there is a very big difference between throwing a competition and making a ski movie. The school would be viewed as endorsing the competition which would encourage participants to push themselves furthering the chance to get hurt,
And finding another senior project is very much an option, I changed my project multiple times last year. I still graduated from high school. For one there are tones of interesting and exciting things out there then skiing, part of the idea of a senior project is to help you explore other ideas out there. Plus it would not come with mother nature deciding if you graduate high school this year or not. But if you are 100% convinced you need to do something related to skiing, my suggestion is ease up on it. Don't do something that is going to need others, you need to be able to make this happen even if no one else goes along with it. A competition is a very difficult thing to put on. For one you need to get competitors. And to Get competitors your going to need prizes, to get prizes your either going to need sponsors or a lot of cash. Plus you would need to get permits for the site you want to hold it at, giving you another insurance loop to jump through. So with that in mind that gives you three places where you need outside cooperation, and if one does not cooperate you get to find out the benefits of the 13th year of public education. All though I would not bother yourself too much with those problems since the odds of your schools insurance giving you the green light on this is probably around 1 out of 1000. So I would defiantly broaden your horizon a little bit when looking for a senior project. unless you want a another year of publicly funded education. Which overall is not a bad option considering all the running start and AP options for College credit.