appendix f: sediment control measures - nz transport agency
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Draft Construction Environmental Management Plan
Appendix F
Appendix F: Sediment Control Measures
This Appendix outlines the following:
The scope of works likely to require sedimentation control and a high level
methodology.
Description of sedimentation control measures that could be used.
Sedimentation control methodology for the pile dewatering.
F1 Scope of Sediment Control Works
The likely sources of sediment from the construction of the Basin Bridge Project can be
broken down into two key areas:
Runoff from exposed surfaces (areas of fill and re-contouring).
Contaminated groundwater from excavations (piles and trenching).
The sediment control measures for the latter are addressed specifically in Section F3
below.
The areas of fill and re-contouring vary throughout the site and include:
Fill for abutments
Fill and retaining wall adjacent to Mitsubishi Motors
Construction of new areas of road pavement
Minor retaining walls and re-contouring as part of landscape works.
Foundations for new buildings
Preparation of car parking areas for surfacing
These areas will be treated using location and task specific methodologies and are
likely to include the following controls (refer to section F2 below for further detail):
All site entrances will be stabilised to prevent the transport of sediment from the
work site on to the road
Treatment of sheet run-off down-grade of works using silt fences and / or filter
socks.
Protection of inlets to the stormwater system using filter socks and other
appropriate mechanisms.
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Appendix F
F2 Description of sedimentation control measures
Some of the methods that may be used in the avoidance and treatment of sediment are
listed in Table 1 below. Further information on these techniques is attached.
Table 1 – Potential erosion and sediment control measures
Technique Use Reference Further details
Stabilise
construction
entrance
Prevent the transport of
sediment from the work
site on to the road. All
construction site
entrances will be
stabilised.
Erosion and
Sediment
Control
Guidelines for
the Wellington
Region, 2006
Attachment 1
Silt fence Treatment of sheet
runoff from construction
areas. Such areas may be
the eastern and western
abutments.
Erosion and
Sediment
Control
Guidelines for
the Wellington
Region, 2006
Attachment 2
Filter sock Treatment of sheet
runoff from construction
areas and for treatment
of stormwater prior to
discharging into Council
stormwater system.
Auckland
Regional
Council
Guideline
Attachment 3
Stormwater inlet
protection
Treatment of water
entering stormwater
collection system
Canterbury
Regional
Council Erosion
and Sediment
Control
Guideline 2007
Attachment 4
Decanting earth
bunds
Treatment of
concentrated flow off
construction areas. This
will be areas up to
3,000m2 where there is
widespread disturbance.
Erosion and
Sediment
Control
Guidelines for
the Wellington
Region, 2006
Attachment 5
Settlement tanks Treatment of water and
sediment removed in the
excavation of the piers.
Attachment 6
Geotextile
Dewatering Tube
Treatment of water and
sediment removed in the
excavation of the piers.
Attachment 7
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Appendix F
F3 Sedimentation control methodology for pile dewatering
The works to construct the piles will be undertaken in four stages. The description of
work at each stage is provided below. Refer to the plans attached (SC.01 and SC.02) for
further information.
Stage 1 – Site Establishment
i. Construction area will be fenced (chain link) and site entrances established.
ii. Depending on location, site entrances will be concrete, asphaltic concrete
(existing or new construction), or stabilised in accordance with GWRC erosion
and sediment control guidelines (section 4.8).
iii. Work areas within the construction area will also be stabilised with coarse
aggregate to prevent debris being tracked out of the construction area and
onto local roads.
iv. Silt fences, will be strategically placed down grade of the immediate work site
to prevent untreated stormwater run-off from the site entering the WCC
stormwater system.
v. An excavation around the location of the pile (approx. 15m x 5m x 0.5m) will
be created to act as a containment area for cementitious material – see stage 4.
vi. A skip or bunded area will be placed/constructed on site to temporarily store
material from the pile excavation.
vii. A dewatering tube or settlement tank will be located on site to use as a method
to allow suspended sediment to settle out.
The dewatering tube (if used) will be either placed in an excavation 500mm deep,
bunded, or sit inside a silt fence or filter sock to allow treated water to slowly soak
away into the surrounding ground.
Stage 2 – Pile Excavation
Once the site has been established, excavation of the piles will commence as follows:
i. Piles will be excavated using an auger.
ii. The soil will generally be wet and will be stored in a skip or bunded area near
the excavation. The material will then be taken away to an approved land fill in
a container with sealed bottom and sides so that no wet material discharges
during transportation.
