Management of Salt-Affected Soils - Practices of Irrigation and On-farm Water Management - page 276

built. The change in the level of groundwater before the construction had enabled
soil erosion, which led to high concentration of salts in the water table. After the
construction, the continuous high level of the water table led to the salination of the
arable land.

8.2.1.7 Salinity from Urban Area

Salinity in urban areas often results from the combination of irrigation and ground-
water processes. Cities are often located on drylands, leaving the rich soils for
agriculture. Irrigation is also now common in cities (gardens and recreation areas).

8.2.1.8 Seepage Salting/Salty Groundwater Discharge
Saline seeps (or seepage salting) can form where salty groundwater discharges at the
ground surface. This is most commonly found in basaltic (open downs) areas. The
occurrence of Black Tea Tree ( Melaleuca bracteata ) is a useful guide to seepage
areas (both fresh and salt water).
Salts occur naturally in many bedrock deposits and in some deposits on top of the
bedrock. Groundwater flowing through these deposits dissolves and transports the
salts. Under certain conditions, groundwater discharges at the soil surface. When
the water evaporates, the salts are left behind. Over time, the salts accumulate in the
groundwater discharge area, forming a saline seep. A white salt crust forms where
the salt concentration is very high.
Salt accumulates by water entering the soil at a “recharge area”; this water flows
through the soil profile and into aquifers in the bedrock. The water flows through
these aquifers accumulating salts into solution, as the water flows through areas
that have high concentrations of salt, the salt concentration in the water increases.
Eventually, due to bedrock formation, the water in the aquifer is forced close to
the soil surface and the water table is elevated. There are different mechanisms that
cause an elevated water table. Once the water table is within 2 m of the soil surface,
it is possible for the salt infected water to creep up to the surface by capillary action.
The location where the water creeps to the surface is called the “discharge area.”
This upward flow of water, accompanied by evaporation, leaves high concentrations
of salt on or near the soil surface.

Factors Affecting the Formation of Saline Seeps
• Generally, recharge areas occur in upper slope positions, while discharge areas

occur in lower slope positions.

• Periods of high precipitation and irrigation canal seepage can increase the risk of

seep.

• Growing high-moisture-use crops, like alfalfa, in recharge areas can reduce the

flow of water to discharge areas.

• Summer-fallow in recharge areas can increase the risk of saline seep formation

because there are no crops to take up moisture from deep in the soil.