application on notification – category 2€¦ · this dredging management and monitoring plan...

APPLICATION ON NOTIFICATION – CATEGORY 2

Applicant: Kingston District Council

Development Number: 010/U074/17

Nature of Development: Marine dredging and associated sediment disposal

Type of development: Merit

Zone / Policy Area: Coastal Open Space Zone/No Zone

Subject Land: Breakwater at entrance of Maria Creek, Kingston SE

(Adjacent Section 603, Lacepede, CT 5621/713)

Contact Officer: Darby Schultz

Phone Number: (08) 7109 7330

Start Date: 16 November 2017

Close Date: 29 November 2017

During the notification period, hard copies of the application documentation

can be viewed at the Department of Planning, Transport and Infrastructure,

Level 5, 50 Flinders St, Adelaide, during normal business hours. Application

documentation may also be viewed during normal business hours at the

local Council office (if identified on the public notice).

Written representations must be received by the close date (indicated above) and can

either be posted, hand-delivered or emailed to the State Commission Assessment

Panel.

Any representations received after the close date will not be considered.

Postal Address:

The Secretary

State Commission Assessment Panel

GPO Box 1815

ADELAIDE SA 5001

Street Address:

Development Division

Department of Planning, Transport and Infrastructure

Level 5, 50 Flinders St

ADELAIDE SA 5000

Email Address: [email protected]

SOUTH AUSTRALIAN DEVELOPMENT ACT, 1993

REPRESENTATION ON APPLICATION – CATEGORY 2

Applicant: Kingston District Council Development Number: 010/U074/17

Nature of Development: Marine dredging and associated sediment disposal

Type of development: Merit

Zone / Policy Area: Coastal Open Space Zone/No Zone

Subject Land: Breakwater at entrance of Maria Creek, Kingston SE (Adjacent

Section 603, Lacepede, CT 5621/713)

Contact Officer: Darby Schultz

Phone Number: (08) 7109 7330

Close Date: 29 November 2017

My name:_________________________________________________________________________________________________

My phone number: _________________________________________________________________________________________

PRIMARY METHOD(s) OF CONTACT: Email address: ____________________________________________________________

Postal address: ____________________________________________________________

_______________________________________________Postcode_________________

You may be contacted via your nominated PRIMARY METHOD(s) OF CONTACT if you indicate below that you wish to

be heard in support of your submission.

My interests are: owner of local property

occupier of local property

a representative of a company/other organisation affected by the proposal

a private citizen

The address of the property affected is ___________________________________________________ Postcode ______________

The specific aspects of the application to which I make comment on are:

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

_________________________________________________________________________________________________

Should the State Commission Assessment Panel conduct a public hearing for this Development Application:

I wish to be heard in support of my submission

do not wish to be heard in support of my submission

(Please tick one)

By appearing personally

being represented by the following person:

(Please tick one)

Date _________________________________ Signature _________________________________________________

Return Address: The Secretary, State Commission Assessment Panel, GPO Box 1815, Adelaide SA 5001 or

[email protected].

Dredging (and Marine Excavation) Management and Monitoring Plan

Maria Creek, Kingston

Kingston District Council

November 17

Ref No. 20170912R002

Ref No. 20170912R002 Dredging (and Marine Excavation) Management and Monitoring Plan Maria Creek, Kingston

© Tonkin Consulting 2017

This document is, and shall remain, the property of Tonkin Consulting. The document may only be used for the purposes for which it was commissioned

and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited.

Document History and Status

Rev Description Author Reviewed Approved Date

A Draft For EPA Comment MTB JCH JCT 30 October 2017


Contents

1 Introduction 1

1.1 Background 1

2 Legislation / Standards / Codes / Guidelines / Conditions 3

3 Objectives 4

4 Monitoring/Management Infrastructure 5

4.1 Dredging Management Activities 5

5 Monitoring Commitments 7

5.1 Climate conditions 7

5.2 Minimisation of noise pollution 7

5.3 Minimisation of air pollution due to dredging activities 7

5.4 Baseline data recorded prior to dredging 8

5.5 Monitoring data and visual assessment of any plume during dredging 9

5.6 Baseline data recorded post dredging activity 11

5.7 Public safety and amenity 12

6 Management Commitments 13

6.1 Implementation of objectives 13

6.2 Plume impact and water clarity 13

6.3 Dissolved oxygen 13

6.4 Reduced pH 13

6.5 Public safety and amenity 13

6.6 Noise 14

6.7 Air quality 14

6.8 Emergency response 14

6.9 Independent verification 14

Figures Figure 1.1 Site Location Plan Maria Creek 2

Appendices Appendix A Additional Notes for Monitoring Procedures

Ref No. 20170912R002 Dredging (and Marine Excavation) Management and Monitoring Plan Maria Creek, Kingston 1

