HR: 14:40h
AN: H23I-05    [Abstracts]
TI: Drawdown Estimation and Quantification of Error
AU: * Halford, K J
EM: khalford@usgs.gov
AF: US Geological Survey, Placer Hall 6000 J St., Sacramento, CA 95819
AB: Drawdowns during aquifer tests can be obscured by barometric pressure changes, tides, regional pumping, and recharge events in the water-level record. These natural and man-induced stresses can create water-level fluctuations that must be removed from observed water levels prior to accurately estimate pumping-induced drawdowns. Simple models have been developed to estimate non-pumping water-levels during aquifer tests. Together these models produce what is referred to here as the synthetic water level. The synthetic water level is the sum of individual time-series models of barometric pressure, tidal potential, or background water levels. The amplitude and phase of each time series are adjusted so that synthetic water levels match measured water levels during periods unaffected by an aquifer test. Differences between synthetic and measured water levels are minimized with a sum-of-squares objective function in an Excel spreadsheet. The root-mean-square errors during fitting and prediction periods were compared multiple times at four geographically diverse sites. Prediction error equaled fitting error when fitting periods were greater than or equal to four times prediction periods.
DE: 1829 Groundwater hydrology
DE: 1872 Time series analysis (3270, 4277, 4475)
DE: 1873 Uncertainty assessment (3275)
DE: 1894 Instruments and techniques: modeling
SC: Hydrology [H]
MN: Fall Meeting 2005