There's a bit of a misunderstanding about hydrostatic pressure here. Phillip is looking at an outlet. The inlet is (somewhere) at a higher elevation. Between the higher elevation and his location the water <might> be confined in a lower elevation layer or tunnel. My money is on the plateau being the ultimate source of the water though. How large is the plateau? 200m is a huge amount of head and a whole lot of water could be stored in 200m lens of karst/limestone.

