In the last half of the 20th century, a large number of new subdivisions were platted out in the deserts of Arizona, road grids were graded, lots were sold, and, occasionally, a few houses were built.

In many of these developments, the inadequacy of a water supply doomed their completion and contributed, with other water supply issues, to the development of the Groundwater Management Act (GMA) of 1980 to prevent such things from happening in the future, at least for the next 100 years.

By early in the 21st century, many sophisticated computer-operated models of groundwater flow had become available. These models provided an opportunity to project far into the future, but as long as an aquifer didn’t go dry until the 101st year, the GMA could not stop a development.

This allowed developers to focus on the details of the hydrologic system in a basin and thus draw attention away from the fundamental issue of sustainability.

A large development has been authorized in the San Pedro Basin near Benson, despite the fact that there is no sustainable groundwater resource to satisfy its residents, let alone the lake(s) and golf course promised by the developer.

Ground water is sustained by the infiltration of rain and snowmelt into the aquifer, and whatever is not used by vegetation along the river corridor or the existing wells, discharges to the San Pedro River as base flow.

The USGS stream gauge in the gorge below Benson has not recorded any base flow in years, which means that there is no additional groundwater being recharged in the Benson sub-basin over the amounts pumped by wells that presently tap the groundwater supply in that basin and the water used by vegetation in the river corridor.

So what will happen? The developers would like to build out the development as quickly as possible so they can take their profits and leave for other ventures before the wells start going dry, as they surely will.

Unfortunately, it will not be only the wells that go dry, as the existing wells in the basin all draw their water from the same unconsolidated aquifer system. But, not to worry, the government will step in to give some help to folks in the Benson area, and our tax money will support that.

Who would have suspected that developers could turn our tax money into their profits?

As district chief for the Arizona District, USGS Water Resources Division, Robert Mac Nish oversaw all data and interpretive project activities in the state. From 1993 to 2001 he was co-director of the Arizona Research Laboratory for Riparian Studies and oversaw and/or advised graduate students working on theses and dissertations on hydrology in the San Pedro River basin.