8. Measures to Mitigate Identified Impacts - Gosford City Council

8. Measures to Mitigate Identified Impacts
8.1 Environmental Management System
The Technical Specifications Report (WRL 1998b) outlines the requirements of the
environmental management plan intended to play an integral part in mitigating the identified
impacts of the proposed terminal protection structure construction.
The objective of this management system is to plan, establish and maintain a strategy to
minimise environmental impact. This strategy is the responsibility of the Contractor.
The documentation requirements for this system of environmental management (WRL 1998b)
include:
• noise, air and water quality monitoring programs
• planned acoustic management measures to be implemented to reduce noise levels
• planned dust control measures
• planned water quality control measures and facilities
• erosion and sediment control plans.
The specifications also require the Contractor to appoint an environmental
management representative (EMR) who will be a full time appointee for the duration
of the sand extraction, filling works and construction of the proposed terminal
protection structure (WRL 1998b). The EMR shall convene an environmental
management committee to review and monitor the implementation and operation of
the environmental management system. This committee will be required to meet at
least monthly and shall include the following key personnel:
• Contractor’s environmental management representative
• Project manager
• Contractor’s corporate quality assurance manager, and
• Superintendent’s assistant.
The committee shall be chaired by the EMR who will be responsible for preparing,
maintaining and distributing an agreed record of minutes for each meeting.
It is also suggested that the EMP includes procedures for the event of uncovering
items of historic interest during excavation. This aspect should be included in
construction staff site induction training.

8.2 Recreational Amenity
8.2.1 Construction
During the construction activity significant impacts on the recreational amenity have
been identified. Most of these are unavoidable. However, there are a number of
measures that can be taken to reduce the level of inconvenience experienced.
Where construction works require an area of the beach to be fenced to restrict
access for residents and public, signposts and detours will be provided advising of
closure and alternate access or recreation areas.
The construction works are programmed in phases in order to maintain a minimum
loss of area for beach amenity and minimise the risk of storm damage during the
excavation and construction process.
It is recommended that, where possible, commencement of the construction process
be timed such as to avoid disruption over the summer months, particularly in the high
recreation areas adjacent to the lagoon entrances and the surf club.
8.2.2 Long Term
A natural trend of long-term recession has been identified which is resulting in the
continued loss of sand and hence recreational amenity at Terrigal/Wamberal Beach.
As discussed in Section 1.3 the principal strategic option recommended for
Terrigal/Wamberal Beach is protection of the narrow dune ridge and the development
thereon, together with necessary action to maintain the beach amenity. The design
of the proposed terminal protection structure is based on sound engineering
principles and has been exposed to numerous tests/ modelling. It is therefore
considered capable of ‘protecting the narrow dune ridge and the development
thereon’. However, in order to meet the principle objective of the Gosford City
Council Coastal Management Plan (WBM 1995), the proposal must include ‘action to
maintain the beach amenity’. This is the reason for the proposal including a strategy
of periodic maintenance sand nourishment. This is discussed in more detail in
Section 8.11.
8.3 Safety
Safety during the construction phase is an important issue. In order to minimise the
risk to public safety, human-proof and stable construction fencing shall be
established around the perimeter of the working area (WRL 1998b). Signs including
‘Deep Excavation’ or ‘Steep Descent’ shall be fixed to the fence at the appropriate
locations. In heavy traffic areas such as the locations for beach access, signposts
illustrating ‘Caution’ and ‘Construction Traffic’, shall be obviously located to maintain
pedestrian awareness.
Safety issues arising from the completion of the construction are addressed in
Section 8.3.3.
8.3.1 Storm Risk
The shoreline of Terrigal/Wamberal Beach is exposed to significant coastal hazards
which threaten the loss of useable beach area during storm events (WBM 1995).
Plant and equipment storage should be maintained in an area outside this hazard
zone (Figure 2.7), when storm events are forecast.

