Modeling Coastal Rivers Operationally. A Case Study in the St. Johns River, Florida by

Reggina Cabrera Garza1, Janice Sylvestre2 and Michael Watts2

1 NOAA, National Weather Service, Southeast River Forecast Center, Peachtree City, GA 2 NOAA, National Weather Service, Silver Spring, MD

The National Weather Service uses the National Weather Service River Forecast System (NWSRFS) to simulate river levels and/or flows at predetermined forecast sites. In 2001, the Southeast River Forecast Center (SERFC) began forecasting water levels for a reach in the middle section (Lake Harney to Deland) of the St. Johns River in Florida. The St. Johns River has a very flat slope and it is also affected by tides and backwater. A river with such characteristics can not be properly modeled by using only hydrologic modeling, thus there is a need to implement a hydraulic model. The 1-dimensional dynamic generalized flood wave routing model (FLDWAV) which is a component within NWSRFS is used to model the St. Johns River.

As a result of the Coastal Storm Initiative (CSI), the St. Johns River in Florida has been selected as the demonstration project to showcase improved forecasting capabilities in coastal river systems. The Office of Hydrologic Development and SERFC have worked toward the development of the St. Johns River model envisioned by CSI. The combined effort involves the expansion of the existing hydrologic model, the improvement of the existing hydraulic model, and the incorporation of new sites in the lower end of the St. Johns River basin. The existing model has been expanded to include the lower end of the river down to its mouth at Mayport, FL. Although the current hydraulic model accounts for the effects of the astronomic tides, the improved model also accounts for storm surge effects. Flood forecast maps are generated as an improved method for visualizing the forecast. The results of implementing these improvements into the operational environment will be presented and discussed in this paper.