The case study is something that has been directly asked about in many past HSC examinations. In recent years, there has been a more indirect but a 7-8 mark question asked at the end of the core section. Part of the answer needs to discuss salinity in some detail and Wagga Wagga could be used as an example.
The initial act that culminated in Wagga Wagga having a salinity problem was the clearing of vegetation. In balanced systems where there existing salt, but no salinity problems, the amount of water in (recharge from rain) equals the amount of water out. The "out" that water can have in that area is by groundwater entering the the Murrumbidgee River or more importantly, by the removal of water by deep rooted native plants. In doing this, the water table is kept well away from the surface, and any salt that is in the soil remains solid. As a result, it cannot cause any harm.
By removing the vegetation, the balance is tipped so that recharge is greater than removal. Therefore, the water begins to build up in the soil and as the levels move closer to the surface, salt is dissolved.
There have also been additional water inputs into the soil which contributed to the salinity problem. These are:
1. Rubble pits for stormwater runoff from roofs.
2. Planting shallow rooted non-natives and grasses.
By the early 1990's Wagga Wagga council realised that they had to take steps to or face an annual bill of $6 million/year (1995 dollars) to maintain infrastructure damaged by salt.
This rising groundwater was not only damaging buildings and roads but was having other effects on the biotic (living) and abiotic (non-living) parts of the environment. You are expected to know and describe some of these.
They did this in a number of ways:
1. Groundwater pumping
2. Draining waterlogged areas into evaporation basins
3. Tree replanting.
You are also expected to know the scientific reasoning behind this and the success/failures of these strategies.
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