Stockpiling of sand is required for the excavation and restoration processes. The
volumes stored should be limited to the minimum required and they should be stored
so as to prevent their erosion by wind, rainfall or wave action.
It has been acknowledged that under severe storm conditions waves could overtop
any existing seawalls, including the proposed terminal protection structure, onto
beachfront properties (WRL 1998a). The responsibility for loss and damage of the
works is upon the construction contractor, who is required to insure the works against
storm loss and damage during construction (WRL 1998b).
8.3.2 Escarpment Stability
Property protection during the construction process is a significant issue. A qualified
geotechnical engineer will be consulted and will be present when activities occur that
are likely to present a risk of slope failure or foundation instability. Particular
attention is to be given to minimising vibration and shock from compaction and
excavation processes, as designated in the construction specification (WRL 1998b).
8.3.3 Safety Following Completion of the Project
The revetment itself poses few issues relating to safety provided it is maintained in
good condition. During maintenance works which could include repairs to access
and fencing, replacement of armouring, repairs to the toe and ongoing beach
nourishment, the hazards associated with general construction as outlined previously
would apply.
In the absence of nourishment or following severe storms, sections of the revetment
may be exposed. This may raise safety issues relating to beach access from the
revetment, particularly if access paths/stairs provided are not long enough or have
been damaged. The loss of beach width seaward of the structure raises issues in
relation to access to and from the beach at high water when the waves may be
running up the structure.
8.4 Materials
The proposed activity requires a broad range of materials for construction.
Sourcing this material will impact on the environment through loss of resources and
environmental transportation costs. Where practical the use of renewable resources
and local suppliers will maximise sustainability for the proposed activity.
Furthermore, all material will be sourced from either existing or approved sources or
will be subject to environmental impact assessment.
8.5 Construction Noise
All components of the proposed activity must concur with the Noise Control Act 1975.
Conformance requires activity to be restricted during the day to between the hours of
7.00 a.m. and 5.00 p.m. The maximum allowable noise levels for machinery working
on the beach during the construction phase are specified in the technical
specification (WRL 1998b) and will be adhered to.

8.6 Air Quality and Dust
The most significant potential source of atmospheric pollution identified with the
proposed activity arises from transportation.
Avoidance of unnecessary transportation and the use of vehicles and machinery with
minimal emissions are the most affective methods to minimise air pollution. Modern
and well-maintained equipment and vehicles generally provide minimum emission
levels.
Dust contamination also represents a minor risk to air quality. Excessive levels of
dust are unlikely during beach excavation although there may be some effects at the
vehicle access locations during high traffic in dry periods. If necessary, application of
water over dry areas or to cement dust will be used to minimise dust generation. Any
material trucked on or off-site must be suitably covered with a tarpaulin.
8.7 Water Quality
Potential adverse impacts on water quality may arise from excavation, concrete
casting, materials supply and equipment and services maintenance.
Where there is risk of discharge of water containing visible suspended matter, the
technical specifications state that the Contractor shall reduce this risk with the
construction and maintenance of suitable settling ponds, separation plants or any
other effective means necessary as a preventative measure (WRL 1998b).
Maintenance works must be carried out over concrete paved areas, with approved oil
separation facilities. Any spill of oils or other contaminant requires immediate
relocation of contaminated material to appropriate treatment and/or disposal facilities.
Contamination of water in any manner likely to breach the Pollution Control Act or
Clean Water Acts requires remediation to a level appropriate to the responsible
authority.
8.8 Waste Management
Minimisation of excess material and re-use of material where possible are important
methods for effectively managing the construction waste. Hazardous wastes must
be handled separately to general waste. Liquid wastes require discharge to the
sewerage system, gaseous waste must be discharged to minimise concentrations to
non-toxic levels, whilst solid waste may be transported to landfill if inappropriate for
re-use or recycling (WRL 1998).
The technical specifications include allowance for the Superintendent to have rubbish
removed at the Contractor’s expense should the Superintendent be dissatisfied with
the Contractor’s performance in this area. This component of the specifications is an
important mitigating measure.

8.9 Site Restoration
A comprehensive site restoration procedure is an integral measure required to
mitigate the identified impacts.
Completion of each phase of construction requires appropriate removal of
construction materials and restoration of all disturbed areas to at least the original
quality. This includes removal of rubbish, debris, equipment oil, fuel, grease,
formwork, excess material, cabling, hoses and any other peripheral material
associated or necessary during the execution of the contract.
Sand for covering the works shall be obtained either from excavation or, should this
not be sufficient, by importing suitable sand from an approved source (WRL 1998b).
The technical specifications for the proposed terminal protection structure define the
following properties as essential for sand obtained from the excavation works which
is to be used to cover the completed structure:
• less than 10% by weight fines (

