QUESTION: AFTER HEAVY RAINFALL IN CAPE TOWN, APRIL 2010, HUNDREDS OF EARTHWORMS SURFACED AND HEADED STRAIGHT FOR OUR SWIMMING POOL - JUST TO DROWN. MY QUESTION IS, WHY DID THEY SPECIFICALLY HEAD FOR THE SWIMMING POOL AND IS THERE ANY EARTHWORMS LEFT IN MY GROUND OR HAVE THEY ALL DROWNED?

All of the reasons that earthworms surface are not actually known, however some reasons like adding chemicals have been known to make them emerge. If there was a recent application of chemicals to their habitat, this could be both fertilizers and pesticides this could irritate their skin and cause them to surface. It could be that the large amount of rain enabled past chemical applications to your lawn/beds to percolate deeper onto the soil than previously. It is however a natural phenomenon, that earthworms surface, so this is not necessarily what has happened here. The fact that there are so many worms in you pool is actually a good sign because this shows how many of them are actually inhabiting your soil. The amount you see in your pool is only a fraction of the total population  that you have in your soil. There is no specific reason they chose the swimming pool. It was maybe just a matter of wrong place at the right time.