Southeast River Forecast Center – St. John’s River Basin Data Analysis and Model Calibration

St. Johns River, Florida

The St. Johns River begins in the marshy areas of Brevard and Indian River counties, traveling approximately 310 miles northward where it discharges into the Atlantic Ocean at Jacksonville. Its slope averages only about one inch per mile, and its width averages approximately two miles between Palatka and Jacksonville. Characterized by marine terrace and karst physiography, the St. Johns basin poses hydrologic modeling challenges related to strong tidal influences and an extremely high degree of stream-aquifer interaction. In many areas within the basin, recharge rates to the underlying Floridan aquifer can exceed 12 inches per year.

Riverside Technology, inc. (RTi) worked with the Southeast River Forecast Center (SERFC) to improve existing hydrologic models within the St. Johns River basin located in the northeast portion of Florida. The project was conducted as part of the National Weather Service (NWS) implementation of the Advanced Hydrologic Prediction Services (AHPS) program. Available hydrometeorological data was reviewed by the SERFC and RTi, and a station database and working environment on a UNIX workstation was created and maintained to facilitate the ensuing data analysis procedures. RTi analyzed the historical precipitation data, using database quality control methods and evaluated consistency using the NWS Preliminary Precipitation Processing Program (PXPP) and NWS Interactive Double Mass Analysis (IDMA) software tools.

Sample Interactive Calibration Program Display

RTi then computed mean areal precipitation (MAP) using Thiessen weighting methodology, and developed Potential Evapotranspiration (PET) estimates for each sub-basin. A water balance analysis was conducted to validate the areal precipitation, potential evapotranspiration, and discharge estimates. Based on results of the data analysis, RTi developed a calibration strategy, and calibrated the Sacramento Soil Moisture Accounting (SAC-SMA) and Unit Hydrograph models for selected streamflow gage locations within the St. John's Basin. The purpose of the calibration was to improve the accuracy of inflow calculations along the St. John's River between De Land and Jacksonville. Associated required flow routing was modeled using Lag/K techniques.

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