At this point, it's surprising we don't just cut off the flow of existing hydro when we have other sources peaking... e.g. it's what you describe but no need fo

At this point, it's surprising we don't just cut off the flow of existing hydro when we have other sources peaking... e.g. it's what you describe but no need for upward pumping. We do this to some extent, but the reality is we do need to ensure rivers continue to flow for a number of reasons (I guess).