10 Most Common Stormwater RFIs From Sydney Councils (Avoid Them)
Ask any builder or developer what hurts most about the DA process and the answer is rarely the fees or the forms. It is the waiting — and nothing extends the wait like a request for further information. An RFI stops the assessment clock, sends the application to the back of someone’s queue, and routinely adds four to eight weeks to a determination. Two rounds of RFIs can push a straightforward duplex approval past the six-month mark.
Here is the frustrating part: stormwater RFIs are overwhelmingly predictable. Council development engineers across Greater Sydney raise the same handful of issues over and over, because the same gaps keep appearing in submitted plans. After years of preparing and reviewing stormwater packages across dozens of NSW councils, we can tell you that the list below covers the vast majority of stormwater-related RFIs we see. None of them is exotic. Every one of them is avoidable at first submission.
This post works through the ten most common stormwater RFIs — what the council letter actually means in plain words, why the assessing engineer raises it, and what to do so it never lands in your inbox.
The Ten RFIs — and How to Avoid Every One
1. Missing or incorrect OSD calculations — or the wrong council method
The RFI says something like: “Submit on-site detention calculations demonstrating compliance with council’s requirements, including PSD and SSR.” The underlying problem is either that no detention calculations were lodged at all, or the designer used the wrong method for that council. Sydney is not one jurisdiction — several councils in the Parramatta and Hills districts still reference the UPRCT On-Site Stormwater Detention Handbook, while others set their own permissible site discharge rates or require pre- and post-development flows to be matched across a range of AEPs, typically demonstrated in DRAINS. Applying one council’s method to another council’s area is one of the fastest ways to earn an RFI. The fix is simple: confirm the OSD method in the council’s DCP and engineering specification before modelling starts, and lodge the full calculation package — catchment plans, model outputs, PSD and SSR summary, orifice and discharge control details — with the DA.
2. No legal point of discharge demonstrated
Council will not assume your water can get to the street. If the plans show a pipe running to the boundary and stopping, or a connection to a kerb that is uphill of the site, expect an RFI asking you to demonstrate a legal point of discharge. This bites hardest on lots falling away from the street, battle-axe lots and rear-of-lot dwellings. Avoid it by showing the complete discharge path on the plans — kerb outlet, street pit connection, or inter-allotment system — with levels proving gravity works, or by documenting the alternative (charged line or pump-out) with the justification council expects for stepping down the drainage hierarchy.
3. Missing easement documentation
Closely related: plans that discharge through a downstream property without evidence of the legal right to do so. If your design relies on an inter-allotment easement, council wants to see it — the deposited plan, the title search, the s10.7 certificate reference. If the easement does not exist yet, council wants evidence it is achievable: a signed letter of agreement from the downstream owner at minimum, and often the executed s88B instrument before consent operates. Lodging a design that quietly assumes an easement will materialise later is an RFI guarantee. Check the title before design starts, and if a new easement is needed, start that negotiation before the DA goes in.
4. Levels not to AHD, or insufficient survey detail
Stormwater is a game of levels, and council engineers cannot assess relative levels. If the plans show assumed datum levels, or no survey underlay at all, the RFI will ask for a detail survey by a registered surveyor with levels to Australian Height Datum — existing surface levels, kerb and invert levels at the point of discharge, and levels on adjoining properties where overland flow matters. Commission a proper detail survey at the start of the project and make sure the stormwater plans are built on it. It is among the cheapest documents in the whole application and its absence is among the most common reasons assessment stalls.
5. Overland flow paths and freeboard not shown
Pipes and pits are designed for the minor storm; the major storm travels over the surface. Councils want to see where that water goes when the pipes are full — the overland flow path through the site — and confirmation that habitable floor levels sit with adequate freeboard above the major storm flow level, consistent with ARR 2019 practice and the council’s DCP. If the site plan shows a driveway ramping down to a garage with no overflow route, or finished floor levels sitting at natural surface in a depression, the RFI is coming. Avoid it by documenting the major-event flow path with arrows and levels on the drainage plan and stating the freeboard achieved to each habitable floor.
6. No climate change consideration on flood-affected sites
Since the updated ARR climate change chapter (Book 1 Chapter 6) was published in late August 2024, councils assessing flood-affected sites increasingly expect flood and drainage assessments to address climate change explicitly — using the current guidance aligned with IPCC AR6, with climate factors applied by scenario and time horizon, and noting the higher uplifts that apply to short-duration storms. A flood impact statement that ignores climate change, or leans on superseded interim guidance, invites an RFI asking for the assessment to be updated. If your site is flood-affected or drains through a flood-affected area, make sure whoever prepares the assessment is working to the current chapter.
