A good farm dam can water stock through a dry year, fight a grass fire and lift the value of your block. Getting it right comes down to the site, the soil, the wall and the water rules. Here’s what South Burnett landholders need to know before the excavator turns up.
The short version: work out whether your site is a watercourse or overland flow, check the rules that apply, confirm you have enough clay, and get the wall built in compacted layers with a proper spillway. Dam clean-outs start from $1,520 + GST a day with our 14.5 tonne excavator, and most take one to three days.
First question: watercourse or overland flow?
In Queensland, the rules depend on where the water comes from. This matters more than anything else in the planning stage.
- Watercourses, lakes and springs: the Queensland Government says a water licence is needed for taking or interfering with water in a watercourse, lake or spring. A dam across a creek or defined gully that counts as a watercourse brings in the licensing rules, so site your dam carefully.
- Overland flow: this is rainwater running across the land before it reaches a watercourse. Under the state’s guidance, you can take overland flow for any purpose unless a moratorium notice or water plan limits it. Taking it for stock and domestic purposes is treated as accepted development, which must comply with the relevant accepted development requirements.
The South Burnett sits within the Burnett Basin water plan area, which has its own rules. If you’re unsure whether the gully on your block is a watercourse, check the state’s watercourse mapping or call your local Department of Local Government, Water and Volunteers business centre before you build.
Don’t forget the paperwork. For accepted development works that take overland flow, the state asks you to notify the Department of Local Government, Water and Volunteers of the new works within 60 days of completion.
When a dam becomes a “referable” dam
If a dam failure would put two or more people at risk, it’s classed as a referable dam and a whole extra set of rules applies. The owner needs an approved emergency action plan, construction needs a development permit, and the design has to involve a suitably qualified Queensland registered professional engineer. Most small farm dams sitting well away from houses and roads aren’t referable, but if your dam is upstream of a house, a road or a neighbour, check first.
The state also recommends talking to anyone who could be affected by your dam before construction starts, and some sites need other approvals, such as a clearing permit for native vegetation.
What makes a dam hold water
The Sustainable Farms farm dams technical guide sets out the basics every good dam follows:
| Design point | Guideline |
|---|---|
| Soil mix for the wall | Sand 40 to 60%, silt 10 to 20%, clay 20 to 40%. At least 20% clay. |
| Cut-off trench | A trench under the wall, keyed into impervious clay, to stop seepage underneath |
| Compaction | Layers 150 to 200 mm thick, compacted at optimum moisture |
| Batter slopes | 2.5 to 3 horizontal to 1 vertical, and at least 3 to 1 on bigger, deeper dams |
| Freeboard | At least 1 metre between full water level and the top of the wall |
| Crest width | At least 3 metres |
| Spillway | Wide enough for the biggest storms. Err on the wide side. |
Test your soil first
Clay content decides whether a dam holds water. Before committing, dig a few test holes across the site with the excavator and look at what comes up. Red soils that are great for crops can be too free-draining to hold water on their own, so the clay may need to come from elsewhere on the block.
Go deep
Evaporation is the silent killer of shallow dams. The same guide notes most dams lose about a metre a year off their surface area, so a deep dam with a smaller surface holds water through a dry spell much better than a wide, shallow one of the same volume.
Size the catchment
A big dam with a tiny catchment rarely fills. A small dam with a huge catchment gets hammered by floodwater. Match the storage to the area that drains into it, and size the spillway for the worst storm you can imagine.
Clean-outs and repairs
Older dams fill with silt, lose capacity and start to leak. A clean-out removes the silt, reshapes the batters and can repair the wall. The best time is when the dam is dry or close to it, which in the South Burnett usually means late winter or spring after a dry run.
What dam work costs
Most dam work is priced on machine time. You get a fixed written quote before we start.
| Job | Starting price (ex GST) | Notes |
|---|---|---|
| Dam clean-out | From $1,520 a day | 14.5 t excavator and operator. Most take 1 to 3 days. |
| Small drainage jobs | From $660 | 4-hour minimum, travel included |
| New dam | Quoted after a site look | Depends on size, soil, spoil placement and access |
The price moves with the size of the dam, how much silt is in it, whether it’s wet or dry, where the spoil goes, and any culverts or pipe needed.
Next step: see our dams and drainage service, grab the free price guide, or send us a map pin and a few photos of the site. If the dam site needs clearing first, read what you can clear without a permit.
This article is general information only. Check the current rules with the Queensland Government before you build.
Want real numbers for your job?
Grab the free South Burnett price guide, or send us a few photos and get a fixed written quote. We reply within 2 business hours.
