NOAA Technical Memorandum NOS CS 10

NOS EXPERIMENTAL GALVESTON BAY 

NOWCAST/FORECAST SYSTEM: 

STORM SURGE STUDIES

Silver Spring, Maryland 

June 2007 

noaa National Oceanic and Atmospheric Administration 

U.S. DEPARTMENT OF COMMERCE 

National Ocean Service 

Coast Survey Development Laboratory 
ii

Office of Coast Survey 

National Ocean Service 

National Oceanic and Atmospheric Administration 

U.S. Department of Commerce

The Office of Coast Survey (OCS) is the Nation’s only official chartmaker. As the oldest 

United States scientific organization, dating from 1807, this office has a long history. 

Today it promotes safe navigation by managing the National Oceanic and Atmospheric 

Administration’s (NOAA) nautical chart and oceanographic data collection and 

information programs. 

There are four components of OCS: 

The Coast Survey Development Laboratory develops new and efficient techniques 

to accomplish Coast Survey missions and to produce new and improved products 

and services for the maritime community and other coastal users. 

The Marine Chart Division acquires marine navigational data to construct and 

maintain nautical charts, Coast Pilots, and related marine products for the United 

States. 

The Hydrographic Surveys Division directs programs for ship and shore-based 

hydrographic survey units and conducts general hydrographic survey operations. 

The Navigational Services Division is the focal point for Coast Survey customer 

service activities, concentrating predominately on charting issues, fast-response 

hydrographic surveys, and Coast Pilot updates. 
NOAA Technical Memorandum NOS CS 10 

NOS EXPERIMENTAL GALVESTON BAY 

NOWCAST/FORECAST SYSTEM: 

STORM SURGE STUDIES 

Richard A. Schmalz, Jr. 

Office of Coast Survey, Coast Survey Development Laboratory, Silver Spring, 

MD 

 

June 2007

noaa National Oceanic and Atmospheric Administration 

U. S. DEPARTMENT National Oceanic and National Ocean Service 

OF COMMERCE Atmospheric Administration John H. Dunnigan 

Carlos Gutierrez, Secretary Conrad C. Lautenbacher, Jr., Assistant Administrator 

 VADM USN (Ret.), Under Secretary 

 Office of Coast Survey Coast Survey Development Laboratory 

 Captain Steven R. Barnum, NOAA Mary Erickson 

iii
iv

NOTICE 

Mention of a commercial company or product does not constitute an 

endorsement by NOAA. Use for publicity or advertising purposes of 

information from this publication concerning proprietary products or the 

tests of such products is not authorized.
v

TABLE OF CONTENTS 

LIST OF FIGURES ...................................................................................................................... vii 

LIST OF TABLES....................................................................................................................... xiv 

BASE MAP....................................................................................................................................xv 

EXECUTIVE SUMMARY ......................................................................................................... xvi 

1. INTRODUCTION .......................................................................................................................1 

2. LONG WAVE HYDRODYNAMIC MODEL............................................................................3 

2.1. Governing Equations ..........................................................................................................3 

2.2. Model Grids ........................................................................................................................6 

3. SHORT WAVE HYDRODYNAMIC MODEL........................................................................11 

3.1. Governing Equations ........................................................................................................11 

3.2. Initial Validation ...............................................................................................................11 

3.3. Joint Computational..........................................................................................................14 

3.4. Overtopping and Barrier Island Breaching Limitations....................................................14 

4. WAVE-CURRENT INTERACTION........................................................................................15 

4.1. Surface Drag Coefficient Adjustment...............................................................................15 

4.2. Bottom Friction Adjustment .............................................................................................15 

4.3. Setup and Runup Limitations............................................................................................16 

5. STORM SURGE METHODOLOGY........................................................................................17 

5.1. Rainfall/Runoff .................................................................................................................17 

5.2. Overland Flooding Scheme...............................................................................................20 

5.3. Hurricane Wind and Atmospheric Pressure Fields...........................................................22 

5.4. Wave Algorithm................................................................................................................25 

5.5. Design of the All-Weather Nowcast/Forecast System......................................................26 

5.6. Additional Hydrodynamic Model Considerations............................................................27 

5.7. Simulation Objectives.......................................................................................................27 

6. HURRICANE CARLA (1961) STORM SURGE SIMULATIONS.........................................29 

6.1. Storm Characteristics........................................................................................................29 

6.2. Simulation Set-up Procedures ..........................................................................................31 

6.3. Experiment One Long Wave Results ...............................................................................32 

6.4. Experiment One Short Wave Results ..............................................................................61 

6.5. Experiment Two Long and Short Wave Results ..............................................................79 

6.6. Wind and Water Surface Elevation Validation ................................................................80 

6.7. Surface Salinity, Surface Current, and Inundation Statistics ...........................................81 

7. HURRICANE ALICIA (1983) STORM SURGE SIMULATIONS.........................................85 

7.1. Storm Characteristics........................................................................................................85 
vi

7.2. Simulation Set-up Procedures...........................................................................................86 

7.3. Experiment One Long Wave Results................................................................................87 

7.4. Experiment One Short Wave Results .............................................................................104 

7.5. Experiment Two Long and Short Wave Results.............................................................116 

7.6. Wind and Water Surface Elevation Validation...............................................................116 

 7.7. Surface Salinity, Surface Current, and Inundation Statistics..........................................117 

8. TROPICAL STORM ALLISON (2001) STORM SURGE SIMULATIONS. .......................129 

8.1. Coastal Surge Propagation Event Characteristics...........................................................129 

8.2. Rainfall/Runoff Event Characteristics ............................................................................130 

8.3. Coastal Surge Propagation Event Simulation Set-up Procedures...................................131 

8.4. Rainfall/Runoff Event Simulation Set-up Procedures ....................................................131 

8.5. Coastal Surge Propagation Event Long Wave Results...................................................132 

8.6. Coastal Surge Propagation Event Short Wave Results...................................................142 

8.7. Rainfall/Runoff Event Experiment One Long Wave Results.........................................145 

8.8. Rainfall/Runoff Event Experiment Two Long Wave Results ........................................171 

8.9. Rainfall/Runoff Event Experiment Short Wave Results ................................................188 

9. OPERATIONAL CONSIDERATIONS..............................................................189 

10. CONCLUSIONS AND FUTURE WORK ............................................................................191 

ACKNOWLEDGMENTS.............................................................................................. 191 

REFERENCES............................................................................................................ 191 
vii

LIST OF FIGURES 

Figure 1.1. Map showing Galveston Bay and the Houston Ship Channel 

 including PORTS stations............................................................................................2 

Figure 2.1. Galveston Bay model grid............................................................................................7 

Figure 2.2. Galveston Bay model bathymetry, contours in meters.................................................8 

