Lockyer Salinity Fact Sheet 1: Identifying saline areas
Causes of salinity
All water, including rain, contains salts. Salinity is a natural result of weathering of rocks and concentration of salts by evaporation or plant transpiration. It becomes an issue when the concentration of soluble salts in soil or water increase to levels that affect water quality, soil properties, plant growth, ecosystem diversity or even built infrastructure.
Saline areas are caused by a rise in underground water-tables, which bring naturally occurring salt to the ground surface. These areas typically occur in low landscape positions and are influenced by geology as well as land use change over time.
Natural and man-made features in the landscape that affect the incidence of salinity include placement of dams (Image 1), drainage characteristics of the catchments including where streams meet, and changes in geology or topography (Figure 1).
Irrigation can also add excess water to some salinity sensitive areas, as well as move salts from the soil zone into the groundwater.
Changing land use impacts on the water balance and has an effect on when and where salinity is likely to occur.
Identifying saline areas
Saline areas might be identified through land that is:
- Waterlogged (Image 2) or remains wet for extended periods;
- Bare or has a poor vegetation cover ;
- Growing salt tolerant plant species such as marine couch, saltbush or black tea-tree;
- Showing signs of vegetation dieback; and
- Suffering from poor yields.
Salinity in the Lockyer
There is a distinct and recurring pattern of salinity in the Lockyer Valley both in small dryland catchments and the major southern tributaries closely associated with the Winwill conglomerate, part of the Koukandowie geological formation (Figure 2). This geologic formation is very resistant to weathering and has caused catchments with restricted water outflows in both small tributaries and in the larger southern tributaries feeding into Lockyer Creek.