Looks fun, nice pics, I live in Thailand, but I'm on the banks of the mighty Mekong river in Mukdahan, a long way from Chiang Mai, Bamboo rafts wouldn't work on the Mekong, it's far to big , deep and fast... have a look at some of my posts if you want.....
RE: Crazy bamboo rafting in Chiang Mai, Thailand - My travel diary