Figure 2.3. Galveston Bay model grid in red with Houston Ship Channel 

 model grid in green......................................................................................................9 

Figure 3.1. Galveston Bay Wave Model vs Observed Wave Parameters 

 at Eagle Point, January 25-30, 1997..........................................................................12 

Figure 3.2. Galveston Bay Wave Model vs Observed Wave Parameters 

 at 42035, January 25-30, 1997..................................................................................13 

Figure 6.1. Hurricane Carla (1961) Storm Track 3-16 September 1961 ...............................29 

Figure 6.2. Hurricane Carla GBM Water Levels Experiment One: 9-10 September 1961...........35 

Figure 6.3. Hurricane Carla GBM Water Levels Experiment One: 10-11 September 1961.......36 

Figure 6.4. Hurricane Carla GBM Water Levels Experiment One: 11-12 September 1961.......37 

Figure 6.5. Hurricane Carla HSCM Water Levels 

 and GBM Water Level Residual Experiment One: 9-10 September 1961..............38 

Figure 6.6. Hurricane Carla HSCM Water Levels 

 and GBM Water Level Residual Experiment One: 10-11 September 1961...............39 

Figure 6.7. Hurricane Carla HSCM Water Levels 

 and GBM Water Level Residual Experiment One: 11-12 September 1961...............40 

Figure 6.8. Hurricane Carla GBM Bolivar Roads Currents 

 Experiment One: 9-10 September 1961.......................................................................41 

Figure 6.9. Hurricane Carla GBM Bolivar Roads Currents 

 Experiment One: 10-11 September 1961.....................................................................42 

Figure 6.10. Hurricane Carla GBM Bolivar Roads Currents 

 Experiment One: 11-12 September 1961...................................................................43 

Figure 6.11. Hurricane Carla GBM Morgans Point Currents 

 Experiment One: 9-10 September 1961.....................................................................44 

Figure 6.12. Hurricane Carla GBM Morgans Point Currents 

 Experiment One: 10-11 September 1961...................................................................45 

Figure 6.13. Hurricane Carla GBM Morgans Point Currents 

 Experiment One: 11-12 September 1961...................................................................46 

Figure 6.14. Hurricane Carla GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 9-10 September 1961.....................................................................47 

Figure 6.15. Hurricane Carla GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 10-11 September 1961...................................................................48 

Figure 6.16. Hurricane Carla GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 11-12 September 1961...................................................................49 

Figure 6.17. Hurricane Carla HSCM Eagle Point Temperature and Salinity 

 Experiment One: 9-10 September 1961.....................................................................50 

Figure 6.18. Hurricane Carla HSCM Eagle Point Temperature and Salinity 

 Experiment One: 10-11 September 1961...................................................................51 
viii

LIST OF FIGURES 

Figure 6.19. Hurricane Carla HSCM Eagle Point Temperature and Salinity 

 Experiment One: 11-12 September 1961...................................................................52 

Figure 6.20. Hurricane Carla GBM Water Surface Elevation Field 

 Experiment One: 11 September 1961 18:00 CST......................................................53 

Figure 6.21. Hurricane Carla GBM Water Surface Elevation Field 

 Experiment One: 12 September 1961 18:00 CST......................................................54 

Figure 6.22. Hurricane Carla GBM Near Surface Salinity Field 

 Experiment One: 12 September 1961 18:00 CST......................................................55 

Figure 6.23. Hurricane Carla GBM Near Bottom Salinity Field 

 Experiment One: 12 September 1961 18:00 CST......................................................56 

Figure 6.24. Hurricane Carla HSCM Water Surface Elevation Field 

 Experiment One: 11 September 1961 18:00 CST......................................................57 

Figure 6.25. Hurricane Carla HSCM Water Surface Elevation Field 

 Experiment One: 12 September 1961 18:00 CST......................................................58 

Figure 6.26. Hurricane Carla HSCM Near Surface Salinity Field 

 Experiment One: 12 September 1961 18:00 CST......................................................59 

Figure 6.27. Hurricane Carla HSCM Near Bottom Salinity Field 

 Experiment One: 12 September 1961 18:00 CST......................................................60 

Figure 6.28. Hurricane Carla GBM Significant Wave Height 

 Experiment One: 9-10 September 1961.....................................................................63 

Figure 6.29. Hurricane Carla GBM Significant Wave Height 

 Experiment One: 10-11 September 1961...................................................................64 

Figure 6.30. Hurricane Carla GBM Significant Wave Height 

 Experiment One: 11-12 September 1961...................................................................65 

Figure 6.31. Hurricane Carla HSCM and GBM 42035 Significant Wave Height. 

 Experiment One: 9-10 September 1961.....................................................................66 

Figure 6.32. Hurricane Carla HSCM and GBM 42035 Significant Wave Height 

 Experiment One: 10-11 September 1961...................................................................67 

Figure 6.33. Hurricane Carla HSCM and GBM 42035 Significant Wave Height 

 Experiment One: 11-12 September 1961...................................................................68 

Figure 6.34. Hurricane Carla GBM Significant Wave Period 

 Experiment One: 9-10 September 1961.....................................................................69 

Figure 6.35. Hurricane Carla GBM Significant Wave Period 

 Experiment One: 10-11 September 1961...................................................................70 

Figure 6.36. Hurricane Carla GBM Significant Wave Period 

 Experiment One: 11-12 September 1961...................................................................71 

Figure 6.37. Hurricane Carla HSCM and GBM 42035 Significant Wave Period 

 Experiment One: 9-10 September 1961.....................................................................72 

Figure 6.38. Hurricane Carla HSCM and GBM 42035 Significant Wave Period 

 Experiment One: 10-11 September 1961...................................................................73 

Figure 6.39. Hurricane Carla HSCM and GBM 42035 Significant Wave Period 

 Experiment One: 11-12 September 1961...................................................................74 

Figure 6.40. Hurricane Carla GBM Significant Wave Height and Direction 

 Experiment One: 11 September 1961 18:00 CST......................................................75 
ix

LIST OF FIGURES 

Figure 6.41. Hurricane Carla GBM Significant Wave Period 

 Experiment One: 11 September 1961 18:00 CST......................................................76 

Figure 6.42. Hurricane Carla HSCM Significant Wave Height and Direction 

 Experiment One: 11 September 1961 18:00 CST......................................................77 

Figure 6.43. Hurricane Carla HSCM Significant Wave Period 

 Experiment One: 11 September 1961 18:00 CST......................................................78 

Figure 6.44. Hurricane Carla GBM Atmospheric Pressure Field 

 Experiment Two: 11 September 1961 18:00 CST ....................................................83 

