Farm Dams, Drainage & Riparian Rules: NSW Landholder Guide

If you own rural land in NSW, water is both your greatest asset and your biggest source of regulatory confusion. Can you build a new dam without a licence? How big can it be? Can you clean out a drainage line, push a crossing through a creek, or fill a boggy corner of a paddock? The answers sit mostly within the Water Management Act 2000 and its supporting regulations, and getting them wrong can be expensive. This guide walks through what landholders can generally do as of right, where the lines are drawn, and when it pays to bring in an engineer before the excavator arrives.

Harvestable rights: the water you can capture without a licence

The starting point for most farm dam questions is the harvestable right. Under the Water Management Act 2000, landholders in NSW can capture and store a proportion of the average annual rainfall runoff from their land in dams without needing a water access licence, a water supply work approval or a water use approval. It is one of the basic landholder rights built into the Act, and it exists precisely so that ordinary farm dams for stock and domestic-scale use don’t get tangled in the licensing system.

Across most of NSW — both the coastal-draining and inland-draining areas — the harvestable rights limit is 10 per cent of the average annual regional rainfall runoff from your property. Different arrangements apply in the Western Division, so landholders out west should check their specific entitlements rather than assume the standard limit applies.

The practical question is what that 10 per cent means in megalitres for your particular property. You don’t have to work it out from first principles: the NSW Government provides an online calculator that determines the maximum harvestable right dam capacity for a property based on its location and area. The figure it produces is the total combined capacity of all harvestable rights dams on the holding — not a per-dam allowance. If you already have three dams, their capacities count against the same cap.

A recent history lesson: the 30 per cent that came and went

If you’ve heard that coastal landholders can capture 30 per cent of runoff, that information is out of date. The coastal harvestable rights limit was temporarily lifted to 30 per cent in May 2022, then returned to 10 per cent in September 2023. As at the date of this article, the limit across coastal NSW is back at 10 per cent. This episode is a useful reminder that water rules genuinely change — sometimes quickly — and that advice or calculator results from a few years ago may no longer reflect the current position. Always confirm the current limit with WaterNSW or DCCEEW Water before committing to a design.

Where a harvestable rights dam can go

Capacity is only half the story. Location matters just as much. Harvestable rights dams must be built on minor streams — that is, first- or second-order streams under the Strahler stream ordering system — or on hillsides and gullies where no defined stream exists. They must not be built on, or within 40 metres of, a third-order or higher stream.

Strahler ordering is straightforward in concept: the smallest headwater channels are first-order streams; where two first-order streams join, they form a second-order stream; where two second-order streams join, they form a third-order stream, and so on. In practice, working out the order of the drainage line through your paddock requires looking at the mapped stream network, because the ordering depends on everything upstream of your boundary, not just what you can see from the fence line.

If you want a dam on a third-order or higher stream, or a dam larger than your harvestable right allows, you are outside basic landholder rights territory. Those dams generally need a water access licence and a water supply work approval through WaterNSW and DCCEEW Water. That is a substantially bigger process, and it is worth understanding before you fall in love with a dam site on the main creek.

Controlled activities: the 40-metre rule around waterfront land

Dams are not the only works the Act regulates. Under the Water Management Act, carrying out works in, on or under — or within 40 metres of — the bed or bank of a river, lake or estuary generally requires a controlled activity approval. This strip of land is called waterfront land, and the sorts of works caught by the rule include:

Creek and river crossings — culverts, causeways and bridges
Bank protection and stabilisation works
Filling or excavation near a channel
Stormwater or drainage outlets discharging to a watercourse
Buildings, sheds and other structures placed close to a bank

Exemptions exist for certain minor works and for some landholder activities, but the safe assumption is that anything mechanical happening within 40 metres of a defined watercourse deserves a check before it starts. The approval process looks at how the work affects the stability of the bed and banks, riparian vegetation and the passage of flows — which is exactly the sort of assessment a civil engineer can prepare or support.

Riparian corridors: wider streams, wider buffers

Alongside the approval trigger, NSW riparian corridor guidelines set out recommended vegetated riparian zone widths either side of a watercourse. The widths scale with stream order: a small first-order gully attracts a relatively narrow vegetated corridor, while higher-order streams warrant progressively wider ones. For anyone planning subdivision, dwellings or intensive works on a rural property, the riparian corridor can materially affect where development can sit — so it is worth mapping early, at concept stage, rather than discovering it during assessment.

Domestic and stock rights

Basic landholder rights extend beyond harvestable rights. If you own or occupy land with frontage to a river, or land overlying an aquifer, you can take water for domestic consumption and stock watering without a licence. Conditions apply — the right covers household use and watering stock, not irrigation or commercial use — but for many rural properties it is the day-to-day water right that matters most. It sits alongside, not instead of, the harvestable right, and the two together cover the ordinary water needs of most grazing properties.

