Catchment Issues
The water management issues facing catchment managers can be many and varied, whether they are over-extraction of water, stream salinity, water quality protection or ecosystem health. The nature and scope of conjunctive water management in a catchment can be tailored to address these management issues. The scale of the issues must be understood to allow for a prioritised approach. Identifying and prioritising water issues are key functions of catchment planning and management.
Outlined below are some key water issues facing Australian catchments and how conjunctive management can be a useful approach.
Management of Water Quantity
In Australia, rainfall tends to be highly variable and evaporation rates high. This makes the storage and delivery of water an enormous challenge. Using aquifers as "water banks" in conjunction with surface water reservoirs allows greater flexibility and efficiency in water supply and delivery. Groundwater can be used to supplement river flows or surface water used to replenish aquifers. This can help us moderate the droughts and flooding rains of the Australian climate.
Management of Water Quality
Movement of water between aquifers and surface water features such as rivers, lakes and estuaries can also mean movement of salt, acid, nutrients or contaminants. Hence, an understanding of surface water groundwater interactions is important in the management of river salinity, acid sulfate soils and algal blooms. Contaminants can migrate from industrial sites, land fills, intensive cropping or septic tanks to reach waterways via the groundwater system. In certain situations, physical and chemical properties of aquifers can be used to advantage to reduce the toxicity of a contaminant.
Management of Ecosystems
Input of groundwater can be important in maintaining aquatic ecosystems. Wetlands, river pools or lagoons may be reliant on a relatively stable inflow of groundwater to maintain water levels, particularly during extended dry periods. Baseflow of groundwater to rivers can be a critical component of the environmental flow regime. Groundwater discharge can affect stream chemistry and temperature and have implications for aquatic ecology. Mixing of surface water and shallow groundwater in the stream bed can provide a unique and dynamic habitat in its own right.
There is a need to assess the dependency of ecosystems (such as in perennial streams, wetlands or estuaries) on groundwater inputs, as well as surface water. This allows for the recognition of any risks to groundwater quantity and quality, and make appropriate management responses. Assessing connectivity and the ecosystem dependencies is a critical part of the assessment of sustainable yields of water resources. In some situations, it may be appropriate to supplement stream flow using pumped groundwater to meet critical environmental objectives.
Management of Natural Hazards
Seepage of floodwaters into underlying or adjacent alluvial sediments can reduce the impact of a major flood event. This is particularly true for floods of Australia's inland rivers, which tend to be slow moving and cover large areas of the floodplain. This seepage can reduce the peak levels of the flood as it progresses downstream.
Excessive lowering of groundwater levels due to pumping can lead to collapse or compaction of the aquifer material. This in turn can lead to subsidence of the overlying land surface, which can cause significant infrastructure and environmental damage. The threat of subsidence can be reduced by using surface water to replenish the aquifer so that groundwater levels are maintained over the long term.
Further Information
Management of Water Quantity:
Managing variable water availability
Efficient water storage and delivery
Water allocation
Management of Water Quality:
Salinity
Acidity
Nutrients
Contaminants
Management of Ecosystems:
Groundwater dependent ecosystems
Riverine Ecosystems
Coastal and marine ecosystems
Management of Natural Hazards:
Buffering of floods
Control of land subsidence