Stage 3 – Pile Cleaning
i. Prior to placing concrete, the bottom of the pile will need to be clean of all
loose/wet material. It is assumed that approximately 1m3
to 2m3
of material will
be involved in this exercise. A bucket auger will be used to remove this
material.
ii. Material will be placed in a skip or bunded area for removal to an approved
landfill at a later stage.
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Appendix F
Stage 4 – Concrete Pour/Dewatering
A steel metal hopper with a pipe leading to the bottom of the pile will be used for
placing concrete under water (called a tremie). The foot of the pipe is always below the
top of the concrete in the pile and the top of the concrete in the pipe above the water
level in the pile. Placing concrete by tremie prevents the segregation of concrete. A
pump (for dewatering) will be located near the top of the pile.
Concrete will be pumped into the pile through the tremie. Ground water from the pile
will be displaced at the top. This water will be discharged/collected or treated in the
following manner:
i. By visual inspection, the clean water (from the top) will be discharged directly
to the stormwater system (bypassing mixing with any sediment laden
construction water).
ii. Dirty water not suitable for immediate discharge (as identified in the Resource
Consent, operational conditions) will be pumped to either a settlement tank or
a geotextile dewatering tube. This water will be left to let the suspended solids
settle out before discharging into the stormwater system (settlement tank), or
left to filter through the dewatering tube and into the surrounding ground (see
stage 1, item 7). The encaptured solids will be periodically removed to an
approved landfill.
The dirty water from the pile will be monitored for pH levels. Once the pH levels
reach 8.5 we will advance to step iii.
iii. Cementitious material (water with a pH greater than 8.5) will be left to flow over
the pile casing and into the excavation around the set of piles. This cement
laden water will be left to sit in the base of the excavation. Water will filter into
the ground and the cement residue will form a layer of cement paste on the top
surface. This material will be taken to an approved landfill.
Approximately 30m3 of displaced water (per pile) will be treated as a result of the
placement of concrete in the pile. It is assumed that 10m3
of displaced water will be
handled in each of operations i, ii and iii above. The size of the settlement tank and
dewatering tube will be of a size to hold at least 25m3
of displaced water.
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Appendix F
Attachment 1: Stabilised Construction Entrances
Extract from Erosion and sediment control guidelines for the Wellington Region;2006,
Greater Wellington Regional Council.
4.8 Stabilised Construction Entrance
Plate 9: Stabilised construction entrance
a. Definition
A stabilised pad of aggregate on a filter cloth base located at any point where traffic
will be entering or leaving a construction site (see Figure 9).
b. Purpose
To prevent site access points from becoming sediment sources and to assist in
minimising dust generation and disturbance of areas adjacent to the road
frontage by giving a defined entry/exit point.
c. Application
Use a stabilised construction entrance at all points of construction site ingress
and egress with a construction plan limiting traffic to these entrances only.
They are particularly useful on small construction sites but can be utilised for
all projects.
d. Design
Clear the entrance and exit area of all vegetation, roots and other unsuitable
material.
Place aggregate to the specifications below (see Table 6).
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Appendix F
Provide drainage to carry runoff from the stabilised construction entrance to a
sediment control measure.
Table 6: Stabilised construction entrance aggregate
Aggregate Size 50-75mm Washed Aggregate
Thickness 150mm Minimum
Length 10m Minimum
Width 4m Minimum
e. Maintenance
Maintain the stabilised construction entrance in a condition to prevent
sediment from leaving the construction site. After each rainfall inspect any
structure used to trap sediment from the stabilised construction entrance and
clean out as necessary.
When wheel washing is also required, ensure this is done on an area stabilised
with aggregate which drains to an approved sediment retention facility
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Appendix F
Attachment 2: Silt Fence
Extract from Erosion and sediment control guidelines for the Wellington Region;2006.
Greater Wellington Regional Council.
5.3 Silt Fence
Plate 14: Silt Fence
a. Definition
A temporary barrier of woven geotextile fabric used to intercept sediment laden runoff
from small areas of soil disturbance (see Figure 20).
b. Purpose
Silt fences should only be used to intercept sheet flow. Do not use silt fences to reduce
the velocity of flows in channels or place them where they will intercept concentrated
flow.
c. Application
On low gradient sites or in confined areas where the contributing catchment is
small, i.e., short steep batter fills and around waterbodies.
