I'm sure that if given permission, they could pull a set of plans out of the drawer to pipe the entire Columbia river down there.
They had plans all done up to drain the entire Columbia around twenty years ago.
Cal & Oregon were in talks way back in the 1960's to divert
SOME NOT
ALL of the Columbia water.
There's even been proposals to pipe water from Alaska.
Not that it will happen, but it can be done in a way with minimal disruption of flow from the Columbia. I doubt the outflow to the ocean would result in no more than a inch or two of depth loss.
Here's a short article dated 2008
http://www.oregonlive.com/news/oregonian/index.ssf?/base/news/1218263105159940.xml&coll=7
