ENID, Okla. — As rain falls over Enid on a cold day in April, it’s hard to concentrate on worries about surface moisture, but way below ground the story is a little drier, and the trend in available water supply in northern Oklahoma aquifers is decline.
Source of water
Enid was built atop its own water source: Enid Isolated Terrace (EIT), a roughly 80-square-mile aquifer below central Garfield County.
The city has long since outgrown the capacity of this aquifer and now relies predominantly on water pumped from wells fed by Cimarron Alluvial Aquifer.
Noel Osborn, a hydrologist with U.S. Geological Survey Oklahoma Water Science Center, told the Enid News & Eagle last summer both aquifers were formed by ancient rivers.
“They’re both related to streams and river deposits,” Osborn said of Enid’s two major water sources. “Rivers and streams carry sediment with them, and over thousands and millions of years you can accumulate fairly thick deposits of sands, gravels and clays that can hold water.”
Water, from rainfall, river flow and irrigation, seeps down through the soil into this permeable layer — the aquifer — where it is stored.
Osborn said Enid Isolated Terrace is so-named because it, at some point in ancient history, became cut off from the river that deposited its permeable layer of rock, sand and clay. She said the Enid aquifer likely once was connected to the Cimarron aquifer or Salt Fork of the Arkansas River to the north, or possibly both.
Osborn said the EIT has much less capacity than the Cimarron for two reasons: it is much smaller in area, allowing for less capture of precipitation from the surface, and the layer of permeable rock and soil in the EIT is much thinner than that in the Cimarron aquifer.
Osborn said the “saturated thickness” of an aquifer is a major factor in its water storage capacity. The EIT is little more than 17 feet in thickness, while the Cimarron aquifer ranges as thick as 110 feet and averages a thickness of 28 feet.
That greater thickness, paired with the Cimarron aquifer’s much larger area, stretching from Woods County to the southeast across Major and Kingfisher counties and into Logan County, gives the Cimarron much greater storage capacity: 4.47 million acre-feet in the Cimarron compared to 470,000 acre-feet in the EIT, according to USGS surveys from the 1980s.
According to OWRB records, most of the city’s wells in the EIT, excluding private wells and rural water districts, date back to the 1950s. Newer wells, beginning in the 1970s, are on the Cimarron, clustered west of Drummond, in the Ames area, near Ringwood and west of Cleo Springs, all in Major and Woods counties.
According to OWRB figures, 87 percent of Enid’s permitted water production now comes from the Cimarron.