Following a significant storm event, and when the structure is exposed an inspection
will be undertaken by appropriately experienced and qualified Council staff. At that
time appropriate minor maintenance works could be initiated as part of a Council
operated maintenance program.
In this context, minor maintenance refers to maintenance that is anticipated, such as
rock settlement or repairing gabions. It does not refer to damage or failure. The
degree of interruption this minor maintenance causes to recreational beach users will
vary. Rock placement will involve large trucks and a temporary loss of access from
the end of the beach in question. Maintenance of the gabion baskets will be less
intrusive, but will still result in some level of interruption to normal beach use to
certain sections of the beach.
8.11 Periodic Maintenance Sand Nourishment
Sand nourishment will be required on a somewhat ad hoc basis depending on storm
frequency and magnitude. It is important that triggers and operating frameworks for
the proposed periodic maintenance sand nourishment are developed. For example,
by means of a condition of consent to the proposed development, a commitment
document outlining a planned approach to nourishment could be developed. It is
envisaged that the document would include aspects such as
•
•
•
•
triggers for sand nourishment
a strategy for obtaining the relevant approvals
an outline of sand volumes and availability
revegetation procedures.
Following storms, when the wall is exposed, there will be less sand to satisfy the
storm bite leaving the beach more vulnerable to wave attack. On the central coast of
NSW, 40% of storms occur within 30 days of the previous storm and 60% occur
within 60 days of the previous storm event. It is therefore imperative that a
continuing commitment to the ongoing periodic maintenance nourishment between
relevant government authorities including a planned approach to sand acquisition
and a strategy for obtaining the relevant approvals be developed to ensure that the
nourishment occurs without delay. A planned approach to regeneration, based on the
information provided in the DLWC Dune Management Manual (2001) should be
included. Without such a plan the recreational amenity at Terrigal/ Wamberal Beach
will continue to degrade (see Section 8.12)
8.12 Monitoring and Triggers for Nourishment
The primary purpose of the nourishment component of the proposed beach
protection works is to maintain visual and recreational amenity. Triggers for sand
nourishment will therefore need to be linked to ‘amenity triggers’. The nourishment
will also promote the structural integrity of the proposed wall.
An important consideration in the design of an appropriate trigger for sand
nourishment will be distinguishing between short and long-term erosion. Wall
exposure will be experienced from time to time, and will often be followed by months
or even years of beach recovery. In such a situation a decision needs to be made as
to what is an acceptable time period for a nominated loss of visual or recreational
amenity to be experienced. Conversely sand may on occasion be effectively lost
from the active Wamberal beach system, either to longshore transport, aeolian

transport or a storm event that is significant enough to carry sand beyond the usual
depth of closure. These events need to be distinguished between to ensure that
nourishment is carried out in an appropriate and timely manner.
Also some sections of the beach will experience higher erosion rates than others.
Again a subjective decision needs to be made as to what is an acceptable level of
disturbance to amenity, this time on a spatial scale.
Such a program will require some level of monitoring. The benefits of monitoring
sand volumes are to:
•
•
•
•
facilitate prompt and appropriate maintenance nourishment
identify unexpected conditions and consequences that may arise
improve the understanding of erosion and accretion and retreat mechanisms at
the site
provide a record of actual environmental impact to be compared to those
predicted.
A further consideration in establishing triggers for nourishment based on amenity is
that the exercise of nourishment activities will themselves impose on recreational and
visual amenity. It is difficult to even qualify these impacts without full knowledge of
the source and method of sand delivery/ placement. It is considered to be in the best
interest of recreational users that superfluous nourishment exercises are not
undertaken.
Monitoring of such a project is essential. The major questions that monitoring should
be designed to answer and fitting approaches are presented in Table 8.1.
Table 8.1 Monitoring Goals
Question
What is the actual nourishment
volume placed on the beach?
What is the colour, texture and
grain size of the material placed on
the beach?
What are the changes to beach
width and slope over time?
Monitoring Approach
Best estimates of the volume placed on the beach to
be obtained and documented by Council from the
contractor.
Physical properties of nourishment material at time of
placement to be sampled and analysed. Further
sampling and analysis of physical properties to be
taken two weeks after placement. Ensure that
baseline data of pre-nourishment sand properties is
available.
Surveys of beach width and slope to be undertaken bimonthly
and as soon as feasible after significant
storms for ten evenly spaced transects along the dry
beach. As far as practicable these should be taken at
spring low tide. Subjective details of subaqueous bar
formation to be made during these exercises. Existing
information on beach width and slope (from
photogrammetry and other survey exercises) should
be entered into a spreadsheet for comparison to this.
Surveys should start immediately after project
approval to ensure a level of baseline data is available
for comparison. (There are OH&S implications for this
survey work).

