I found what appears to be a much more scholarly work on water erosion
at the Sphinx.
The following is the link and some excerps;
http://www.hallofmaat.com/modules.php?name...icle&sid=93"With regard to the location of the Sphinx, the fact that the degradation of the Sphinx enclosure is more intense in the west and, moreover, is restricted to the walls of the enclosure is highly significant.
Although arid conditions dominated during the dynastic period of Egyptian history, wetter periods are known to have been experienced up until as late as the end of the 5th Dynasty (OC approximately 2350 BC). [26] So, the rainy conditions of 5000 to 7000 BC, to which Schoch attributed the degradation of the Sphinx, were separated from the later arid conditions by a transitional phase which, between the Predynastic period and the end of the 5th Dynasty, was characterised by an increasingly arid climate interrupted by occasional, probably heavy, seasonal rains.
The Giza necropolis sits on a gently sloping limestone plateau, which falls from its highest point in the west (beyond the pyramid of Khafre) for a distance of over one and a half kilometres before reaching the former limit of Nile inundation (a short distance east of the Sphinx). With limited vegetation or sub-soil cover, sporadic heavy rainfall would have quickly saturated the fine grained limestones which form the surface of the plateau. Any excess water, unable to infiltrate through the saturated surface, would have been shed downslope as run-off. Although these rain-storms would have been of short duration, the momentum gained by run-off across an extensive catchment (such as that at Giza) must have produced surface flows capable of significant erosion.
The presence of a small wadi to the north of the Sphinx (as already discussed above) suggests that the area originally lay within part of the natural drainage system of the Giza plateau. This natural drainage system may actually have been modified by the excavation of the Sphinx but the extent of any such modification cannot be assessed with any certainty. However, the important issue is that the eastward sloping topography of the site, together with the orientation of the Sphinx enclosure and any effect the excavation of the Sphinx may have had on the local surface hydrology, is likely to have led to the discharge of run-off into the west part of the Sphinx enclosure, eroding the limestone along the exposed western enclosure walls and selectively exploiting any joints exposed along the cut face.
This rainfall run-off model is fully consistent with the distribution of the degradation which is present within the Sphinx enclosure. Not only would rainfall run-off lead to more intense degradation in the western part of the Sphinx enclosure but the less intense degradation elsewhere is also explained. Comparatively little run-off will have discharged over the exposed faces in the east of the enclosure and the body of the Sphinx generated little run-off itself as it was isolated from the plateau by the surrounding excavation of the Sphinx enclosure.
The influence of water at Giza
So, the more intense degradation of the western walls of the Sphinx enclosure can be readily explained by the erosive potential of rainfall run-off. However, although erosion by run-off appears to offer the most likely explanation for observed features, it is important to give consideration to other processes in order to establish whether the degradation of the Sphinx enclosure could, perhaps, be explained in some other way.
Having already identified the problems associated with the wet sand hypothesis, I considered if there were any means by which chemical weathering and exfoliation may have led to the pattern of degradation which could be observed. The effects of chemical weathering could be modified in three ways:
(1) By certain exposures being protected from degradation by, for example, accumulations of wind blown sand. Under such a scenario, unprotected areas would be more heavily degraded;
(2) By variations in the intensity of chemical weathering itself, brought about by factors such as aspect (i.e. the orientation of an exposure with respect to the sun);
(3) By the effect of sand abrasion.
Given the dominant northerly wind direction and the easterly slope of the plateau, dry, windblown sand is most likely to start filling the Sphinx enclosure from the north and west, with the covering of windblown sand protecting the underlying exposures. The exposures which were the first to be covered with sand are therefore those in the west of the enclosure - which happen to be the most heavily degraded."
This dovetails with the flow of water from above at the site of the pyramids.
The water flowed naturally around a hard spot in the rock which was later to
become The Sphinx. The top of this rock was hard limestone which sat on softer
material which would become the neck. The causeway followed the original river
bed and deviated only enough to circumvent The Sphinx which was likely already
carved and somewhat old. Water flowed normally around this structure before and
after completion of the pyramids. The enclosure was heavily eroded by a steady
stream of water. This would flow only from July to September and only when it was
in excess.
Weathering is nearly non-existent on the east side of the enclosure because there
would have been a wide dam to retain water in this area for effect. The dam would
have taken all the wear.