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Stormwater engineer in Hobart: drainage plans and detention design
In Tasmania, stormwater work beyond a small, simple connection is notifiable plumbing work. It must be designed by a licensed designer and approved by council before it is built. We prepare drainage plans, stormwater reports and on-site detention designs for houses, units and subdivisions across Greater Hobart.
Engineering only
We design the drainage and sign the Form 35. Your licensed plumber builds it.
Fixed quote in 1–2 business hours
Get a fixed quote for your stormwater design
Send the site plan or architectural drawings, your council area and what you're building.
Fixed quote for your job. No obligation. Or call 03 6146 4747
In short
A stormwater engineer designs how rain from your roof and paving reaches the council system. In Tasmania, stormwater work over a 290 m² catchment, or with on-site detention, is notifiable plumbing work: a licensed designer signs a Form 35 and council issues a Certificate of Likely Compliance before it is built. We design drainage plans, detention tanks and stormwater reports across Greater Hobart, by fixed quote.
- Fee
- Fixed quote per job, within 1–2 business hours
- You receive
- Drainage plan, calculations and a Form 35
- Low-risk limit
- 290 m² catchment, 100 mm connection, no detention
The rules
When does stormwater work need an engineer in Tasmania?
Stormwater work needs a licensed designer whenever it goes beyond the low-risk limit in Tasmania's plumbing categories: a catchment of up to 290 m², a connection of at least 100 mm and no on-site detention. Anything more is notifiable plumbing work.
| Compare | Low-risk plumbing work | Notifiable plumbing work |
|---|---|---|
| Category | Category 2, item 2.3.4 | Category 3, item 3.0.1 |
| Applies to | Stormwater from a catchment up to 290 m², with a connection of at least 100 mm and no on-site detention | All other new stormwater work, including any job with a detention tank |
| Design | No designer needed | Must be designed by a licensed designer, who signs a Form 35 |
| Approval | The licensed plumber notifies council and lodges as-constructed drawings | Council issues a Certificate of Likely Compliance before work starts |
From the Director's Determination on categories of plumbing work (v1.4, applying from 18 August 2022). In practice the licensed designer is a hydraulic building services designer or a licensed civil engineer.
Other consents that apply on top
- Council's written consent at least 48 hours before connecting to its stormwater system (Building Regulations 2016, reg 43)
- Consent to connect to or interfere with the public system (Urban Drainage Act 2013, s14)
- Consent to build, fill or cut on an easement or within 1 m of a public pipe (s13)
The Tasmanian Planning Scheme has no stormwater code. Councils can still set conditions on stormwater volume and quality, so each council applies its own policy, and the policy is where most of the design numbers come from.
Ownership
Who owns stormwater pipes in Hobart: council or TasWater?
Councils own the public stormwater system in Tasmania, not TasWater. Under the Urban Drainage Act 2013, each council must provide a public stormwater system and keep it in order, prepare a system management plan and keep maps of its pipes.
A system that sits wholly inside one property is private, so pipes, pits and tanks on your land are yours to look after. TasWater runs water and sewerage. That's why stormwater questions on your job, from the connection point to an easement, go to your council.
City of Hobart
What does the City of Hobart stormwater policy require?
The City of Hobart's Stormwater Management Policy for Development, adopted on 27 May 2024, sets the design standards, detention tank sizes and consent rules for development in the Hobart council area.
Design standards
Designs follow Australian Rainfall and Runoff, Australian Runoff Quality and the Tasmanian stormwater guidance. Pipes (the minor system) carry a 5% AEP storm, one with a 1 in 20 chance of being equalled or exceeded in any year. Overland flow paths (the major system) carry a 1% AEP storm. Both add an allowance for climate change.
Building within 1 m of a council pipe
Work within 1 m of the public system needs consent under the Urban Drainage Act (s13) and the Building Act 2016 (ss73–74). Council weighs the risk of damage, access, flood risk and waterway values, and consent can carry indemnities and a duty to remove the structure. It usually comes through the planning or plumbing application, and council may ask for a camera survey of the main before and after construction. Our guide to building over a stormwater easement covers this in detail.
