Dealing with salinity in Wheatbelt Valleys - Department of Water

WHEATBELT HYDROLOGY
Flow in the Yilgarn and Lockhart Rivers is highly variable which is shown in Figure 1. The Mean Annual
Flow (MAF) for the Yilgarn River at Gairdners Crossing is 7,300 ML while for the Lockhart River at
Kwolyn Hill it is 11,000 ML. At Yenyening Lakes the MAF of the outflow is approximately 13,000 ML.
While the total inflow into the lakes is 18,000 ML, a large proportion is lost in evaporation when the
runoff is trapped by the lakes.
Annual Flow (ML/a
120,000
100,000
80,000
60,000
40,000
20,000
0
Yilgarn River
Lockhart River
1975 1980 1985 1990 1995 2000
Figure 1 Recorded flows in the Lockhart and Yilgarn rivers
The total amount and duration of rainfall play a large part in the hydrology of the catchment. There are
many lakes along each of the rivers which need to fill before longitudinal flow will occur. At least 280
mm of annual rainfall is needed for substantial flow in either the Yilgarn or Lockhart rivers (Figure 2).
Significant flow events can occur from rainfall derived from either severe summer events or above
average winter rainfall.
Annual Flow (ML)
120,000
100,000
80,000
60,000
40,000
20,000
Yilgarn River
Lockhart River
0
150 250 350
Annual Rainfall (mm)
450 550