You are probably thinking of the controversy that was around a few years ago regarding the age of the Sphinx. Graham Hancock and Robert Bauval's Orion alignment theory suggested that the pyramids and the Sphinx were built in 10,500BC. This was further supported by Robert Schoch's assertion that the Sphinx enclosure showed signs of water erosion which, by their severity suggested a similar date.

This has since been disproven and GH & RB have retracted their theory. The pyramids have been RC dated to around 2,600BC by means of debris found within the mortar. The water erosion around the Sphinx was apparently caused by occasional heavy rain storms which produce severe flash floods on the plateau. The bedrock is soft and marly in places and washes out quite quickly under these circumstances.

The same thing happens in otherwise arid conditions elsewhere. I was surprised when visiting the Dead Sea in Israel that there were storm drains alongside the road. My guide assured me that they do very occassionally get torrential rain and flooding is a major problem due to the thin covering of sand above the bedrock.