warming, rising seas: As the sea water warms, it expands,
raising the sea level by up to 50cm for each degree. As the polar ice caps
melt, they release some of the 75m sea water still locked up there. It
affects sick beaches but nor healthy ones.
Beach high-rise: Not only beach hotels and apartments, but also
shelter belts lift the sea wind up from the beach, thereby impairing its
self repair mechanism. Most beach resorts suffer from this problem.
Sewage: Sewage increases the bacterial activity in the sand. Bacteria
glue the sand particles together and the sand dries more slowly or it crusts
when dried. As a consequence, the sand grains cannot be blown in the sea
Dune planting: Dunes must move in order to preserve their shapes
and to transport excess sand inland. They tolerate only sparse vegetation.
When planted artificially, they lose their shapes, grow tall and lift the
sea wind from the beach. The beach then dies, not able to repair itself.
Beach dwellings: Beach dwellings, although lower than hotels, are
placed close together and owners plant sheltering vegetation. The houses
and trees lift the sea wind from the beach. Also the moving dunes are paved
over and the sand can't move. Beach dwellers are highly motivated to stop
sand from moving.
Acid rain: The burning of fossil fuels brings the nutrients locked
up in ancient organisms, into the air where it rains down as acid rain.
It fertilises the land and can cause problems in enclosed waters (freshwater
lakes). It also fertilises the dunes, encouraging dune vegetation, eventually
leading to beaches eroding. See dune planting.
Development: Present-day housing development involves extensive
landscaping, the scraping and shifting of enormous quantities of soil.
Much of this soil washes into the sea, polluting beaches.
Soil erosion: Since native forests have been cleared and the soil
is farmed, erosion has increased considerably. Nutrients, sand and fine
particles are washed into the sea, polluting beaches and causing excessive
plankton blooms that also pollute beaches. It slows the drying of the beach.
Roading: Like developments mentioned above, motorways these days,
require extensive shifting of soil, causing pollution of the sea.
Roadside maintenance: The sides of all roads have been cut out of
the land and expose the soil which washes into the sea. Although often
revegetated, the maintenance process (mowing, spraying, etc.) is often
too radical, resulting in erosion and pollution of our coastal waters.
Farm runoff: Farm runoff (the storm water from farms) contains nutrients
and soil. It causes the same problems as sewage and erosion do.
Hydro lakes: Dams in rivers obstruct new sand from reaching the
sea. Where beaches depend on a constant supply of new sand, this causes
beaches to erode while otherwise healthy. Because soils world-wide erode
much more rapidly today than in the past, more sand is reaching the coast
than ever before and there appears to be an excess of sand in most coastal
Because the demise of our beaches is directly linked to human activity,
today's problems are likely to accelerate in the future. The economies
of societies expecting to become wealthier each year, grow annually between
3% and 6%. Growing at 3%, our problems will double in 25 years and quadruple
in 50. Growing at 6% will quadruple our problems in 25 years and four times
again in the next 25! Extrapolating this scenario implies that all our
beaches will eventually die.
Because the health of our beaches is so intricately entwined with everything
we do, it seems almost impossible to salvage them. Is there anything
we could do?
What we could do When
asked, people do like their beaches. They are just not aware that their
daily actions destroy the very things they like. Many of our actions do
not only destroy beaches but also to a larger extent, our terrestrial and
marine environments. Obviously, our societies will need to make major environmentally
friendly adjustments. All over the world, environmental groups are championing
this cause. It will take time and public education.
But what could we do immediately? The following suggestions seem outrageous
because they go against established beliefs and well intentioned effort.
Remember that each beach has its own problems and remedies and that some
beaches cannot be salvaged at all.
Education: People are unaware of how they destroy the very things
they like, including their beloved beaches. Extensive education is necessary,
both at school and on television and radio and in newspapers.
Tree cutting: Trees close to the beach are of major concern, particularly
when they have been planted in closed ranks. Removing them would be a very
easy and effective solution, saving beaches that would otherwise be healthy.
As a rule, rows of trees should not be placed closer than 300m from the
high water line. An individual tree here and there is of less concern because
they would allow the wind to pass around them, not lifting it from the
beach. Even shrubs closer than 100m from the high water line should be
taken out or left in small groups.
