This big structure in the middle of nowhere is part of the eyre peninsula water supply system. It is along the polda basin water supply pipeline, which thravels from the polda basin pumping station, 30 or so km's to the west, and on to the Lock pumpung station, about 6km to the east. From there it joins the Pt. Lincoln to Thevenard pipeline, which roughly travels along much of the length of the Tod Hwy. This water supply system is the lifeblood of the Peninsula's farming and town communities, which without, not much settlement, agriculture, etc. would exist here.
From what I can gather, I think this may be some sort of pressure relief valve, something similar to that gadget on top of a pressure cooker!!!