1 Introduction

1.1 Background

This Dredging Management and Monitoring Plan (DMMP) has been prepared for the Maria Creek

Outfall, which incorporates the Kingston recreational boat launching facility, for the purpose of

maintaining creek flows and navigable channel for recreational boating activites.

As dredging operations are a prescribed activity under the Environment Protection Act, these

operations will be carried out under a licensed approval granted by the Environment Protection

Authority (EPA). This DMMP identifies the impacts of the dredging operations on the marine

environment, and outlines the monitoring that will be undertaken to ensure acceptable

management of water quality.

It is estimated that approximately 4000 cubic metres of sand and seagrass wrack is to be

removed for the maintenance of the entrance channel. The sands are generally medium grained

clean sands of high carbonate content (70-80%), with a representative median (D50) particle size

of 0.3 mm and only a few percent silt and clay. Some minor seagrass wrack is expected and this

is not expected to have a significant impact on dredging discharge water quality.

The accumulation of material is as a result of an interruption of the natural coastal process of

longshore sand drift where the breakwater and mouth of the creek extend into the ocean

environment. Maintenance dredging is required to maintain access to the Maria Creek

Breakwater and Kingston Boat Ramp facility.

The sea floor of the channel is predominantly sand. The proposed dredging activities stops short

of the established sea grass meadows which exists further seaward. Therefore, the dredging of

sediments within the channels will not directly impact on any sea grass. It is proposed that the

sand bypassing activity will assist in managing the accumulation of materials on the southern

side of the breakwater and mimic the natural processes along this area of coastline.


Figure 1.1 Site Location Plan Maria Creek


2 Legislation / Standards / Codes / Guidelines / Conditions

The following legislative guidelines have been consulted in preparing this DMMP:

• Environment Protection Act 1993

• Environment Protection (Marine) Policy 1994

• Environment Protection (Water Quality) Policy 2015

• Environment Protection (Noise) Policy 2007

• Environment Protection (Air Quality) Policy 2016

• National Assessment Guideline for Dredging 2009

• EPA Guideline Dredging and Earthworks Drainage June 2010

• EPA Guideline Regulatory Monitoring and Testing: Independent Verification Requirements

December 2006

• Development Application number DA: 640/048/17.


3 Objectives The aim of the dredging management and monitoring plan is to meet the following objectives in

undertaking the dredging operation:

• Monitor the effects of dredging and sediment disposal on the marine environment to ensure

that the impacts on water quality are local and temporary and are minimised.

• Maintain the amenity of the beach and marine environment for public use and primary

contact.

• Monitor and manage the potential effects of reduced oxygen content, increased turbidity

and reduced pH of the water column in the dredged area.

• Monitor and manage the behaviour of any dredging plume that may occur under varying

tides, currents and weather conditions, and to manage and minimise the potential effects of

a plume.

• Minimise the effect of noise pollution from the dredging operation.

• Maintain records and reports of monitoring results and management practices, to allow

review and auditing of procedures and thus confirming compliance to legislative

requirements, applicable conditions of licence or authorisation, codes of practice, policies,

standards, procedures and guidelines.

• Carry out dredging activities in accordance with licensed approvals, environmental policies,

OHS&W regulations and other relevant legislation and guidelines


4 Monitoring/Management Infrastructure The maintenance dredging works are proposed to be undertaken utilising council plant which at

this point is assumed to be a dredge which will employ cutter suction dredging techniques. The

dredging activities are proposed to commence following written advice to the EPA and will be

conducted in accordance with the Councils dredging licence and the approved development

application. The frequency and volume of materials removed during each dredging event will be

detailed in the written advice to the EPA and undertaken in accordance with this Dredging

Management Plan.

In general maintenance dredging works are expected to be completed within one week of

commencement however may take multiple days due to weather and tide conditions, monitoring

requirements and controls and resource availability. Monitoring and management will be the

responsibility of Council.

