A detailed study involving drilling, geophysics, hydrogeochemistry, and
groundwater monitoring over a 10-year period has been carried out at a small
catchment south-east of Yass on the Southern Tablelands of New South Wales to
investigate the source of salt causing dryland salinity. The catchment is
within 2 km of the top of a regional groundwater and surface water divide and
remains substantially tree covered. The investigations have found a highly
heterogeneous distribution of salt, most of which is associated with swelling
clay. Dispersion of this clay causes the surface features commonly associated
with dryland salinity.
There is no hydrogeochemical evidence to suggest evaporative or transpirative
concentration of salt in the groundwater. The short flow path from the top of
the catchment cannot provide a significant source of salt from bedrock
weathering. An alternative model of salt accumulation is proposed with the
salt imported into the catchment with silt during dust storms in the arid and
windy conditions during the last glacial. The management implications of this
model of salt distribution and the associated dryland salinity development are
discussed.
