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Drainage Requirements

Drainage Requirements. Principles of Designing a Drainage System. Ensure platform levels of the development site are not lower than the road level/ ground level at the outlet discharge point or the specific minimum platform level imposed by the Department (whichever is higher).

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Drainage Requirements

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  1. Drainage Requirements

  2. Principles of Designing a Drainage System Ensure platform levels of the development site are not lower than the road level/ ground level at the outlet discharge point or the specific minimum platform level imposed by the Department (whichever is higher) Platform levels within the development site lower than the adjacent road / ground levels at the outlet discharge point.

  3. Principles of Designing a Drainage System Provide crest levels at all openings (eg ventilation openings, stairways, pipelines, voids, rampdown etc to basement served by pumped drainage system. • The crest level does not comply with the requirements as specified in the Code of Practice on Surface Water Drainage. No crest level provided

  4. Principles of Designing a Drainage System Select the outlet discharge point at the roadside/outlet drain where the adjacent road/ground level is the lowest. The existing outlet discharge point(s) at the development site shall be adopted. If the roadside drain is located on a sloping road, the proposed internal drain should be connected to the downstream end of the roadside drain fronting the development site.

  5. Principles of Designing a Drainage System For development with basement not fully covered, keep the catchment area to the minimum. Runoff from RWDPs should be discharged to 1st storey drain and not into the basement pump sump. Runoff from basement discharges by gravity to roadside/outlet drain which is on higher ground level. Runoff from roofs, rainwater down- pipes and all premises at and above ground level discharges into the basement.

  6. Principles of Designing a Drainage System Ensure runoff within a development site is drained off by internal drains and is not discharged into adjacent premises.

  7. Principles of Designing a Drainage System Design the drainage system for safety and ease of maintenance besides adequate capacity.

  8. Principles of Designing a Drainage System Do not alter or realign existing roadside/outlet/ common drains unless approval is given by the Department.

  9. Principles of Designing a Drainage System All services shall undercross the drains at minimum 1.0m (1.5m for earth drains) below the invert levels of the drains. QPs shall seek the Department’s approval for proposals on services overcrossing. Drainage Dept will consider services overcrossing if the Services Providers request it and the services pipes overcrossing drain will not affect the flow or not cause maintenance problem.

  10. Debris trapped by overcrossing pipe

  11. SOME COMMON ISSUES RAISED DURING WALK-IN PRECONSULTATION

  12. Can the Drainage Reserve be Realigned ? A drainage reserve (DR) may be realigned subject to the following conditions:- a) The proposed drain diversion is technically feasible. b)Maintenance access to the upstream and downstream DR is not affected. c) Concurrence from SLA/URA.

  13. Can the Common Drain be Fenced -In Within Development Lot ? Drainage Department can consider fencing-in of the existing common drain within the development lot if the access to maintain the existing upstream or downstream common drain is not affected.

  14. Required Sizes of Entrance Culvert/Roadside Drain QP is to write to the Department for the required size of proposed entrance culvert/roadside drain before submitting the plan to CBPU for registration.

  15. Must Existing Roadside Drain be Realigned to Abut the New Road Reserve Line? • The existing roadside drain can be retained if it is not required by LTA to be realigned to abut the new Road Reserve Line. • If the existing roadside drain is to be realigned, it shall be constructed to the required drain size.

  16. Must Roadside Drain be Constructed as Closed Drain? • The roadside drain can be constructed as closed or open drain.

  17. Can Rainwater Downpipe be Smaller Than 150mm ? Smaller rainwater downpipes of less than 150mm diameter are allowed in accordance with Singapore Standard CP26:1983 “Code of Practice for Drainage of Roofs” on condition that the roof drainage channels are provided with leaf covers.

  18. THANK YOU

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