Well I finished my irrigation drainage system yesterday and it got an unintentional stress test. I'd re-assembled the water timer and manifold and forgotten to include the pressure regulator which meant that there was a LOT more water going through the irrigation system than normal.

Fortunately the new drain system worked flawlessly and is not flooding my next door neighbours driveway anymore. You can't even see where the work has been done as a frame and net supports three slabs and surrounding gravel over the drains.

Just goes to show.. when installing an irrigation system ALWAYS make sure your soil is either free draining or if not (like my thick clay) to work out the lowest point and then run some sort of drainaway system to your main drains.