Scrapheap Challenge Season 4 Episode 5 White Water Rider ( Air Date 2001-10-07 ) Genre Reality, Action & Adventure category. Overview "The challenge is to build a powered craft to negotiate a stretch of white-water river. The craft must be powerful enough to get up the rapids but also have enough manoeuvrability to avoid treacherous rocks and to make a U-turn at the top of the course. Whoever sets the fastest single time in the course of three heats is the winner.".