Driftwood: Driftwood has a beneficial influence on beach formation.
It works like dune plants do, but in a zone which is out of reach of dune
plants. Unlike dune plants, driftwood will not prevent dunes from rolling
inland. Driftwood should be left in place.
Surf/life saving club houses: Club houses located near the water's
edge should be moved backward and turned sideways to provide a smaller
wind profile. They should be constructed in such a way as to be mobile
and streamlined to not obstruct the wind. Likewise, observation platforms
should be placed on a tall tower.
Stop dune replanting: as has been shown extensively, dune planting
has very serious long-term effects and should be halted immediately. Conservation
groups and local bodies should be educated to redirect their effort and
resources. Where the dunes have been planted, the vegetation should be
removed or thinned (see burning). Wind blow-outs should be left undisturbed.
Stabilisation of rear dunes should still be allowed.
Remove exotic dune plants: Exotic dune plants have not evolved in
our climate together with the living dune/beach system and behave in ways
that cause damage. The introduced European marram grass (Ammophila
arenaria) should be declared a noxious weed and removed from our country
Bulldozing: In many places the dunes need to be reshaped for a wind
profile that does not lift the wind from the beach and which has a low,
unvegetated fore dune. Where a bank or scarp borders the beach, it should
be bulldozed into a low, gently sloping fore dune.
Fourwheel drive vehicles and bikes: have fun and at the same time
save the beach by hooning over the first hundred metres of dunes and the
entire beach above half tide. Vehicles can successfully destroy vegetation
and scarps while at the same time streamlining the beach profile. They
can crush the salt crusts on the upper beach.
Sand mining: Accelerated erosion in the past century, together with
reduced sand transport into the dunes, have accumulated too much sand in
the sea. Where sand banks appear offshore, they should be mined for construction
and roading. Tall dunes should be mined too, in order to reduce their height.
Burning: By burning the dune vegetation, rather than bulldozing
it under, nutrients and organic matter will be removed most effectively
by evaporating into the atmosphere. Dunes close to the beach must have
sparse vegetation and the slightest amount of fertiliser could make this
Laws: Local and national laws should protect a wide beach zone from
human development, for people's own sake and for creating natual wilderness.
Dune parks: Over the years, people have been altering the dune environment
so much that practically no wild dunes remain. By accident some beaches
may have escaped human development. These are candidates for establishing
pristine dune wilderness areas (dune reserves) which contain the dunes,
a large part of the water catchment area behind it and a vast amount of
sea in front. Action must be taken now to establish these parks before
it is too late. Funds must be made available to buy back private property.
Cost recovery: People like to live near the beach in a high risk
area but are often not aware of danger. They rely on Governments to help
out when disaster strikes. Consequently, coastal properties and living
on the beach, have been overvalued. By zoning the whole coast into risk
areas, potential buyers are made aware of potential risk. Home owners should
privately insure their risk, rather than expecting help from the public
purse. The cost of public remedial work such as building groynes and sea
walls should be recovered entirely from property owners.
Erosion control: There is no doubt that land erosion is still far
too high, particularly in recently developed countries (like New Zealand).
More awareness should be fostered and more effort spent on curbing erosion.
Today, erosion is estimated 10-20 times of what was natural - clearly an
Improved farming: Once the plough goes in, erosion accelerates many
times. Many good practices are known to minimise the loss of land but also
on pastoral land, farming practice can be improved considerably.
Fertiliser subsidy: People who work with the land know that the
best and most cost-efficient method of erosion control is fertilising.
Yet here in New Zealand, the subsidy on fertiliser has been abolished in
1986, leading to accelerated erosion and problems in coastal seas in the
nineties. Farmers now apply considerably less fertiliser than before 1986.
Root systems and foliage are reducing, which accelerates erosion. By introducing
a fertiliser subsidy for hill country, erosion is reduced considerably
for very little effort and cost. Often the argument is voiced that the
fertiliser will run off to the sea and cause more problems. But the first
fertiliser components needed on land are lime (calcium), potassium, phosphate,
sulphate and trace elements. All these components are already copiously
available in the sea, and phosphates bind strongly to the soil's clays.
Note that under no circumstance, fertiliser is be used on dunes.