Figure 6.45. Hurricane Carla GBM Wind Field 

 Experiment Two: 11 September 1961 18:00 CST.................................................... 84 

Figure 7.1. Hurricane Alicia (1983) Storm Track 15-21 August.................................................. 85 

Figure 7.2. Hurricane Alicia GBM Water Levels 

 Experiment One: 16-17 August 1983..........................................................................89

Figure 7.3. Hurricane Alicia GBM Water Levels 

 Experiment One: 17-18 August 1983..........................................................................90

Figure 7.4. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

 Experiment One: 16-17 August 1983..........................................................................91

Figure 7.5. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

 Experiment One: 17-18 August 1983..........................................................................92

Figure 7.6. Hurricane Alicia GBM Bolivar Roads Currents 

 Experiment One: 16-17 August 1983..........................................................................93

Figure 7.7. Hurricane Alicia GBM Bolivar Roads Currents 

 Experiment One: 17-18 August 1983..........................................................................94

Figure 7.8. Hurricane Alicia GBM Morgans Point Currents 

 Experiment One: 16-17 August 1983..........................................................................95

Figure 7.9. Hurricane Alicia GBM Morgans Point Currents 

 Experiment One: 17-18 August 1983..........................................................................96

Figure 7.10. Hurricane Alicia GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 16-17 August 1983........................................................................97

Figure 7.11. Hurricane Alicia GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 17-18 August 1983........................................................................98

Figure 7.12. Hurricane Alicia HSCM Eagle Point Temperature and Salinity 

 Experiment One: 16-17 August 1983........................................................................99

Figure 7.13. Hurricane Alicia HSCM Eagle Point Temperature and Salinity 

 Experiment One: 17-18 August1983.............................................. ........................100 

Figure 7.14. Hurricane Alicia GBM Water Surface Elevation Field 

 Experiment One: 18 August 1983 18:00 CST.........................................................101 

Figure 7.15. Hurricane Alicia GBM Near Surface Salinity Field 

 Experiment One: 18 August 1983 18:00 CST.........................................................102 

Figure 7.16. Hurricane Alicia GBM Near Bottom Salinity Field 

 Experiment One: 18 August 1983 18:00 CST.........................................................103 

Figure 7.17. Hurricane Alicia GBM Significant Wave Height 

 Experiment One: 16-17 August 1983......................................................................106 

Figure 7.18. Hurricane Alicia GBM Significant Wave Height 

 Experiment One: 17-18 August 1983......................................................................107 
x

LIST OF FIGURES 

Figure 7.19. Hurricane Alicia HSCM and GBM 42035 Significant Wave Height 

 Experiment One: 16-17 August 1983......................................................................108 

Figure 7.20. Hurricane Alicia HSCM and GBM 42035 Significant Wave Height 

 Experiment One: 17-18 August 1983......................................................................109 

Figure 7.21. Hurricane Alicia GBM Significant Wave Period 

 Experiment One: 16-17 August 1983......................................................................110 

Figure 7.22. Hurricane Alicia GBM Significant Wave Period 

 Experiment One: 17-18 August 1983......................................................................111 

Figure 7.23. Hurricane Alicia HSCM and GBM 42035 Significant Wave Period 

 Experiment One: 16-17 August 1983......................................................................112 

Figure 7.24. Hurricane Alicia HSCM and GBM 42035 Significant Wave Period 

 Experiment One: 17-18 August 1983......................................................................113 

Figure 7.25. Hurricane Alicia GBM Significant Wave Height and Direction 

 Experiment One: 18 August 1983 18:00 CST.........................................................114 

Figure 7.26. Hurricane Alicia GBM Significant Wave Period 

 Experiment One: 18 August 1983 18:00 CST.........................................................115 

Figure 7.27. Hurricane Alicia GBM Water Levels 

 Experiment Two: 16-17 August 1983.....................................................................119 

Figure 7.28. Hurricane Alicia GBM Water Levels 

 Experiment Two: 17-18 August 1983.....................................................................120 

Figure 7.29. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

 Experiment Two: 16-17 August 1983.....................................................................121 

Figure 7.30. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

 Experiment Two: 17-18 August 1983.....................................................................122 

Figure 7.31. Hurricane Alicia Wind and Atmospheric Pressure at Morgans Point 

 Experiment Two: 16-17 August 1983.....................................................................123 

Figure 7.32. Hurricane Alicia Wind and Atmospheric Pressure at Morgans Point 

 Experiment Two: 17-18 August 1983.....................................................................124 

Figure 7.33. Hurricane Alicia GBM Atmospheric Pressure Field 

 Experiment Two: 17 August 1983 18:00 CST........................................................125 

Figure 7.34. Hurricane Alicia GBM Atmospheric Pressure Field 

 Experiment Two: 18 August 1983 18:00 CST........................................................127 

Figure 7.35. Hurricane Alicia GBM Wind Field 

 Experiment Two: 17 August 1983 18:00 CST .......................................................127 

Figure 7.36. Hurricane Alicia GBM Wind Field 

 Experiment Two: 18 August 1983 18:00 CST........................................................128 

Figure 8.1. Tropical Storm Allison Storm Track 5-6 June 2001.................................................130 

Figure 8.2. Tropical Storm Allison GBM Water Levels: 

 5 June 2001 Nowcast/Forecast Cycle......................................................................134 

Figure 8.3. Tropical Storm Allison GBM Water Levels: 

 6 June 2001 Nowcast/Forecast Cycle......................................................................135 

Figure 8.4. Tropical Storm Allison HSCM Water Levels and GBM Water Level Residual: 

 5 June 2001 Nowcast/Forecast Cycle......................................................................136 
xi

LIST OF FIGURES 

Figure 8.5. Tropical Storm Allison HSCM Water Levels and GBM Water Level Residual: 

 6 June 2001 Nowcast/Forecast Cycle......................................................................137 

Figure 8.6. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity: 

 5 June 2001 Nowcast/Forecast Cycle......................................................................138 

Figure 8.7. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity: 

 6 June 2001 Nowcast/Forecast Cycle.......................................................................139 

Figure 8.8. Tropical Storm Allison HSCM Morgans Point Wind and Atmospheric Pressure: 

 5 June 2001 Nowcast/Forecast Cycle.......................................................................140

Figure 8.9. Tropical Storm Allison HSCM Morgans Point Wind and Atmospheric Pressure: 

 6 June 2001 Nowcast/Forecast Cycle......................................................................141 

Figure 8.10. Tropical Storm Allison GBM Significant Wave Height: 

 5 June 2001 Nowcast/Forecast Cycle....................................................................143 

Figure 8.11. Tropical Storm Allison HSCM and GBM 42035 Significant Wave Height: 

