Water resources in karst and quarrying impacts

Prof. David GilliesonEarth & Environmental Sciences

James Cook UniversityCairns, Australia

Outline of talk

• Karst hydrological zones and the epikarst

• Limestone mining for cement• Quarrying impacts and

rehabilitation• Expect the unexpected!

Zonation of karst aquifers

Diagram by Ken Grimes, Regolith Mapping P/L

Porosity types and karst aquifer properties

Primary porosity

Secondary porosity

Conduit porosity

Components Pore spacesVughs

Linked joints and fractures

Open channels and pipes

Flow regime Laminar Laminar to just turbulent

Turbulent

Governing law Darcy Hagen-Poseuille

Darcy-Weisbach

Response to input water

Slow<1mm/day

Moderate 1-10 metres/day

Rapid 100s of metres/day

Gillieson D 1996 Caves: Processes, Development, Management, Blackwells

Clearwater Cave, Sarawak – 135km long

Karst is a triple porosity aquifer!

conduits 100s of metres/day

fissures 10s of metres/day pore spaces mm/day

Epikarst- the karst engine house

Close relations between • vegetation• soils• microbiota • epikarst fissures• solution processes• and drainage

Gillieson D 1996 Caves: Processes, Development, Management, Blackwells

Epikarst depth & zonation

Epikarst storage and transmission

• The epikarst or subcutaneous zone is located at the top of the aerated or vadose zone• From the epikarst, water percolates downwards and delivers slow recharge to the phreatic zone• Epikarst storage can buffer the effects of rainfall events on water percolation

Karst groundwater

• fragility of karst environments evidenced by karst groundwater systems

• extremely important water supplies - about 25% of the global population is supplied largely or entirely by karst waters

• but whose quality is VERY susceptible to degradation

What goes down, must come up...

• rapid transport of pollutants in cave conduits

• main problems are turbidity and sewage

• also herbicides (Atrazine) and pesticides (Metamidophos)

Mining and quarrying

• Limestone widely used for building stone, cement manufacture, agricultural lime, industrial flux and toothpaste

• Caves may be totally quarried away

• Local pollution of groundwater

• Rehabilitation costly and slow

Mining for cement

• Top graph is % change in use

• Lower graph is volume of limestone quarried for cement

Limestone quarry rehabilitationBenders Quarry, Lune River,

Tasmania• Quarry operating in World

Heritage Area for 40 years

• Operations affecting WH values, especially in large cave underlying quarry

• Commonwealth closed quarry and funded rehabilitation and monitoring

• Joint project with Tasmanian Parks & Wildlife Service

Exit CaveTasmanian WHA

• Cave is 25km long with extensive glowworm colonies and other rare invertebrates

• Extensive dye tracing using Rhodamine WT

• Proved connection between quarry drainage and Eastern Passage of Exit Cave

• Monitoring sites established with water quality probes and dataloggers

Quarrying impacts at Lune River, Tasmanian World Heritage Area

• Removal of cave passages and destruction of palaeokarst fills by quarrying

• Increased sedimentation of fine clays in caves underlying the quarry

• Recurrent turbidity in Eastern Passage and Exit Cave Creek• Changes in pH, conductivity and sulphate ion concentrations

in passages draining the quarry• Re-solution of stalactites by acidified drainage waters • Reduced densities of indicator species of hydrobiid snails

(Fluvidona spec. nov.) in passages draining the quarry

Gillieson & Houshold, 2000. In Drew & Hotzl eds. Karst Hydrogeology & Human Activities, Balkema

Dissolved sulphate (ppm) at Benders Quarry, Lune River, Tasmania

Rehabilitation strategy

• Restore the hydrology of the site by simulating the drainage characteristics of the unimpacted karst

• Reduce peak runoff by the creation of small internal drainage basins which simulate dolines

• Control sediment movement at source by the use of control structures and filters

• Establish a stable vegetation cover, preferably of perennial plants

• Reactivate the soil biology• Monitor progress above and below ground

Quarry rehabilitation strategy

Detail of drainage control

Expect the unexpected in karst!

• "Nature to be commanded must be obeyed", Francis Bacon, Lord Chancellor of England, ('Essays' 1620)

• Karst surface and subsurface systems are integrated and this renders karst especially susceptible to human impacts

• Epikarst is of fundamental importance in the control of recharge. It stores and mixes water and redistributes recharge - and any pollution

• Conventional groundwater models should not be applied to karst for management purposes, because karst aquifers have triple porosity characteristics

• Best place to monitor the condition of karst is at the outflow spring, because spring outflows integrate the effects of all upstream activities