4.1 Dredging Management Activities

Activity/Guideline Rationale

Dredging a navigable channel depth from breakwater

entrance to achieve a depth of -3.0m AHD (approx.) at

Kingston boating facility by dredging the breakwater

entrance, and seaward of the entrance.

To enable access to the Kingston boating facility

via the Maria Creek Breakwater.

Dredging of built up material located up shore of the

breakwater and within the mouth of Maria Creek.

To enable natural longshore drift of materials to

continue

No disposal of sediment into the marine environment. All

sediment is to be pumped or excavated and trucked to

land based spoil location.

To avoid the increased risks to marine environment

related with disposal of sediments to the sea.

When dredging to the Spoil Locations as shown on the

Proposed Dredge Monitoring Locations plan in Appendix

A, a turkey’s nest will be formed, and spoil will be

pumped into this and allowed to free drain and return to

the natural environment on the down shore side of the

coast as it would have naturally occurred.

To allow the sediment to settle and the water to

infiltrate through the beach, so as to avoid the

increased risks to marine environment.

If monitoring indicates that acceptable water quality

cannot be achieved, dredging will cease until additional

measures can be undertaken.

To minimise the potential effects of dredging to

acceptable standards.

Dredging will be avoided during mid-winter This minimises the reduced availability of light to

seagrasses related to turbidity, thereby minimising

the potential effects on the seagrass beds of the

area. It also minimises the risk of a weather related

incident that might have adverse effects on the

marine environment.


Dredging works include utilising an excavator to remove

the sea grass wrack from the mouth of the Maria Creek

Breakwater this will include minor amounts of sand that

will also be removed during this process however

predominantly mobilised and accumulated sea grass

wrack.

To enable water to flow in and out of Maria Creek

to prevent fish death and also reduce the risk of

flooding of low lying properties in the Kingston

Township in the event of heavy Spring Rains.

Dredging of built up sea grass wrack to be relocated

along shore of the breakwater to the north and allowed to

move back into the marine environment through natural

processes.

To enable natural longshore drift of materials to

continue

No disposal of sediment into the marine environment is

proposed. As an additional measure during dredging the

erection of a silt curtain will be placed across the mouth

of the breakwater on the seaward side of the dredge

location to reduce turbidity in the marine environment,

(where sea conditions permit) . All minor sediment

excavated will be placed with sea grass.

To avoid the increased risks to marine environment

related with disposal of sediments to the sea.

Dredged/excavated sea grass will be trucked and placed

in Spoil Location as shown on the Proposed Dredge

Monitoring Locations plan in Appendix A.

To allow the water and minor sediment to settle

and the water to infiltrate through the beach, so as

to avoid the increased risks to marine environment.

If monitoring indicates that acceptable water quality

cannot be achieved, dredging will cease until additional

measures can be undertaken.

To minimise the potential effects of dredging to

acceptable standards.

Dredging will be avoided during incoming and slack tides

where the use of the silt curtain will be less effective. The

use of a silt curtain will typically be deployed in outgoing

tides in calm conditions. In the event of outgoing tide and

adverse conditions including wind generated waves the

silt curtain will not be deployed however close monitoring

of dissolved oxygen to ensure conditions do not drop

below 6mg/L in Maria creek. Activities will be undertaken

during suitable weather conditions

Minimising the potential effects on the seagrass

beds of the surrounding area. It also minimises the

risk of a weather related incident that might have

adverse effects on the marine environment.


5 Monitoring Commitments The monitoring during the dredging is proposed to be practical and to protect the surrounding

environment and people accessing the environment. Monitoring using water quality multi-probes

will establish the conditions at the start of the day prior to any dredging activities.

The establishment of the silt curtain will help reduce any potential turbidity and sediment flows

out into the marine environment and the monitoring point on the seaward side of the silt curtain

will determine the effectiveness of the silt curtain and provide indication of tidal conditions for

optimum dredging activities. In the event of outgoing tide and adverse conditions including wind

generated waves the silt curtain will not be deployed however close monitoring of dissolved

oxygen to ensure conditions do not drop below 6mg/L in Maria Creek.

5.1 Climate conditions

Purpose Requirement Criteria Action/Response Responsibility

To assess the risk of

dredging plume

spread.

Frequency: Daily during

dredging

Recorded parameters: Wind

speed and direction tides %

cloud cover

Nil Determine the most

appropriate

monitoring location.

