What's the Difference Between "Inverse Condemnation" and a "Regulatory Taking?"

There's an interesting discussion going on over at The Volokh Conspiracy about the recent $37 million inverse condemnation/regulatory takings federal judgment against the City of Half Moon Bay, California.  I wrote about the decision here and here. 

The comments to Professor Somin's post are particularly thought-provoking, especially the ones dealing with whether the decision is an "inverse condemnation" case or a "regulatory takings" case.  On one hand, government causing flooding on private property is a classic inverse condemnation situation; the intrusion of water onto private property is the equivalent of the government taking a flowage easement, so it is required to pay fair value for it.  That's what happened in the Half Moon Bay case.  On the other hand, the "wipeout" of economically beneficial uses and a "physical invasion" are two per se categories of regulatory takings, both of which also occurred in the case. 

So the case is somewhat of a hybrid, although the difference is mostly academic and is really a question of doctrinal neatness, not something that requires a different analysis or result.  I'm going to come down on the side of "inverse condemnation," since the flooding was not the result of government regulation, and because the remedy sought was just compensation.  It just seems like more of an inverse condemnation case than a classic regulatory takings case.

In those regulatory takings cases involving physical invasions, the property owners challenged a regulation or government actions that would have allowed physical trespass.  See, e.g., Kaiser Aetna v. United States, 444 U.S. 164 (1979) (federal agency informed property owner that it could not exclude the public from a navigable marina); Loretto v. Teleprompter Manhattan CATV Corp., 458 U.S. 419 (1982) (local ordinance required property owners to allow installation of cable TV boxes on their buildings); Nollan v. California Coastal Comm'n, 483 U.S. 825 (1987) (agency required landowner to dedicate public easement as a condition of development approvals). 

In those cases, the property owners did not seek just compensation, only invalidation of the unconstitutional regulation.  In the Half Moon Bay case, the property owner did not challenge the "wetlands" regulations that wiped out the value of the property, but sought just compensation since the government had de facto taken her land.