Two‐zone transient storage modeling using temperature and solute data with multiobjective calibration: 2. Temperature and solute

Abstract

This paper presents the multiobjective calibration results for temperature and solute from a two‐zone temperature and solute (TZTS) model which separates transient storage into surface (STS) and subsurface (HTS) transient storage components. This model contains terms associated with surface heat fluxes in the main channel (MC) and STS, heat and mass exchange between the STS and MC, heat and mass exchange between the HTS and MC, and heat exchange due to bed and deeper ground conduction. To estimate the additional parameters associated with a multiple‐zone model, a data collection effort was conducted to provide temperature time series and solute tracer curves representing the movement of heat and/or solute through each zone. A multiobjective calibration algorithm was linked to the TZTS model to assist in parameter estimation and to provide information about parameter uncertainty and tradeoffs associated with matching different combinations of observations (e.g., solute and/or temperature data gathered in various zones). Results generated from three different combinations of calibration data illustrated that the two‐zone model accurately reproduces temperatures and tracer concentrations observed in different zones when considered independently. However, there were many parameter sets that resulted in objectively indistinguishable results. When tracer and temperature observations were considered simultaneously in model calibration, the simplistic representation of the surface and subsurface zones did not adequately reproduce both observation types in each zone. If the uncertainty in model parameters and the data are taken into account, however, the results of the study suggest that it is plausible to use temperature and tracer information simultaneously to better inform transient storage modeling approaches.