Dredging

Supervisor

5.2 Minimisation of noise pollution


To ensure noise

levels during

operations do not

exceed EPA

prescribed levels.

Frequency: Weekly on an as

needs basis during hours of

operation.

Recorded Parameters: Noise

level readings.

Noise level <52dB

(A) between 7am and

10pm, or <45dB (A)

between 10pm and

7am or, short term

typical maximum

noise >60dB (A),

measured and

adjusted at the

nearest existing

residential boundary.

Continue dredging

operations and

periodic monitoring.

Dredging

Supervisor

Location: At source of sound

site boundary adjacent nearest

receptor.

Noise level >52dB

(A) between 7am and

10pm or >45dB (A)

between 10pm and

7am or, short term

typical maximum

noise >60dB (A),

measured and

adjusted at the

nearest existing


Stop dredging.

5.3 Minimisation of air pollution due to dredging activities


To ensure air quality

is maintained during

operation

Frequency: Periodically as

required. Recorded

Parameters: Odour.

Presence of

offensive odour due

to seagrass decay.

Cover seagrass with

layer of dredge spoil

to prevent odour.

PASSMMP

Dredging

Supervisor


Location:

Adjacent to breakwater

Presence of

excessive exhaust

emission – possible

leak in engine

exhaust system.

Stop dredging.

Refer Section 6.7.

5.4 Baseline data recorded prior to dredging


To establish a

baseline for the

project for low, ebb,

flood and high tide

conditions over a 24-

hour period.

Frequency: Ebb, low, flood &

high tides conditions over a

single day 24 hrs prior to

dredging.

Recorded parameters:

Dissolved Oxygen (DO)

Temperature Secchi Depth

Turbidity pH GPS location

Water depth Photographs

Plume visibility and location.

Monitoring Locations: At

specified control sites, as per

attached plans for each site.

DO approx. 1m from the

seabed, or as deep as probe

will reach and at surface.

Turbidity / pH at least 1.2m

below the water surface.

Applicable

Standard/Guideline:

DO/temp/turbidity/pH gauge

calibration < 12 months old.

Secchi Depth per AS3550.7

Turbidity per EPPWQ. GPS

coords in WGS84.

Water depth +/- 10%.

Photographs recorded

digitally. Plume visibility and

location to be sketched on

attached plan of monitoring

locations. See also attached

monitoring notes.

Probe Calibration: Daily

calibration (as per applicable

Standard/ Guidelines)

recorded with monitoring data.

N/A – baseline data. Dredging

Supervisor


5.5 Monitoring data and visual assessment of any plume during dredging


To ensure water

quality criteria are

maintained as

organic sediments

can reduce oxygen

content of water,

which has a negative

impact on the marine

flora and fauna.

Frequency:

Daily (at/soon after dawn);

and

Twice daily at D1 (see

attached plan); and

Periods of calm weather and

low tidal movements.

DO > 6.5mg/L at any

location

Continue normal

dredging operations

and monitoring.

Dredging

Supervisor

6mg/L < DO <

6.5mg/L

Reduce dredging

rate and repeat

monitoring at the

same location every

2 hrs until results

normal i.e. DO >

6.5mg/L.

Reduction in pH may

indicate the presence

of acid sulphate

sediments, which will

affect water quality.



Temperature

Secchi Depth

Turbidity

pH

GPS location

Water depth

Photographs

Plume visibility and location

DO < 6mg/L at any

location

Immediately stop

dredging and check

for visual indicators.

Advise Dredging

Supervisor

Monitor until results

return to DO > 6mg/L

then repeat

monitoring at the

same location every

2hrs until results

normal i.e. DO > 6.5

mg/L.

Monitoring Locations: At


attached plans.

DO approximately 1m from

the seabed, or as deep as

probe will reach and at

surface.

Turbidity/pH at least 2m below

the water surface.

Secchi > 2m. Continue normal

dredging operation

and monitoring.

If depth reducing i.e.

approaching 2m,

reduce dredging rate

and repeat

monitoring at same

location every 2hrs

until results normal.

Applicable Standard/Guideline



Secchi Depth per AS3550.7

Turbidity per EPPWQ.

GPS coords in WGS84.

Water depth +/- 10%.

Photographs recorded

digitally.

Plume visibility and location to

be sketched on attached plan

of monitoring locations.

See also attached monitoring

notes.

