Lumen Sites for mine & construction sites

Rain, the wet season and haul roads

A few millimetres of rain can make an unsealed haul road slippery, and a wet-season downpour can close roads, flood pits and cut off access for days. This guide covers when the rain comes in each mining region, what it does to a site, and how sites plan around it.

When the rain comes

Across the north, the year’s rain is packed into the wet season. From December to March, Weipa gets 87% of its rain, Darwin 81% and Mount Isa 77%, and the Pilbara towns two-thirds to three-quarters. Further south it spreads out: the Bowen Basin gets 55–60% in those months, the Goldfields a little under half and the Hunter Valley about 40%, while Perth gets 8% and most of its rain in winter.

Averages for 1995–2024 from SILO (Queensland Government, CC BY 4.0), interpolated from Bureau of Meteorology observations. Rain days have 1 mm or more. Select a town for its month-by-month figures.
Town	Rain a year (mm)	Wettest month	Share falling December to March	Rain days a year
Darwin	1746	Jan 478 mm	81%	101
Weipa	1981	Feb 508 mm	87%	107
Port Hedland	329	Feb 76 mm	75%	25
Karratha	311	Feb 86 mm	66%	21
Newman	363	Jan 87 mm	72%	36
Mount Isa	488	Jan 126 mm	77%	41
Moranbah	588	Feb 105 mm	59%	49
Emerald	563	Jan 90 mm	55%	48
Muswellbrook	640	Nov 74 mm	41%	74
Kalgoorlie	275	Feb 41 mm	46%	40
Roxby Downs	160	Feb 18 mm	37%	24
Perth	692	Jul 143 mm	8%	83

The totals vary enormously, from about 160 mm a year at Roxby Downs to nearly 2,000 mm at Weipa, where February alone averages 508 mm, close to double Kalgoorlie’s whole year. And in the Top End the dry season really is dry: Darwin averages 1–2 mm a month from June to August.

What rain does to a site

Haul roads: a wet surface cuts tyre grip and lengthens braking distances, and roads built from clay or fine material turn slippery after only a little rain. Heavy trucks then rut and pothole the softened surface.
Pits: runoff collects in the pit floor and sumps, ramps can flood, and saturated walls need closer watching. Dewatering pumps have to keep up.
Access: unsealed public roads close, creek crossings flood and airstrips shut, so crew changes and supply runs stop until the water drops.
Blasting: wet holes need water-resistant explosives, because ANFO breaks down in water, and storms bring lightning near charged blast patterns.
Water storage: tailings dams and water storages need room to take a big rain event.

How sites manage it

Rain in the TARP

Many sites write rain into a trigger action response plan (TARP): rainfall thresholds, usually millimetres in an hour or in 24 hours, tied to actions such as lowering speed limits, stopping haulage on steep ramps, closing roads, and inspecting them before they reopen. The right thresholds depend on the road material, grades and drainage, so they are set site by site.

Before the wet season

Grade roads with a proper crown or cross-fall so water runs off instead of pooling.
Clear table drains, culverts and sumps, and check pumps and spares.
Stockpile ore ahead of the wettest months, and schedule shutdowns and maintenance into them where you can.
Plan for crew changes and supplies if roads or the airstrip close.

Watch the water cart

Over-watering a haul road for dust can make it as slippery as rain does, so water carts belong in the same plan as the weather.

Reading rainfall numbers

Australia’s official daily rainfall is measured for the 24 hours to 9 am, so the figure for a date is mostly the rain that fell the evening and night before. Forecasts, on-site gauges and TARPs don’t always use the same window, so agree on which one your thresholds refer to.

Averages also hide big swings. In the north, one cyclone or monsoon low can bring more rain in a few days than an average year, and a dry year can bring almost none. Plan for the wet years, not the average one.

How Lumen Sites helps

Lumen Sites shows the rain forecast for the next 48 hours at each site against two thresholds you set, 10 mm and 25 mm over 24 hours by default, so road closures and haulage plans can be made the day before. For Australian sites it also shows the past year of daily rain from SILO, alongside lightning, storm risk, gusts and heat.