METHOD STATEMENT FOR BEST MANAGEMENT PRACTICES

METHOD STATEMENT FOR BEST

MANAGEMENT PRACTICES

Projek Mengganti Jambatan Sedia Ada di FT006/041/93 Barat

Day, Pulau Pinang (Schedule 2).

Prepared by:

Nilaimas Services

EIA & Traffic Consultant

2

Proposed method statement for “Projek Mengganti Jambatan

Sedia Ada di FT006/043/93 Barat Daya, Pulau Pinang

(Schedule 2).”

Work method statement for

Portable Silt Trap

Reference:

JKRBD/RESB/NMS/JTK/2019_1

Portable Silt Trap BMP No.: 1/12

Portable silt trap

Silt trap

3

1.0 INTRODUCTION

Silt trap is a designated area where water that is contaminated with suspended sediment as a

result of construction activity or water runoff is contained. While the water is in the trap, the

sediment can settle to the bottom of the trap until it can be removed. Silt trap can be made

using silt curtains, silt fences or a series of shallow ponds to naturally filter the sediment from

the water before it reaches a stream or clean body of water.

Environmental protection efforts, such as the silt trap, are often seen in conjunction with

mining or construction. Activity from these industries can result in the production of grain-

size particles, stone dust and other components that create suspended sediment when caught

up in water runoff during rainfall. As the rainwater carries these particles and other pollutants

to streams, the suspended sediment can cause a serious issue for the fish and other wildlife

that inhabit these waters.

However, in case of limitation space, portable silt trap is preferable. Also known as settling

tank, this device is used to remove sediment/ silt from water pumped from excavation and

other confined spaces where a traditional sediment basin/ sediment pond would be

impractical. Treatment of the sediment-laden water may involve chemical coagulation to

control turbidity levels.

2.0 METHOD STATEMENT

The best sites to install silt traps are:

Where run-off pathways can be intercepted.

Areas of low productivity.

Areas with easy access for maintenance where compaction can be avoided.

Size and shape: generally, a larger size portable silt trap will be more effective at trapping

sediment.

However a number of factors should be considered:

Soil type.

Run-off volumes.

Amount of sediment removal needed (by calculating the upslope catchment area to decide

on silt trap sizes).

Limitation of portable silt trap:

Only suitable for low to medium flow rates.

Control over silt and turbidity vary from unit to unit, and may require chemical dosing.

Some authorities may place restrictions on the use of certain coagulants.

Petroleum based polymers should not be used.

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Advantages of using portable silt trap:

Suitable for use in confined spaces.

Tanks are reusable.

Suitable for batch and continuous flow.

One of the few treatment system that can be used for turbidity control.

Disadvantages of using portable silt trap:

Can be more expensive than one – off silt trap/ sediment basin, but can be cost effective

of reused on several sites.

Can be difficult to clean out.

Can be labour intensive operation.

Removal of portable silt trap:

Disassemble and remove all components of the settling tank and remove from the site.

Dispose of the consumables and sediment in a manner that will not create further erosion,

sedimentation or environmental problems.

Rehabilitate all disturbed ground as necessary to minimize the erosion hazard.

3.0 SPECIAL REQUIREMENTS

Portable sediment tanks should be located so that trapped sediments can be readily

removed without interference to construction activities.

Water quality monitoring is usually required.

Use of chemical coagulants requires expert advice and formal operational procedures.

Chemically treated tank effluent must be non-toxic to aquatic organisms. Samples of

treated water should be tested for acute (lethal) toxicity.

A pH adjustment may be required prior to discharge of the treated water.

4.0 OPERATION OF PORTABLE SILT TRAP

1. Refer to approved plans and associated environmental management plans for operational

details. If there are questions or problems with the method of installation or operation,

contact the product supplier and/or responsible on-site officer for assistance.

2. Prior to use, conduct flocculation tests to demonstrate suitability of treatment additive and

approximate dosage rate.

3. Use of chemical additives must be within limits specified by relevant authorities,

including State agencies.

4. Chemical flocculants/coagulants must be allowed to mix rapidly with the waters to insure

proper dispersion.

5. Ensure the tank operates in a manner that prevents the re-suspension and discharge of the

settled sediment.

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6. Maintain a daily log of batch rates (volume and time), type and amount of chemical usage

(including pH adjustments if any), and water quality monitoring.

5.0 MAINTENANCE OF PORTABLE SILT TRAP

1. Inspect the sedimentation tank regularly and at least daily during de-watering operations.

2. Make repairs/adjustments as needed to maintain the required treatment standard.

3. De-silt the tank and maintain all replaceable components (such as filters) in accordance

with supplied operational instructions. Unique site-modified units should be de-silted

once settled sediment exceeds one third of the storage volume.

4. Dispose of all sediment in a manner that will not create an erosion or pollution hazard.

6



(Schedule 2).”


