Aug 07, 2019

Rainfall Critical to San Pedro River Groundwater Levels

Environmentalists argue WOTUS regulations & business developments will run the river dry

Environmentalists argue WOTUS regulations & business developments will run the river dry

In Sierra Vista, Ariz., despite low levels in the San Pedro River, cottonwood trees are unaffected at the height of the dry season in June. 

Summer monsoons raised groundwater in the area approximately 12 ft , which increased river levels and keeps the trees neighboring the river green and lively, according to E&E News. The river spans 170 miles, flowing north from Cananea in Mexico's Sonora province before then flowing entirely into Arizona's Gila River. According to E&E News, the San Pedro River “is one of the last free-flowing rivers in the Southwest.”

"The river is even wider than the roads here," said Chris McVie, a board member for A Coalition for Sonoran Desert Protection, according to E&E News

McVie flew in a helicopter above the river, 12,000 ft above to exact, to show the importance of the rain-fed flows during Arizona’s dry season as rainfall is critical in overcoming groundwater depletion concerns. According to E&E News, the coalition and other environmental groups argue the Waters of the U.S. (WOTUS) proposal eliminates Clean Water Act protections for waterways, and that this ultimately would hinder bodies of water like the San Pedro River and others that only flow after rainfall. 

The San Pedro River overcame many challenges, including the WOTUS regulatory change. According to E&E News, homebuilders in the area harness the river’s groundwater to serve residential and business developments. Meanwhile, environmentalists like McVie fear the river could become completely dry without careful thought of the river’s water use.

"WOTUS really makes me want to shake somebody," McVie said to E&E News. "What's important is it's still a living river, and a salvageable one, if people get their heads out of a very dark place and start treating it like the resource that it is."

Another threat to the river is persistent groundwater pumping that has threatened base flow for decades. According to E&E News, the pumping creates a “cone of depression” which sucks water from other areas of the aquifer. A new pump can create a new cone of depression, or expand existing ones, lowering groundwater tables.