To delineate the limit of disturbance on earthworks sites such as riparian areas
or bush reserves.
Do not install silt fences across waterbodies or in areas of concentrated flow.
d. Design
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Appendix F
Excavate a trench minimum 100mm wide and 200mm deep) along the
proposed line of the silt fence. Install the support posts on the downslope edge
of the trench and silt fence fabric on the upslope side of the support posts to
the full depth of the trench. Backfill the trench with compacted soil.
Place supporting posts or waratahs approximately 3m apart and 0.4m deep.
Ensure the top height of the fence is 400mm above ground level.
To attach fabric, double over and fasten to the support wire and posts with wire
ties or cloth fastening clips at 150mm spacings.
Join lengths of silt fence together by doubling over fabric ends around the
supporting posts (wooden posts/battens). Staple the fabric ends to the batten
and butt two battens together.
Maximum slope lengths, spacing of returns and angles for silt fences are shown
in Table 9.
Install silt fence wings at either end projecting upslope to a sufficient height to
prevent outflanking.
Table 9 – Silt fence design criteria
Slope
(%)
Slope Length (m) Spacing of
Returns
(m)
Length (m)
<2% Unlimited NA Unlimited
2-10% 40 60 300
10-20% 30 50 230
20-33% 20 40 150
33-50% 15 30 75
>50% 6 20 40
e. Construction Considerations
Always install silt fences along the contour. Where this is not possible or where
there are long sections of silt fence, install short silt fence returns projecting
upslope from the main fence to minimise concentration of flows. Silt fence
returns are a minimum 2m in length and can incorporate a tie back. They are
constructed by continuing the silt fence around the return and doubling back,
eliminating joins.
Where impounded flow may overtop the silt fence make provision for a rip-rap
splash pad or other outlet protection device.
If water ponds behind a silt fence, provide extra support with tie backs from
the silt fence to a central stable point on the upward side. Extra support can
also be provided by stringing a wire between support stakes and connecting
the filter fabric to this wire.
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Appendix F
Use supporting posts of tanalised timber (50mm x 50mm), or steel waratahs at
least 1.5m in length.
Reinforce the top of the silt fence fabric with a wire support made of galvanised
wire (minimum diameter of 2.5mm). Tension the wire using permanent wire
strainers attached to angled waratahs at the end of the silt fence.
Use of silt fences in catchments of more than 0.5 ha requires consideration of
other site control measure
f. Maintenance
Inspect silt fences at least once a week and after each rainfall.
Make any necessary repairs when bulges occur or when sediment accumulation
reaches half way up the fabric height. Remove sediment deposits as necessary
to a secure area.
Any areas of collapse, decomposition or ineffectiveness need to be
replaced.
Do not remove the silt fence until the catchment area has been stabilised.
When the silt fence is removed stabilise the area occupied by the fence.
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Appendix F
Attachment 3: Filter Sock (Publication of Auckland Regional Council)
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Appendix F
Attachment 4: Stormwater Inlet protection
Extract from Erosion and Sediment Control Guideline 2007- A better way of managing
earthworks and the environment. Environment Canterbury; Report No.: R06/23
7.2.6 Stormwater inlet protection
Description and purpose
Stormwater inlet sediment control devices are used to intercept and treat sediment-
laden runoff before it enters a reticulated stormwater system and before subsequent
discharge into a receiving environment. Inlet protection may take various forms
depending upon the type of inlet to be protected.
Control measures are installed in areas of concentrated flow (the roadside kerb and
channel) and will usually have to contend with significant flow velocities, although their
sediment retention efficiency is usually low. Stormwater inlet protection is, therefore, a
secondary, or supplementary sediment control measure and should not be used as a
stand-alone technique.
Accordingly, stormwater inlet protection devices must be used in conjunction with a
full range of other erosion and sediment control management practices that have been
strategically deployed in an integrated approach. Take care with these control devices
to ensure that they do not cause secondary flooding: their aim is to remove as much
sediment as possible from site runoff and allow water to flow past the retention
measure to enter the stormwater system further downhill.
Where to use it
DO use stormwater inlet sediment control devices as an integral component of a
much broader and more comprehensive erosion and sediment control system.
DO use on areas with low sediment yields and runoff volume.