Check Dam

Reference:


Check Dam BMP No.: 2/12

Concrete Check Dam

Sandbag Check Dam

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Gabion check dam

Stones/Rock Check Dam

1.0 INTRODUCTION

A check dam is a small temporary dam constructed across a diversion channel or swale.

Check dam reduce the velocity of concentrated stormwater flows, thereby reducing erosion of

the diversion channel or swale and promoting sedimentation behind the dam.

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Check dams are primarily used in small channels in steep terrain were velocities exceed 0.6

m/s. This BMP acts to prevent erosion by reducing the velocity of channel flow in small

intermittent channels and temporary swales.

Checks dams should only be placed in small open channels and never on a flowing river or

natural stream. Maintenance is therefore required to remove trapped sediment and to check

for structural stability on regular basis.

2.0 REQUIREMENT

Table 2 shows the design criteria for Check Dams.

Table 2 Design Criteria for Check Dams

PARAMETER REQUIREMENT

Runoff Quantity

Design 2 year ARI unless specified otherwise by Authorities

Overspill All flow greater than 2 year ARI shall safely bypass the crossing

Maximum

Contributing Area 4 ha

Dimension

Height (centre) of dam shall not exceed 1 m

For rock check dam:

- Upstream slope: 2(H) : 1(V) or flatter

- Downstream slope: 4(H) : 1(V) or flatter

Centers of the dam shall be notched to centre to promote

concentrated flow (approx. 0.15 m)

Outer sides of dam shall be at least 0.5 m higher than centre to

avoids undermining

Spill crest shall be at least 100 mm in width parallel to flow

Scour Protection

Structure shall withstand the shear force induced by a 2-year ARI

flow. Materials (rocks, earth and gabion) must be selected to meet

this requirement.

Additional scour protection downstream of check dam shall be

provided if deemed necessary


General layout requirements of check dam structures:

The center of the dam should be at least 150 mm lower than either edge, so as to form

an outfall weir for any active flows. However, the actual freeboard to be incorporated

should be based on the risk and hazard of flooding to the surrounding areas.

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Stabilization works with channel lining or protection works (such as riprap or gabion

mattresses) should be provided immediately downstream of the check dam to prevent

any possible toe erosion and undercutting.

The embankment/barrier of check dam should be extended adequately into the

existing bank to prevent any excessive seepage and potential breaching of the banks.

If a series of check dams are required, the dams should be spaced so that the

difference in the water levels between any two dams do not fall below 300 mm as

illustrated in Figure 1.

Figure 1 Proposed Location of Series of Check Dam Structures along the Waterway

Check dam should never be placed in live streams unless approved by appropriate local, state

and/or federal authorities. It should be located in straight sections of a watercourse or drain.

4.0 TYPE OF CHECK DAM STRUCTURE

Sand/Local Earth Filled Bags Check Dam

Sand /Local Earth Filled Bags check dam is a series of earth-filled bags placed on a level

contour to intercept flows. It provides a relatively quick and effective way in holding the

water flow to create a pond. Some of the general requirements of earth filled bags are:-

Bags should be made from durable, weather resistance fabric e.g. Geotextile (unless for

short-term). The fabric pores must be tight enough to retain the filler material. The bags

usually measure about the standard size of 1 m x 2 m x 0.15 m or other size as required.

Low quality polypropylene (PP) woven Sugar bags or sacks, commonly used in check

dams construction, are found to be not durable as they are easily damaged by the flows

and have low UV resistance. As such, these materials are not recommended as they

normally do not last longer than a years and required regular maintenance, and as such are

only suitable for short-term check dam structure.

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On both side of the check dam structure, earth filled bags must be extended and tightly

abutted into the banks to prevent excessive seepage or breaching at the banks of the check

structure.

The center of the check dam must be lower by at least 150mm (min) to allow normal

flows spilling to occur within the mid portion of the structure.

Material specification are as below:

Container bag - They are many types of fabric bags available in the industry, varying both

in term of raw materials and their properties. However, selection of the types of bags

normally takes into consideration factors such as the service life required, accessibility of

site, ease of construction as well as relative cost of the structure.

Filled materials - Fill materials for earth-filled bags should be well graded non-cohesive

material or free from any deleterious materials. For short-term check dam where suitable

filled materials are not available, then local earth materials may be used.

Stones/Rock Check Dam

Stones or rocks placed on top of a blanket of engineering fabric either in loose form or

stacked tightly can also be used to block the water flows in the waterways to create check

dam structure in peat land. Hand or mechanical placement of stones or rocks can be used

depending on the accessibility of the site. Some general requirements of stones/rocks check

dams are discussed below:

Maximum side slopes 1.5H: 1 V

Center portion of the crest of the check dam should at least 150 mm lower that the sides

to prevent normal flows from going around the dam, and eroding the sides of the channel.

