I'd like to have a group of teenagers wandering round their local beach for some sort of school-related reason. (Ideally I'd like them to be in year ten or eleven, but can fudge it down to the end of year nine if that's a more plausible age for this sort of outing.) A geography or science day trip seems like the logical answer, but I'm having trouble figuring out exactly what form that would take.
So, can anyone suggest any sort of activity that might plausibly lead to a group of 14 to 16-year-olds trudging about the local beach on school business? Any kind of help with the logistics would also be extremely useful - i.e., would it likely be an all-day trip or just an afternoon/single lesson, would it be a single class or several together, how many teachers are likely to accompany them? Etc.
I've Googled multiple variations on "year nine/ten" + "geography/science" + "[day] trip" + "coast/beach" without any real success.