Existing dams: maintenance versus new works

A common grey area is the old dam that needs attention. As a general principle, maintaining an existing lawful dam — desilting it back to its original capacity, repairing the wall, keeping the spillway clear — is treated differently from constructing a new dam or enlarging an existing one. The moment work increases a dam’s capacity, raises its wall or changes its footprint, you may have created a new work that needs to fit within your harvestable right or be separately approved. Keep records of what existed before you start, take photos, and if you’re unsure whether the dam was lawfully built in the first place, get advice before spending money enlarging something that may already be a compliance problem.

Drainage works, wetlands and erosion

Drainage is the other side of the water coin, and it carries its own traps.

Wetlands: avoid draining or filling mapped wetlands without advice. Wetlands attract specific protections under water and planning legislation, and works that drain them can require approvals that landholders rarely anticipate.
Drainage lines and erosion: concentrating flow — through contour banks, table drains, culverts or dam spillways — into a natural drainage line can trigger erosion that quickly becomes a headcut migrating upstream through your paddock. Once gully erosion starts, it is far cheaper to arrest early than to remediate late.
Gully erosion control: effective control usually combines grade-control structures, flow spreading, revegetation and sometimes rock work — and where those works sit within 40 metres of a watercourse, the controlled activity question comes straight back into play.

When to involve an engineer

Plenty of small farm dams get built by experienced earthmoving contractors without a drawing in sight. But there are situations where engineering input protects both your wallet and your legal position:

Dam sizing within your harvestable right: confirming your maximum harvestable right dam capacity, allocating it across existing and proposed dams, and documenting the basis so you can demonstrate compliance later.
Dam wall design and stability: wall geometry, compaction requirements, cut-off trenches and foundation conditions — especially on dispersive or reactive soils where poorly built walls fail.
Spillway design: an undersized or poorly located spillway is the most common cause of dam failure. Sizing it for a sensible design storm is core civil engineering work.
Stream order and setback checks: verifying whether your proposed site is genuinely on a first- or second-order stream, and clear of the 40-metre buffer to higher-order streams.
Controlled activity approvals: preparing the plans and assessments that support crossings, outlets and bank works on waterfront land.
Erosion and drainage design: designing works that move water without creating tomorrow’s gully.

It’s also worth saying plainly: penalties exist for unauthorised dams and unauthorised works on waterfront land, and enforcement does happen. The cost of checking the rules first is trivial compared with the cost of being directed to remove a dam or remediate a creek bank.

Rules change — check before you dig

The single most important habit for NSW landholders is to treat water rules as current-affairs knowledge, not settled folklore. The coastal harvestable rights change of 2022–2023 showed how quickly the numbers can move in both directions. Before any significant dam or drainage project, confirm the current position with WaterNSW or DCCEEW Water, run the online harvestable rights calculator afresh, and get the stream ordering on your property checked against the mapped network. An hour of due diligence up front beats a compliance notice every time.

Frequently asked questions

Do I need a licence to build a farm dam in NSW?

Not always. If the dam sits within your property’s harvestable right — generally 10 per cent of average annual regional rainfall runoff across most of NSW — and it is built on a first- or second-order stream, hillside or gully, you can build it without a water access licence or work approval. Dams on third-order or higher streams, or dams exceeding your harvestable right, generally need a licence and approval.

How do I find out how big my dams can be?

Use the NSW Government’s online maximum harvestable right dam capacity calculator. It gives a total capacity for your property based on location and area, and all your harvestable rights dams together must fit within that figure. Keep a copy of the result with your property records.

Can I do works near a creek on my own land?

Works in, on or within 40 metres of the bed or bank of a river, lake or estuary generally need a controlled activity approval under the Water Management Act, though exemptions exist for certain minor works and some landholder activities. Check before starting crossings, bank works, filling or outlet construction near any watercourse.

Can I clean out or repair an existing dam?

Maintaining an existing lawful dam — desilting to original capacity or repairing the wall — is generally permissible. Enlarging the dam, raising the wall or increasing capacity is treated as new work and must fit within your harvestable right or be separately approved. Document the dam’s existing condition before you start.

Planning a dam or drainage works? Talk to Contrive Consultants

Contrive Consultants is a civil and stormwater engineering consultancy based in Rouse Hill, serving landholders, builders and developers across all of NSW — including regional properties, which we support through remote delivery. We can check your harvestable right, assess stream ordering and setbacks, design dam walls and spillways, prepare controlled activity documentation and design erosion control that lasts. Explore our civil and stormwater engineering services, or get in touch through our contact page, call +61 497 848 111 or email info@contriveconsultants.com.au for a plain-spoken conversation about your property before the earthworks start.