I’m looking forward to Requiem for the Santa Cruz: An Environmental History of an Arizona River, a forthcoming University of Arizona Press book by Robert Webb, Julio Betancourt and colleagues. While we spend a lot of time talking about how to return water to rivers in the arid southwestern United States, this group of authors is entertaining a more subtle point – it’s not just about the water flowing in the river, it’s about the groundwater beneath:
In prehistoric times, the Santa Cruz River in what is now southern Arizona saw many ebbs, flows, and floods. It flowed on the surface, meandered across the floodplain, and occasionally carved deep channels or arroyos into valley fill. Groundwater was never far from the surface, in places outcropping to feed marshlands or cienegas. In these wet places, arroyos would heal quickly as the river channel revegetated, the thriving vegetation trapped sediment, and the channel refilled. As readers of Requiem for the Santa Cruz learn, these aridland geomorphic processes also took place in the valley as Tucson grew from mud-walled village to modern metropolis, with one exception: historical water development and channel changes proceeded hand in glove, each taking turns reacting to the other, eventually lowering the water table and killing a unique habitat that can no longer recover or be restored. (emphasis added)
Thus, when a river runs low, a shallow water table still leaves refugia, muddy holes that stay wet even as the flow in the river itself dries. As we pump down our aquifers, we lose that, even as environmental restoration efforts focus on adding more flow to the rivers themselves.