Sphinx water erosion hypothesis - Wikipedia, the free encyclopedia
This second link is a site run by the geologist who first championed the water erosion theory: Robert Schoch.
Robert M. Schoch: The Great Sphinx
There's also a documentary about it narrated by Charleton Hestin called "Mystery of the Sphinx", available on Netflix. It's pretty entertaining for a documentary, with some good evidence at the beginning, but degenerates into wild alien theories toward the end.
Basically, there appears to be good agreement among many geologists that the erosion pattern on the walls surrounding the Sphinx would only make sense if they were the result of sustained, heavy rainfall, which would have been unlikely to have occurred during the time since Egyptologists believe the Sphinx to have been constructed, but quite possible at a much earlier time, but that would place its original construction in pre-history.
Basically, instead of being yet another grand construction project during the high point of Egypt's Old Kingdom, it would be an anomaly similar to Stone Henge, possibly created by a more primitive culture, or at least one that didn't last.