 5 June 2001 Nowcast/Forecast Cycle....................................................................144 

Figure 8.12. Tropical Storm Allison Standard Inflows 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................147 

Figure 8.13. Tropical Storm Allison Standard Inflows 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................148 

Figure 8.14. Tropical Storm Allison GBM Water Levels 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................149 

Figure 8.15. Tropical Storm Allison GBM Water Levels 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................150 

Figure 8.16. Tropical Storm Allison HSCM Water Levels and GBM Water Level Residual 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................151 

Figure 8.17. Tropical Storm Allison HSCM Water Levels and GBM Water Level Residual 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................152 

Figure 8.18. Tropical Storm Allison GBM Bolivar Roads Currents 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................153 

Figure 8.19. Tropical Storm Allison GBM Bolivar Roads Currents 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................154 

Figure 8.20. Tropical Storm Allison GBM Redfish Bar Currents 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................155 

Figure 8.21. Tropical Storm Allison GBM Redfish Bar Currents 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................156 

Figure 8.22. Tropical Storm Allison GBM Morgans Point Currents 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................157 

Figure 8.23. Tropical Storm Allison GBM Morgans Point Currents 

 .Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................158 

Figure 8.24. Tropical Storm Allison GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................159 

Figure 8.25. Tropical Storm Allison GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................160 

Figure 8.26. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle.......................................161 
xii

LIST OF FIGURES 

Figure 8.27. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle.......................................162 

Figure 8.28. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle........................................163 

Figure 8.29. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle........................................164 

Figure 8.30. Tropical Storm Allison Wind and Atmospheric Pressure 

 at Morgans Point Experiment One: 10 June 2001 Nowcast/Forecast Cycle...........165 

Figure 8.31. Tropical Storm Allison Wind and Atmospheric Pressure 

 at Morgans Point Experiment One: 11 June 2001 Nowcast/Forecast Cycle...........166 

Figure 8.32. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment One: 11 June 2001 Nowcast End.........................................................167 

Figure 8.33. Tropical Storm Allison HSCM Near Bottom Salinity Field 

 Experiment One: 11 June 2001 Nowcast End.........................................................168 

Figure 8.34. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment One: 11 June 2001 Forecast End..........................................................169 

Figure 8.35. Tropical Storm Allison HSCM Near Bottom Salinity Field 

 Experiment One: 11 June 2001 Forecast End..........................................................170 

Figure 8.36. Tropical Storm Allison City of Houston Inflow Set One 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle.......................................172 

Figure 8.37. Tropical Storm Allison City of Houston Inflow Set One 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle.......................................173 

Figure 8.38. Tropical Storm Allison City of Houston Inflow Set Two 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle.......................................174 

Figure 8.39. Tropical Storm Allison City of Houston Inflow Set Two 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle.......................................175 

Figure 8.40. Tropical Storm Allison HSCM Water Levels and GBM Water Level Residual 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle.......................................176 

Figure 8.41. Tropical Storm Allison HSCM Water Levels and GBM Water Level Residual 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle.......................................177 

Figure 8.42. Tropical Storm Allison HSCM Morgans Point 

 Currents Experiment Two: 10 June 2001 Nowcast/Forecast Cycle.......................178 

Figure 8.43. Tropical Storm Allison HSCM Morgans Point Currents 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle.......................................179 

Figure 8.44. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle.......................................180 

Figure 8.45. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle.......................................181 

Figure 8.46. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle.......................................182 

Figure 8.47. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle.......................................183 

Figure 8.48. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment Two: 10 June 2001 Nowcast End........................................................184 
xiii

LIST OF FIGURES 

Figure 8.49. Tropical Storm Allison HSCM Near Bottom Salinity Field 

 Experiment Two: 10 June 2001 Nowcast End.........................................................185 

Figure 8.50. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment Two: 11 June 2001 Forecast End.........................................................186 

Figure 8.51. Tropical Storm Allison HSCM Near Bottom Salinity Field 

 Experiment Two: 11 June 2001 Forecast End.........................................................187 
xiv

LIST OF TABLES 

Table 5.1. Major Runoff Descriptors for Use 

 in USGS Rainfall/Runoff Regression Relations.......................................................... 17 

Table 5.2. Basin Characteristics for Major Runoff in the City of Houston.................................. 18 

Table 5.3. USGS Runoff Characteristic Regression Equations from Liscum (2001).................. 19 

Table 5.4. Average Daily Flow (cfs) Comparison June 3-12, 2001 

 during Tropical Storm Allison..................................................................................... 20 

Table 5.5. Empirical Reduction Factors for Large Rainfall Events..............................................20 

Table 5.6. Test Topography Based on Cell-Centered Distance 

 from mid-Bay (29.4o

N,95.0oN)................................................................................... 22 

Table 5.7. Test Storm Surge Specifications Based Upon 

 Hurricane Carla (1961) and Alicia (1983) Surge Levels............................................. 22 

Table 5.8. Simulated Mean Water Surface Elevation (m) 

 JD 249.75-250.75 Nowcast Cycle with Test Storm Surge.......................................... 22 

Table 5.9. Hurricane and Pressure Fields For An Arbitrary Storm Based 

 On SPH, Tetra Tech, and Holland Methods................................................................ 24 

Table 5.10. Major Storm Characteristics for Galveston Bay, Texas............................................ 27

Table 6.1. Hurricane Carla Storm Characteristics 3-16 September 1961.................................... 30 

Table 6.2. Hurricane Carla (1961) Windspeed Validation........................................................... 80 

Table 6.3. Hurricane Carla (1961) GBM Storm Surge Validation............................................... 81 

Table 6.4. Hurricane Carla (1961) GBM Minimum Surface Salinity. 

 and Maximum Surface Current Speeds....................................................................... 81 

Table 6.5. Hurricane Carla (1961) Inundation Statistics.............................................................. 82 

Table 7.1. Hurricane Alicia Storm Characteristics 15-21 August 1983....................................... 86 

Table 7.2. Hurricane Alicia (1983) Windspeed Validation........................................................ 117 

Table 7.3. Hurricane Alicia (1983) GBM Storm Surge Validation............................................ 117 

Table 7.4. Hurricane Alicia (1983) GBM Minimum Surface Salinity. 

 and Maximum Surface Current Speeds..................................................................... 118 

Table 7.5. Hurricane Alicia (1983) Inundation Statistics........................................................... 118 

Table 8.1. Tropical Storm Allison Storm Characteristics 5-6 June 2001................................... 130 

Table 9.1. Hurricane Carla (1961) Long and Short Wave Computational Time....................... 189 

Table 9.2. Hurricane Alicia (1983) Long and Short Wave Computational Time...................... 189 

Table 9.3. Tropical Storm Allison (2001) Coastal Surge Propagation Event 

 Long and Short Wave Computational Time.............................................................. 190 

Table 9.4. Tropical Storm Allison (2001) Rainfall/Runoff Event 

 Long and Short Wave Computational Time.............................................................. 190 
BUFFALO BAYOU SAN JACINTO RIVER 

TRINITY RIVER 

SABINE PASS 

NDBC 42035 

FREEPORT 

Galveston Bay Base Map

xv
xvi

EXECUTIVE SUMMARY 

Since the transfer of the NOS Galveston Bay Experimental Nowcast/Forecast System (GBEFS) 

to operational status in June 2004, the experimental system has continued to be run and 

enhanced. This report documents the work to extend the modeling system to consider storm 

surge within the context of an all-weather nowcast/forecast capability. The long wave and short 

surface gravity wave equations are developed. Some initial approaches to wave current 

interaction are outlined but are not considered in the computations, nor are wave runup, 

overtopping, and barrier island breaching, which all represent areas for additional research. 