Sewage treatment: In many places, sewage runs off into the sea,
particularly during rain storms. That causes problems but even properly
treated sewage does. After treatment, the sewage has become ideally balanced
fertiliser and when let loose in the sea, it fertilises the plant plankton
which blooms excessively, causing problems to our seas and preventing beach
sand from either drying or moving (crusting). Ironically, just past the
continental shelf, there exists a shortage of nutrients and fish. By transporting
our treated or untreated sewage that far into the sea, using tanker ships,
we can turn a liability into an asset. It is a feasible and cost-effective
Research: Many of the work and ideas presented in this section on
beach erosion and its probable causes, need to be backed by solid scientific
investigation. Funds should be made available to do so. The ideas in this
section also require rigorous discussion.
Examples of beaches worth saving Using the information presented in this section Our disappearing
beaches, everyone should be able to assess which beaches are worth
saving and which ones can best be left alone. You will be able to determine
when a sea wall is the only remaining solution left. It would of course
be impossible to do a review for the whole of New Zealand here, let alone
one for the entire world.
Let's start with a popular beach which is beyond rescue, Orewa Beach,
just north of Auckland, New Zealand. Houses and trees are too close to
the water's edge, the beach lies flat for many hundreds of metres, soil
erosion is vast, sewage from the population of 30,000 is released nearby,
the beach sand is polluted and the sea has progressed too far. For Orewa
the only protection remaining is a sea wall. This sea wall could be constructed
anywhere up to 500m in the sea, reclaiming land for a buffer zone, but
it would diminish the value of local property if what remains of the beach
is moved further away.
Note that Orewa beach may well be a good candidate for beach dewatering
applied in several stages. Dewatering allows the sand to dry and blow towards
the present wall, creating a dry beach zone. The amount of sand can be
controlled by turning the pumps on or off, such that the right amount of
mobile sand is created, not to blow onto properties and roads. During storms
the dry beach will disappear but it will rebuild rapidly due to dewatering.
Orewa Beach at low tide during very calm weather, shows how
flat this beach is. The sand can no longer dry. Houses encroach right to
the water's edge. There are rows of tall trees and tall buildings. It would
economically not be possible to restore the sea wind but dewatering is
Orewa Beach just before low tide during rough weather, shows
how far the shallow sand and sand banks extend into the sea (about 500m
from the high tide line). It is where all the sand of the beach and all
renourishment efforts, have gone.
Orewa Beach during high tide shows the water lapping at the
boundary of private properties. Along most of the water front, the local
council has erected sea walls. After breakers have crossed the vast stretch
of flat sand, they have lost nearly all their energy. It makes people believe
they are safe here, but they are not protected against storm surges.
The beach sand of Orewa Beach looks polluted by fine particles
(silt and clay) and it never dries. Erosion from urban development and
roading and sewage from the local sewage treatment plants, end up in the
A drawing from recent plans for renovating Orewa's beach
centre. The three steps in the foreground are the only barrier between
the city and the sea. At the other end of town, engineers are constructing
a sea wall with entirely different proportions (see right). The coastal
area has not been zoned by hazard rating. Property owners do not know the
risk of living or building here.
After winter storms in Nov 1998 had carved some foreshore
away, it was decided to construct a sea wall there. The design involved
a ditch of about 1m in the beach sand from which a plastic, permeable cloth
(geotextile) slopes up the shore. The whole is covered in large boulders.
The cloth is supposed to hold back the sand while letting ground water
and storm water through.
Otama Beach on the Coromandel Peninsula, New Zealand,
is an example of a pristine pocket beach that somehow has escaped development.
It is backed by a wetland reserve and is a prime candidate for a pristine
dune wilderness area, fronted by a large marine reserve.
Otama Beach is a pocket beach strung between headlands, facing
north. It is very exposed. The peninsula is sparsely populated and produces
relatively little run-off. The waters are clear most of the year. The beach
is backed by a wetland nature reserve and the Otama River has a small catchment
area. The beach reserve should enclose the entire catchment area and ocean
extending to 40m deep.
