MODOPTIM: A general optimization program for ground-water flow model calibration and ground-water management with MODFLOW

Potential effects of groundwater pumping on water levels, phreatophytes, and spring discharges in Spring and Snake Valleys, White Pine County, Nevada, and adjacent areas in Nevada and Utah

“…Water-level declines during the 2000-03 irrigation seasons were analyzed in Snake Valley because crops had been inventoried and drought conditions existed during this period. Hydraulic properties were estimated by minimizing a weighted sumof-squares objective function that compared simulated and measured drawdowns (Halford, 2006). Seasonal drawdowns from spatially distributed groundwater pumping were simulated with a three-dimensional, MODFLOW model.…”

Tabulated Transmissivity and Storage Properties of the Floridan Aquifer System in Florida and Parts of Georgia, South Carolina, and Alabama

“…Walton (2007) recommends analysis of multi-well aquifer tests through simulation utilizing parameter estimation. Some of the tests conducted since the mid-1990s were analyzed with numerical models (Sepulveda, 2006;Yobbi and Halford, 2008;Gonthier, 2011) that utilize a modifi ed version of MODFLOW 1996 (Harbaugh and McDonald, 1996) called MODOPTIM (Halford, 2006).…”

Effects of Model Layer Simplification Using Composite Hydraulic Properties

“…(1)-(3) use lithologic thicknesses to calculate composite hydraulic properties to simplify model layering. However, the use of regression-based PE techniques (Halford, 2006) requires using the radial axisymmetric 2D flow models similar to the ones used to analyze the aquifer-test data, but with simplified model layers and calibrated to the same aquifertest data. The models that simulated the combined flow in the SAS and ICU as one lithologic unit (quasi-2D flow model) were developed assuming an ICU layer with zero specific storage and zero horizontal hydraulic conductivity in Eqs.…”

“…The first method presented in this chapter is to compute the thickness weighted average horizontal hydraulic conductivity and specific storage and the thickness weighted harmonic mean vertical hydraulic conductivity for a reduced number of layers in the unconfined aquifer and the leaky confining unit. The second method is to compute hydraulic properties by using the observed head from aquifer tests and applying the regression-based parameter estimation (PE) techniques (Poeter et al, 2005;Halford, 2006;Hill & Tiedeman, 2007). As the number of simulated layers in the unconfined aquifer is decreased, the performance of each model is assessed by analyzing changes in simulated heads under aquifer test conditions and by simulating flow exchanges between the hydrogeologic units under hypothetical but realistic recharge rates to the unconfined aquifer and withdrawals from the confined aquifer.…”

“…Radial axisymmetric models are typically used to approximately simulate 3D flow to wells (Reilly & Harbaugh, 1993;Langevin, 2008). The computer code MODOPTIM (Halford, 2006), based on MODFLOW-96 (Harbaugh & McDonald, 1996), was used to derive the hydraulic properties for each lithologic unit using regression-based parameter estimation techniques to minimize the sum of square residuals (SSR) between measured and simulated drawdown (Figs. 3, 4).…”