Overland flooding, rainfall/runoff, and blended hurricane wind and pressure field forcing have 

been incorporated within the system. In addition, surface gravity wave algorithms have been 

incorporated in both hydrodynamic models to simulate hurricane wave conditions. Simulations 

of Hurricane Carla (1961), Hurricane Alicia (1983), and Tropical Storm Allison (2001) are 

presented with results compared to observations. Operational considerations are also addressed 

and recommendations for further improvements are presented. 
1

1. INTRODUCTION 

To assess the feasibility of including storm surge computations within the NOS Galveston Bay 

Experiment Nowcast/Forecast System thereby moving towards an all weather capability, the 

following processes have been considered: 1) rainfall/runoff inflows from four major basins 

within the City of Houston, 2) overland flooding, 3) tropical storm and hurricane wind and 

pressure fields, and 4) surface gravity waves. The governing long wave and short surface gravity 

wave equations are developed in Chapters 2 and 3, respectively and wave-current interaction is 

discussed in Chapter 4 as further development. The algorithms used to describe each of the 

above processes are presented in Chapter 5 followed by the design of the all weather 

nowcast/forecast system. Simulations of Hurricane Carla (1961), Alicia (1983), and Tropical 

Storm Allison (2001) are considered in Chapters 6, 7, and 8, respectively. Tropical Storm Allison 

consists of a storm surge event on 5-6 June and a rainfall/runoff event on 10-11 June. Results for 

each event are presented. Operational considerations are discussed in Chapter 9, while 

conclusions and recommendations for future work are outlined in Chapter 10. 
Figure 1.1. Map showing Galveston Bay and the Houston Ship Channel including PORTS 

stations.

2
2. LONG WAVE HYDRODYNAMIC MODEL

2.1. Governing Equations

A three-dimensional sigma coordinate Galveston Bay and near shelf model (GBM) has been 

developed (Schmalz, 1996) based on a version of the Princeton Ocean Model (POM) developed 

by Blumberg and Mellor (1987) extended to orthogonal curvilinear coordinates. GBM is a threedimensional baroclinic circulation model for simulating water levels, current velocities, and 

density. The model is forced with: water levels at the near shore open boundaries based on 

observed levels at Galveston Pleasure Pier; freshwater inflows from the Buffalo Bayou, San 

Jacinto, and Trinity Rivers; and surface winds. In addition, a high resolution Houston Ship 

Channel model (HSCM) has been incorporated to provide finer spatial resolution along the 

channel (Schmalz, 1998a; 2000a; 2000c). The governing equations in a vertical sigma coordinate 

are briefly given as follows. Detailed formulation is contained in Blumberg and Mellor (1987), 

Mellor (2003b), and Schmalz (2001). 

=I 0)1( , (2.1) 

x

a M Fd

x

DgD d

x

gDU

D

K

x

P gDfDVU +

∂

∂

∂

∂

+

∂

∂ −⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = ∂

+∂ +−I ∫ ∫ σ

σ

ρ σ

ρ

σ ρ

ρσσ

η

σ σ

0

0

0

0

2 )( )( , (2.2) 

y

a M Fd

y

DgD d

y

gDV

D

K

y

P gDfDUV +

∂

∂

∂

∂

+

∂

∂ −⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = ∂

+∂ ++I ∫ ∫ σ

σ

ρ σ

ρ

σ ρ

ρσσ

η

σ σ

0

0

0

0

2 )( )( , (2.3) 

T

H F T

D

K

T +⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

σσ

)( , (2.4) 

S

H F S

D

K S +⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

σσ

)( , (2.5) 

q

q M H F

lB

VU gK Dq

D

q K

D

K

q +−

∂

∂

+

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎟ + ⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

1

3

0

2 2 2

2 2 2 2 )(

σ

ρ

σσ ρσσ

, (2.6) 

H l

q M FW

B

Dq K VU gE

D

K lE lq

D

K

lq +−⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

∂

∂

+⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎟

⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎟ + ⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I ~

1

3

0

3

2 2

1

2

2 )( )(

σ

ρ

σσ ρσσ

, (2.7) 

where 

σ

ω

∂

∂

+

∂

∂

+

∂

∂

+

∂

∂ =I****

(*)

y

VD

x

UD

t

D and σ = (z-η)/(H+η). Here (x,y,z,t) are the Cartesian 

spatial and temporal coordinates and D=H+η is the total water depth with H the depth and η the 

water surface elevation with respect to model datum. Patm is the sea level atmospheric pressure in 

millibars with 

g

P

P atm

a

0

100

ρ = , U and V horizontal velocities, S and T salinity and temperature, KM

and KH the vertical kinematic viscosity and diffusivity, respectively, Kq the vertical turbulence 

mixing coefficient, q

2

 twice the turbulence kinetic energy, and l is the turbulence length scale. 

Note 2

2

~

)(1

L

l EW

κ

+= , κ = 0.4 is the von Karman constant with L-1=(η-z)-1+(H+z)-1, and BB

1, E1, 

E2, and E3 are constants. g is the acceleration due to gravity, f is the Coriolis parameter, ρ=f(S,T)

3
is the water density, and ω is the transformed vertical velocity normal to a sigma surface. The 

relation of ω ( σ / dtHd ) to the Cartesian vertical velocity w is 

tt

D

yy

D V

xx

D Uw

∂

∂

+

∂

∂

+⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

+

∂

∂

+⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

+

∂

∂

+= η σ η σ η σω . (2.8) 

The horizontal viscosity Fx and Fy and diffusion terms F* are defined as 

⎥

⎦

⎤ ⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+

∂

∂

∂

∂

+⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = x

V

y

U DA

yx

U DA

x

Fx 2 M M (2.9) 

⎥

⎦

⎤ ⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+

∂

∂

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = x

V

y

U DA

xy

V DA

y

Fy 2 M M , (2.10) 

⎥

⎦

⎤ ⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

∂

∂

+⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = y

DA

yx

DA

x

F H H

* * * , with *=(T,S,q,l,C) (2.11) 

where AM = AH are the horizontal eddy viscosity and diffusivity, defined by the Smagorinsky 

formula (1963) 

 5.0 2 2 2

5.0 ⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+

∂

∂ ⎟ + ⎠

⎞ ⎜

⎝

⎛

∂

∂ ΔΔ=

y

V

x

V

y

U

x

U

NM yxCA , (2.12) 

with CN being a non-dimensional parameter. 

