February 2012, Issue 57: Editors’ Notes

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We continue our analysis of the Water Resources Development Commission (WRDC) reports and take a closer look at the Little Colorado River Plateau (LCRP) in northern Arizona.

The WRDC certainly should be commended for attempting the monumental task of quantifying how much water Arizona has currently and how much it will need in the future. However, its estimates for the LCRP planning area fail to consider some key hydrogeologic and jurisdictional limitations.

The LCRP covers one-fourth of Arizona and, according to the WRDC statistics, it contains two-thirds of the groundwater stored in the state’s aquifers. In fact, the WRDC numbers indicate that about one-half of Arizona’s groundwater resides in aquifers that underlie the Navajo and Hopi Reservations. Given these numbers, it sounds like the LCRP has the potential to be a “water farm” for thirsty Arizona communities. If so, why then is the City of Flagstaff planning to pipe water 40 miles to maintain its supply? And why has the City of St. Johns moved its wellfield 12 miles to obtain decent quality water? Likewise, why is hauling water a way of life for tens of thousands on the Navajo Nation? In other words, why don’t the WRDC numbers match reality in the LCRP?

In a nutshell, it’s because the WRDC developed these estimates based on the same assumptions it used for southern Arizona basins. Unfortunately, political and hydrological conditions in northern Arizona differ radically from the rest of the state.

For one thing, natural groundwater quality is generally good in most of southern Arizona. Not so in the LCRP. Groundwater in the regional Coconino aquifer is brackish or saline in an area that encompasses about 8,000 square miles (about 30 percent of the planning area). In addition, because so few perennial streams still flow in southern Arizona basins, groundwater withdrawals are less likely to be limited by interactions with surface water. In contrast, the LCRP features many streams, and the ability to pump groundwater may be limited by surface water / groundwater connections in certain areas.

Political realities also limit groundwater availability in the LCRP planning area. According to the WRDC numbers, about 80 percent of the groundwater stored in the LCRP underlies the Navajo and Hopi Reservations or associated Trust land. This water is almost certainly unavailable for non-Indian uses. In addition, a substantial amount of LCRP groundwater is stored beneath National Forest land and, as such, remains generally unavailable for other uses.

Ultimately, planners and regulators will need to take water supply estimates one step further and account for these hydrologic and political realities in the LCRP. After all, groundwater is not truly available if its quality is severely impaired or if the right to use it is in question.

This month’s Editors’ Notes were written by M&A hydrologist Ed McGavock, who presented this information at last week’s Winter Watershed Conference in Show Low. The former Assistant District Chief of the USGS’ Water Resources Divisions in Arizona and Washington, Ed has worked on the Colorado Plateau throughout much of his nearly 50-year career.

Juliet M. McKenna, MS, PG | Taylor D. Shipman, MS | Michele Robertson, PG | Mark H. Myers, MBA