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Appendix F
DON’T completely block the storm drain system; always include a bypass arrangement.
DON’T use straw bales in roadside water tables or around stormwater inlets because
they
are easily broken and straw can block the inlet to the stormwater system.
DON’T use sediment fencing around stormwater inlets.
Limitations
Stormwater inlet protection:
is only useful in very small catchments;
should not be used as a stand-alone technique (although at times this is
navoidable);
measures have relatively low sediment removal efficiency and low hydraulic
capacity;
measures have very limited sediment storage capacity; extremely high
maintenance requirements;
measures and/or debris may partially block the stormwater system, increasing
the likelihood of localised flooding;
often leaks, particularly against the kerb;
measures may cause stormwater and sediments to pond on footpaths,
carriageways or newly constructed pavements;
are easily damaged by vehicles and/or construction equipment; and
pose potential public safety issues, particularly if not removed following
construction.
Design criteria
Maximum catchment area of 0.25 hectares to each inlet; stormwater inlet
treatments should be limited to areas with a general slope of less than five
percent, and the area immediately around the inlet should be less than one
percent.
Do not completely block the stormwater system; always include a bypass
arrangement.
Devices must not be used near the edge of fill material and must not divert
water over cut or fill slopes, or away from the storm drain inlet.
Stormwater inlet protection around stormwater inlets in the low points of the
road must be set back to allow the drain to function normally during periods of
heavy rain (see Figure 7.19).
Stormwater inlet protection must not cover or block stormwater inlets, as storm
flows may be deflected around the inlet; instead use small sediment traps like
sandbags placed in the kerb and channel upslope of the inlet (see Figure 7.20).
Height of sediment control devices around stormwater inlets must be kept to
less than 300 millimetres so that runoff does not cause local flooding and/or is
not inadvertently directed into nearby catchments.
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Appendix F
An earthen bund placed immediately downslope of the device may hold ponded
water around the inlet and prevent it from bypassing the drain.
Figure 7.19 Typ ical concret e b lock and gravel st o rm d rain in let p ro t ect ion at
road low p o in t s ( So urce Inst it u t ion o f Engineers, Aust ralia, 1996)
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Appendix F
Figure 7.20 Typical sandbag storm drain inlet protection for stormwater inlets (Source
Institution of Engineers, Australia, 1996)
Figure 7.21 Typical excavated catchpit inlet protection (Source Institution of Engineers,
Australia, 1996)
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Appendix F
Construction specifications
Construction methodology and detail will vary according to the type of inlet
protection measures proposed in the erosion and sediment control plan.
Always ensure an emergency spillway or bypass facility is included on all
devices.
Ensure the device will not cause water to bypass the storm drain system and/or
does not divert water away from its intended flow path.
Ensure the location and/or operation of the device will not cause a public safety
issue.
Keep all stockpiles or loose sediments away from roadside water tables.
There are an increasing number o f p rop r iet ary p rod uct s now availab le t h at
can und er t ake t h is f un ct ion .
Performance inspection and maintenance
Inspect daily and during and after each rainfall event and look
for blockage of the drain inlet by sediments, debris or sediment control
materials that may have been damaged during the storm event;
check for leaks in the facility which may affect its performance;
check to see that the control device has not inadvertently directed water away
from the drain and/or has not caused localised flooding; augment or modify as
required;
clean up all accumulated sediments immediately;
repair, augment and/or modify control devices as required; and
ensure all above-slope stockpiles or loose sediment is away from the roadside
water table.
Decommissioning
Decommissioning and removal procedures will vary according to the type of
inlet protection measures proposed in the erosion and sediment control plan.
Remove all accumulated sediments and dispose of them appropriately.
Remove control measure and reuse or recycle materials wherever possible.
Stabilise any areas disturbed as part of the removal process.
Useful tips
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Appendix F
Stormwater drain inlet
protection measures
must not cover or block
inlets on-grade; use
small sediment traps
placed in the kerb and
channel upslope of the
inlet.
Stormwater and
sediments will pond on
footpaths, arriageways or
newly constructed
avements unless
provision is made to
bypass flows at a suitable
height.
Stormwater inlet
protection around inlets
at road low points must
be set back to allow the
drain to function
normally during periods
of heavy rain.
Additional support
should be provided to
ensure gravel-filled
sausage is not pushed
into the inlet by the force
of the water.
