Gravel will work if the footing is solid but since this one is mud, the gravel will squeeze out and down. Eternity will be shortlived. Move the blocks before they topple(not that far down the road) because they are hard to pick up out ot muck. Then dig your footing. Make a barrier of plywood so that it taller then the water level. Try to make it as waterproof as possible. Then clean as much mud as you can from your trench. Then pour 8" of concrete and you will be good to go. Good luck.