Adequate freeboard to be provided for annual flood flows

Adequate scour protection downstream of check dam is to be provided for a length at

least 1.5 times the height of the check dam

Rocks or stones armoring layer of at least 400mm thick should be extended into the banks

of the waterway sides to prevent erosion and breaching of the sides of the check dam

To reduce the loss of water through foundation seepage, the underlying peat soil below

the check structure should be removed and replaced with highly impermeable soils.


Stones/rock size - All stones/rocks shall be dense, hard, durable broken or crushed

granitic rocks. They should be heavy enough to prevent the flows from pushing individual

stones downstream. For height of dam with flow velocity less than 1 m/s maximum, the

nominal stone diameter should be 100 mm to 350 mm. For flow velocity higher than 1

m/s, the stones shall be sized in accordance standard engineering practices.

Gabion Check Dam

Stacked stones in wire cages (gabions or gabion mattresses) are also commonly used to

construct check dams. Gabions check dams are essentially the same as stacked stones/rocks

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check dam structure, except that the former is wrapped in wire fence meshes for added

stability and strength. Some of the general requirements for gabion check dam structures are:

The gabions formed check dams are highly porous and as such a layer of impermeable

sheet such as HDPE need to be provided within the gabions to reduce the seepage of

water. Alternatively, highly impervious clayey soil can be placed upstream of the gabions

(together with a layer of geotextiles filter layer) to retain the water in the channel.

A layer of gabion flexi-mattress is usually placed on the channel bed and banks before the

required gabions are placed. The mattresses would provide a better sitting on the uneven

ground of the channel bank/bed besides providing a more stable support for the gabions

block.

A layer of geotextile fabric filter is placed on the soil in contact with the gabions

mattresses to prevent ingress of soil into the gabions and washing away by the water

flows.

Proper foundation seepage cut-off needs to be provided to enable effective control of

water level upstream. This could be done by removing the peat soils and replacing with

less permeable soil (clayey) or embedding appropriate cutoff barriers.

Opening in the check dam structure may also be provided for passing flood flows and can

be gated (e.g. using timber drop boards) to raise the water level during the dry weather.

Gabion check dams can provide a very cost-efficient alternative to those constructed using

concrete and are more resilient than concrete. They are also more durable than sand/earth

filled bags, timber logs or loose stacked stones / rocks check dams.


Each stone-filled gabion usually measures about the standard size of 1.0m x 1.0 m x 1.0

m. Other size of up to 4.0 m x 1.0 m x 1.0 m are also available

The wire box cage or mattresses shall be made from galvanized wire or PVC coated

galvanized wire depending on whether they are to be used for temporary or long-term

installation

The stones in-filled shall be dense, sound and durable stones of size between 100 mm to

200 mm nominal diameter.

The gabion check dam should be designed based on the principle of mass earth retaining

walls against both the hydraulic as well as earth pressures.

5.0 MAINTENANCE

1. The check dams should be inspected after each runoff event.

2. Correct all damage immediately.

3. If significant erosion has occurred between structures, a liner of stone or other suitable

material should be installed in that portion of the channel.

4. Remove sediment adjacent to and accumulated behind check dams before it reaches

halfway to the top of the dam.

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5. Restore dislodged or washed out check dams to their original configuration.

6. Fill in or otherwise repair areas where check dam undercutting or bypasses have occurred.

7. Add stones to dams as needed to maintain design height and cross section. Use larger

stone, if necessary, to counter higher-than-expected flow velocities.

8. Repair ditch/channel areas where excessive down cutting or side scour have occurred.

9. Where fiber logs become dislodged by high ditch/channel velocities, use longer stakes

and reduce the spacing between stakes.

10. If the selected configuration is not preventing channel erosion, consider other materials or

closer spacing in areas experiencing the most problems.

11. If significant erosion occurs between dams, install a protective turf reinforcement mat or

section of riprap liner in that portion of the channel.

12. Rock weirs should be replaced when filtering capacity is reduced by one-half.

6.0 INSPECTION

Check dams should be inspected regularly, especially after rainfall exceeding 0.5 inch.

During each inspection, surface waters, including drainage ditches and conveyance systems

but not curb and gutter systems, must be inspected for evidence of erosion and sediment

deposition. All deltas and sediment deposited in surface waters, including drainage ways,

catch basins, and other drainage systems must be removed and destabilized the areas where

sediment removal results in exposed soil. Removal and stabilization must be completed

within seven (7) calendar days of discovery unless precluded by legal, regulatory, or physical

access constraints. Specific inspection guidelines for check dams include the following:

Inspect check dams and channels for damage after each runoff event and correct all

damage immediately.

Regular inspections should be made to ensure that the center of the dam is lower than the

edges.

Check the structural integrity of the check dams – shape, anchoring, and overall

condition.

Look for scour underneath the check dam and bypasses on the sides.

Note the amount of sediment deposited upslope of the check dams.

Observe erosion of ditch segments between check dams – downcutting and side scour.

13



(Schedule 2).”