Probe Calibration:

Secchi < 2m Immediately stop

dredging until

turbidity levels

confirmed. Assess

rate of dispersion

and the return to

normal conditions.

Immediately stop

dredging operation

and assess rate of

dispersion and the

return to normal

conditions.

Turbidity < 10 NTU Continue normal

dredging operation

and monitoring.



Daily calibration (as per

applicable

Standard/Guidelines)

recorded with monitoring data.

Turbidity > 10 NTU If levels increasing

i.e. approaching 10

NTU; reduce

dredging rate and

repeat monitoring at

the same location

every 2hrs until

results normal.

NB: if swimmers

nearby, perform

additional monitoring

between dredging

activities and

swimmers to check <

20 NTU at swimming

site.

pH > 6.5

Continue normal

dredging operation

and monitoring.

5.5 < pH <6.5

Reduce dredging

rate and monitor at

the same location

every 2hrs. Monitor

in the surrounding

area to identify

possible source.

pH < 5.5

Stop dredging activity

Take water samples

for further analysis.

Visual Indication of

Plume:

Assess and record

extent of any visible

plume and indications

of health of marine

life.

Photographs to work

area, settlement pond

and settling pond

overflow area

If any plume appears

to expand or affects

other activities,

reduce or suspend

dredging activity until

reason identified or

returns to normal

conditions.


5.6 Baseline data recorded post dredging activity


To determine a

return to baseline

recordings for the

project for low, ebb,

flood and high tide

conditions over a 24-

hour period.

Frequency:

Ebb, low, flood & high tides

conditions over a single day

5-10 days’ post dredging.



Temperature

Secchi Depth

N/A – baseline data. N/A – baseline data. Dredging

Supervisor.

Turbidity

pH

GPS location

Water depth

Photographs

Plume visibility and location

Monitoring Locations: At four


attached plan.

DO approx. 1m from the

seabed, or as deep as probe

will reach and at surface.

Turbidity / pH at least 1.2m

below the water surface.

Applicable

Standard/Guideline:



Secchi Depth per AS3550.7.

Turbidity per EPPWQ. GPS

cords in WGS84. Water

depth +/- 10%. Photographs

recorded digitally. Plume

visibility and location to be

sketched on attached plan of

monitoring locations. See

also attached monitoring

notes.


5.7 Public safety and amenity


Provision of a safe

and secure work site

with clear

identification of

hazards and

maintaining

appropriate buffer

distances between

construction and

recreational activities.

Frequency: Daily on a

periodic basis during hours

of operation.

Location: General work

zone.

Monitor the extent of

any plume spread

under different tidal

conditions

Dredging

Supervisor


6 Management Commitments

6.1 Implementation of objectives

Issues Action/Response Responsibility

To ensure compliance with

environmental legislation and

works approvals.

All subcontractors to undergo site induction to ensure that

their environmental responsibilities are understood.

Undertake regular inspections to ensure implementation

and compliance with DMMP.

Dredging Supervisor

6.2 Plume impact and water clarity


Low water clarity will occur and

should be confined to the

dredging area.

Slow the rate of extraction to minimise the spread of fine

sediments.

Stop dredging operation if weather and tidal conditions are

accentuating spread of the plume.

Dredging Supervisor

6.3 Dissolved oxygen


Organic sediments can reduce

oxygen content of water which

has a negative impact on the

marine flora and fauna

DO target level > 6.5mg/L

DO level < 6.5mg/L and > 6mg/L, reduce rate of dredging

DO level < 6mg/L, immediately stop dredging operation.

Dredging Supervisor

6.4 Reduced pH


Reduction in pH may indicate the

presence of acid sulphate

sediments, which will affect water

quality.

pH level 6.5 continue dredging

pH level <6.5reduce rate of dredging, increase frequency of

monitoring

pH level <5.5 stop dredging activity. Take water sample for

further analysis

(Note: Criteria to be reviewed based on results of acid

titration.)

Dredging Supervisor

6.5 Public safety and amenity


Provision of a safe and secure

work site with clear identification

of hazards and maintaining

appropriate buffer distances

between construction and

recreational activities.

Establish a work zone with suitable buffers to prevent

unauthorised entry.

Dredging Supervisor


6.6 Noise


To ensure noise levels during

operations do not exceed EPA

Construction Noise Guidelines.

