I'm at work downtown, and we're putting our disaster recovery plan into action with some temporary work locations. And for people that just work downtown, that's fine.
But people who live near downtown, or in other areas affected by the flooding river, need help. Serve the City has a page dedicated to emergency flood assistance. I think they are coordinating with Linn County Emergency Management. It sounds like the needs are constantly changing, so check the emergency flood assistance page and call in.
Also, check Erin's post below or the various news outlets (KCRG, Gazette, etc) for more ways to serve.