. 

For the passive tracer sulfur hexafluoride (SF6), the concentration equation is 

C

H F C

D

K C +⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

σσ

)( (2.13) 

where C is the concentration of SF6.

Boundary conditions at the free surface (σ=0) are as follows: 

*3/2

1

2 ~~~

,0 ),,(, ,0),,,(,, s

H

sysx

M uBqlCTS CTS

H

VU K

H

K ⎟ = == ⎠

⎞ ⎜

⎝

⎛

∂

∂

∂

∂

∂

∂ ⎟ =

⎠

⎞ ⎜

⎝

⎛

∂

∂

∂

∂ = σσσ

ρττ

σσ

ρω (2.14) 

Boundary conditions at the bottom (σ=-1) are as follows: 

*3/2

1

2 ,0 ),,(, ,0),0,0,0(,, b

H

bybx

M uBql CTS

H

VU K

H

K ⎟ ===⎠

⎞ ⎜

⎝

⎛

∂

∂

∂

∂

∂

∂ ⎟ =

⎠

⎞ ⎜

⎝

⎛

∂

∂

∂

∂ = σσσ

ρττ

σσ

ρω (2.15) 

where τs and τb are the wind stress and bottom friction and ),,( are surface fluxes. ~~~

CTS

The above equation set is transformed into orthogonal horizontal coordinates after Blumberg and 

Herring (1987) with 

dt

d hU

dt

d hUdhdhdydxdsdhdydhdx 2

22

1

11

2

2

2

2

2

1

2

1

222

11 22 , , and , ε ε = ε = ε +=+= εε = = . 

=I 0)1( (2.16) 

4
12

0

11

0

0 11

1

11

)

2

2

~

1

( )( Fd

h

D d

h

D U gD K

D

K

h

P

h

gD U DU M

a M f ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂

+

∂

∂ −⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = ∂

+∂

+−I ∫ ∫ σ

σ

ρ σ

ε

σ

ε

ρ

ε ρσσ

η

σ σ

(2.17) 

21

0

22

0

0 22

2

221

1

~

2

)( )( Fd

h

D d

h

D U gD K

D

K

h

P

h

gD U DU M

a M f ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂

+

∂

∂ −⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ = ∂

+∂ ++I ∫ ∫ σ

σ

ρ σ

ε

σ

ε

ρ

ε ρσσ

η

σ σ

(2.18) 

T

H F T

D

K

T +⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

σσ

)( (2.19) 

S

H F S

D

K S +⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

σσ

)( (2.20) 

q

q M H F

lB

U U gK Dq

D

q K

D

K

q +−

∂

∂

+

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ ⎟

⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎟ +

⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

1

3

0

2

2

2

1

2

2 2 2 2 )(

σ

ρ

σσ ρσσ

 (2.21) 

H l

q M FW

B

Dq K U U gE

D

K lE lq

D

K

lq +−⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

∂

∂

+

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ ⎟

⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎟ +

⎠

⎞ ⎜

⎝

⎛

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I ~

1

3

3

2

2

2

1

1

2

2 )( )(

σ

ρ

σσ σ ρσ

 (2.22) 

where 

σ

ω

ε ε ∂

∂

+

∂

∂

+

∂

∂

+

∂

∂ =I *)( *)(*)( *)( (*)

221

21

121

12

hh

DUh

hh

DUh

t

D

2

1

21

1

1

2

21

2

~

∂εε

∂ − ∂

∂

+=

h

hh

Uh

hh

U f f

The relationship of ω with the Cartesian vertical velocity w is 

tt

D D

h

D U

h

U

w

∂

∂

+

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

+

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

+

∂

∂

+= η σ

ε

η

ε

σ

ε

η

ε

σω

1 22

2

2 11

1 . (2.23) 

The horizontal viscosity Fij and diffusion terms F* are defined as 

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+

∂

∂

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =

ii

jj

jj

ii

M

ii j

ij

M

iji

ij h

Uh

h

Uh DA

h

Uh

DA

hh

F

ε εε εε

2 1 (2.24) 

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

∂

∂ ⎥ +

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =

22

1

11 2

2

121

*

1 * *

ε εε h ε

h DA

h

h DA

hh

F H H , with *=(T,S,q,l,C) (2.25) 

where 

5.0 2

2

2

2

1

2

2

1

2

1

1

21 5.0 ⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂

+

∂

∂

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∂

∂ == ε εεε

U UU U

NHM hhCAA , (2.26) 

where CN, a non-dimensional parameter, is set to be 0.005 for both Bay and Channel models. 

. 

For the passive tracer SF6, the concentration equation is 

5
C

H F C

D

K C +⎥

⎦

⎤ ⎢

⎣

⎡

∂

∂

∂

∂ =I

σσ

)( (2.27) 

where C is the concentration of SF6.

Boundary conditions at the free surface (σ=0) and at the bottom σ=-1) remain as given above, 

while the concentration lateral open boundary condition during the outflow is specified with onedimensional advection, ( ) ( ) = 0

∂

∂

+

∂

∂

ii

i

h

DCU

t

DC

ε

, where Ui is the velocity in the normal direction to 

the boundary while the following gradient condition is used for inflow, ( ) ( ) = 0

∂

∂ = ∂

∂

ii

i

h

DCU

t

DC

ε . 

2.2. Model Grids

The GBM computational grid as shown in Figure 2.1 consists of 181x101 horizontal cells (dx = 

254-2482m, dy= 580-3502m) with 5 levels in the vertical. GBM water depths range from 1 m in 

the shallows to 20m along the shelf boundary (Figure 2.2). The HSCM grid shown in Figure 2.3 

was developed in three sections. Each grid section was linked in order to develop the final 

composite channel grid consisting of 71 x 211 horizontal cells (dx=63-1007m, dy=133-1268m) 

with the same 5 sigma levels as in the GBM. Note navigation channel depths are order 14m. The 

HSCM was then nested inside the GBM using a one-way coupling scheme, wherein GBM water 

surface elevation, salinity, temperature, turbulent kinetic energy, and turbulent length scale time 

histories were saved at 6-minute intervals to provide boundary conditions to drive the HSCM. 