Silt Fence

Reference:


Silt Fence BMP No.: 3/12

Silt fence

1.0 INTRODUCTION

A silt fence is a temporary sediment barriers consisting of filter fabric stretched across and

attached to supporting posts, entrenched and depending upon the strength of the fabric used,

backed by a wire fence for support. Silt fence can be considered an on-site control as it caters

to small overland sheet flow. It is most effective in securing site perimeter, protecting topsoil

stock pile and intercepting sheet flow along slope contours. Silt fence requires regular

inspection and maintenance as it is easily damaged. Sediment built-up behind fence should be

regularly removed.

2.0 REQUIREMENT

Table 3 shows the design criteria for Silt Fence.

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Table 3 Shows the Design Criteria for Silt Fence


Design Storm First 50mm of rainfall over the contribution (equivalent impervious)

catchment

Slope Slope draining to fence shall be 1(H) : 1(V) or flatter

Length of path draining to fence shall not exceed 60 m

Maximum

Contributing Area 0.4 ha

Hydraulic

For any point along the fence,

- Concentrated flow shall not exceed 50 L/s

- Maximum water depth shall not exceed 600 mm

Sitting of facility

Fences SHALL NOT be installed in areas receiving concentrated

flow, i.e. streams or ditches

Maximum length of each fence segment shall not exceed 30 m

The at least 1 m from ends of each segment shall be turned uphill to

prevent runoff flowing around the fence

Storage Area Storage area to be provided behind fence

Approximately 280 m2 per ha of contributing area is required


Three principal aspects of silt fence design:

Proper placement of fencing

Adequate amount of fencing

Appropriate materials

Installation of a silt fence will typically involve a procedure of digging a trench and securing

the barrier into position. Standard silt fencing will feature an overall height of three feet (3')

to accommodate various sediment build up and water flows. One of most commonly used

approaches for installing silt fence is Static slicing method.

Static sling machine pulls a narrow blade through the ground to create a silt 12” deep, and

simultaneously inserts the silt fence fabric into the slit behind the blade.

The blade is designed to slightly disrupt soil upward nest to the slit minimize horizontal

compaction thereby creating an optimum condition for compacting the soil vertically on

both side of the fabric.

To compact the soil to achieve nearly the same or greater compaction as the original

undisturbed soil is by rolling a tractor wheel 2 to 4 times.

The compaction is to reduce air spaces between soil particle to avoid infiltration saturate

the soil so that water5 will not find a pathway under the fence.

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When the silt fence is holding back several tons of accumulated water and sediment, it

needs to be supported by posts that are driven 2 ft into well-compacted soil.

The installation of silt fence is complete after the posts are driving in and the fabric is

attaching to the pot.

Figure 2 Static slicing

4.0 MAINTENANCE

1. Use J-hooks (Figure 3) along silt fences, berms, and other structures to break up long

flow paths, reduce flow velocities, and trap sediment before it reaches down gradient

locations.

2. Add more/longer stakes where fiber rolls become dislodged by runoff.

3. Repair or replace silt fence found to be non-functional, due to severe weather conditions,

age, extended use, damage, or other causes.

4. Use rock berms along dips and in low corners of silt fences if blowouts and bypasses

occur frequently in these locations.

5. Where repeated failures occur, install additional upgradient erosion prevention and/or

sediment control practices or redundant BMPs to eliminate the problem.

6. Repair or replace ineffective fabric and fiber rolls due to collapse, tearing, decomposition,

etc. within 24 hours of discovery.

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Figure 3 J-hooks along silt fences

5.0 INSPECTION

1. During installation, make sure support posts are on the downhill side of the fabric.

2. Inspect silt fences at least once a week and after each rainfall, as required by permits, and

make required repairs immediately.

3. Verify posts are correctly spaced.

4. After installation, tug on the top of the fabric between posts to ensure that it is embedded

tightly.

5. Make sure fabric is securely attached to the posts, without excessive sagging.

6. Ensure geotextile overlap is used on heavy duty type fence.

7. Ensure soil is compacted (not turned over/loosened) for machine-sliced fence.

8. After a rain, check silt fences for bypasses below or around the ends of each silt fence

section.

9. Note and record blowouts, sections where the fence is down, etc.

10. Note the condition of support posts along each section of silt fence.

11. Observe and record the amount of sediment deposited on the upslope side of the silt

fence.

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(Schedule 2).”


Wash Trough

Reference:


Wash Trough BMP No.: 4/12

1.0 INTRODUCTION

A wash trough system is a device for cleaning the tires of trucks when they are leaving a site,

to control and eliminate the pollution of public roads. The installation can be made in or

above the ground for either temporary or permanent applications.

The two most important considerations when deciding where to install a wheel wash are:

1. Distance from the exit

2. Proximity to water and drainage

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The sludge which is washed off may be directed into a recycling tank, with the sedimentation

of the solids accelerated by the use of flocculants. The solids which settle at the bottom of the

tank are removed by an automatic scraper or excavating plant. The aim is for clean water to

be used for every wash.