Height of sediment
control devices around
catchpit inlets must be
kept to less than 300mm
so that runoff does not
cause local flooding
and/or is not
inadvertently directed
into adjacent catchments.
Re-use or recycle
material found around
the site wherever
possible.
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Appendix F
Attachment 5: Decanting earth bund
Extract from Erosion and sediment control guidelines for the Wellington Region; 2006.
Greater Wellington Regional Council.
5.6 Decanting Earth Bund
a. Definition
A temporary berm or ridge of compacted earth constructed to create impoundment
areas where ponding of runoff can occur and suspended material can settle before
runoff is discharged (see Figure 23).
b. Purpose
Used to intercept sediment-laden runoff and reduce the amount of sediment leaving
the site by detaining sediment-laden runoff.
c. Application
Earth bunds can be constructed across disturbed areas and around construction sites
and subdivisions. Keep them in place until the disturbed areas are permanently
stabilised or adequately replaced. Earth bunds are particularly useful for controlling
runoff after topsoiling and grassing before vegetation becomes established. Where
works are occurring within the berm area, compact the topsoil over the berm area as a
bund adjacent and parallel to the berm. This will act as an impoundment area and
controlled outfall while also keeping overland flow away from the construction area.
d. Design
Earth bunds require a constructed outlet structure and spillway as specified for
sediment retention ponds (see Section 5.1). Alternatively, construct an outlet of
perforated pipe connected to a non-perforated pipe that passes through the
earth bund and either discharges to a gutter or directly to a stormwater inlet.
The section of pipe within the impoundment area should be supported by
means of a rigid post, allowing filtration to occur.
Make sure the top opening of the perforated pipe is 150mm lower than the
stabilised spillway.
The section of pipe leading through the earth bund and continuing downslope
below the earth bund is non-perforated.
The maximum contributing catchment should not exceed 0.3 ha.
Position the decant inlet to provide 5% live storage volume with a minimum
distance of 5m of flat ground (or under vertical) from the outlet. Otherwise
raise the outlet so the dead storage level extends out at least this far.
e. Maintenance
After each rainfall event check the level of accumulated sediment which may cause
overtopping of the bund. If scouring is evident (after heavy rain), armour discharge
points to prevent bund collapse.
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Appendix F
Attachment 6: Settlement tanks
A common practice in the construction of foundations is to dewater the foundation to
make construction easier. The water from foundation construction activities may have
significant sediment loading which is not suitable for the discharge directly to
stormwater without treatment.
An effective treatment method is to pump this water into a settling tank and allow
gravity to settle the sediment out prior to discharge to stormwater. In some instances
gravity separation is sufficient to reach a suitable discharge standard. Where this
occurs chemical flocculation can be used settle out the suspended sediment. A number
of flocculation chemicals are readily available and if applied correctly have no adverse
effects on the Environment.
Photos 1 and 2 below show the settling tank used for the construction of the Paramata
Duplicate Bridge on State Highway 1. The water and sediment from the casing to form
the piles were pumped into the sediment tank. The black arrow in photo 1 shows how
the incoming sediment is discharged intothe bottom of the tank. The clean water
decanted from the top of the tank and is discharged out of the shown by the blue
arrow. In this instance the discharged was into Porirua Harbour.
Photo 1: Interior of settling tank
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Appendix F
Photo 2 shows the size of the tank which is approximately 20m3. The tanks are
emptied on a regular basis. Usually the tanks are emptied when 20% of storage is
taken up with deposited sediment.
Photo 2: Exterior of settling tank
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Appendix F
Attachment 7: Geotextile Dewatering Tube
A common practice in the construction of foundations is to dewater the foundation to
make construction easier. The water from foundation construction activities may have
significant sediment loading which is not suitable for the discharge directly to
stormwater without treatment.
An effective treatment method is to pump this water into a geotextile dewatering tube.
The geotextile dewatering tube allows for the slow release of water free of sediment
which is retained within the tube.
Following the release of the majority of the water, the tubes can be reused in the same
location for further dewatering of adjacent excavations / piles.
On completion of dewatering works in a certain area, the tubes are left in place to
allow the final consolidation of sediment as the remaining water seeps or evaporates
from the tubes. The tubes and sediment are then removed for disposal in an
appropriate landfill.
Photo 3 below shows a series of geotextile dewatering tubes being used to dewater a
wastewater pond.
