It takes two days of backpacking, roping over an overhanging cliff and then wading knee deep into water deep inside a cave to get close to the mouth of Roaring Springs inside the Grand Canyon.
Casey Jones, a master’s student at Northern Arizona University, and Abe Springer, a hydrogeologist at the university, have completed the trek multiple times to measure how fast the water in the cave channel is flowing, a process that involves standing for more than half an hour in the 50-degree water to collect velocity data.
The variations in the spring’s flow reveal what scientists can’t see: the characteristics of the source aquifer, located thousands of feet below the ground, and how precipitation and snowmelt at the surface travel through groundwater systems to feed canyon springs and seeps.
The data gathering is one of several components of a large-scale study being undertaken by researchers at Grand Canyon National Park and Northern Arizona University to study how water makes its way through faults, fractures, caves and porous rock deep underground to eventually emerge as springs and seeps along the canyon’s walls. The work is focused on the North Rim, which is the source of most major springs in the park.
While the Colorado River is, for many, the defining water feature of the Grand Canyon, the aquifer-fed springs and seeps are equally important to life in the canyon.
Springs support more species than any of the canyon’s other ecosystems and nearly one-tenth of the 1,800 plant species in the Grand Canyon are found only at springs. Roaring Springs on the North Rim is the sole water source for Grand Canyon National Park.
But park managers are still largely in the dark about the underground, geologic plumbing that feeds those seeps and springs -- how water travels underground, how long it stays there and how much of it is stored in the Coconino and Redwall-Muav aquifers.
The picture is becoming clearer thanks to the researchers’ recent work.
Jones’ studies of the deeper Redwall-Muav aquifer have found that water moves at different speeds through the Grand Canyon-area groundwater system. Some water seeps into the tiny pores in the limestone aquifer and moves slowly through system. Other times, water from monsoon rainstorms or heavy snowmelt rapidly streams through underground conduits like caves and faults and ends up in springwater in as little as a few days, Jones said. People might assume that because these rocks are thousands of feet deep, it must take millions of years for water to travel through them, but this study shows that’s not the case, Springer said.
What that means is if a gasoline truck flipped over and spilled gasoline someplace on the North Rim, under certain conditions the pollution could make way into springwater in just a few days, he said.
Once water on the surface gets into the groundwater system, other members of the research team found it can travel to some surprising places. Grand Canyon National Park hydrologist Ben Tobin used food-grade dyes placed into snow at sinkholes on Kaibab Plateau to trace where the water went when it melted. Charcoal packets at springs and seeps in the canyon registered where the dye traveled and how long it took to make it there. In one instance, a large pulse of snowmelt carried the dye through almost 6,500 vertical feet of rock and 25 miles horizontally. In another case, two different types of dyes injected into separate sinkholes associated with the same fault were detected at completely different water sources in the canyon.
Knowing which sinkholes connect to which groundwater sources is especially important for Grand Canyon National Park officials, so they can properly manage and protect the surface areas that contributes water to the drinking water source of Roaring Springs, Springer said.
Researchers are still trying to figure out those source sinkholes, he said.
Jones also looked at what type of precipitation acts as the baseflow for Roaring Springs and found that snowmelt is the main contributor because it seeps slowly into the ground and recharges the aquifer instead of rushing quickly through underground conduits. That fact could be concerning for the spring’s flows in the future as more precipitation is expected to fall as rain instead of snow in the coming years due to climate change, Jones said.
Another component of the groundwater system is the porosity of the limestone that makes up the Redwall-Muav aquifer. Jones compared that porosity to similar aquifers around the world and found it to be much lower, which means the rock is storing less water than previously thought, Springer said.
He pointed out that the findings of the research have applications beyond the Grand Canyon because groundwater recharge is similar across the entire Colorado Plateau.
“It’s directly transferable to this whole region,” he said.
Emery Cowan can be reached at (928) 556-2250 or email@example.com
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