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This paper evaluates the importance of seven types of parameters to virus transport: hydraulic conductivity, porosity, dispersivity, sorption rate and distribution coefficient (representing physical–chemical filtration), and in-solution and adsorbed inactivation (representing virus inactivation). The first three parameters relate to subsurface transport in general while the last four, the sorption rate, distribution coefficient, and in-solution and adsorbed inactivation rates, represent the interaction of viruses with the porous medium and their ability to persist. The importance of four types of observations to estimate the virus-transport parameters are evaluated: hydraulic heads, flow, temporal moments of conservative-transport...
A modular approach to model design and construction provides a flexible framework in which to focus the multidisciplinary research and operational efforts needed to facilitate the development, selection, and application of the most robust distributed modelling methods. A variety of modular approaches have been developed, but with little consideration for compatibility among systems and concepts. Several systems are proprietary, limiting any user interaction. The US Geological Survey modular modelling system (MMS) is a modular modelling framework that uses an open source software approach to enable all members of the scientific community to address collaboratively the many complex issues associated with the design,...
We integrated soil models with an established ecosystem process model (SIPNET, simplified photosynthesis and evapotranspiration model) to investigate the influence of soil processes on modelled values of soil CO2 fluxes (RSoil). Model parameters were determined from literature values and a data assimilation routine that used a 7-year record of the net ecosystem exchange of CO2 and environmental variables collected at a high-elevation subalpine forest (the Niwot Ridge AmeriFlux site). These soil models were subsequently evaluated in how they estimated the seasonal contribution of RSoil to total ecosystem respiration (TER) and the seasonal contribution of root respiration (RRoot) to RSoil. Additionally, these soil...
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Hypothetical two-dimensional, steady-state groundwater flow models of a previously published 1988 model calibration exercise were developed using the finite-difference computer code, MODFLOW-2005, to demonstrate the power of modern parameter estimation and uncertainty approaches. For this study, an initial run recreated the 1988 "truth" model. The true model was then simplified to account for information not provided the participants in the 1988 calibration exercise. Increasing sophistication was brought to bear to demonstrate how problems identified in 1988 were overcome using modern software approaches. This USGS data release contains all of the input and output to run the model simulations described in the associated...
Survival or extinction of an endangered species is inherently stochastic. We develop statistical methods for estimating quantities related to growth rates and extinction probabilities from time series data on the abundance of a single population. The statistical methods are based on a stochastic model of exponential growth arising from the biological theory of age or stagestructured populations. The model incorporates the socalled environmental type of stochastic fluctuations and yields a lognormal probability distribution of population abundance. Calculation of maximum likelihood estimates of the two unknown parameters in this model reduces to performing a simple linear regression. We describe techniques for rigorously...
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The existing three-dimensional groundwater flow model (MODFLOW-2005) of the Mississippi Embayment Regional Aquifer system (MERAS), South-Central United States, was updated with: 1) higher stream density; 2) more spatially refined recharge; 3) better estimates of water use; 4) more recent time period simulated; 5) more realistic storage conceptualization; and 6) more robust handling of dry nodes through use of MODFLOW-NWT. For this study, the MODFLOW-NWT groundwater flow model was used to evaluate four parameter estimation algorithms with lower computational burdens. This work was performed to update the previous version of the MERAS groundwater flow model for decision making in the Mississippi Alluvial Plain (MAP),...
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A series of Jupyter notebooks documenting a self-guided, interactive curriculum for the PEST++ family of software codes for uncertainty analysis, parameter estimation, and management optimization. For a currently maintained version of these materials, please visit https://github.com/gmdsi/GMDSI_notebooks.
A modified version of the Hydrus software package that can directly or inversely simulate water flow in a transient centrifugal field is presented. The inverse solver for parameter estimation of the soil hydraulic parameters is then applied to multirotation transient flow experiments in a centrifuge. Using time-variable water contents measured at a sequence of several rotation speeds, soil hydraulic properties were successfully estimated by numerical inversion of transient experiments. The inverse method was then evaluated by comparing estimated soil hydraulic properties with those determined independently using an equilibrium analysis. The optimized soil hydraulic properties compared well with those determined...
    map background search result map search result map MODFLOW-NWT models and calibration files for the Mississippi Alluvial Plain, USA MODFLOW-NWT models and calibration files for the Mississippi Alluvial Plain, USA