Subject
Flow rate assumption · chainage 0+340
Drawing C-201 Rev B specifies a 600mm RCP pipe based on 12 L/s flow rate. Site investigation (May 2026) suggests catchment may be larger than assumed.
Clarification requested
Question
Please confirm whether the design flow rate of 12 L/s at chainage 0+340 remains appropriate given the revised catchment boundary identified during May site survey (refer attached SK-04). If revised, please advise:
(a) the new design flow rate;
(b) any required pipe diameter change (currently 600mm RCP); and
(c) impact on adjacent structures (manhole MH-12, headwall H-04).
Context · why it matters
- Pipe procurement long-lead item; we hold an order for 600mm at our supplier until 20 Jun 2026.
- Headwall H-04 design is dimensioned against 600mm pipe — a change cascades.
- Programme: a 7-day response holds programme. Beyond 17 Jun, schedule impact ~3 days per week of delay.
Cost / programme exposure
If pipe diameter increases, indicative additional cost ~$8,400 ex GST (pipe + bedding + extra excavation). Programme impact 3–5 days. Will raise Change Request CR-05 upon clarification.
Attachments
- SK-04 — Site survey sketch · revised catchment boundary (3 pages)
- Photo set — Existing kerb & channel condition at chainage 0+340 (6 photos)
- C-201 Rev B — Issued for Construction drawing (1 page, marked-up)
Engineer response · to be completed
Raised by
A. Lieblich
Contractor PM
Response by
J. Park
Consulting Engineer · Engineer of Record