Thomas Sokolow

Geography Assignment
Coastal Erosion – Year 10 Assessment Task

Part 1: Introduction

Collaroy-Narrabeen Beach, located on Sydney’s Northern Beaches, is the 3rd most eroded
strip of coastline in Australia. The recent East Coast Low event of 2016 was the worst
recorded coastal erosion event since 1974, causing widespread scouring of the beach, with
over 410,000m3 sand lost and property damage worth an estimated $17.5m, with insurance
claims totalling $45m. Fieldwork was conducted to investigate the causes and impacts of
coastal erosion on this strip of coastline (see figure 1 below). This field work intends to
address the following questions:

1. How do natural processes influence the coastal morphology of Collaroy-Narrabeen?

2. To what extent has Collaroy-Narrabeen Beach impacted by coastal erosion?
3. How should we sustainably manage coastal erosion impacting Collaroy-Narrabeen
Beach?
Thomas Sokolow

Part 2: Research methodology

This report is guided by both primary and secondary research which has been used to
investigate the coastal morphology of Collaroy-Narrabeen Beach and the effectiveness of
various sustainable management strategies to minimise the impacts from coastal erosion
events.

2.1 Primary research:

A field study of Long Reef and Collaroy-Narrabeen Beaches was conducted on Monday the
8th of March 2021. During fieldwork at Long Reef beach the natural coastal processes that
form and transform coastal environments were examined through the conducting of various
beach profiles, observing longshore drift and different sediment types:

 Investigation 1: Required instruments such as

compass’, thermometers and anemometers to observe
and calculate data in order to identify current weather
and ocean conditions at Long Reef.

 Investigation 2: Measured a beach profile cross section

at Long Reef to investigate the formation and features
of sand dunes, identify primary succession of
vegetation on the dune and understand the variation
in coastal sand dune protection. This was completed Figure 1 depicts the current weather
conditions at Long-Reef Beach on the 8th of
by using a tape measure and the clinometer field app March 2021
to calculate the distance from water’s edge and the
gradient of the beach. This
determined the profile of the Hind dune
beach and the importance of sand Foredune
accumulation in the form of sand
Insipient dune
dune in protecting the hinterland
from coastal inundation. Beach berm Nearshore bar

 Investigation 4: Measuring longshore drift and current rip processes to understand

Swash
Figure 2 shows a labelled beach profile cross section of a natural sand dune system
Shoreline

Surf zone
direction and
Backwash rates of
Direction of
sediment
longshore drift transportation
Updrift

along the
ft
Downdri

Direction of beach. This

prevailing wind
was
Figure 3 captures the natural process of longshore drift which occurs on beaches
Thomas Sokolow

completed by placing a cork into shallow-water and timing how long it took to travel
a certain distance, however, the distance the cork travelled would fluctuate because
it was dependent on the current ocean conditions.

 Investigation 5: Sediment analysis to identify key differences in the sediment types at

Long Reef and Collaroy Narrabeen beach, whilst observing the correlation between
sediment size and rates of erosion. This supported the report because it showed the
differences in sediment size between Long Reef and Collaroy-Narrabeen Beach,
which showed that bigger grain sizes leaded to increased abrasion, resulting in
increased rates of erosion.

 Investigation 6: Observing the

headland to identify and
explain the natural
processes causing the
formation of cliffs and the
wave cut platform of Long
Reef headland. This was
used because it showed
that natural processes such as
hydraulic wave action and
weathering broke down Figure 4 captures the different sizes of sediment/grains found on
beaches.
the clay bold stone cliffs,
creating wave cut notches
which resulted in the Figure 5 depicts
collapse of sections of cliffs, Receding the natural
headland Cliff processes which
forming the wave cut have formed
platform. Hydraulic action the cliffs and
wave cut rock
platform at
Rockfall Long-Reef
Wave cut rock headland
At Collaroy-Narrabeen the causes, platform Wavecut notch
impacts and level of erosion and
risk were examined along with an evaluation of current management strategies through a
number of specific field investigations.

 Investigation 8: Examining the

effects of the June 2016 East
Coast Low coastal erosion event
on Collaroy-Narrabeen Beach.
This was analysed between the
Collaroy surf club and the carpark
where there was extensive
damage and was utilised to

Figure 6 shows the low-pressure system that moved through Sydney on

June 6th, 2016
Thomas Sokolow

examine the impact on the coastal environment and the infrastructure in the
surrounding area.