Photo 3: Geotextile Dewatering Tube
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Appendix F
Attachment 8: Sediment Control – Pile Construction Dewatering
NEW STORMWATER CULVERT FROM
TUNNEL TO CAMBRIDGE TERRACE
NEW MANHOLE
S1
S2
S3 S4
S
5
EXISTING SUMP
EXISTING
SUMP
E
X
IS
T
IN
G
K
&
C
N
E
W
K
&
C
BUCKLE STREET
CA
MB
RID
GE
T
ER
RA
CE
KE
NT
T
ER
RA
CE
N
O
R
T
H
FOR REPORT
SC.01
SEDIMENTATION CONTROLPILE CONSTRUCTION DEWATERINGSHEET 1 of 2
BASIN BRIDGE PROJECT
R0
LEGEND
ROAD SUMP
SITE ENTRY/EXIT
SEDIMENT RETENTION TANK
CHAINLINK FENCE - SITE BOUNDARY
CONCRETE BARRIER
BUILDING WALL
DISCHARGE FLOW
PILE GROUP ARRANGEMENT
EXCAVATION AROUND PILE
NOTES
1. A GEOTEXTILE DEWATERING TUBE IS AN ALTERNATIVE SYSTEM TO THE
SETTLEMENT TANK. IF THE DEWATERING TUBE IS USED IN PLACE OF THE
SETTLEMENT TANK, THE TUBE WILL BE PROTECTED BY ONE OF THE
FOLLOWING MEASURES:
- EARTH BUND, APPROX 500mm HIGH
- PLACED IN 500mm DEEP DEPRESSION BELOW EXISTING GROUND LINE
- FILTER SOCK
- SILT FENCE
2. CONSTRUCTION AREAS TO BE STABILISED IN ACCORDANCE WITH GWRC
EROSION AND SEDIMENT CONTROL GUIDELINES FOR THE REGION.
3. SILT FENCES TO BE PLACED DOWNHILL OF CONSTRUCTION AREAS TO
CATCH STORMWATER RUN-OFF.
SEQUENCE OF WORKS
STAGE 1 - PILING FOR S1, S2 & S4.
STAGE 2 - PILING FOR S8.
STAGE 3 - PILING FOR S3, S5, S6 & S7.
0
SCALE. 1:500 @ A3
5 10 15 20 25 30
S
5
S
6
S
7
S
8
NEW SUMP (PART OF
NEW ROAD ALIGNMENT)
EXISTING SUMP
ELLICE STREET
HA
NIA
S
TR
EE
T
BR
OU
GH
AM
S
TR
EE
T
PATERSON STREET
DU
FF
ER
IN
S
TR
EE
T
N
O
R
T
H
FOR REPORT
SC.02
SEDIMENTATION CONTROLPILE CONSTRUCTION DEWATERINGSHEET 2 of 2
BASIN BRIDGE PROJECT
R0
LEGEND
ROAD SUMP
SITE ENTRY/EXIT
SEDIMENT RETENTION TANK
CHAINLINK FENCE - SITE BOUNDARY
CONCRETE BARRIER
BUILDING WALL
DISCHARGE FLOW
PILE GROUP ARRANGEMENT
EXCAVATION AROUND PILE
NOTES
1. A GEOTEXTILE DEWATERING TUBE IS AN ALTERNATIVE SYSTEM TO THE
SETTLEMENT TANK. IF THE DEWATERING TUBE IS USED IN PLACE OF THE
SETTLEMENT TANK, THE TUBE WILL BE PROTECTED BY ONE OF THE
FOLLOWING MEASURES:
- EARTH BUND, APPROX 500mm HIGH
- PLACED IN 500mm DEEP DEPRESSION BELOW EXISTING GROUND LINE
- FILTER SOCK
- SILT FENCE
2. CONSTRUCTION AREAS TO BE STABILISED IN ACCORDANCE WITH GWRC
EROSION AND SEDIMENT CONTROL GUIDELINES FOR THE REGION.
3. SILT FENCES TO BE PLACED DOWNHILL OF CONSTRUCTION AREAS TO
CATCH STORMWATER RUN-OFF.
SEQUENCE OF WORKS
STAGE 1 - PILING FOR S1, S2 & S4.
STAGE 2 - PILING FOR S8.
STAGE 3 - PILING FOR S3, S5, S6 & S7.
0
SCALE. 1:500 @ A3
5 10 15 20 25 30