At times, karst environments seem out-of-sight, out-of-mind. However, failure to consider these environments could result in groundwater contamination and the effects will flow-on.
What is karst?
Karst is the landforms that result because some rock types are relatively soluble in water. These rocks tend to gradually dissolve, rather than be eroded by physical processes that shape landforms in other environments. Karst landscapes are known as karstlands
. Tasmania's karstlands are formed mainly in limestone and dolomite rocks.
Karst landscapes feature sinkholes, springs and streams that sink into subsurface caverns. Karst terrain is hollow by nature and the potential for groundwater pollution is high. Streams and surface runoff enter sinkholes and caves, and bypass natural filtration. Groundwater then travels through underground networks, and can move rapidly from one part of a catchment to another. If polluted, the groundwater carries contaminants into wells and springs in the area.
Protecting karst areas
Groundwater pollution often originates within the district or property dependent on the groundwater supply for drinking water and household use. Given this is so, property owners may wish to think about their own catchment and be aware of the potential impact of activities within it.
Within karst catchments, activities that could impact on groundwater flows and quality are best planned with particular care. In some instances, it may be appropriate to obtain specialist advice to clarify catchment boundaries and to ensure that appropriate planning steps are followed. This can help to ensure that an activity will not cause unacceptable impacts to groundwater.
Karst wells and springs used for domestic and other purposes can be contaminated from a number of poor practices, including:
- Uncontrolled stock damaging streambanks and vegetation, resulting in eroded soil entering groundwater via streamsinks and caves.
- Human and animal wastes entering and contaminating waterways.
- Loss of native vegetation, particularly in the vicinity of streams, caves and sinkholes.
- Inappropriate use of herbicides, pesticides or fertilisers. To reduce water pollution, consider whether less environmentally harmful products are available and use all chemicals as specified on product labels. Wick wiping techniques may be appropriate if it is necessary to apply chemicals in the vicinity of watercourses, sinkholes and caves.
- Filling sinkholes or caves, or using them to dispose of animal carcases or rubbish. This can damage the karst environment and cause impacts to groundwater.
Sinkholes are natural drainage points for the groundwater system and should never be filled or used as rubbish dumps.
When contaminants enter groundwater through sinkholes, it does not mean "out of sight, out of mind". The problems associated with contaminated water will emerge, posing a health concern and threat to the environment. In karst areas, groundwater may resurface at springs and spread the contamination into streams and rivers - our water supplies.
Plugging a sinkhole may cause:
- Poor drainage
If you purchase a property where a sinkhole was previously used as a dump, consider cleaning it out and restoring the vegetation.
Sound Management Practices
The following measures can help manage karstlands sustainably:
- Reduce the entry of eroded soil and other pollutants into surface watercourses, sinkholes and caves by retaining a buffer of natural vegetation around these features.
- If natural vegetation has been cleared around surface watercourses, sinkholes and caves, consider replanting a buffer of local provenance native species.
- Fence surface watercourses, caves and sinkholes to exclude stock (provide alternative watering facilities if necessary). This will reduce trampling damage and loss of water quality.
- If diversion of water from natural sinking points (e.g. caves, sinkholes) is necessary, this should be planned to ensure that unacceptable impacts on the karst system are avoided.
- Pumping of groundwater from wells should not exceed the rate of recharge to the aquifer, resulting in a lowering of the water table.
- Manage caves to protect their natural values by ensuring that persons entering the cave behave responsibly. Members of caving clubs affiliated with the Australian Speleological Federation are required to abide by a minimal impact caving code.
- Consider karst issues in the design and location of built structures (e.g. roads, sheds, houses, etc.). It is generally advisable to locate built structures away from karst features, such as sinkholes and caves, as natural drainage characteristics may be disrupted and/or subsidence can occur.
- Consider the potential for groundwater pollution when planning septic systems, feed lots, animal waste lagoons or stormwater basins. Alternative waste management practices or sites may be worth considering in some instances.
- Avoid the application of fertilisers, pesticides or other chemicals in the vicinity of sinkholes, caves and surface watercourses. Seek specialist advice if in doubt about what is appropriate.