Lack of sufficient field data adds difficulties to the calibration and evaluation of predictive accuracy of groundwater models. This paper investigates the use of interpolation of hydraulic heads observed at limited nodal measurement points below Indian River Lagoon to aid improve calibration and evaluation of groundwater models at two vertical-plain transects across the lagoon. Additional nodal head values were extracted from the interpolated head distributions. Models were developed using SEAWAT to estimate magnitudes of submarine groundwater discharge (SGD) into the lagoon. Calibration objective was to minimize hydraulic head residuals, and make sure that simulated head distributions compare visually well to the interpolated distributions. Calibration results were evaluated using: 1) root mean square error (RMSE), 2) Nash-Sutcliffe efficiency (NSE) index, 3) two-sided t-test, and 4) visual comparisons of measured and simulated head distributions. Statistical analysis results with and without the additional interpolation-based head values were compared. RMSE results were found to be meaningless since the models overpredicted annual SGD up to 278% even at RMSE as small as 0.089m. NSE produced misleading results at one of the transects when comparisons were made without the additional interpolation-based head data. However, adding those points, improved NSE statistical results. Two-sided t-test didn’t show differences in results after adding more observation points. However, it agreed relatively well with visual comparisons. It is recommended to conduct interpolation of observed data to obtain complete hydraulic head distributions prior to conducting statistical analyses. Interpolation not only improves statistical analyses but also provides another calibration tool through visual comparison.
Ashok Pandit– 2Professor and Department Head, Civil Engineering Department, Florida Institute of Technology, Melbourne, Florida
2Professor and Department Head, Civil Engineering Department
Florida Institute of Technology
Dr. Pandit is a professor and department head of the Civil Engineering and Construction Management department at the Florida Institute of Technology. His research interestes include groundwater modeling and stormwater management. For the past 10 years he has been involved in estimating groundwater nutrient loads into the Indian River Lagoon, an estuary on the east-central coast of Florida.