Dealing with salinity in Wheatbelt Valleys - Department of Water

Figure 1. Hydrological cross-section of the Merredin catchment
Hydrogeology
According to George (1992), groundwater occurs in the following aquifer types in the Wheatbelt:
(i) coarse grained soils overlying pallid sandy clay (Collgar-duplex soils and Norpayellow
sandplain soils),
(ii) just above the bedrock in the intensely weathered granites,
(iii) in alluvial deposits within major valleys (Belka unit),
(iv) possibly in aquifers deep within the bedrock.
There are two aquifer systems in the Merredin Catchment
(i) Deep system with a recharge area extending from the highest part of the catchment
through to the valley floor and a discharge area at the lowest point which is the salt
lake chains at Hines Hill (Figure 4). Groundwater velocities in the deep aquifer system
are very low (5cm/day in the mid to lower catchment).
(ii) Shallow system controlled mainly by variation in local topography.
Recharge
There are three main mechanisms of recharge in Merredin district:
(i) direct recharge through general infiltration over wide area (dominant in the eastern
part of the catchment);
(ii) indirect recharge from concentrations of creek flow along water ways (e.g. Cohns
Creek that drains to the West of Merredin);
(iii) recharge from garden irrigation, septic tanks, leaking pipes, reticulation systems and
other anthropogenic (man-made) influences.
Depth to Groundwater and Salinity
Depth to groundwater in the town area ranges from 2 to 7 m. In other parts of the catchment, depth of
groundwater varies from 0 to 35m. Groundwater salinity in the Merredin catchment ranges from 630 to
43930 mg/L (Electrical conductivity ranges from 30 to 4700 mS/m).