you also have to remember the water table will be pretty high right next to the creek, digging a hole in the sand will just make a tiny pond, and if you put a bucket in there you would have even more draining problems, because the dirt will constantly wick water up from the surrounding sand, causeing root rot. sand could work, but you would need to fert it all the time, as the nutrients wont stay in the sand long.your best bet would be to step a few yards back, where the land is a few feet higher and the soil not as sandy. the ground will still stay pretty moist but the soil will hold better.