Dealing with salinity in Wheatbelt Valleys - Department of Water

APPENDIX 1
BACKGROUND
HYDROLOGY AND SALINITY NOTES FOR WHEATBELT TOUR
by John Ruprecht and Peter Muirden (Water and Rivers Commission)
The Swan and Avon Rivers have a large catchment area of 125,000 km² which stretches from Dalwalinu
in the north, Southern Cross in the north east and Lake King in the south east down to the mouth at
Fremantle.
Most of the catchment area to the mouth of the Swan (73 %) is upstream of Yenyening Lakes (east of
Beverley) which is made up of an ancient and very flat landform called the Yilgarn System. The Yilgarn
System is likely to have originally flowed out into the Southern Ocean in a series of rivers including the
Gairdner, Fitzgerald and Phillips.
Following a rise in landform on the South Coast, the whole system now flows out to the west and into
the Avon River through the Caroline Gap south of Kellerberrin. This gap is located just downstream of
the confluence of the Lockhart and Yilgarn Rivers, where they join to become the Salt River flowing
southwest through the Yenyening Lakes and out into the Avon River.
The north of the Yilgarn System is drained by the Yilgarn River which originates north-east of Southern
Cross with Lake Seabrook and Lake Deborah, but with tributaries to the north and south-east. It flows in
a south-westerly direction past Merredin to its confluence with the Lockhart River south of Kellerberrin.
Its catchment area is 55,900 km².
In the south of the Yilgarn system, the land is drained by three major rivers which join south of Kondinin
into the Lockhart River an which have a total catchment area of 32,400 km²:
• the mainstream Lockhart River originates at Lake Magenta and winds its way northwest to
Newdegate, Kondinin, Corrigin and Bruce Rock, before joining the Yilgarn River south of
Kellerberrin.
• the Camm River to the east draining from Lake King through Hyden to Kondinin where it meets the
Lockhart River.
• The Pingrup River which arises near Lake Cairlocup and flows North to Lake Grace and the
Lockhart River.
•
Flows have been measured in the Yilgarn and Lockhart Rivers since 1976 and contrary to popular belief
flow occurs every year (although some years the flow is very small). For instance, on the Lockhart
River, the annual flow was in excess of 10 GL in seven out of the 25 years of record, while in 10 years it
was less than 1 GL.
The Avon River itself, originates at Yealering and upstream of the confluence with the Salt River at
Yenyening Lakes has a catchment area of 3,200 km². From there it flows past Beverley, York and
Northam before the confluence with the Mortlock River. Excluding the Salt River (Yenyening) catchment
(91 500 km²) the Avon River at Northam is 8 100 km² while the Mortlock River adds a further