 Investigation 9: At Collaroy,
observations were made about
risk of erosion and human
influences on erosion. This was Figure 7 portrays
the infrastructure
investigated through conducting that was the most
beach width, vulnerability to vulnerable to
erosion, and strategies used to erosion events
such as the East
prevent erosion. Afterwards, a Coast Low in 2016
risk assessment was conducted
against the types of infrastructure
that were most susceptible to the
risk of a coastal erosion event
along the strip of coastline and was justified by a range of coastal management
strategies that could be used to protect them.

 Investigation 10: Measuring beach width at

Collaroy-Narrabeen Beach in two different
locations in order to identify the relationship
between beach width and erosion risk. This
was completed by using a tape measure and
measuring the width of the beach (from swash
zone to foredune). The tape measure was
then used to calculate the height of the
foredune compared to the swash zone. This
provided evidence that the beach had less
width and height than Long Reef beach with
overall less volume of sand, resulting in a
more vulnerable strip of coastline to erosion
events. Figure 8 shows the change in elevation from the
shoreline to the dune at Collaroy-Narrabeen beach

● Investigation 11:
Conducting a cost-
benefit analysis of
management strategies
at Collaroy-Narrabeen
Beach in order to
identify which ones
were the most cost
effective and had the
greatest benefit in
Figure 9 depicts a successful management strategy being conducted at a beach
terms of protecting the
high-risk area of coastline. This was calculated by the value of land it protected
divided by the cost of defence over a certain number of years. This investigation was
Thomas Sokolow

vital for the report because the evaluation required two management strategies and
the overall outcome of each management strategy, and how successful they were in
protecting the beach.

 Investigation 12: Required an

evaluation of the seawall management
strategy by conducting an
environmental quality assessment,
using the bi-polar analysis method of
the new sea wall at Collaroy-
Narrabeen Beach. This was completed
by answering the seawall’s
effectiveness in response to the
positive and negative questions
throughout the analysis. This indicated Figure 10 shows the sea wall being constructed at Collaroy-
Narrabeen beach
that the seawall management strategy
was ultimately successful.

2.2 - Secondary Research

Fieldwork booklet and stimulus booklet as well as internet research sources were utilised –
be explicit to the ones that you included in your report.

Source B is used to show the natural processes of coastal erosion and coastal morphology,
whilst conveying the detrimental impact humans have on beach systems. This source
provided evidence of the importance of beaches in Australia, and the negative impact
humans inflict on these natural systems.

Source R is used to portray the changes in cross-section measured at Narrabeen Beach as

part of the long-term coastal monitoring program.

Source O is used to show the build-up of sand at the northern side of Collaroy-Narrabeen
beach due to longshore drift and sand nourishment strategies.

Source E is used to portray the historical Images of storm damage at Collaroy Narrabeen

Source G is used to depict the vegetated and non-vegetated areas of Collaroy-Narrabeen

Beach to show which areas of the beach are naturally protected and which parts aren’t.

Source H is used to show the different elevation heights of dune along developed parts of
Collaroy-Narrabeen Beach

Source I is used to show the variation in maximum elevation in different beach profiles along
Collaroy-Narrabeen Beach
Thomas Sokolow

Source P is used to depict the low elevation of the profile cross section of the dune at
Ramsay St, Collaroy Beach.

The very bad precedent article (https://www.surfline.com/surf-news/a-very-bad-

precedent/115106) is used to show information about the seawall that is being, include
costs.
Part 3: Analysis of Causes and Impacts of Coastal Erosion Events at
Collaroy-Narrabeen Beach

The analysis section of this report aims to demonstrate both the natural processes and
human causes and the extent of coastal erosion along this strip of coastline with specific
emphasis around the 2016 East Coast Low event.

