The Murchison Palaeochannels groundwater investigation project has taken an innovative approach to mapping palaeochannels (ancient buried river-beds) across very large areas using airborne electromagnetics (AEM) technology.
The Department of Water commissioned an AEM survey in the Murchison River catchment. The survey included a helicopter that flew at approximately 90 m above the ground over the survey area with a coil slung 60 m beneath. The Department is working with CSIRO, whose researchers provide geophysical expertise on this project.
Why is it important?
Palaeochannel aquifers – ancient buried river channels – are an important groundwater resource where larger, regional sources are absent. While we know that significant groundwater resources may exist in the East Murchison area, to access them in the future we need more precise information on their location, their quality, and how much is available to use.
This survey will help us more accurately map the paleochannels and will ensure the water resources can provide for sustainable agriculture and industry development without compromising the environmental qualities that support the area’s unique ecology, indigenous values and human interests.
Why this approach?
AEM technology started in the minerals industry but has become very widely used in the last decade for groundwater mapping. AEM data is acquired at regular intervals along flight lines, with the distance between these flight lines determined by the amount of mapping detail required. Closer flight lines result in higher resolution data, but this will similarly increase costs. As a general rule AEM survey designs also try to collect data by flying across the target being mapped rather than along it.
A 'traditional' AEM survey design would cover the entire investigation area in a regular pattern. In the case of the Murchison Palaeochannels investigation this was not a practical approach. The size of the overall investigation area is around 180 000 km2, and to cover such a large area within the limits of the project budget would mean flying at such a wide line spacing that the final mapping would be unacceptably coarse.
To solve this problem the project team adopted an innovative design approach for the Murchison Palaeochannels AEM survey. Because the overall project objective was to map the palaeochannels, and not the material in between, it was decided to attempt to constrain the survey design by limiting it to those areas where these features were most likely to be. This was done using other data such as the Multi-resolution Valley Bottom Flatness (MrVBF) – a method of determining where the lowest points in the landscape are - and other existing mapping. This information was also used to break the total survey area into smaller survey blocks, based on the most likely flow-direction of the palaeochannels (and therefore the flight lines).
By taking this approach and concentrating our data collection on those areas that were most relevant, the project team was able to map the more than 52 000 km2 of palaeochannels within the 180 000 square kilometre project area for around a third of the cost of flying a traditional survey over the entire area.
How will this help manage our water?
This survey is part of a four year project that will map groundwater resources and assess aquifer sustainability so the Department of Water can develop and optimise groundwater models to manage water abstraction.
The data gathered by the survey will be used by the Department of Water in a scientific process to assess the quantity, quality, availability and recharge of the region’s groundwater resources.
By looking at existing and new groundwater sources, this work will contribute to better information on groundwater availability in the region and build further knowledge about groundwater recharge and sustainability.
Reliable knowledge on available groundwater ensures future economic expansion and population growth in the region will not be constrained by a lack of information on water availability.
This survey received funding from the State Government’s Royalties for Regions program.
The Department is working together with CSIRO.