For salinity, temperature, turbulent kinetic energy, and turbulent length scale, a one-dimensional 

(normal to the boundary) advection equation is used. On inflow GBM values are advected into 

the HSCM domain, while on outflow HSCM internal values are advected through the boundary. 

6
Figure 2.1. Galveston Bay model grid. 

7
Figure 2.2. Galveston Bay model bathymetry, contours in meters.

8
Figure 2.3. Galveston Bay model grid in red with Houston Ship Channel grid shown in 

green. 

9
10
3. SHORT WAVE HYDRODYNAMIC MODEL 

Schmalz (2003) has compared two USACE parametric wave models (CETN-I-6, 1981; 

Project CW-167, 1955) with the finite difference based Donelan (1977) wave model for 

wind events over Galveston Bay. The two parametric models were run on the same grid 

employed for the Bay circulation model (Figure 2.1), while a uniform square grid was 

used for the Donelan model. Further details on the Donelan (1977) wave model may be 

found in Schwab et al. (1984). Details of the initial testing may be found in Schmalz 

(2003). Best results were achieved by the mixture of the two parametric models as 

presented in the governing equations below and described in section 3.2. 

3.1. Governing Equations 

CETN-I-6 (1981) significant wave height, Hs (ft): 

]

]]/[530.0tanh[

]/[00565.0 tanh[]]/[530.0tanh[283.0 75.02

5.02

75.02

2

A

A

A

A

S

UgD

UgF UgD U

gH = (3.1)

CW-167 (Project CW-167, 1955): significant wave period, Ts (sec): 

4507.0

2 )(262.6

A

A

S U

gD

g

U T = (3.2) 

using the following notation: 

g = Gravitational acceleration (32.2 ft/sec2

) 

UA = Windspeed (kts) 

F = Fetch (nm) 

D = Total water depth (ft) 

3.2. Initial Validation 

The January 25-30, 1997 time period was studied due to the availability of USACE wave 

measurements off Eagle Point. Application of the models to this period revealed that best 

results were achieved by using a combination of the two simpler parametric wave 

models, even though the finite difference based Donelan model incorporated the shallow 

water effects by using a linear reduction in transfer of wind to wave momentum as 

described in Schmalz (2003). Total significant wave height was computed as the sum of 

the CETN-I-6 results plus the swell, which was determined at the open boundary from 

the NDBC Buoy 42035 measurements. The total significant wave period was taken as 

equal to the CW-167 result alone. Results for January 25-30, 1997 are shown in Figure 

3.1 at Eagle Point and in Figure 3.2 at NDBC Buoy 42035, respectively. Note, the peak at 

Eagle Point is no longer delayed relative to the observations as experienced using the 

Donelan model with the shallow water adjustment (results not shown) and the peak at 

NDBC Buoy 42035 is well reproduced. 

11
 Figure 3.1. Galveston Bay Wave Model vs Observed Wave Parameters at Eagle Point, 

January 25-30 1997. 

12
 

Figure 3.2. Galveston Bay Wave Model vs Observed Wave Parameters at 42035, 

 January 25-30 1997.

13
3.3 Joint Computation 

The mixed parametric wave model has been included as a subroutine within both the Bay 

and Channel long wave models and uses the same wind field. The waves are computed 

every six-minutes. In the Bay model, fetch data are specified for each octant of wind 

direction at 25 locations surrounding the Bay. An inverse distance squared interpolation 

is performed to determine the fetch distribution over the Bay for each wave computation. 

The long wave model provides the updated total water depth. At each wave computation 

in the Bay model, the swell height and fetch at each boundary point required by the 

Channel model are written on the transfer file in addition to the one-way coupled long 

wave information. Swell effects in the Bay model are input as a boundary condition and 

are reduced from the offshore boundary by a inverse distance squared interpolation of 

empirical reduction factors supplied at the above 25 locations around the Bay. 

3.4. Overtopping and Barrier Island Breaching Limitations 

Several effects associated with milder waves, such as refraction due to changes in 

bathymetry are not specifically treated. The wave field is represented here by a single 

frequency, height, and direction rather than a continuous spectrum. Thus no wave-wave 

interaction is considered. Wave diffraction around breakwaters and jetties and wave 

reflection are also not included. 

The erosion of the barrier island system and breaching of the barrier islands are not 

considered. This would involve the description of the stress and the nature of the barrier 

island soil structure as well as the prediction of soil pressure and sediment transport 

mechanics. The islands may be and are during Hurricane Carla (1961) overtopped by 

overland flooding. 

14
 4. WAVE-CURRENT INTERACTION MECHANICS 

We consider a wave field with significant wave height, H s, dominant period, C, and wave 

direction, φ. The wave direction is assumed to be in the direction of the wind. To 

determine the wave age, it is necessary to compute the wave phase speed, k

Cp

ω

= , where 

C

π

ω

2 = , and )tanh(

2

rkg

k ω = , with , 

where with D and g as defined previously as reported at 

http://web.mit.edu/fluids-modules/www/potential_flows/Lectures. 

⎪⎭

⎪

⎬

⎫

⎪⎩

⎪

⎨

⎧

++ ≤

−+ =

− −

2 031.0169.01(

2 )1221(

5.0 2

2 4

S SS S

eeS S

rk

S S f

/ gDS 2 = ω

The friction velocity, u*, is then computed as = 10* CUu DN 10 , and the wave age is formed 

as the ratio of Cp to u*. 

4.1. Surface Drag Coefficient Adjustment 

In the presence of waves, the surface drag coefficient is increased. Following Drennan et 

al. (2003), we employ their Figure 10 in which the drag coefficient, CD10N, and wind 

speed, U10N, are given versus inverse wave age, u*/Cp. Wind speed ranges are from 5 to 

20 m/s. The following relationships are used in the algorithm to define the adjustment 

factor of the surface drag, F, based the ratio of measured CD10N with respect to inverse 

wage age to the Smith (1980) relationship. 

N p

N p

N p

N p

F U Cu

F U Cu

F U Cu

F U Cu

/ 0.10 /15)5)(05.0(38.1

,10.0/ 0.08 15/)5)(07.0(27.1

,08.0/ 0.06 15/)5)(13.0(16.1

,06.0/ /15)5)(16.0(.1

10 *

10 *

10 *

10 *

p

p

p

−= −

−= − ≤

−= − ≤

−= − ≤

 (3.3) 

The effective surface drag coefficient, is given as the product of the adjustment factor, F, 

and the Large and Pond (1981) surface drag relation: 

eff ND

N N

N

ND

FCC

U smU

smU

xC

10

10 10

3 10

10 / 11 )065.049.0(

 2.1 / 11

10

=

⎭

⎬

⎫

⎩

⎨

⎧

+

≤ = f (3.4) 

Note with no wave current interaction, F=1.0. 

