Jelly,
The big problem of landing on a beach is the state of the sand, when damp sand (ie tide gone out, or comming in)is subject to vibration such as the vibes put thru the skids when the engine is running up or down you can get a situation know as Liquifaction(spelling) its when the water level is forced up to the surface, at that point you could get uneven sink rates or even one skid well stuck in.
dry sand has already been discussed, so beware !......I was always told never land on a tidal beach!
Peter R-B