The only way that a dry stream bed will never sprout any weeds - regardless of location - is to line it with concrete. And that pretty much defeats the purpose of using it as a drainage system in times of heavy rains.

My contractor lines the bed with a thick layer of coarse playground sand before laying the weed fabric....one of the few valid uses for this material :-)) Then scatter the stones, using a variety of sizes, with larger stones more to the side and mostly smaller river rock to fill in.

This is not maintenance free. You will need to routinely clear out any leaves, debris and dirt from the stream bed and keep on top of any weeds that may sprout up. But it will generate fewer weeds than any planted areas.