FOR all the talk over the years of dams in the Fitzroy River, the more likely pathway to development lies far beneath in the extensive groundwater system which underlays the vast catchment.
This is according to reports from CSIRO’s 2.5-year assessment of the catchment’s water resources and what is described as the ‘low-cost, low-risk’ potential for irrigated development using groundwater which has the added advantage of allowing for staged development.
Starting small-scale might be the unexpected possibility in this vast landscape more attuned to big cattle stations and bigger ideas.
The Fitzroy River is more than 700km long. Its main source is in the King Leopold Ranges and it flows out to sea in King Sound, the ninth-largest median annual discharge of the rivers in northern Australia.
The catchment itself covers nearly 94,000 km². It was one of three priority areas investigated as part of the Northern Australia Water Resource Assessment. More than 100 scientists and technical experts conducted the most extensive, integrated investigation of water resources in northern Australia, also investigating the Finniss, Adelaide, Mary and Wildman river catchments around Darwin in the Northern Territory, and the Mitchell catchment in Queensland. The work was commissioned by the Australian Government as part of the Agricultural Competitiveness White Paper and was released at the end of August.
The Fitzroy River catchment was the largest catchment area examined. About 90 per cent of the area is under leasehold tenure, with 16 of the 44 stations in the catchment under Indigenous management or ownership.
It’s predominantly cattle country with just over half of the Kimberley region’s pastoral leases being located in the Fitzroy River catchment.
What can an investigation into the potential for water resources to support irrigated agricultural development tell communities rooted in a history of pastoralism?
The CSIRO-led Assessment comes as public consultation is underway into the potential expansion of Fitzroy River National Park, which includes development of a management plan of the Fitzroy catchment incorporating the water allocation plan.
A case study from the Assessment provides an example of how information in the reports can help communities understand the type and scale of opportunity in the catchment.
According to the catchment reports, the case studies are illustrative only, not designed to demonstrate, recommend or promote particular development opportunities. Instead, the case studies “explore subtleties that become more apparent during the process of combining information from multiple disciplines”.
First, you need to know a little about the major aquifer systems in the Fitzroy Basin, in the geological Canning Basin.
Town and community water supplies are already heavily dependent on these aquifers.
Joint project leader, CSIRO’s Dr Cuan Petheram says that of the various systems, it’s the interconnected Grant Group and Poole sandstone aquifers that offer the greatest potential for use in agriculture.
“It’s the scale and volume of water – this is a large system which hasn’t had a lot of work done on it before. The extensive groundwater investigation undertaken in the Assessment found there is a reasonable volume of water that you could extract with a number of bores. There’s growing interest and acknowledgement that there might be potential in this water system.”
This water in the Grant Group and Poole sandstone aquifers is artesian or close to artesian meaning it is stored in the geological layers under pressure and requires little or no pumping – minimising operational costs.
This system is replenished – or recharged – from intense wet-season rainfall events where the aquifers outcrop at the surface. Groundwater hydrologists who worked on the Assessment put the mean annual recharge at 3,500 GL.
In some places these aquifers also replenish, in turn, the river. This is called discharge and, in particular, it supports water holes and groundwater-dependent ecosystems.
So, there are limits in drawing down on this precious resource. The Assessment found that with appropriately-sited groundwater bores, up to 120 GL/year (< 5 percent of recharge) of groundwater could be extracted from the interconnected Grant Group and Poole Sandstone aquifers for irrigated agriculture.
“The regional scale (of the aquifer) means you can sink a bore where you have got infrastructure. It’s low cost and low risk.
“Low cost because provided the groundwater is not too deep, groundwater infrastructure is not as expensive as other options. It can also be sited near existing infrastructure and near better soils.
“It’s low risk because you can site development to minimise environment impacts, and it lends itself well to staging. That is, you can start small and scale up.”
Mosaics of irrigation using this groundwater to grow crops and forage as part of an integrated cattle production has potential in the Fitzroy catchment, according to the report’s case study.
The mosaic case study specifically discusses the potential for irrigated land under a cotton-mungbean-forage sorghum rotation.
The return from two cash crops – cotton and mung beans – could bolster the cattle business. Wet-season cotton would be economically more viable if there is a local cotton gin, and in that case could bring high returns by reducing the cost of transport. Mung beans prices aren’t high but nor are they sensitive, with an existing export market.
Two cuts of the sorghum and by-product cotton seed would help grow out young cattle for an existing beef enterprise.
The case study estimates that 12,000 ha (0.1 per cent of catchment area) of cotton-mungbean-forage sorghum rotation spread across multiple properties could produce a combined gross value of production of about $84m per year, potentially creating 490 jobs.
Petheram says double cropping on the lighter soils could allow an increase on return with the same infrastructure costs.
“The groundwater system is underlying much of the catchment, so the question is location – to get a sweet spot to minimise and maximise various elements: where you have the right loamy soils and where you can do double cropping with the groundwater.”
Another advantage in using groundwater is it allows for staged development.
“Development of mosaics infused within pastoral business will support those businesses or grow new businesses. A development pathway we might see across Northern Australia could be small scale mosaic irrigation,” says CSIRO’s Northern Australia research leader Dr Chris Chilcott.
Being able to stage any development is an advantage.
There would be challenges to making such a case study work, timing for one. According to the case study, pasture production is December to April; cotton would need to be planted in January/February and picked mid-June/July before mungbeans are sown so that it can be harvested in early November before the early wet-season rains. The timing of the cotton planting becomes critical but also potentially difficult if planting in the wet season when there might be problems of trafficability when soils are sodden and planting equipment to sow the cotton is restricted.
“The feeling is it’s achievable but there’s very little double cropping experience in northern Australia. It will need on-ground trials to work put how best to make it happen to basically prove it up,” says Petheram.
“It’s then about staging and learning but you can do this well with groundwater, it can be fairly modularised. You learn how to do it and minimise your losses and when you’ve learned what to do, you scale up.
“Rather than starting with full-scale enterprise from day one and involving huge losses.”
Kimberley Pilbara Cattlemen’s Association CEO Emma White says the study provides a robust and comprehensive scientific evidence base to underpin discussions bringing together all stakeholders, including Traditional Owners and Aboriginal Corporations who hold 30 per cent of pastoral leases in the Kimberley.
That includes working to get better returns per hectare and optimising what the land can sustainably deliver to underpin future economic development in the catchment to the benefit of all residents.
“The fact that we now have got this comprehensive scientific study on land and water suitability across the catchment is fantastic for supporting informed decision making and helping people to create a shared vision and look to what’s possible in the future and what can be considered.”
Read more about the Fitzroy catchment, and the Darwin and Mitchell catchments and also the extensive Indigenous engagement undertaken as part of the Assessment.