westwall After the initial investment of providing the reservoirs, they are virtually free of charge. The arability of the land above underground storage is a non-issue. In the case I cited on the Columbia--the land is just not productive. The same cases can be made for any lake/river that runs through a canyon as most desert lakes do. Examples, Lake Powell in Utah, Lake Mead in NV, Lake Shasta in CA, the Snake River gorge in ID/OR, the Columbia River gorge in WA/OR. The Columbia River uses this same technology with Dams providing the drop at numerous points along its run, the largest being Grand Coulee Dam which backs up Lake Roosevelt. That dam alone provides peak energy to 11 western states while also providing irrigation for the entire southeastern portion of WA which would not be farmable. Grand Coulee refers to the natural reservoir that they pump water into for that irrigation. There are numerous ways to use the same flowing water to produce positive results without diminishing the resource.