HomeAbout UsGeneral InfoOur BusinessE-ServicesMedia/PublicationsCustomer ServiceTenders/ContractsCommunityA-Z


Code of Practice

6. REQUIREMENTS FOR CONSTRUCTION ACTIVITIES


6.1      General Requirements

6.2      Laying and Diversion of Services

6.3      Earth Control Measures

6.4      Earthworks

6.5      Roadworks

6.6      Reclamation Works

6.1

General Requirements

6.1.1

The execution of any work shall not change, disrupt, fill, block, divert or disturb the existing overland flow or the existing system of drains unless an alternative drainage system has been approved by the Board.

6.1.2

The runoff within, upstream of and adjacent to the worksite shall be effectively drained away without causing drainage problems within the worksite or in areas outside the worksite.

6.1.3

All earth slopes shall be set outside the Drainage Reserve.

6.1.4

No obstruction of any kind shall be placed, laid or erected within Drainage Reserves and drains unless authorised by Board. If so, the Drainage Reserves and drains shall remain accessible at all times to workers and plant/equipment of, or authorised by the Board.

6.1.5

No temporary structures such as cofferdams, crossings, stagings, etc. shall be constructed in or over an existing drain without the approval of the Board.

6.1.6

Any temporary structure if approved within a drain or Drainage Reserve shall be removed immediately on completion of the construction works or as directed.

6.1.7

Drainage inlets such as drop-inlet chambers and scupper drains shall not be blocked by any material or debris.

6.1.8

Drains shall not be covered without the approval of the Board.

6.1.9

Bunds of stockpiled materials such as earth from trench work shall not be longer than 10 m and gaps of at least 1 m width shall be provided between the bunds to allow the free flow of surface runoff.

6.1.10

Material from any stockpile shall not be allowed to fall or be washed into the drain. Adequate preventive measures, including the provision of proper and stable barricades or screens where necessary, shall be provided.

6.1.11

Any damage to existing drain/drainage facilities arising out of any work shall be immediately reported to the Board. Any obstruction to flow arising from the damage shall be immediately and completely cleared. The damaged drain shall be repaired or reinstated to the requirements of the Board.

6.2

Laying and Diversion of Services

No services shall be laid or left (in conjunction with development works) within a Drainage Reserve. Where the services have to cross a Drainage Reserve, approval of the Board shall be obtained.

6.3

Earth Control Measures

Water Quality Parameters to be Complied with
The discharge from any construction / earthwork sites into storm water drainage system shall not contain Total Suspended Solids (TSS) in concentrations greater than, the prescribed limits under Regulation 4(1) of the Sewerage and Drainage (Surface Water Drainage) Regulations.
6.3.2
Minimal or No Discharge  
A construction / earthwork site should practice recycling of water. The recycled water could be used for non-potable purposes in order to minimise discharge into the stormwater drainage systems.
6.3.3
ECM Specifications in Tenders
Developers / owners and Qualified Persons should include the earth control measures (ECM) specifications and schematic or conceptual ECM plans in the tender documents and allow for the cost of ECM in the tenders.
6.3.4
Permit to start Earthworks  
The site operator / contractor shall obtain a written permission (or a clearance certificate) from Board before the commencement of any earthwork.
6.3.5
Submission of ECM proposal before commencement of works 
Before commencement of works, the site operator / owner shall engage a Qualified Erosion Control Professional (QECP) to plan and design a system of earth control measures (ECM) to meet the requirements cited in Clause 6.3.1.
The site operator / owner shall submit the detailed ECM proposal, endorsed by his QECP, to the Board for record, prior to the commencement of works.  The ECM proposals (with calculations) shall include a plan (a typical plan is as shown in Drawing No.13).
6.3.6
Design Criteria of ECM 
The ECM shall be designed to cope with a minimum design rainfall intensity of a return period of 1 in 5 years storm.
6.3.7
ECM to be installed before commencement of work
The ECM shall be installed by the site operator / contractor according to the endorsed plans and the completed ECM at site shall be approved by the QECP before commencement of construction and earthworks.
6.3.8
General Guidelines for Effective ECM 
An effective ECM requires 2 components which shall include, but is not limited to, the following minimum measures in order to meet the legal requirements cited under Regulation 4(1) of the Sewerage and Drainage (Surface Water Drainage) Regulations:
(A)
Erosion Control Measures 
The erosion control measures shall minimise the extent and duration of any exposed / bare / erodible surfaces by:
a) Proper Work Sequencing
- Adopting proper construction staging and work sequencing will help to ensure that no large bare / erodible surfaces are exposed for a long duration of time.
b) Covering up of all bare / erodible surfaces
- All bare surfaces (including earth stockpiles) shall be by concrete-lining, concrete-paving, milled waste, erosion control blankets, close turfing or other suitable materials.   Accesses within the site and at exit / entrance as well as the surfaces where site facilities (such as office, fabrication and storage yards) shall be paved. For those work areas, they shall be covered by canvas sheets, tarpaulin sheeting or other suitable materials during rains or before work stops every day.
c) Progressive and timely revegetation and stabilisation
- This is to ensure that all bare surfaces are restored immediately upon completion of work at every stage.
If a construction site has very little bare / erodible surfaces, the operator / contractor will have less difficulty in containing and treating the silty discharges as described in Clause 6.3.8 (B) below.  For those areas within a construction site which have been paved / covered and will not cause silty discharge, it is possible to drain these areas directly into the storm water drainage system without treatment.
(B)
Sediment Control Measures 
The sediment control measures shall trap, contain and treat the silty discharges from within a construction / earthworks site (including rain, runoff, water from washbay, underground water at basement, etc) by providing:
a) Perimeter Cut-off Drain

