SIMULATING EFFECTS OF DROUGHT ON WATER RESOURCES OF THE BEAVER-NORTH CANADIAN ALLUVIAL AQUIFER, NORTHWEST OKLAHOMA

The Beaver-North Canadian alluvial aquifer is an unconfined surficial aquifer consisting of sand and gravel with beds of silt and clay. The aquifer occupies the Beaver and North Canadian River valleys and the section from the Oklahoma panhandle to the western edge of Oklahoma City was studied (approximately 175 miles) to describe the hydrogeology and simulate the groundwater system using numerical groundwater-flow models. The Bear-North Canadian River and Canton Lake, two water sources for Oklahoma City, are located on the alluvial aquifer.

The aquifer was divided into two “reaches”. Reach 1 was to the northwest and Reach 2 to the southeast. A transient simulation was calibrated to head measurements for the period 1980-2011 for both reaches. The primary inflow was recharge as a portion of precipitation and discharge was to plants and streams. Recharge was estimated to be much greater than base flow.

A hypothetical drought was simulated by decreasing recharge in the models by 75 percent for an arbitrary 10-year period from 1994 to 2004. All other model flows were not changed during the drought. The effects of the drought were assessed by comparing simulated streamflow and lake storage of the unmodified simulations with the drought simulations. In Reach 1 Canton Lake storage decreased by as much as 83 percent during the drought and did not fully recover by the end of the simulation in 2011. Mean streamflow at the Seiling streamgage decreased by 50 percent and took three to four years to recover. In Reach 2, streamflow decreased by approximately 60 percent at the Yukon, Okla. Streamflow-gaging station during the simulated drought and at the end of the model (2011) run streamflow was still reduced by about 15 percent. In Reach 2 as much as 45 percent of streamflow was water released from Canton Lake, and during a drought when storage is low releases may be decreased. Thus, the effects of drought on Reach 2 due to decreased base flow alone may have been underestimated.