"...regarding Stonehenge at Avebury, Wiltshire"

Aerial photography is a wonderful thing [I spend hours each day staring at shapes on photos] but it does cause features to appear as they are not. Yes, it would appear that a river ran across the Avenue, but it doesn't come from anywhere and yet is still powerful enough to create a valley wider than the existing Avon! Chalk downland is also impossible to judge properly because of the amount of chalk on the surface, creating fake highlights, plus any disturbance to the bedrock at any time in the past is almost always recorded by the ploughsoil. So there are remains of sheep-pens, huts, sheds, tracks, gateways, field markings etc etc, all designed in the past 5000 years to bemuse and confuse, all etched into the earth forever.

I think most archaeologists welcome aerial photography as an aid and a guide, but it ceases to become useful once they're on the ground, faced with undulations that are never apparent on a piccie.

Relying on it to reinforce a theory without the fieldwork to back it up is dangerous!