A wheel cleaning procedure will be used in order to mitigate the amount of mud that could

potentially be deposited on the road by vehicles exiting the construction site. An area close to

the site exit will be utilized for wheel washing prior to vehicles leaving site. A power washer

or water nozzles (manually using manpower) will be used to wash off any mud from the

vehicle’s wheels, with excess mud / slurry being collected and disposed of.

It is anticipated that this will only be required during the initial weeks of the development

when the existing ground is removed and the footings for the new road are constructed.

However, the wheel wash station will remain on site until the development is complete. The

proposed wheel cleaning procedure will consist of:

Before leaving the site, vehicles will be inspected for any heavy deposits left on wheels.

If present, these will be removed manually.

Following inspection, all wheels are to be washed down using a high pressure wash until

clear of all deposits.

Vehicles will be permitted to leave site following approval of the site manager / site

representative that the above steps have been completed to a satisfactory standard.

On site roads will be kept as free of mud as is practicable during ground working operations.

Machine and wagon trafficking around the site will be kept to a minimum in order to reduce

the effects of rain on ‘broken’ ground.

If this is not sufficient, a road sweeper will also be used in the immediate area which will be

ordered directly via the site manager.

In case of confined space, wash water jet pumped is preferable as it is more practical. Pipe

jetting and cleaning is the process of bending a high pressure water nozzle through a pipe,

beating debris and sediment from the pipe. Sediment and debris is collected and removed

through an access point via vactor truck. Water flows from the cleaning vehicles will be drain

into temporary drainage/ existing concrete drainage before flows into silt trap and then

discharge into water body.

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(Schedule 2).”


Sand Bag

Reference:


Sand Bag BMP No.: 5/12

1.0 INTRODUCTION

A sandbag barrier consists of a row of sand-filled bags placed on a level contour. When

appropriately placed, a sandbag barrier intercepts and slows sheet flow runoff; causing

temporary ponding. The temporary ponding provides quiescent conditions allowing sediment

to settle. While the sand-filled bags are porous, the fine sand tends to quickly plug with

sediment, limiting the rate of flow through the barrier. The advantages are that the bags and

sand are inexpensive. When empty, the bags are compact and lightweight for easy storage

and transportation. They can be brought to a site empty and filled with local sand or soil.

Disadvantages are that filling bags is labor-intensive. Without proper training, sandbag walls

can be constructed improperly causing them to fail at a lower height than expected, when

Sandbag

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used in flood-control purposes. They can degrade prematurely in the sun and elements once

deployed.

2.0 REQUIREMENT

Table 4 shows the design criteria for Sand Bag.

Table 4 Shows the Design Criteria for Sand Bag


Material Polypropylene, polyethylene or polyamide woven fabric

Minimum Unit

Weight Four (4) ounces per square yard

Dimension

Length : 24 to 30 inches

Width : 16 to 18 inches

Thickness : 8 inches

Sand Bag Filling

(Percent by

Weight)

Passing no. 4 sieve - minimum 97%



or as approved by the engineer


Sand Bag will be installed to stop the sediment outflow into the river.

General construction method of Sand Bag:

Sand Bags shall be used to construct along the water flow and drainage system to prevent

water runoff from disturbed area.

Sand shall be placed in the sand bag so that at least the top six (6) inches of the sand bag

is fulfilled to allow for proper tying of the open end.

The sand bag shall be placed with their tied ends all in the same direction.

Any subsequent rows of sand bags shall be offset one-half the length of the preceding

sand bag row to provide a layered brick-type arrangement.

A single layer of sand bags shall be placed downstream to prevent erosion from falling

water over the river.

The sand bag installation shall be maintained in good condition by the Contractor.

The sand bag shall be inspected weekly in good condition or after each significant rainfall

to determine if the installation is functioning as intended.

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Suitable applications

As a linear sediment control measure:

Below the toe of slopes and erodible slopes

As sediment traps at culvert/pipe outlets

Below other small cleared areas

Along the perimeter of a site

Down slope of exposed soil areas

Around temporary stockpiles and spoil areas Parallel to a roadway to keep sediment off

paved areas

Along streams and channels

As linear erosion control measure:

Along the face and at grade breaks of exposed and erodible slopes to shorten slope length

and spread runoff as sheet flow

At the top of slopes to divert runoff away from disturbed slopes

As check dams across mildly sloped construction roads

Figure 4 Detail of sandbag barrier

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Figure 5 Detail of sandbag barrier

Limitations

It is necessary to limit the drainage area upstream of the barrier to 5 acres.

Degraded sandbags may rupture when removed, spilling sand.

Installation can be labor intensive.

Barriers may have limited durability for long-term projects.

When used to detain concentrated flows, maintenance requirements increase.

Burlap should not be used for sandbags.

4.0 INSPECTIONS AND MAINTENANCE

1. Inspect BMPs prior to forecast min, daily during extended rain events, after rain events,

weekly during the rainy season, and at two-week intervals during the non-rainy season.