– Perimeter cut-off drains shall be concrete-lined and adequate to capture all runoff from the site . For sites located above slope, a solid kerb of at least 600 mm high should be provided along the entire perimeter of the site to prevent overflow onto adjacent properties.

b) Perimeter Silt Fence

- Silt fences shall be erected along the perimeter cut-off drain (between the construction site and perimeter cut-off drain). The silt fence is to be embedded firmly into the ground and made from an approved geotextile filter fabric or equivalents to capture the sediment from stormwater runoff. The sediment built-up behind the silt fence must be regularly removed.

c) Intermediate Silt Trap

 

- Intermediate silt traps of suitable size shall be installed at regular intervals along the perimeter lined cut-off drain.  Within the intermediate silt traps, suitable geotextile filter fabric or equivalents shall be installed across the full depth and width and / or coagulation-assistance materials shall be placed.  Silt traps relying primarily on hardcore, granite chips or sands for filtration, are not acceptable.

d) Sedimentation Basin or Storage Pond / Tank
- Before silty discharge leaves the site, the silt and sediments shall be separated from the water.  This can be achieved by either:
i.    in a sedimentation basin / pond (which will take days for settlement to take place and a large basin volume), or
ii.   through a treatment system–cum–storage tank.
The basin / tank shall have a storage capacity to cope with the volume of water from a rain based on a minimum design return period of 1 in 5 years storm.
e) Treatment System
- If the design of a sedimentation basin cannot meet the TSS requirement, then other suitably-sized treatment system shall be installed to treat all silty discharge from construction and earthwork sites.  The treated effluent could be recycled for non-potable use.
f) Turbidity Curtains
- For works in or adjacent to water bodies, such as canals, rivers, sea or in a reclamation work, turbidity curtain(s) shall be installed along all the exposed slopes / riverbanks.  The silty discharge trapped within the turbidity curtain shall be allowed to be settled or treated, and the settled silt removed.
g) Wheel wash
- the waters used to wash the wheels of the trucks / vehicles shall not be discharged into stormwater drainage system at any time. The silty water within the wheel wash basin shall be connected to the sedimentation basin / treatment system.  The silt collected at the bottom of the wheel wash shall be removed.
6.3.9
Review of ECM during Contract duration 
The site operator/ contractor shall ensure that the ECM designed and installed shall be continuously reviewed by the QECP for every stage of the construction and earthworks. The ECM shall remain effective throughout the whole duration of works.  The site operator / contractor shall add or amend the ECM at site according to the design of the QECP.
6.3.10
Maintenance of ECM during Contract duration
The site operator / contractors shall operate and maintain the ECM regularly to ensure the ECM remains effective throughout the whole duration of works.  This may involve replacing of silt fences and erosion control blankets or re-paving of concrete surfaces or replacing of membrane module or polymers blocks.
6.3.11
Monitoring of Discharge during Contract duration

The site operator/ contractor shall monitor the discharge water quality as cited in Clause 6.3.1 before it enters the storm water drainage system. The site operator/ contractor shall for this purpose provide a continuous monitoring system which include the necessary monitoring instrument and CCTV system upon requested by the Board for their ECM. The site operator/ contractor shall submit regular reports (including photographic and monitoring records) of the site ECM as well as those for discharge quality to the Board over the whole duration of the project.

6.3.12
Removal upon Completion
The ECM shall not be removed before the completion of work.  The site operator/ owner shall inform Board prior to removal of the ECM on completion of the project.

6.4

Earthworks

(a)

The approval of the Board shall be sought for all earthworks affecting the existing drainage system or the flow pattern of surface runoff. In the event that earthworks are to be carried out adjacent to major drains and canals, the developer/owner shall engage a Qualified Person to carry out soil investigation works and slope stability analysis to ensure that the earthworks will not cause any damage to the drainage structures.

(b)

The developer/owner shall take all necessary steps and measures, such as implementing suitable soil stabilisation methods and temporary protection works to ensure the stability and structural integrity of the existing drainage structures.

(c)

Earth control measures shall be provided in accordance with the requirements as stipulated in Section 6.3.

6.5

Roadworks

A temporary drainage system shall be provided for all roadworks to prevent flooding or water ponding on the road. Where the road is being raised and the new road drainage outlets are at a higher level than the existing ones, the existing outlets shall not be blocked unless temporary alternative drainage system has been provided. The developer/owner and the Qualified Person shall be responsible for implementing all necessary measures to ensure that the site is kept flood free at all times. Where necessary, the Board may require the submission of hydraulic calculations, programme of works, temporary drainage arrangements at various stages of the roadworks, etc by the Qualified Person.

6.6

Reclamation Works

6.6.1

All reclamation works shall be carried out in accordance with Sections 2.3 and 4.11.

6.6.2

During reclamation, a temporary drainage system including perimeter cut-off drains, silt-traps, silt fences and outlet connections shall be provided. The temporary drainage system shall include erosion protection linings, such as concrete, geotexile mattress and other suitable materials to be approved by the Board. The proposals of the temporary drainage system shall be submitted to the Board for approval.

6.6.3

The temporary drainage system shall be cleansed and maintained regularly by the reclamation agency to remove all obstructions, silt and rubbish during the reclamation period.

 
Last updated on 5 Dec 2011