Dealing with salinity in Wheatbelt Valleys - Department of Water

APPENDIX 2
WATER MANAGEMENT OPTIONS
Bus Tour Notes - Doodlakine to Merredin.
This conference tour will cover aspects of Wheatbelt valley water management, in particular,
engineering options for lowering watertables and reducing inundation and waterlogging of valley soils.
The bus trip travels east from Doodlakine then turns south at Hines Hill through extensively saline soils
of the ‘Baandee’ soil association. These areas contained large areas of primary salinity that were once
covered by ‘boree’ (Melaleuca) and other salt tolerant trees and shrubs, prior to clearing. Prior to
clearing, there was little or no salinity south of Hines hills at settlement (c1910). The distribution of
salinity and valley form should be noted.
Turning east, the bus crosses the lower Belka Valley (catchment area ~170,000 ha) at a site where
surface water management, such as pumping impounded waters and other forms of drainage were
undertaken in the late 1970s and early 1980s. To the southeast, WISALTS banks were monitored over
several years (1980s) and their impacts documented.
The Belka valley was the first studied in the Wheatbelt (Bettenay et al, 1964). Research on the
hydrologic processes concluded that valley morphology was a good indicator of risk, with ‘Baandee’ at
highest risk, ‘Belka’ type valleys at high risk and ‘Merredin’ type valleys at lower risk. The later had
higher mainstream slopes. Bettenay also drilled shallow wells and indicated that salinity was mainly
associated with ‘…a more spatially extensive wet zone…’ than watertable rise. There was no
documented evidence of the later. They also associated recharge with granite runoff and valley
recharge in extreme events.
Recent monitoring has shown that watertables remain close (< 2-3m) throughout much of the Belka,
and salinity is expanding in most areas, especially in tributary valleys and to the east. Watertable
monitoring in these valleys (cleared 1910 to 1950) and on slopes, mainly cleared in the 1950’s and
1960’s show 0.2-0.3 m/yr. rates of rise. Sandplain seeps are common.
Current drainage works in the valleys are restricted by infrastructure such as roads and railways. The
bus will stop and discuss the impacts of restricted drainage on upstream managers.
Groundwater pumping is an alternative for salinity management in valleys, although little experience
exists to determine its practicability in valleys such as the Belka. Several aquifers systems exist
although most are relatively low yielding and the radial impact of wells uncertain. The location of
palaeochannel and related sediments has not been determined although airborne geophysics (AEM)
maybe a means of locating such features. Aspects of pumping will be discussed and compared to other
forms of drainage.
Management of discharged water within and from drains represents a significant issue for land
managers. Groundwater seepage may either be lost to larger lakes, evaporate or infiltrate as
transmission losses through sediments can be high, especially where drains and watertables are
shallow.
The bus will pass an extensively altered remnant (Belka Rail reserve), typically saline ‘Salmon Gum’
dominant valley soils, giving visitors a view of damage due to shallow watertables and salinity.
Remnants in valley locations are at significant risk of salinity, with many reserves in valley locations.
Surface and groundwater drainage examples, upstream and downstream, can be seen.
Turning north towards Merredin on the Bruce Rock Rd, the bus will stop to discuss large surface water
management systems. Large floodways were constructed to the Belka to reduce the impacts of severe
flooding experienced in the 1960s and again in the 1970’s. Recently, deep drains have been
constructed near these banks.
Jones’ drains are an example of salinity management at the foot of a sandplain slope. Drainage
systems into well-structured clays will be shown and the landowner and contractor will discuss their
effectiveness, problems and constraints.
Leaving this site, the bus will travel to Merredin, passing upland remnants as we head onto the Merredin