2. Sandbags exposed to sunlight will need to be replaced every two to three months due to

degradation of the bags.

3. Reshape or replace sandbags as needed.

4. Repair washouts or other damage as needed.

5. Sediment that accumulates in the BMP must be periodically removed in order to maintain

BMP effectiveness.

6. Sediment should be removed when the sediment accumulation reaches one-third of the

barrier height Sediment removed during maintenance may be incorporated into earthwork

on the site or disposed at an appropriate location.

7. Remove sandbags when no longer needed. Remove sediment accumulation, and clean, re-

grade, and stabilize the area.

23



(Schedule 2).”


Turfing

Reference:


Turfing BMP No.: 6/12

24

1.0 INTRODUCTION

It is important that the bare soil constructed during site clearing phase need to be turfed or

covered as soon as possible to prevent from wind erosion or further erosion into the

waterways which will lead to sedimentation. Replanting through close planting or grass

seeding are the most effective ways to control erosion of soil surface where the dense growth

grass is needed. For close planting, clumps of grass are planted next to the other. For planting

of grass patch, it is suitable when planted on low slope. Bare slopes along the roadside and

construction site slope can be planted with the grass by using hydroseeding method.

Lands recently turfed will be watered regularly until an effective cover has properly

established and plants are growing vigorously. Further application of seed re-turfing might be

necessary later in areas of inadequate vegetation establishment. Prior to the completion of

construction, apply permanent erosion control to remaining disturbed soil areas. Sufficient

erosion control materials shall be maintained onsite to allow implementation in conformance

with this LD-P2M2.

Cover crops is also one (1) of an effective way to control soil erosion. Cover crops can

provide effective protection from the impact of rain, bind the soil structure by holding from

dissociation by water flow on the surface, also improve and maintain the absorption capacity

of the soil. The lack of using cover crop is the cost to develop cover crops is high. However,

cost related to recurrence erosion and work siltation can be reduced


General layout requirements of turfing:

Turfing shall be carried out at the slope and terrace of the designated area.

The grass sod used for turfing will be cut for about 300mm square and minimum

thickness 50mm with original sod adhering to the roots.

Close turfing shall consist of about 300mm square turfing laid side by side with gaps not

exceeding 30mm.

The sods shall be laid onto the surface of prepared ground with leaf turfs upwards, but

jointed as closed as possible to achieve uniform cover.

The turf shall be laid off planks working over turns previously laid.

The whole turf area should present an even smooth surface when finished.

Top dressing of turf area shall be carried out immediately after the turf is laid and

monthly intervals thereafter.

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3.0 INSPECTION AND MAINTENANCE

1. Inspect the turfing area immediately after seeding (if applicable) to verify seed coverage.

2. The site must be relatively smooth and free of rocks larger than 2 inches, sticks,

protruding roots, clumps of vegetation, trash, and other debris.

3. Pay particular attention to installations on long steep slopes.

4. Flag off the area after installation to keep equipment, vehicles, and foot traffic off turfing

area.

5. After installation, inspect weekly and within 24 hours after each rainfall of ½ inch or

more.

6. Do not mow turfing area until vegetation is at least 8 inches tall and dense. Mower blades

must be kept 6 inches off the mat to prevent snagging and pulling.

7. Use scissors or shears to cut out bulges or large sags, and stake the area securely.

8. Seed missing or damaged sections.

26



(Schedule 2).”


Temporary Drainage System

Reference:


Temporary Drainage System BMP No.: 7/12

1.0 INTRODUCTION

Before commencement of earthworks, temporary perimeter drains shall be constructed to

channel surface runoff for control of sediment discharge. Perimeter drains are essential to

prevent any sediment-laden runoff from discharging off-site and also to prevent sediment

originated from off-site to enter. All runoff from undisturbed areas should not be allowed to

mix with runoff from the disturbed area.

The design of temporary drainage system should be adequate to ensure that it will not cause

flooding upstream or downstream of the site. All temporary earth drains must be

adequately compacted and the sides cut to slope and maintained t prevent collapse of the

27

sidewalls. If possible, stronger temporary drains in the form of precast concrete drains are

recommended. If the site conditions permits, wider diversion drains and dykes should be

constructed and where the flow velocity is greater than 0.6 m/s, check dams should be

constructed to slow down the flow.

Temporary culvert will be laid to provide access point across the temporary drainage system

for construction purpose. Scour protection shall be provided at the drainage outlet of

culverts to prevent scour caused by high flow velocities and to absorb flow energy to

produce non-erosive velocities.

The temporary drainage system should be regularly inspected and maintained, especially

after each heavy downpour, to prevent clogging, unexpected sediment built-up or erosion,

overtopping and cover failure. The temporary drainage system will be remained at site until

permanent drainage is installed.

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(Schedule 2).”


