SR SSD 2000-06

Technical Attachment

Tidal Model for the NWS River Forecast System:
Results of a COMET Cooperative Project

Reggina Garza
Southeast RFC, Atlanta, Georgia

Scott C. Hagen
University of Central Florida
Orlando, Florida

With support provided by a COMET Cooperative Program outreach grant in 1999, a partnership was developed involving researcher Dr. Scott C. Hagen, from the University of Central Florida, and senior hydrologists Reggina Garza and Wylie Quillian from the NWS Southeast River Forecast Center (SERFC) in Atlanta. The objective of this project was to develop a two-dimensional tidal model for the coastal region surrounding Conway, South Carolina, on the Waccamaw River.

At present, river forecasting efforts by the SERFC do not include effects of tidal fluctuations for Conway, because tidal data are not readily available for this site. Existing tide tables for the location may be out of date due to changes which have occurred over time to the coast and the ocean floor. Data from tide tables that are up-to-date and available are not transferable to this location.

The tidal model which was developed was used to simulate six real-time stage hydrographs at the downstream end of the Waccamaw River. The resulting stage hydrograph will serve as a downstream boundary condition for the Flood Wave model (FLDWAV) that is used by the National Weather Service River Forecast System (NWSRFS). Results from this project are expected to enhance river forecasts provided by the SERFC.

The tidal model is a finite element model (ADCIRC) which at its present stage incorporates astronomical forcing, i.e. only periodic gravitational attraction of the moon and sun are considered. In the future this model could incorporate wind effects and pressure forcing as well. The calibration of the model was done using the tide gauge at Charleston, South Carolina. The final study includes tide hydrographs for six sites in the lower end of the Waccamaw River, for the period of January to December, 2000. The time interval used in the simulation is 30 sec, in order to meet the conditions set by the model.

The Civil and Environmental Engineering Department at the University of Central Florida accomplished three major tasks during this study:

  1. A two-dimensional, finite element domain was developed for the coastal region surrounding Conway, S.C.
  2. Simulations were performed to calibrate and verify the model based on historical data at the gage at Charleston, S.C.
  3. Simulations were conducted to generate six separate real-time stage hydrographs, which will be used by the SERFC

Based on this study it is recommended future work focus on the following five major tasks.

  1. Meteorological forcing should be included in order to better predict the historical records.
  2. It may be prudent to expand the domain further up the Waccamaw River such that the Intracoastal Water Way can be included. The tidal effect from this reach may have a direct influence in the Waccamaw River stage. Simulation could then include the comparison of tidal hydrographs at different locations along the coastal boundary, as well as the combined effect of two inlets.
  3. Storm surge simulations should be conducted with the present tidal model. It may be beneficial to compare ADCIRC output to SLOSH model output.
  4. A simulation of the effects of a flood wave routed from upstream of the location of interest, coincident with the arrival of a storm surge. This would allow for the evaluation of the impacts of the double effect at Conway.
  5. The domain should be expanded to include the entire East Coast of the United States and that of the Gulf of Mexico. The resulting model would be capable of providing tide-stages for all the affected rivers in one simulation. This larger model could benefit five of all thirteen NWS River Forecast Centers.

During the course of work on this project, Dr. Hagen visited and provided several seminars at the SERFC. In addition, a number of other presentations and publications, listed below, were generated from this project. Those interested in more details on all aspects of the research should contact Reggina Garza at or Wylie Quillian at at SERFC.

Related References

Bennett, R.J., 1999: Finite element grid development for the Waccamaw River: a reproducible approach, Master Thesis, Department of Civil and Environmental Engineering, University of Central Florida, Orlando.

Hagen, S.C., O. Horstmann, and R.J. Bennett, 1999: A reproducible approach to unstructured mesh generation for shallow water models, Proceedings of the 8th International Meshing Roundtable, Sandia National Laboratories, Albuquerque, NM, 245-354.

Hagen S.C., O. Horstmann, and R.J. Bennett, 1999: A reproducible approach to unstructured mesh generation for shallow water models, Presentation at the 8th International Meshing Roundtable, South Lake Tahoe.

Hagen, S.C. and R.J. Bennett, 1999: A tide-stage hydrograph for the Waccamaw River, Proceedings of the 6th Estuarine and Coastal Modeling Conference, In review.

Hagen, S.C. and R.J. Bennett, 1999: A tide-stage hydrograph for the Waccamaw River, Presentation at the 6th Estuarine and Coastal Modeling Conference, New Orleans.

Westerink, J.J., C.A. Blain, R.A. Luettich, and N.W. Scheffer, 1994. ADCIRC: and advanced three dimensional circulation model for shelves, coasts and estuaries, report 2; users's manual for ADCIRC-2DD,I. Technical Report DRP-92-6, Department of the Army.