527and direct groundwater seepage is apparent, saline areas are referred to as ‘saline
seeps’ or ‘seepage scalds’ and may be associated with baseflow contributions to
rivers and streams (Peck 1978 ).
4.4 Regional, Intermediate and Local Groundwater Systems
Groundwater systems that result in dryland salinity can be categorised according to
aquifer scale (local, intermediate or regional) (Coram et al. 2000 ; NLWRA 2001 ;
Walker et al. 2003 ). This enables the cause (location, area) to be defined and the
scale of the flow systems reflects the ease with which salinisation can be managed.
On the basis of size and responsiveness to treatment, aquifers were classified by
NLWRA ( 2001 ) as:
(i) Local flow systems – recharge and discharge are close to each other (within
1–3 km) and groundwater levels equilibrate quickly (10–100 years) after dis-
turbance such as clearing. Localised flow systems are discontinuous and com-
monly overlie an intermediate or regional flow system.
(ii) Intermediate flow systems – recharge and discharge may have a horizontal
extent of 5–10 km and generally occur across the entire catchment. They have
a higher storage capacity than local flow systems and take longer to equilibrate.
Intermediate systems may occur in areas with palaeochannels (buried, prehis-
toric drainage channels).
(iii) Regional flow systems – recharge and discharge may be separated by many
tens to hundreds of kilometres. Groundwater movement may be independent
of local topography (sub-catchments), involve long flow paths and are typical
of large sedimentary basins. Groundwater levels outside the recharge area are
slow to respond and equilibrium may take many hundreds of years. Regional
aquifers often contain local and intermediate flow systems.
4.4.1 Artesian and Non-artesian Groundwater Systems
Given proximity to a watertable and the scale of aquifer defines the processes
responsible, and may impact the severity and responsiveness to treatment, salinity
managers are also concerned to determine whether the aquifer responsible is arte-
sian (under pressure beneath a confining layer) or non-artesian. Artesian groundwa-
ter conditions can occur where there is sufficient topographic slope and connectivity
to enable hydraulic connection to the saline area. Artesian conditions may result in
a flux of groundwater of up to 2400 mm m−^2 to the land surface as a result of heads
of up to 2–6 m above ground (George 1992 ; George and Conacher 1993 ). These
conditions are typically associated by discharge to streams where saline groundwa-
ter contributes to perennial base flow.
Salinity in Dryland Agricultural Systems: Challenges and Opportunities