Water resources in karst and quarrying impacts

1. Water resources in karst and quarrying impacts Prof. David Gillieson Earth & Environmental Sciences James Cook University Cairns, Australia

2. Outline of talk • Karst hydrological zones and the epikarst • Limestone mining for cement • Quarrying impacts and rehabilitation • Expect the unexpected!

3. Zonation of karst aquifers Diagram by Ken Grimes, Regolith Mapping P/L

4. Porosity types and karst aquifer properties Gillieson D 1996 Caves: Processes, Development, Management, Blackwells

5. Karst is a triple porosity aquifer! fissures 10s of metres/day pore spaces mm/day conduits 100s of metres/day Clearwater Cave, Sarawak – 135km long

6. 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

7. Epikarst depth & zonation

8. 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

9. 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

10. 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)

11. 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

12. Mining for cement • Top graph is % change in use • Lower graph is volume of limestone quarried for cement

13. 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

14. 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

15. 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

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

17. 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

18. Quarry rehabilitation strategy

19. Detail of drainage control

20. 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