A borehole survey is pretty empirical, my dude. It's basic geoarchaeology and used heavily in geoscience and engineering. Most responsibile construction projects use them and you know they're not spending money on things that aren't tried and true. It is how I hunt extinct rivers and other watercourses in other parts of the world. They don't just go poof. Plus the palaeo record would show what lived in and around it.

Archaeology works backwards from the known to the unknown. We bring our own biases to science, so that's why we have to build our case for theories brick by brick, to avoid those and check ourselves. He's welcome to provide proof, but so far he hasn't had any that fits the data. We welcome these ideas when there's proof. Rivers with the ability to carve rock like that leave large footprints. Multiple people's careers would be made if there was such evidence, but there isn't. Large discoveries are good for archaeology and bring funding. Science with a capital S isn't perfect, but the data disproves it, if anything.