I paddle the Ark a lot, but you should contact Larry Rice in BV. He cboats the Ark probably more than anybody. A fair number of Front Rangers get there in the summer, too. I live a couple of hours south of BV.
There's a bunch of us oc-1 and c-1ers from the front range that head over to the Ark each summer on random weekends - usually after peak runoff.
And like cadster says, find Larry. He is right in BV and paddles the Ark all the time.
Park you rig in downtown BV and wait for him to stop and talk to you. That's how i met him when I was learning to canoe in Colorado. Chris Kelly is there in the summer, too. Another great open boater who was nice enough to go out with me when I was stumbling around in that blasted Paradigm.