3.1 - Natural processes influencing the coastal morphology of Collaroy-Narrabeen

Image x

Beaches are dynamic and constantly changing in response to a range of natural processes,
which includes longshore drift, deposition and accretion of sand along the beach profile,
transportation of sediment along the beach, different sediment sizes, swells, storm systems,
currents, tides and winds. These are all clear factors that culminate in the process of natural
coastal erosion (Refer to Source B). Collaroy-Narrabeen beach is affected by ongoing
processes of sediment transportation by ocean currents, waves and wind, as well as
sediment supplied from adjacent beaches. One of the strongest influences shaping the
coastline is the constant impact of hydraulic action in the form of waves, which causes
longshore drift. Longshore drift is a geophysical process that consists of the transportation
of sediments along a coast and leads to the creation of many types of landforms (refer to
image x). Waves approaching the beach at an angle cause a longshore current to form
parallel to the shoreline. This longshore current can transport sand along the beach, from
the updrift to downdrift direction. On Australian Beaches sand is transported in a northerly
direction. Over time, beach sediments continuously accrete and erode. There are two main
types of sand movement on beaches. Short-term erosion which normally occurs during
storm events, causing sand to be rapidly removed from the beach. It then comes back over
several weeks or months resulting in no loss of sediment in the long term. The other type of
sand movement is long-term coastal recession which occurs when sand removed by a storm
or by longshore drift does not all return to the beach or is not replaced by new sediment
from the updrift direction. This results in a sediment deficit.
 Thomas Sokolow

Coastal erosion is part of the natural response of a beach to changing wave and water level
conditions. However, many areas of Australian coastline are no longer in a natural state due
to the deleterious impacts of human developments in coastal areas, and a growing
population, which ultimately exacerbates the natural coastal erosion on beaches.

3.2 - How have humans altered the beach system at Collaroy-Narrabeen?

Increasing population growth has

led to the development along the
Northern Beaches coastline. 85% of
Australia’s population lives in coastal
areas. This high-density of people
has increased the amount of
development along certain parts of
Image A the coastline. More infrastructure is
being built too close to the shore,
placing it at immense risk of coastal
erosion, and creating major
management problems. This over-development on the primary sand dunes (refer to
image A which shows the overdevelopment of Collaroy-Narrabeen) disrupts the
protective barrier (dune) creating heightened erosion
vulnerability, altering natural accretion and erosion
cycles as well as increasing the risk of coastal
inundation. The overdevelopment has also decreased
sediment budget and rates of accretion have been
disrupted. This is prevalent from areas of Collaroy-
Narrabeen beach that are near Ramsey and Stuart
street where there is 3 metres of elevation from the
shoreline to the dune (refer to source P). Another
human impact is stock grazing, fires or walking tracks
through dunes which damages the vegetation, hence
removing its ability to protect land behind the dunes.
This alteration of the natural coastal process
exacerbates erosion patterns. This is evident in Source
G which shows that South of Devitt Street at Collaroy- Source G
Narrabeen beach, there is limited dunal vegetation
and extensive lengths of protection works. It is this section of Collaroy-Narrabeen
Beach where public and private assets adjacent to the beach are most exposed to
the impacts of coastal storms.

3.3 - East Coast Low of 2016 & Socio-

Economic/Environmental Impacts
Thomas Sokolow

The East Coast Low that occurred on Collaroy-Narrabeen beach in 2016 left devastating
impacts on the nearby infrastructure and coastal processes. (Refer to source E) The 3.6km
stretch of Collaroy-Narrabeen was battered by the ferocious East Coast Low, collapsing
houses and causing many businesses to become bankrupt. This is primarily due to the
fact that Over $45million in claims were made from insurances. Dominant north- Image A
easterly plunging waves peaked 6.5m and exceeded 3m for three days between 4-7 th June
2016. Strong south-easterly winds coinciding with a major 2.4 metre King Tide and heavy
precipitation, resulted in significant stormwater runoff on the beach. Collaroy-Narrabeen
was heavily impacted by this because of a multitude of factors. The elevation heights of
dune along developed parts of Collaroy-Narrabeen Beach were extremely low, averaging 7
metres. (Refer to sources H and I). Furthermore, this area of coastline is significantly
exposed to natural process such as longshore drift and the accretion cycle due to the
extensive human overdevelopment at Collaroy-Narrabeen, which has amplified the erosion
process and is a major reason why this beach is the 3rd most eroded beach in Australia. This
culminated in the destructive impact of the East Coast Low. See Image A – Aerial image of
property between Ramsay and Stuart Streets following the 2016 storm event. The Socio-
economic impacts included displaced people due to the extensive property damage
inflicted, damage and destruction of various coastal infrastructure assets. This is evident in
source E (refer). Other socio-economic impacts include loss of beach amenity and use, and
tourism. Due to the severe scouring of the beach, tourists and the public were unable to
access the beach resulting in decreased local economy and decreased number of people
visiting Collaroy-Narrabeen. The environmental impacts included 410,000m3 of sand which
was lost to offshore sand banks and represented over 50m of beach (see Source R). This
sand was transported and deposited 250 metres offshore to a depth of 8 metres, eventually
re-joining the beach a few months later. The main reason why this East Coast Low had a
disastrous socio-economic and environmental impact is because private development
dating back to the 1900’s was situated on the active beach zone, leading to severe erosion
and scouring of the beach.

