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This paper discusses the calibration process of hydrology models for the St. Johns River Watershed, including input observations, model representation, parameter adjustment, and validation. It also explores the impacts of meteorologic inputs, the watershed description, and the weight of evidence on the calibration results.
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Calibration of St. Johns River Watershed Hydrology Models Tim Cera, P.E. Senior Professional Engineer
L2-11 + + + + + ERROR ERROR ERROR ERROR ERROR Meteorologic Inputs Calibration Process MODEL VERSUS NATURAL SYSTEMS: INPUTS, OUTPUTS AND ERRORS Input Observations SYSTEM INPUTS Observed Parameter Values Estimation Watershed Model (Representation) Watershed Parameters MODEL NATURAL Model Results Adjust (System Representation) SYSTEM Output Observations Calibration Calibration Parameter Adjustment Observed Model Values Calibration Outputs Accept Calibrated Model Results System Results System Outputs MODEL VALIDATION
Meteorologic Inputs Meteorologic Input Input Observations
Meteorologic Inputs Rain • Point rain gauges • Daily • Hourly • Assigned to sub-watershed by Thiessen polygons Input Observations
Meteorologic Inputs Evaporation • Estimated using Hargreave’s equation • Min and max daily temperatures • Correction factor to Penman-Monteith method • Assigned to sub-watershed by Theissen polygons Input Observations
Watershed Description Watershed Model (Representation) Watershed Parameters
Flow Observations • Primarily USGS stations • Rating curve estimating flow from stage • Sometimes uses velocity as additional index Output Observations System Results
Weight of Evidence • Annual runoff volume • Monthly runoff volume • Mean runoff volume over entire period • Daily flow time-series • Flow exceedance curves • Deep recharge Output Observations System Results
Parameter Common Logic • Developed parameter ranges based on • Understanding of HSPF • Understanding of Florida hydrology Watershed Model (Representation) Parameters
Calibration Watershed Model (Representation) Parameters Model Results Adjust Output Observations Calibration Accept Calibrated Model Results
Parameter Estimation • Parameter ESTimation (PEST) • HSPF utilities • Training • Assist in the optimization of model parameters (Adjust and Accept) • Rapidly assess more parameter combinations • Evaluate interactions between parameters • Sometimes requires hundreds of runs • Parallel processing
Calibration • Calibrated 51 watersheds • 1995-2006 inclusive • 1995 land use • 1995 operation of Upper Basin Projects • Peer review
St. Johns River Basin
Peer Review Recommendations • Re-examine consistency between 1995 and 2030 land use • Decrease percent impervious area • Increase retention storage for impervious areas • Re-examine saturated zone groundwater transpiration • Implement surface storage
Re-Calibration • Implementation of peer review recommendations led to a complete re-calibration of the models
Areal Discharge Rate LKGB LSJRB MSJRB USJRB OCKRB
Calibration Performance • Statistical measures • Nash-Sutcliffe • 1 is perfect fit • 0 if the model was equal to the average observed value • Percent error of the mean Calibrated Model Results System Results
Calibration Performance Moriasi, D. N., Arnold, J. G., Van Liew, M. W., Bigner, R. L., Harmel, R. D., & Veith, T. L. (2007, vol 50, #3). Model evaluation guidelines for systematic quantification of accuracy in watershed simulations. Transactions of ASABE, American Society of Agricultural and Biological Engineers, 885-900.
