To solve salinity and other environmental issues we need to manage whole catchments, not just little parts. One town or one farm upstream can cause problems for others downstream.
The satellite image shows a section of the Murrumbidgee catchment with three of it’s sub-catchments.
Dark green/brown represents areas of remnant vegetation (natural bushland). Lighter colours, brown/white, indicate cleared farming areas.
There are very few areas of deep rooted, natural bushland left which would use groundwater through transpiration, causing water tables to rise in lower catchment areas.
Over 410 000 tonnes of salt pass Wagga Wagga each year, dissolved in the waters of the Murrumbidgee River. The Murrumbidgee flows into the Murray River and down to Adelaide which takes about 30% of it’s drinking water from the Murray.
At present the salinity of the Murray near Adelaide is over the 830 EC threshold for desirable drinking water some of the time and within a few years it is predicted it will be much worse if nothing is done. To fix the problem, land managers need to know where the salt is coming from.
Researchers’ in the Wagga Wagga area have been testing sub-catchment creeks of the Murrumbidgee. The worst catchments have been identified, so that land degradation problems which cause salinity can be targeted and the catchments managed on an ecologically sustainable basis. Below are some of their results. Note that the salinity of the Murrumbidgee is low (100 EC) but it’s large volume means the river transports a lot of salt each day. Salinity units used are EC’s ( electrical conductivity).
The Kyeamba sub-catchment within the Murrumbidgee catchment has been divided into smaller catchments again and the salt content of flowing creeks was measured. From this we can get an idea of the land areas contributing the most salt to the creeks. It shows the salt problem is not even across the landscape.
Farmers generally get the catchment concept reasonably quickly, particularly in relation to environmental issues like salinity. I can recall being a little surprised, just after handing each of the farmers in the Wilga (WA) group their salinity maps, to see how keen they all were to look at their neighbour’s maps as well as their own.
This was because the farmers realised that their opportunity to impact on the salt issues of their property was almost entirely dependant on whether their upstream neighbour was also prepared to manage their problem at the same time.
Also, they felt under pressure from their downstream neighbour to minimise the amount of salt coming from their property. The consequence of this was they all got together quickly to discuss and decide on community targets for salt management to minimise the amounts supplied to the rest of the catchment from their properties.