In this pic, you'll see a tag line tied to the climber; some advice here is not to put the climber on a belay and otherwise make sure the climber can release away from the tag line if they need to.
Swift water responders usually have a knife at their chest to cut away anything that snags; and a helmet, you won't last long in this creek during a strong flow without one.
Anyway, just some advice. Any climber would think when they are on belay, they are protected. In a swift-water case, you could actually be setting yourself up to be more in danger.
(P.S. -- I'd take a single solid tyrol over two marginally installed lines any day; it's all in the anchor rigs that it matters, not the lines. Though, I will also use a tag, but to help bring someone across quicker.)