A zero-flow reading at Priest Drive is mostly a century-old design choice

The stream gauge on the Salt River at Priest Drive, near where the Verde River joins in below Scottsdale, read zero cubic feet per second on August 26.¹ It's tempting to read that number as this summer's drought finally squeezing the last water out of the channel, and the numbers backing that read are real: Maricopa County is sitting at nearly 80 percent severe drought coverage, and Phoenix has been running more than five degrees above normal for daily highs.^2, 3

But the fuller explanation for a dry channel at this exact spot is infrastructure, not weather. This reach sits just below Granite Reef Diversion Dam, where the Salt River Project has for more than a century routed nearly all of the river's natural flow into the Arizona and South canals rather than leaving it in the bed. A USGS reconstruction of the system found this stretch running dry even in comparatively wet years back in the late 1970s. A zero reading at Priest Drive, in other words, is often the river doing exactly what it was engineered to do a hundred years ago; this year's drought and heat are simply added pressure on a channel that was already designed to run empty here most summers.

A separate concern for this same stretch of the Gila/Salt Intermediate Basins is a permitted discharger rather than a diversion structure. MODERN INDUSTIES, INC holds a Clean Water Act discharge permit for this area, and its record is worth tracking precisely because the receiving channel is already this stressed.⁴ A waterway with no assured base flow has far less capacity to dilute or buffer any wastewater discharge than the same channel would in a normal year, so whatever this facility is permitted to release matters more here than it would somewhere with a reliable perennial flow underneath it.