Silt Curtain

Reference:


Silt Curtain BMP No.: 8/12

1.0 INTRODUCTION

Silt curtain is a temporary sediment barrier installed parallel to the bank of a stream or lake. It

is installed in water to contain the sediment produced by construction operations on the bank

of a stream or lake and allow for its removal. for preventing spread of environmental

containments. It is used at riverside construction with its proven effectiveness at minimum of

45% to maximum of 95%. Its superior and durable material also enables the system to

withstand tides, waves and wind action. Accumulated sediment must be removed

periodically. The curtain must be inspected often and after each storm. Any damage must be

immediately repaired. For this proposed project, silt curtain will be installed at the

downstream of project site.

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2.0 REQUIREMENT

Table 5 shows the design criteria for Silt Curtain.

Table 5 Shows the Design Criteria for Silt Curtain


Type of silt curtain:

Type I – (Light weight) this is designed for use in lower energy environments where there

are no currents and the deployment location is sheltered from any wind and waves.

Type II – (Medium weight) are suited to sites where there is only a small to moderate

current of up to about 1 m/s. Wind and wave action can be present but not considered

major force.

Type III – (Heavy duty) is for sites with higher energy environments, with currents in

excess of 1.5 m/s. Curtains can be deployed in a tidal region and be subject to wind and

wave action.

When developing a turbidity curtain installation plan, consider factors such as:

Current velocity and direction

Wind velocity and direction

Wave height and frequency

Water depth and variances

Tides

Soil type and stability beneath the project area


Screen/Skirt

can be woven, non-woven and knitted in construction with

compositions varying between polyester, polypropylene fabric and

geo-textile

Screen weight 270g/m2 to >700g/m2

Float diameter 0.1 m to 0.3 m depending on the type of screen

Ballast Comprises typically from steel or galvanized chain. Typical chain

thickness approximately 6 mm

Connectors Designed to allow the sections of the curtain to be joining together

while preventing from any leakage between them

Anchor weight Ranging from 4.5 kg to 45 kg

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General installation for floating silt curtain

Prefabricate a 15m X 12m rectangular shape floating steel frame using 400mm diameter

X 8mm thick steel circular hollow section

Tie the top end of the geotextile to the steel frame by nylon strings/ steel wires

Tie the bottom end of the geotextile with ballast steel chain. This arrangement shall

maintain the geotextile in vertical position during the course of dredging

Place and unfold thee silt curtain parallel to the river by grab dredger/ derrick barge. Fix

the floating steel frame alongside the grab dredger/ derrick barge with a movement joint.

Slowlyput the geotextile together with the ballast steel chain to the sea

Prepare different length off geotextile for replacement in order to suit the various steel

chain to the river.

4.0 INSPECTIONS AND MAINTENANCE

If the silt curtain installation is for an extended period (greater than 3 months), it is

recommended that a visual inspection and maintenance schedule be implemented to check

that the silt curtains are not damaged and performing as required. Visual inspections need to

be carried out on a basis determined by the Contractor and can range from daily to quarterly.

Typical visual inspection and maintenance activities recommended include:

Checking the silt curtain installation maintained the correct position with no obvious

defects or entanglements

Monitoring the curtain skirt against the river bed to ensure it is free moving and not held

down by sand or dispersed mud

Replacing worn or broken anchor lines

Reviewing the integrity of the PVC flotation chamber and connection points

Removing aquatic growth from the curtain

Inspecting the hardware for wear and tear, especially at anchoring points

Inspecting marker buoys and lights (if required) to ensure they present and operational

Removing floating refuse trapped by the silt curtain

As visual inspections are limited to the section above and immediately below the water level,

it may be necessary to use underwater divers to conduct a more thorough inspection of the

skirt and connections. A failure in the curtain resulting in a sediment plume is a typical

trigger for such a thorough inspection. It is common to keep a spare section of silt curtain on

site in case of a rip or tear in an existing section. This minimizes project down time since

replacement of a panel is often quicker than a repair. Where an inspection or maintenance has

been carried out, an inspection report should be completed. The report should record

observations and subsequent actions taken to repair or maintain the silt curtain. The use of

photographic records is recommended where available.

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(Schedule 2).”


Cascade Run

Reference:


Cascade Run BMP No.: 9/12

1.0 INTRODUCTION

Cascade run is a step drainage constructed at sloping area. The purpose of cascade run is to

allow water flow from high area to the lower area without causing soil erosion. The step

allow the water to flow down the slope slowly by reducing its velocity

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(Schedule 2).”


Debris Netting

Reference:


Debris Netting BMP No.: 10/12

1.0 INTRODUCTION

Debris netting is used on construction sites to contain debris and on scaffolding to prevent

debris from falling. It is generally made from a durable, heavy-duty, plastic netting. Debris

netting are used in construction, building maintenance, entertainment, or other industries.

There are a number of benefits to using debris netting on a construction scaffold:

It provides safe containment of debris, protection of workers, the public and traffic.