Other rules worth knowing
- One connection point per property
- Soakage, reuse or pumped disposal needs a report from a suitably qualified engineer (CPEng, RPEng, NER or RPEQ)
- The owner designs the connection and pays for any easement and survey
On-site detention in the City of Hobart
| Net added hard surface | What the policy requires |
|---|---|
| Under 100 m², no change of use | Exempt from detention (lot-creating subdivisions are not exempt) |
| Under 200 m² | 2,000 L tank with 500 L of detention, 20–25 mm orifice |
| 200–300 m² | 4,000 L tank with 1,000 L of detention, 20–25 mm orifice |
| Over 300 m² | Site-specific design by a suitably qualified engineer |
Summarised from clauses 20–27 of the policy. Your design follows the version current when you apply.
Clarence and other councils
How do Clarence and other councils handle detention?
Clarence City Council uses its own Stormwater Management Procedure for New Development (31 August 2021), with a detention table that starts at a smaller area than Hobart's. Above 250 m² it wants a design by a suitably qualified engineer, and it accepts MUSIC modelling for water quality.
Other councils across Greater Hobart run their own processes. Glenorchy, for example, has a consent application for work over or within 1 m of a main or easement. We check your council's current requirements before we design, so the plan suits the council that approves it.
On-site detention in Clarence
| Hard surface area | Detention tank |
|---|---|
| 40–65 m² | 1,800 L |
| 65–100 m² | 2,500 L |
| 100–150 m² | 3,000 L |
| 150–200 m² | 3,500 L |
| 200–250 m² | 4,000 L |
| Over 250 m² | Site-specific design by a suitably qualified engineer |
Summarised from Clarence's procedure. We confirm the current table for your site.
Water quality
Does your development need stormwater treatment?
Stormwater treatment applies to developments that add 500 m² or more of hard surface, under the EPA's State Stormwater Strategy (2010). The targets are an 80% cut in suspended solids and 45% cuts in phosphorus and nitrogen, usually shown with MUSIC modelling. The 2021 Tasmanian Stormwater Policy Guidance and Standards for Development, which Hobart's policy draws on, adds a 90% target for gross pollutants (litter) at its higher level.
The City of Hobart exempts these from treatment:
- A single dwelling on one lot
- Under 500 m² of new hard surface, unless there are more than six car parks or a contaminating use
- Subdivisions of five lots or fewer
- Lots over 5,000 m² with under 500 m² of roads
Car parks and service stations must also target hydrocarbons, and a cash offset is possible in some cases.
Load reduction targets for larger developments
What you receive
What's in a stormwater management plan or drainage plan?
A stormwater management plan or drainage plan shows council how water leaves your site, how much is held back and where it connects. Depending on the job, the stormwater design includes:
Drainage plan and Form 35
Pipes, pits, grades and the connection point, with the hydraulic design and a Form 35 for council's Certificate of Likely Compliance.
On-site detention calculations
OSD tank size, orifice and overflow, to your council's table or a site-specific design.
Stormwater management plan
The stormwater report council asks for: catchments, flows, overland flow paths and how the design meets its policy.
Water quality modelling
MUSIC modelling and treatment design for developments adding 500 m² or more of hard surface.
Pump and soakage reports
Where water can't drain to a council pipe by gravity, the engineer's report council needs for pumping or soakage.
Connections, easements and consents
Connection and easement design, and the engineering for a council consent under the Urban Drainage Act (s13 and s14).
Subdivision stormwater
Subdivisions follow the council's policy plus LGAT's infrastructure design guidelines and the Tasmanian Municipal Standard Drawings. LGAT lists the Tasmanian Development Manual (November 2025) in place of the 2013 subdivision guidelines. The City of Hobart uses that manual for subdivisions and publishes its own departures. In Hobart, lot-creating subdivisions are not exempt from detention, while subdivisions of five lots or fewer are exempt from treatment.
For units and townhouses, stormwater usually sits alongside the structural design. See townhouses and units.
What to send for a quote
- Site plan or architectural drawings showing roofs, paving and driveways
- The title plan, with any easements and council pipes
- Planning permit conditions on stormwater, if you have them
- The address and council, so we apply the right policy
- Photos of the site, kerb and any existing pits
Stormwater design is a fixed quote per job, sent within 1–2 business hours with what's included and the delivery date. Request a stormwater quote
Related services
Often needed alongside stormwater design
Townhouses & units
Structural and civil design for townhouses, units and small multi-residential developments, from site classification and footings to framing, retaining walls and stormwater.
Learn more
Swimming pool engineering
Concrete shell designs and site engineering for pools on slopes and near footings or boundaries, with the Form 35 your building surveyor needs.
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Site classification & footings
Soil tests and AS 2870 site classification, then slab and footing designs that suit the ground, with a Form 35 for your building surveyor.
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