Otama Beach has all the symptoms of a healthy beach: glistening
clear quartz sand that squeaks when walked on , a gently sloping fore dune
which is sparsely vegetated by the native spinifex dune grass (Spinifex
hirsutus), while mid and rear dunes are low in profile. There are no
the northern part of the North Island, New Zealand, I have earmarked a
number of beaches that are worth saving first. The accompanying map shows
where they are. Each beach is worth saving for a different reason. It is
of course impossible to be complete but everyone knows a beach in his/her
locality that is worth saving first. From the Otama Beach example and the
examples below, a number of reasons and conditions become evident. By focussing
effort on those beaches that are still in a salvageable or even healthy
state, quick progress can be made, while the result is also likely to remain
Parengarenga spit: The Parengarenga sand spit consists of almost
pure, extremely white looking, quartz sand. The sand is mined for glass
making. The spit is very sparsely vegetated and has no tall dunes. The
Parengarenga harbour is sparsely populated and it is a traditional homeland
for the native Maori people. It is a unique place. The sand spit, harbour
entrance, sea and part of the estuary could be made into a beach/marine
reserve yielding many benefits. But the area is under threat of dense plankton
blooms and siltation from recent agricultural developments. Even the polluted
water from Auckland's west coast arrives here. The water, only ten years
ago (1990), praised for its clarity, has recently become very turbid. Sea
life in the harbour has been decimated.
Karikari Bay: Facing north on the Karikari Peninsula is Karikari
Bay (Puheke Beach), strung between three headlands. It is a pristine area
with clear water and clear sand, but dune revegetation has formed a steep
bank on its fore dunes. It can be salvaged easily and turned into a dune/beach/marine
reserve. Part of the adjoining unique Rangaunu Harbour and the exposed
rocky shore to the East, with some offshore islands, could be included.
Hokianga dunes: Most visitors visiting Northland, come past the
Hokianga Harbour where they marvel at the tall sand dunes marking its entrance.
The dunes are unique and wild and bare and very sparsely vegetated. They
are worth preserving as a unique wilderness habitat. But they are threatened
by planted pine forests on the rear of the dune and wilding pines (wild
pine seedlings) from these forests. They can still be saved and turned
into a pristine wilderness area. Due to pollution, the dunes are no longer
replenished to keep up with natural erosion.
Ocean Beach: Ocean Beach is found on the Bream Head peninsula, east
of the township of Whangarei (population 40,000). It can be reached easily.
Ocean Beach faces north and is very exposed. Its steeply sloping beach
consists of clean sand and it is backed by gently sloping fore dunes and
low profile rear dunes. But it is under threat from dune planting. It is
an excellent candidate for encompassing the entire, uninhabited peninsula,
mountains, beach, dunes, sea, exposed rocky shore and part of the entrance
to the Whangarei Harbour, into a pristine wilderness area. Because the
peninsula can be isolated from noxious animals such as possum, wild cat,
rat and stoat, the peninsula can be made to act like a 'mainland island'.
Mangawhai spit and dunes: The Mangawhai spit is an uninhabited overwash
area (the sea washing over it during large storms), with low dunes. It
has a large wild, bare dune to its south and is flanked by a small estuary
to the west. Its entrance is plagued by drifting sand banks that are presently
being mined for sand. It is a place to save for posterity. But the dunes
are threatened by revegetation and a planted pine forest. The river's catchment
area is prone to erosion.
The Parengarenga sandspit (Kokota) must be preserved as a
Parengarenga Harbour is the northernmost harbour in NZ. Its
sand spit consists of almost pure quartz sand. It is sparsely vegetated
and its sand can wander freely.
Location of Puheke Beach and Karikari Bay on the Karikari
Peninsula. Bottom centre is the Rangaunu Harbour.
Puheke Beach showing dunes and vegetation. In the top right
corner Mt. Camel, guarding the entrance to Houhora Harbour.
The tall Hokianga Harbour dunes on its northern spit have
been planted estensively in pine forests. The wild bare dune is worth saving
as a dune/beach reserve.
The Hokianga Harbour with its entrance on left behind the
rocky promontory. The unique wild and tall sand dunes are threatened by
pine plantations in the far distance and they are shrinking.
Ocean Beach is found on the ocean side of Bream Head, a sparsely
populated peninsula. A dune/beach protection reserve could be combined
with a marine reserve rounding Bream Head and extending into the harbour
Ocean Beach extends from an easily accessible bay (behind
us) past an inconvenient headland, into the far distance. On left a tall
rock face but in the distance low profiled dunes and a steep beach with