HYDROGEOLOGIC ERROR ANALYSIS WITH APPLICATION TO THE HIGH PLAINS AQUIFER

The analysis of errors in hydrogeologic data using GIS methods is conducted and the effects of these errors on groundwater analyses evaluated. Definitions, nomenclature, and methodology for the systematic identification and quantification of hydrogeologic errors are developed. A distinction is defined between relative error, where the error value is dependent on the magnitude of the variable measurement, and absolute error, where the error value is independent of the magnitude of the variable measurement. Error propagation equations based on Taylor-series analysis are developed for groundwater flow equations, including the Darcy and Theis equations, and statistical groundwater level and statistical groundwater depletion regression equations. The resulting propagation equations are implemented using Mathematica® for quantification and display. GIS-based techniques for quantifying errors are illustrated using data from a High Plains (Ogallala) aquifer study area in northwestern Kansas. Quantified measurement and interpolation errors include depth to water, water level elevation, hydraulic conductivity, storage coefficient, well location, aquifer top and bottom, saturated thickness, recharge rates, well pumping rates, and streamflow. The effects of these errors on standard hydrogeologic flow analyses and numerical modeling efforts are illustrated.