Without buttressing and making a bow shape, a 10ft tall block wall can be blown over by a strong wind, let alone water. The rebar would just assure it would all fall over together. I am thinking there would be a lot more to it than a simple line of block with rebar to hold back water.
I would imagine it being cheaper and easier to dozer up a proper dam/berm, then line the basin with impermeable material. It would probably look better too.
