529(iii) Irrigation salinity usually occurs under the irrigated area whereas dryland
salinity can occur some distance from the area of salt accumulation and excess
recharge. This can result in conflict between farmers if one is causing the
problem and the other receiving the impact. However, such externalities are
relatively uncommon (Pannell et al. 2001 );
(iv) Irrigated areas are usually flat and very valuable that justify the adoption of
expensive drainage practices compared with often scattered and small areas of
dryland salinity on less valuable land making cost-effectiveness on intensive
interventions problematic;
(v) Being flat, irrigated areas are less susceptible to water erosion and the loss of
topsoils once vegetation cover has been lost. Their flatness can however make
drainage more difficult as there are low gradients towards a discharge point.
Excess water from irrigated areas can infiltrate deeper profiles and aquifers and
contribute to ‘dryland’ salinity in down-gradient areas. Similarly, water and salt
from dryland agriculture can contribute to salinity in irrigated areas.
50 m Break of slope seeps0(^01000) m
- Basement+
- x
xxxx
xseepage zonex
xx
xx
50 m Sandplain Seep
0
01000 m
seepage zone
perched watertable
regional watertable
50 m
1000 m
0
0
- x
- Basement + + + + + + + + +
- xxxxxxx
Topographic low discharge
- xxxxxxx
- Basement + + + + + + +
- 50 m Bedrock high seep
0
(^01000) m
watertable xx
x
x
xxxx
Fig. 1 Types of dryland salinity discharges – bedrocks highs obstructing groundwater to flow
(upper left); a topographic change of slope reduces groundwater discharge rates (upper right);
perched groundwater coming to the surface because the aquifer pinches out (lower left); and
groundwater filing the aquifer under a flat valley such that the storage is exceeded (lower right),
and are four examples of types from the classification of Coram et al. ( 2000 )
Salinity in Dryland Agricultural Systems: Challenges and Opportunities
- 50 m Bedrock high seep