[jaddood]

You don't really need a river to pump hydro up and down. As long as you have some kind of container for the water (usually a dam though not necessarily so,) you can pump any water. The cheapest to pump is probably sea water. I'm not really sure how cheap that would be compared to batteries, but it's still an option.

[pjc50]

To make it cost-effective, you need a height advantage and a "natural" container. The ideal sites are mountaintop lakes. It's a fairly rare topography.

[erikpukinskis]

Could be a dry lake tho, no? Are those rare?