With the flood and collapse cases, isn't it generally a pre-requisite that the defendant adopted or continued the nuisance (knew or should have known, ie committed what would amount to a breach of the standard of care expected of a reasonable landowner)?  That seems to be the requirement with the trees cases that I have seen (see eg, Caminer (HL)). 

It seems strange to me that if something falls over without any fault on my part (ie through the operation of invisible and unknowable natural forces) and without any intention on my part that it fall on your property, that I am strictly liable for that eventuality.  My gut reaction is that these are generally cases of negligence in disguise (nuisance is the label and negligence the normative basis for liability) and hence only a state of affairs is a true nuisance.

Sincerely,

-- 
Jason Neyers
Cassels Brock LLP Faculty Fellow in Contract Law
Associate Professor of Law
Faculty of Law
Western University
N6A 3K7
(519) 661-2111 x. 88435