Pictured: Roebuck Plain, along with Eighty Mile Beach and Mandora Marsh rely on groundwater and cover the La Grange aquifer. Image:yaruman5THE Department of Agriculture is conducting an airborne geophysical groundwater survey of the La Grange aquifer, in the Kimberley south of Broome.
Hydro-geologist Dr Richard George, who is the principal research scientist, describes the project as “a pre-assessment of an aquifer, a long time before anyone goes about developing it.”
He says while there are already irrigated farms at Shamrock and Shalimar, the department expects future applications to develop horticulture and possible diversified beef production on what are now pastoral leases.
Dr George says the project aims to assess four main aspects.
“The saltwater interface [near the coast] is one of our main ones,” he says.
“[The second is to] map the base of the Broome Sandstone [which contains the aquifer].
“We are also doing it to try and map the special distribution of water quality in terms of the salinity of the aquifer both by depth and … laterally.
“The fourth reason is that we know from recent work by Geoscience Australia that there are some ancient drainage systems [paleochannels] that have come across the Canning Basin and have been in-filled by the Broome Sandstone system.
“We believe they left a legacy of different materials around them but it also may help explain regional variations in salinity.
“They have probably been cut into an older part of the Broome Sandstone, so they should have an electrical signature. They also might be saltier, particularly along the Mandora marshes.”
Dr George says Salt Creek to the south is known to be saline and is most probably a paleochannel.
“There are a couple of others that are less certain for which the system geometry has been set up to help describe,” he says.
He says the reason for using airborne geophysics rather than conventional drilling is the size of the aquifer (250km north to south and as much as 300km inland), and logistical problems in its eastern portion.
“Once you get away from the highway that runs up the coast and you get through the first 30 to 40km of station country … you are into very difficult-to-access terrain: sand dunes,” he says.
“It’s not a flying drilling rig but it’s the way we’re perceiving it.
“We are using geophysics to make sure that when we do go drilling, we target the most important locations.”
The results should be published late in 2014.