Source R depicts the changes in elevation at Collaroy-Narrabeen beach due to the East Coast Low in 2016
 Thomas Sokolow

Source H: Elevation heights of dune along developed parts of Collaroy-Narrabeen Beach

Shaded contours (2m interval) Shaded contours (2m interval) Shaded contours (2m interval) along
along northern end of along Middle section of Narrabeen southern end of Collaroy-Narrabeen
Narrabeen Beach Beach Beach

Source H shows the level of dunes and the degradation of the dunes after development
along Collaroy-Narrabeen Beach. Source shows beach was impacted worse on the south.

4: Evaluation
There were a range of management strategies that were intended to deal with coastal
erosion at Collaroy-Narrabeen Beach. However, the most effective strategies were the
seawall and the sand nourishment and recycling. This is predominantly due to their cost-
effectiveness and their successfulness in protecting the vulnerable strip of coastline at
Collaroy-Narrabeen Beach.

A seawall is a form of coastal defence constructed where the sea, and associated coastal
processes, directly impact the coast. Seawalls are primarily made of concrete and boulders.
The seawall was built and now covers 1.3 kilometres of beach from Collaroy to South
Narrabeen, encompassing 49 private properties dotted with 11 public land areas, including a
car park and a surf club. This intends to be a long-term solution to protect a large number of
public and private amenities, so the devastating impact of the 2016 east coast low event
won’t return (Source E). As depicted in investigation 12, the seawall is successful in
protecting and preserving beach environments and beach amenity and managing current
and projected future risks from coastal hazards. However, it is unsuccessful in providing
undiminished public access to beaches and waterways and it didn’t promote the culture and
heritage environment. This is primarily because the seawall is created to protect the
Thomas Sokolow

sediment budget of the beach and infrastructure in the area, not as an aesthetically pleasing
building. Similarly, the cost of the wall is $25 million which presents a major disadvantage
due to the price of the wall according to an article, “the very bad precent”. Ultimately, the
sea wall is a relatively effective long-term strategy due to the positive impact it upholds as it
will elevate the height of the beach, whilst protecting amenities and people.

Sand recycling and nourishment refers to adding large quantities of sand or sediment to
beaches to combat erosion and increase beach width. This practice uses natural sediment
(sand) and isn’t a man-made barrier, instead it replenishes the lost sand to help stabilise the
coastal morphology of a beach. Sand is sourced from local building sites to supplement sand
and build up sand on eroded beaches. Sand is also degraded every 2-5 years from
Narrabeen Lagoon. 40,000m3 is used to replenish Collaroy-Narrabeen Beach in this period.
This strategy has led to volumetric accretion of +0.5m3/m/year which makes it a viable and
extremely successful strategy (refer investigation 11 and source O). The limitations are that
sand will eventually move with coastal processes northwards along the beach or offshore.
The erosive forces of waves, storms and rising sea levels will continue to chew on the sand,
and eventually it erodes away, moving down the coast and offshore. Therefore,
nourishment can protect coastal structures for as long as the sand lasts, but after a certain
period of time, the beach will have to be renourished. However, the price of this is much
lower than other management strategies ($2 million/year), resulting in this being a viable
and effective management strategy.

5: Conclusion
Ultimately, this report has demonstrated that coastal erosion is a pervasive issue affecting
the Collaroy-Narrabeen Beach coastline through natural processes and human impacts
exacerbating coastal erosion. Natural coastal process has been significantly disrupted due to
increased development within the active beach zone including the once protective
foredunes. As a result, this has led to widespread social/environmental/economic impacts,
including property damage, active beach zone lost and displacement of people. In effort to
combat this, the construction of the sea wall and constant development of the sand are
deemed to be the most successful management strategies because of their proven
successfulness in protecting the beach and amenities in the surrounding area, and overall
cost-effectiveness. However, in the context of increasing coastal populations, rising sea
levels and increasing severity of storm events, it is critical that current management
strategies need to be adapted to ensure a sustainable future for our coastlines, such as
Collaroy-Narrabeen beach which is highly susceptible to coastal erosion.