Sinkholes

A sinkhole is a cavity in the ground caused by water dissolving the rock over time.

They can be small or big, and happen slowly or quickly.

They're often found in places with limestone or dolomite rock.

Sometimes, sinkholes can show an opening to a cave below the ground.

They can be circular and up to tens of meters in size.

Sinkholes happen a lot in the Top End, especially in the Katherine region.

Causes

Sinkholes usually happen when there's a change in water flow, like after a big storm.

It can also be caused by:

• human activities, like pumping too much groundwater
• changes in the surface or subsurface flow of water
• leaking water lines.

Sinkholes can develop suddenly when, for example, a soil plug in an existing solution cavity is washed away or when there is a catastrophic collapse of the roof of a cave.

Problems

The most obvious danger of sinkholes is that a deep hole is a potential hazard for people and animals.

They can also undermine and destroy infrastructure such as buildings or roads.

In Katherine, roads, fences and agricultural land have been affected, but to date no houses have been seriously damaged by sinkholes.

Sinkholes can also provide a pathway for surface waters to drain rapidly down to the water table. This creates the potential for any pollutants to contaminate groundwater.

Potential signs

Signs of a sinkhole can be:

• slumping or sagging soil or infrastructure
• structural cracks
• development of erosion rills or gullies.

If you find a sinkhole

Known sinkholes should be buffered from any areas of infrastructure development or clearing, to reduce the chance of:

• sinkhole collapse
• groundwater contamination or sedimentation.

Where possible, you shouldn't divert water:

• into a sinkhole
• in areas prone to sinkholes where it can pool.

If you have a sinkhole on your property, you need to find out what's causing it and fix the problem.

If it's not hurting anyone or anything, you can just fence it and keep an eye on it.

But if it's a problem, you need to get help from an expert, like a geotechnical engineer.

How to prevent

To prevent sinkholes:

• don't build houses and roads on or near caves
• never direct water towards sinkholes
• never dump rubbish in sinkholes
• reduce soil erosion
• cover bare ground with plants, which can help stop sinkholes from happening.

Contact

If you have any questions, contact the Water Resources office.