The use of multiobjective calibration and regional sensitivity analysis in simulating hyporheic exchange

Abstract

We describe an approach for calibrating a two‐dimensional (2‐D) flow model of hyporheic exchange using observations of temperature and pressure to estimate hydraulic and thermal properties. A longitudinal 2‐D heat and flow model was constructed for a riffle‐pool sequence to simulate flow paths and flux rates for variable discharge conditions. A uniform random sampling approach was used to examine the solution space and identify optimal values at local and regional scales. We used a regional sensitivity analysis to examine the effects of parameter correlation and nonuniqueness commonly encountered in multidimensional modeling. The results from this study demonstrate the ability to estimate hydraulic and thermal parameters using measurements of temperature and pressure to simulate exchange and flow paths. Examination of the local parameter space provides the potential for refinement of zones that are used to represent sediment heterogeneity within the model. The results indicate vertical hydraulic conductivity was not identifiable solely using pressure observations; however, a distinct minimum was identified using temperature observations. The measured temperature and pressure and estimated vertical hydraulic conductivity values indicate the presence of a discontinuous low‐permeability deposit that limits the vertical penetration of seepage beneath the riffle, whereas there is a much greater exchange where the low‐permeability deposit is absent. Using both temperature and pressure to constrain the parameter estimation process provides the lowest overall root‐mean‐square error as compared to using solely temperature or pressure observations. This study demonstrates the benefits of combining continuous temperature and pressure for simulating hyporheic exchange and flow in a riffle‐pool sequence.