Question
If the material is placed on the
nearshore berm is it moving
onshore and if so how quickly?
Are sections of the wall being
exposed and if so for how long?
Do more people use the beach
after nourishment? What were the
new and enhanced recreational
opportunities?
Were the temporary short-term
impacts as expected?
Were there any changes to lagoon
entrance behaviour?
What are the final dimensions and
alignment/location of the
constructed revetment?
Has the revetment shifted or tilted
since construction?
Does scour develop in front of or
beside the revetment after a
significant storm event. If so, how
long after does the scour hole
remain?
Are there any long-term end
effects from the revetment such as
accelerated bluff retreat (where the
pattern of bluff retreat decreases
rapidly with distance away from the
wall?
Monitoring Approach
Above survey information to add to knowledge of
sediment transport Consider undertaking offshore
surveys over longer time scales.
During monthly surveys, a record to be made of
sections of wall exposed for the 10 evenly spaced
locations along the dry beach selected for surveying.
Beach user surveys to be undertaken before, during
and after nourishment exercises
Turbidity monitoring to be undertaken before, during
and after nourishment exercises.
Ghost crab numbers to be assessed as an indicator
species as per the recommendations of TEL
(Appendix F).
An assessment of sand coverage of the offshore reefs
should also be considered.
The berm is presently surveyed fortnightly by Council.
There are over ten years of berm survey records held
with Gosford City Council. This will provide a good
data set to compare to the post-nourishment berm
surveys.
Contractor to supply a statement which either confirms
that the structure conforms with the detailed design or
points out all ways in which the final product differs
from that which was approved.
Yearly surveys.
To be observed during surveying activities mentioned
above, with particular focus during post-storm
conditions. In the event of long-term scour being
suspected, scour depths should be surveyed.
To be observed during surveying activities mentioned
above, with particular focus during post-storm
conditions. In the event of long-term end effects being
suspected, surveying should be undertaken.
As well as monitoring the impacts of sand nourishment to feed into planning, the
monitoring will also provide a good data set on which triggers for nourishment can be
based.
Possible triggers for sand nourishment include:
• minimum beach levels acceptable for toe protection
• when sections of the revetment are exposed for a set period of time
• when the lack of beach sand inhibits recreational amenity
• when long-term scouring or end effects are observed.

Quantified levels for these triggers are suggested in Table 8.2. As there is limited
information available to base these on it is important that the triggers are adaptive.
Utilising the expertise of the Department of Infrastructure, Planning and Natural
Resources and the knowledge and aspirations of the community through the CLP
Committee, the details of the approach should be refined. As many of the goals will
be based on recreational amenity, it would be helpful if this review included a
component of public participation, including user (locals and tourist) surveys and
preferences.
When sections
of the revetment
are exposed for
a set period of
time*
Table 8.2 Triggers for Nourishment Exercises
Trigger Level Monitoring Issues
Exposure over a given Visual inspections
area of any section of the undertaken during
wall for more than two survey work
consecutive months
When the lack of
beach sand
inhibits
recreational
amenity*
Minimum beach
levels
acceptable for
toe protection
When long-term
scouring or end
effects are
observed
When the dry beach is
less than a specified
width (e.g. 20 m) at any
given point along the
beach for two
consecutive months, or
when mean widths are
less than a specified
width (e.g. 35 m) for six
consecutive months
Any toe exposure
When scour or end
effects are noticeably
present for six months
(three surveys)
Bi-monthly beach
width surveys
Visual inspections
during survey (it is
noted that
reductions in
beach width would
be observed well
before toe
exposure)
Visual inspections
and surveying
undertaken during
survey work
Philosophy of management
study was for the wall to be
buried at all times. Where
possible this should be
managed by NABE (natureassisted
beach
enhancement) strategies,
such as beach scraping
Widths should be spatially
specific and determined on
the existing variation in
width along Wamberal
Beach, as well as on
community expectations.
The widths would be best
determined from baseline
data (e.g. existing
photogrammetry and data to
be collected before
construction of the proposed
wall) and a workshop
involving the committee
The physical modelling
(WRL 1998) reported failure
of the structure in tests that
simulated the complete
long-term recession of
Wamberal Beach
*It is interesting to note that the spatial impacts of erosion were very different for the significant storms
on record of 1974, 1978, 1986 and 1995. A review of photographs and slides held with the Department
of Infrastructure, Planning and Natural Resources and discussions with Mr David Hanslow of the
Department suggest that
• in 1974 erosion was experienced along the entire embayment
• In 1978 significant erosion was concentrated north of Terrigal Lagoon where a persistent rip
formation may be viewed in the 1978 photography. The eroded section stretches about 200 m
• In both 1986 and 1995, erosion was concentrated further north adjacent to a rock outcrop and
spanned 200-300 m.

Such information could be used in trigger establishment.