It's still the same height at the moment but Deanom's theory's have placed a bit of light on this problem.
The run off from the driveway going to the abelflex which would divert the water to the right hand corner and making the grass greener.
Also my storm water outlet is about 2m from that right hand corner so i suspect there might be a leak around that area.....but is down hill?:?
I will monitor it when it hasnt rained for awhile and see if any reduction in height occurs. I have a feeling it wont drop unless something heavy drives on it. :U