7. Water quality (MUSIC) report missing where the DCP triggers it
Many Sydney DCPs trigger water quality requirements once a development exceeds a certain scale or land-use threshold — and when triggered, council expects a stormwater quality assessment, typically MUSIC modelling, showing the treatment train achieves the DCP’s pollutant reduction targets. Applicants who assume water quality only applies to big subdivisions get caught out on medium-density and commercial projects. Read the DCP’s water-sensitive urban design provisions early; if the project triggers them, lodge the MUSIC report and treatment details (rainwater reuse, bioretention, gross pollutant traps as applicable) with the DA rather than waiting to be asked.
8. Discrepancies between architectural and stormwater plans
The assessing engineer overlays the drainage plan on the architect’s site plan, and the two disagree: the OSD tank sits under a different corner of the driveway, downpipes appear in different positions, finished floor levels differ by 150 millimetres, the landscape plan shows a garden bed over the discharge control pit. Discrepancies destroy the engineer’s confidence in the whole package and produce an RFI asking for consistent documentation. The cause is nearly always sequencing — stormwater designed from an early architectural revision and never updated. The fix is a coordination check before lodgement: same base plan, same levels, same tank location, same downpipe positions across every consultant’s drawings.
9. Missing OSD maintenance and positive covenant details
An OSD system only works if someone maintains it, so most councils require a positive covenant registered on title — an instrument under s88B or s88E of the Conveyancing Act 1919 — obliging owners to maintain the system, usually accompanied by a maintenance schedule. If the drainage plans are silent on the covenant and no maintenance schedule is provided, some councils will raise it at RFI stage rather than simply conditioning it. Pre-empt the question: reference the covenant on the plans, include the council’s standard maintenance schedule where one exists, and your submission reads like it was prepared by someone who has done this before — which is exactly the impression that gets applications through.
10. Incomplete erosion and sediment control plans
The humble ESC plan is the most frequently botched drawing in the stormwater set. A generic detail sheet with no site-specific measures — no sediment fence located on the plan, no stabilised access point, no stockpile locations, no protection to the street gully — will attract an RFI, because councils are accountable for sediment reaching their drainage systems and waterways. The avoidance is straightforward: a site-specific ESC plan showing measures in their actual locations, staged if construction is staged, consistent with council’s engineering standards and the widely referenced managing-urban-stormwater guidance.
What a Clean First Submission Is Actually Worth
Look back through that list and notice the pattern: not one of those RFIs involves a hard engineering problem. They are documentation gaps, coordination failures and skipped homework — the wrong method, the missing survey, the unchecked title. Each one costs weeks: council issues the letter, your consultant re-documents, the response goes back into the assessment queue, and the clock that stopped does not restart where it left off.
A complete first submission inverts the economics. The extra effort up front is measured in days — a survey ordered early, a title search, a DCP check, a coordination review before lodgement — while the saving is measured in months of holding costs, finance interest and lost construction windows. For a developer carrying land at Sydney prices, one avoided RFI round typically pays for the entire stormwater consultancy fee several times over. Council engineers also read submissions the way certifiers read builders: a package with the calculations present, the levels to AHD, the easements evidenced and the plans coordinated gets assessed faster and questioned less, because it signals that the answers to any further questions will exist too.
The practical takeaway for builders, developers and certifiers alike: treat the stormwater package as an approval document, not a drawing set. Engage the drainage engineer at concept stage, hand them the survey and the title early, and have them design to the specific council’s method from day one. That is the whole trick — and it is the difference between a determination in weeks and a file that celebrates birthdays in the assessment queue.
Frequently Asked Questions
How long does a stormwater RFI delay a DA in Sydney?
Typically four to eight weeks per round, sometimes longer. The assessment clock stops when the RFI issues, your consultant needs time to respond, and the application then re-enters the assessment queue. Two RFI rounds can add three or more months to a determination, which is why a complete first submission matters so much.
Do all Sydney councils use the same OSD method?
No. Several councils in the Parramatta and Hills districts still reference the UPRCT On-Site Stormwater Detention Handbook, while others publish their own permissible site discharge rates or require pre- and post-development flow matching across a range of AEPs, usually modelled in DRAINS. Always confirm the method in your council’s DCP and engineering specification before calculations begin.
Can council refuse my DA instead of issuing an RFI?
Yes. If the stormwater information is so deficient that the application cannot be properly assessed — no legal point of discharge, no OSD calculations, no survey — council can refuse rather than request information, particularly where earlier RFI responses were inadequate. A refusal means starting again or appealing, both far more costly than getting the package right initially.
What should a complete stormwater DA package include?
As a minimum: a drainage plan on a registered surveyor’s detail survey with levels to AHD, OSD calculations to the council’s nominated method, a demonstrated legal point of discharge with any easement documentation, overland flow paths and freeboard to habitable floors, water quality modelling where the DCP triggers it, an erosion and sediment control plan, and documentation coordinated with the architectural set.
Tired of RFIs stalling your approvals? Contrive Consultants prepares complete, council-specific stormwater packages for builders and developers across Greater Sydney — designed to the right method the first time. Explore our stormwater engineering services or get in touch before your next lodgement — call +61 497 848 111 or email info@contriveconsultants.com.au.