Its versatility as an enclosure system means it is easy and economical to handle and can

hang vertically or horizontally to achieve maximum coverage.

The edges are reinforced with eyelets for quick and easy attachment to a scaffold using

wire or plastic ties.

It allows air movement, which can ventilate the scaffold and reduce wind loading.

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It provides shading against bright sunlight whilst allowing enough light in for tasks to be

carried out.

It gives some protection to work areas and workers from inclement weather conditions.

It is flame retardant.


Wear appropriate safety equipment for working near a leading edge or other fall hazard

String top and bottom of the cables through the eye bolts anchored into the concrete

columns or side wall of the construction

Hang netting panels from top cable with the top edge snap hooks. (The excess fine mesh

debris liner flap should be positioned at the floor end of each netting section)

Fasten the adjoining netting panels to one another with the side edge snap hooks

Fasten the bottom edge snap hooks to the bottom cable

Securer the fine mesh debris flap to the floor with tie-down plates and concrete nails.

Installation

Nets shall be installed in accordance with the net manufacturers' specifications and

instructions. The user responsible for net installation and for the design and installation of the

net supports. Nets shall be installed as close under the working level as practical, but not

lower than 30 feet (9.1m). They shall be hung with sufficient clearance to prevent contact

with the surface of structures below when the user's impact load testing is applied. There

shalt- be no intervening members between the working surface and the net that could be

impacted during a fall. It is intended that only one level of nets be required for bridge

construction provided that

There are no intervening members between the working surface and the net that could

be impacted during a fall.

the net and supports will sustain the impact of a 150 kg bag of sand 30 inches (.76m)

+1¬2 inches (.05m) in diameter and no more than 36 inches (.91 m) high, dropped

from the highest working surface into the lowest point of the net without permanent

distortion of the net pattern or suspension system.

There should be sufficient clearance to ensure against contact of the test weight or the

net with anything below.

3.0 INSPECTION AND MAINTENANCE

Personnel and debris nets shall be inspected by a competent person utilizing any inspection

instructions supplied by the manufacturer. The inspections shall be conducted after each

installation and not less than once each week thereafter. Additional inspections shall be made

after alterations, repair, and impact loadings. If any welding or cutting operations our above

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the safety nets, debris nets, or both, weld protection shall be provided for that area, and more

frequent inspections shall be conducted in proportion to the danger involved.

The care, maintenance, and storage of nets shall be in accordance with the net manufacturer

recommendations. Due attention shall be given to the factors affecting debris net. Nets

installed for the protection of personnel shall have debris removed at least daily.

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(Schedule 2).”


Hydroseeding

Reference:


Hydroseeding BMP No.: 11/12

1.0 INTRODUCTION

Hydroseeding is a planting process that uses slurry of seed and mulch. It is one of the erosion

control technique practices on the construction site. Hydroseeding can be effectively

completed in a very short period of time to cover large area coverage. It can be very effective

for hill slopes area to help erosion control and quick planting of grass. The hydroseeding is

applied with pressure via hose pump onto the soil to create the ideal environment for seed

germination and turf development.

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Hydroseeding should be done immediately after the completion of a phase of grading

Hydroseeding can be completed using two (2) different steps that is one-step process or

multiple-step process

Multiple-step process ensures maximum direct contact of the seeds planted to the soil

When the one-step hydroseeding process is used to apply the mixture of seed, fiber, etc.,

the seed rate shall be increased to compensate for all seeds not having direct contact with

the soil

Follow-up applications shall be made as needed to cover weak spots

Avoid overspray on existing vegetation, waterways, sidewalks, and roadways

Straw or other mulch should be applied to reduce the erosive capacity of storm water and

to keep the soil and seed in place

Inspect every week within 48 hours after rain event that causes storm water runoff to

occur on-site

Hydroseeded areas should also be inspected for failures and must be re-seeded and

mulched within the planting season, using not less than half of the original application

rates

Supplemental watering may be required

Watering on the hydroseeded area can start immediately the next day and must be

continued daily in the initial stage to ensure speedy seed germination and growth

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(Schedule 2).”


Cover Crops

Reference:


Cover Crops BMP No.: 12/12

1.0 INTRODUCTION

Cover crops is also one (1) of an effective way to control soil erosion. Cover crops can

provide effective protection from the impact of rain, bind the soil structure by holding from

dissociation by water flow on the surface, also improve and maintain the absorption capacity

of the soil. The lack of using cover crop is the cost to develop cover crops is high. However,

cost related to recurrence erosion and work siltation can be reduced.

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General procedure for planting the cover crop:

The soil/ slopes area should be prepared before plantation

Large seeded cover crops (peas, vetch and wheat) will be planted in shallow, closely

spaced furrows

Small seeded cover crops (ryegrarass, buckwheat) placed over the surface and cover with

light raking

If the soil is dry, irrigate often enough to keep the soil damp and germinate the seed

METHOD STATEMENT FOR BEST MANAGEMENT PRACTICES

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