If noise readings >45dB (continuous) between 7am and

7pm or, or short term typical maximum noise >60dB

(maximum), measured and adjusted at the nearest existing


Carry out necessary modifications to equipment or

operations to reduce noise level, before resuming dredging

operations.

Dredging Supervisor

6.7 Air quality


To ensure air quality is

maintained during operation.

Presence of excessive exhaust emissions may indicate

possible leak in engine exhaust system.

Carry out necessary servicing and maintenance, prior to

resuming dredging operations.

Dredging Supervisor

6.8 Emergency response


Identification of incident which

may require implementation of

emergency response.

Notify emergency services and EPA as required. Dredging Supervisor

6.9 Independent verification


To ensure that the dredging

activity has been carried out in

accordance with licence

conditions to minimise the

effects on the environment.

The results of all calibration checks, monitoring results and

visual records are to be submitted to the independent

verifier.

Dredging Supervisor


Appendix A Additional Notes for Monitoring Procedures


Additional Notes

• Monitoring during dredging should not be carried out until at least 1 hour of dredging has

occurred.

• Dissolved oxygen is normally lowest, and hence the greatest risk to marine life occurs at

about dawn, particularly in periods of calm weather and minimal tidal movement. Hence, in

addition to the daily dawn/early morning measurements, additional monitoring events are to

be conducted when calm weather and slack tides occur together.

• DO measurements are taken 1 metre from the bottom or as deep as the probe allows. If

water depth prevents reaching 1 metre from the bottom, the depth of probe is to be

recorded. The DO probe is to be kept moving gently during measurement.

• Any exceptional circumstances that might affect the monitoring results, such as storm

events or other construction activities, are to be recorded.

• Photographs are to be taken from an elevated position where possible, and in a direction

that avoids reflection/glare off the water. Plume visibility and location is to be sketched daily

on copies of the attached Monitoring Locations Plan.

• The Daily Monitoring Report must include all of the monitoring data collected and copies

kept onsite for the duration of the dredging period.

Monitoring Locations

Kingston Boating Facility

• Control Sites

The control sites are intended to monitor the natural background water quality conditions.

− C1: Control Site 1, south of the channel and nearshore.

− C2: Control Site 2, approximately 50m seaward (west) of the breakwater entrance.

− C3: Control Site 3, approximately 100m north of the channel and nearshore.

− C4: Control Site 4, within the channel, approximately 75m from dredging area. This

site is monitored to confirm water quality moving from Maria Creek.

• Dredging Sites

The dredging sites are intended to monitor areas of potential risk of impact on water quality.

− D1: Dredging Location, at the dredging location and moving with the dredge.

− D2: Nearshore, in the downstream direction of a potential plume, and in the vicinity of

potential swimming and primary contact in the water. This site is monitored to

confirm water quality is suitable for recreational activities in that area.

Risks to Benthic Communities from Dredging

The potential negative effects on the marine environment include reduced water clarify, reduced

oxygen content or reduced pH.

Fines contained in the dredged and discharge flow can reduce water clarity, reducing light

availability to seagrasses and hence their ability to grow. Dredging is expected to form a

moderate plume. Turbidity above 10 NTU for extended periods can reduce seagrass growth and

although the criteria defined in the Water Quality EPP may not always be able to be achieved,

monitoring and management defined in this MMP will minimise these potential effects. Re-

suspension of organic sediment can reduce oxygen content of the water quality as a result of

sulphides and ammonia released into the water column, which can stress fish and other fauna.

Dissolved oxygen content below 4 mg/L can cause fish death. Seagrass, particularly dead and


decaying seagrass, are the major potential source, and can also result in reduced dredging

efficiency. This can then result in reduced pH of the water column and in severe cases, result in

black and odorous discharge, particularly if decaying seagrass is dredged.

Given the location of Maria Creek Breakwater following storm events during the winter months

significant quantities of mobilised seagrass enters the channel of the creek which requires

clearance via excavation methodology at certain times of the year. This DMMP implements

monitoring and management procedures to manage these potential effects.

Release of sulphides from decaying seaweed, mangroves, or the dredging of ASS sediments

can reduce the pH of the water column, stressing marine fauna and increasing the risk of metals

that might be in the sediment being released to the water column. At this site the sediments are

high in lime (carbonates), which acts as a natural buffer against the reduction of pH, and ASS

are unlikely. Nevertheless, this DMMP implements monitoring and management procedures to

manage these potential effects in case they occur.

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