Death of the San Pedro: Not if, but when

  • U.S. Geological Survey workers install a piezometer along the San Pedro River near Palominas. The device helps geologists better understand the interactions between the river and the underlying aquifer

    US Geological Survey
 

Note: this is a sidebar to a main story about the political struggles over protecting the San Pedro River.

New evidence has surfaced that pumping in the Sierra Vista area may already be reducing groundwater flow to the San Pedro River.

Water levels in seven monitoring wells on U.S. Army property have dropped by roughly a half-foot per year since 1995, according to recently released U.S. Army Corps of Engineers data. The wells range from less than one mile to seven miles west of the river, on Fort Huachuca’s property.

The dropping levels, measured from 1995 to 2003, are reducing the rate at which water flows toward the river, says Don Pool, a United States Geological Survey hydrologist in Tucson. If that trend continues, groundwater discharges to the river from the aquifer will eventually decrease, reducing the river’s flow.

But when? "That’s the $64 question," says Mark Anderson, associate Tucson district office chief for the U.S. Geological Survey. So far, officials say they haven’t seen water level declines in 60 to 70 monitoring wells closer to the river.

Anderson says that pumping in the Sierra Vista area, about 16 miles north of Mexico, is probably not yet imperiling the river to the south. The first declines would most likely be felt at the San Pedro Riparian Conservation Area’s lower end, north of the largely abandoned village of Charleston, where the river flows intermittently, he says.

But if the Sierra Vista area’s population doubles as predicted over the next 25 years, pumping could affect the river directly east of town. In that northern end, the water table is a little more than nine feet underground. Some willow trees are already showing signs of stress that could be caused by pumping or drought, says Julie Stromberg, an Arizona State University associate plant ecologist; another three-foot drop could kill many of them. The Arizona Department of Water Resources says that water-level declines have caused the loss of wetland plants and prevented cottonwood seedlings from surviving in parts of the northern end of the river.

The Corps data means the river’s demise is at hand, warns Robin Silver, the Center for Biological Diversity’s board chairman. "We can’t wait around and do more studies," he says. "We now need to control the excessive groundwater pumping."

But Anderson says most aquifers near population centers in the United States are dropping, and "declining water levels are relatively common across the West."

The San Pedro’s flows have been dropping for many decades, according to the survey. An unfinished study, due for publication in six months, found that the river’s summertime minimum flows fell from 50,000 acre-feet to less than 10,000 acre-feet annually between 1910 and 2000. Anderson says it’s not certain why. In addition to groundwater pumping, decreased surface runoff from rainfall and from "return flow" from irrigated farm fields may be causes.

Then there are all those water-sucking trees. Over the past 50 years or so, tree growth has increased along the river, possibly due to the decline of agriculture, removal of livestock and natural downcutting of the river’s channel, Anderson says.

Though the scientific picture is complex, Anderson says that doesn’t mean action isn’t needed to reduce the groundwater pumping deficit. One option for the Sierra Vista area would be to find a basin to pump from that is farther away from the river, he says.

"With pumping, you may not see the effects for years," Anderson says. "It’s just that at some point, the price will be paid."

High Country News Classifieds
  • COPPER STAIN: ASARCO'S LEGACY IN EL PASO
    Tales from scores of ex-employees unearth the human costs of an economy that runs on copper.
  • FEATURES DIRECTOR - HIGH COUNTRY NEWS
    High Country News, an award-winning news organization covering the communities and environment of the Western United States, seeks a Features Director to join our editorial...
  • GENERAL MANAGER
    The Board of UYWCD seeks a new GM to manage operations & to implement our robust strategic plan. Details at www.upperyampawater.com. EOE
  • IN TUCSON, FOR SALE: A BEAUTIFUL, CLASSIC MID-CENTURY MODERN HOME
    designed by architect David Swanson in 1966. Located a block from Saguaro National Forest, yet minutes to Downtown and the UofA campus, 3706 sqft, 6...
  • EXECUTIVE DIRECTOR
    The Friends of the San Juans is seeking a new leader guide our efforts to protect and restore the San Juan Islands and the Salish...
  • 80 ACRES
    straddles North Platte Fishery, Wyoming. Legal access 2 miles off 1-80. Call 720-440-7633.
  • DIRECTOR OF PRODUCT AND MARKETING
    High Country News seeks a Director of Product and Marketing to join our senior team during an exciting chapter of innovation and growth. This individual...
  • OWN A THRIVING MOUNTAIN GUIDE SERVICE.
    Eastern Sierra guide service for sale to person with vision & expertise to take it onwards. Since 1995 with USFS & NPS permits. Ideal for...
  • IMPROVED LOT
    Private road, hillside, views. Well, pad, septic, 99 sq.ft. hut. Dryland permaculture orchard. Wildlife. San Diego--long growing season
  • UNIQUE INVESTMENT OPPORTUNITY
    Profitable off-the-grid business located 2 miles from Glacier National Park. Owner has 6 years operating experience. Seeking investor or partner for business expansion and enhancement....
  • REMOTE SITKA ALASKA FLOAT HOUSE VACATION RENTAL
    Vacation rental located in calm protected waters 8 miles from Sitka, AK via boat with opportunities to fish and view wildlife. Skiff rental also available.
  • EXPERT LAND STEWART
    Available for site conservator, property manager. View resume at http://skills.ojadigital.net.
  • CONSERVATIONIST? IRRIGABLE LAND?
    Stellar seed-saving NGO is available to serious partner. Package must include financial support. Details: http://seeds.ojaidigital.net.
  • CANYONLANDS FIELD INSTITUTE
    Colorado Plateau Natural & Human History Field Seminars. Lodge, river, hiking options. Small groups, guest experts.
  • WESTERN NATIVE SEED
    Specializing in native seeds and seed mixes for western states.
  • CHUCK BURR'S CULTUREQUAKE.COM BLOG
    Change will happen when we see a new way of living. Thinking to save the world.
  • COMING TO TUCSON?
    Popular vacation house, furnished, 2 bed/1 bath, yard, dog-friendly. Lee at [email protected] or 520-791-9246.
  • OJO CALIENTE COMMERCIAL VENTURE
    Outstanding location near the world famous Ojo Caliente Mineral Spring Resort. Classic adobe Mercantile complete w/living quarters, separate 6 unit B&B, metal building and spacious...