When I worked at ZDNet as a tech producer, the term "river" meant "flood of new content". I guess CNET uses the same terminology. CNET River is a new perspective on their content. It includes blog posts, videos, photo galleries, and Twitter updates from the staff:
CNET is basically saying that a tweet should receive equal coverage next to blogs and videos. I think this is a breakthrough for journalism world. It will force the old print guys to take another look at micro-blogging as a respectable source for real-time info.