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To Keep Desert Rivers Flowing, Protect Groundwater

People who don’t live here in the desert southwest are often surprised to hear about our rivers. The common vision of a desert is a place without water. But in fact, in a desert—where water is scarce—its importance is elevated, its beauty and centrality made perfectly clear. As clear, you could even say, as a deep blue pool in the dry heat of a southwestern canyon.

My home state of Arizona is spectacular. It’s the third most biologically diverse state in the lower 48, second only to California and Texas—making it the most biologically diverse state without a coastline. The diversity of landscapes and lifeforms comes in part from the huge range of topography and elevations—from near sea level in Yuma to more than 12,000 feet at the top of the San Francisco Peaks. It is also made possible by the network of desert rivers, streams, and springs that crisscross and dot the landscape. Rivers, streams, and springs create the small and large oases of green that are the hub of the state’s abundant life.

The desert’s waters have of course also been the hub of and central to human life—providing shade and cooling, solace and inspiration, not to mention drinking water and water to feed the rest of our human endeavors.

But, as I wrote about in a previous post, the continued flow of these waterways is not guaranteed, and in fact once-iconic springs and significant stretches of river in the state are now dry—because we have not built a structure to protect them.

Some people who care about Arizona’s rivers and streams ask me: what’s the single most important thing we can do to protect them? And of course any answer to the question will be a simplification, because problems are always complex and often require a suite of approaches. The social changed needed to get to solutions certainly does.

But if we could change one thing in order to protect the state’s rivers, I would argue with passion and conviction that it is to protect Arizona’s groundwater.

Why? The year-round flow in Arizona’s springs, streams, and rivers comes from groundwater.

Flow in rivers and streams in general can also come from rain and snow-melt. Mountain streams in wetter states, for example, may be fed by snowmelt all through the summer, and further swell in their banks when rain falls on the lands they drain.

But in Arizona and the rest of the desert southwest, rain is scarce, and snow even more so. At some times of year, Arizona rivers and streams carry snowmelt down from the high country. During monsoon season they can surge with floodwaters. But during parts of the year when rain and snow are rare (think mid-June in Arizona), some rivers and streams still flow. Why? Groundwater.

Groundwater moves underground according to subsurface geology, gravity, and pressure gradients. It percolates up in places and creates springs, that can then flow into creeks. It intersects with low points in the land surface and feeds streams. It moves through canyon walls and emerges as a waterfall. Scientists suggest that every river or stream that flows year-round in Arizona is likely fed by groundwater.

(“Base flow” is the name of this year-round portion of a river’s flow that comes from groundwater. It’s the flow you can typically count on even when the rain isn’t falling on our desert lands.)

So groundwater feeds our rivers. But groundwater, in Arizona, is unregulated and unmanaged throughout much of the state. More on this in a future post. But we’re pumping water out of the ground and in many cases not even monitoring, let alone managing, the locations or quantities.

And rivers, streams, and springs feel the effects. We’ve already lost iconic springs and river stretches to groundwater pumping—for example parts of the Santa Cruz River near Tucson; Del Rio Springs, and the headwaters of the Verde River it used to feed; parts of the Gila and San Pedro River, whose flows are diminished from both groundwater pumping and diversion of surface waters; and the Agua Caliente Hot Springs that used to be a tourist attraction and respite in central Arizona before they dried up several decades ago. At least 35% of the Arizona river miles that used to flow freely year-round no longer do.

But we could lose more. One 2007 study identified a set of other Arizona river stretches that could dry up or be substantially degraded from municipal pumping alone, as projected through 2050—in many of our lifetimes—if we don’t do something to change the system.

There are many other good reasons for us to protect our groundwater resources. Groundwater is the drinking supply for much of our state’s population and many cities and towns.

Given how critical groundwater is as a water supply, though, its role in our landscape can sometimes be overlooked. Thus, I tell people: if you care about our state’s magical and remarkable springs, streams, and rivers that are so often at the heart of the places we love: you need to care about groundwater, and how we use, manage, and protect it. To keep rivers flowing… protect groundwater.