Adjustment of Parameters to Improve the Calibration of the Og-n Model of the Ogallala Aquifer, Panhandle Water Planning Area

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This study involved adjusting parameters within a model of the Ogallala aquifer in the northern part of the Texas Panhandle and adjacent parts of New Mexico, Oklahoma, and Kansas. The model, known as the "Ogll-n" GAM (Groundwater Availability Model) or Panhandle Water Planning Area (PWPA) model, was developed in 2000, updated in 2001 for the Panhandle Water Planning Group, and is one of the GAM models adopted by the Texas Water Development Board (TWDB). Major adjustments included:

  • Assigning elevation of the base of the Ogallala aquifer to selected model cells,
  • Applying recharge rates to parts of the aquifer in the model based on soil properties, and
  • Modifying parameters of the MODFLOW Drain and GHB (general head boundary) packages used to simulate the flow of groundwater at the edge of the aquifer.

The steady-state (predevelopment) model error (RMSE or root mean square error) was reduced by more than 3 feet to 32 feet, which is less than 2 percent of the change in hydraulic head in monitoring wells across the model area. The RMSE error in all counties was lowered to less than 10 percent. For example, the RMSE error for Roberts County was reduced from about 26 to 22 feet, which is less than 5 percent of the hydraulic-head change across the county. The transient model RMSE error was reduced by about 6 feet to 53 feet, which is about 2 percent of the hydraulic-head change across the model area. For instance, the transient-model RMSE for Roberts County was reduced from 51 to 45 feet, which is about 6 percent of hydraulic-head change across the county. The transient-model RMSE for 10 of the 17 counties with monitoring well data is less than 10 percent. The largest RMSE (17 percent) was for Randall County where model-edge boundary conditions highly impact simulation results.


Data for this report is available at the Texas Data Repository:

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