4.2. Bottom Friction Adjustment 

In the presence of waves, the near bottom wave orbital velocity based on linear wave 

theory, Uo is first computed as )sinh(

5.0

kD

H

U s

o

ω = after Signell et al. (1990). The near bottom 

excursion amplitude, ab, and effective roughness, kb, are then determined as 

15
0 30 and zk U

a b

o

b = = ω

, with z0 the bottom roughness. The wave friction velocity, u*w, is 

determined based on in the relationship reported by Grant and Madsen (1982) 

in the following manner: 

bbb = / akS

2

*

62.0

40.0

 with , 5.0

 23.0 0.1

23.0 0.08 0.1

13.0 08.0 

w ow

b

b b

b b

w Ufu

S

S S

S S

f =

⎪

⎭

⎪

⎬

⎫

⎪

⎩

⎪

⎨

⎧

= ≤≤

f

p

 (3.5) 

Next the current friction velocity, u*c, is determined based on the model horizontal 

velocity components (Ub,Vb), at the level nearest the bed as follows (see Davies and 

Lawrence, 1995): 

 with ,)]/1.0ln(/[2 )(5.0 22

*

2

c 0 c VUfu bbc f = κ z = + (3.6) 

The total friction velocity is then determined based on the current friction velocity and 

the wave friction velocity in the direction of the current as follows: 

( )

2

*

2

* * )cos( T wc wc += uuu θ , where θ wc , is the angle between the wave and wind 

directions (refer to Grant and Madsen, 1979). A roughness adjustment is determined 

as T

c

u

u

b

T

p S

U

u

F *

* 1

0

* )( 24 −

= as reported by Signell (1990). The bottom friction adjustment 

factor, Fpb, is given by

2

0

0

)/ln(

)/ln(

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ = zFh

zh F

pb

b

pb . In the present study, Fpb cannot exceed 2. 

The effective bottom roughness is the product of the bottom roughness and this 

adjustment factor. Note in this approach, wave and current effects are considered 

independently (z0 is never altered) and are then combined to determine the adjustment 

factor. In theory, an iterative approach on z0 is desired. 

4.3. Setup and Runup Limitations 

Wave setup and the associated runup at the shoreline due to breaking waves are not 

considered. These effects were considered by Schmalz (1986) in Lake Okeechobee by 

using empirical relations. In general, the radiation stresses induced by the waves must be 

included as an additional stress in the long wave model. This has been accomplished by 

Mastenbroek et al. (1992) within a two-dimensional vertically integrated model. 

Recently, Mellor (2003; 2005) has developed the radiation stress relations in three 

dimensions and initial work has been reported by Mellor and Donelan (2006) on coupling 

a short wave and three-dimensional long wave model including the radiation stresses. 

16
5. STORM SURGE METHODOLOGY 

Storm surge is considered as a rise in water levels associated with either the propagation 

of the offshore storm surge or from the associated river and basin flooding generated by 

the storm rain/runoff. To be able to account for this phenomena within the 

nowcast/forecast system, algorithms for the rainfall/runoff, overland flooding, hurricane 

wind and pressure fields, and surface gravity waves are discussed in Sections 5.1 – 5.4, 

respectively. Next the design of the all-weather nowcast/forecast system is presented in 

Section 5.5. In section 5.6 additional hydrodynamic model considerations are presented 

followed by the discussion of the storm surge simulation objectives. 

5.1. Rainfall/Runoff 

In conjunction with the Houston Urban Runoff Program, the USGS has obtained 

streamflow and rainfall data for major drainage basins throughout the City of Houston 

during 1964 to1989. In an effort to characterize the influence of development on drainage 

characteristics, sets of regression equations for basins north (based on 408 storms) and 

south (based on 331 storms) of Buffalo Bayou have been developed by Liscum (2001) for 

the major descriptors of the runoff as given in Table 5.1. To apply these relations to the 

City of Houston, four major basins are considered with basin characteristics given in 

Table 5.2. 

____________________________________________________________________________ 

Table 5.1. Major Runoff Descriptors for Use in USGS Rainfall/Runoff Regression 

Relations. 

Stormwater Runoff Characteristics

QPEAK = Peak flow (cfs) 

RODUR= Runoff duration (hrs) 

TRISE=Time of rise from base flow to QPEAK (hrs) 

Q75DUR=Duration of flow that equals or exceeds 75 percent of QPEAK (hrs) 

Q50DUR=Duration of flow that equals or exceeds 50 percent of QPEAK (hrs) 

TRECES=Time of recession from QPEAK to base flow (hrs) 

BLAG=Duration from centroid of storm rainfall to centroid of direct runoff (hrs) 

Rainfall Event Characteristics

RTOT=Total rainfall (in) 

R60MAX=Maximum 60-minute rainfall (in) 

RDUR=Rainfall duration (hrs) 

R85DUR=Shortest 85 percent RDUR (hrs) 

RI=Antecendent rainfall index (in) 

______________________________________________________________________________

17
Table 5.2. Basin Characteristics for Major Runoff in City of Houston. Note Region 1 is 

located North and Region 2 South of Buffalo Bayou. 

Characteristic Greens Bayou Brays Bayou Sims Bayou Hunting Bayou 

USGS Gage 

No. 

08076700 08074760 08075500 08075770 

Region 1 2 2 1 

Total Basin 

Drainage Area 

(DA) (mi2

) 

182.0 94.9 20.2 16.1 

Gage Drainage 

Area (DA) 

(mi2

) 

182.0 94.9 64.0 16.1 

Basin 

Development 

Factor (BDF) 

(0-12) 

7 8 8 8 

Basin Slope 

(SL) 

(ft/(ft/mi)0.5

4.5 3.9 3.9 3.9 

Base flow (cfs) 0.0 0.0 0.0 0.0 

Daily hyetographs are separated into nevent, rainfall events by specifying a no rainfall 

minimum duration of 12 hours between events. Then for each event, the rainfall event 

characteristics in Table 5.1 are computed for use in the regression equations given in 

Table 5.3. 

The antecedent rainfall index is a key parameter and is determined at the start of each 

event based on the hourly rainfall of the previous 5 days using the following relation: 

RI RI k r t n (5.1) t t

t =+= −1 t

Δ

Δ 1,...

where 

 RI0=Initial value (inches) 

 RIt=Reduced value of the index t hours later (inches) 

 k=Recession factor set to 0.9 after Linsley et al. (1982) 

 Δt=Tt – Tt-1 (hrs) 

 rΔt=Rainfall during Δt 

For each t=1,...n, the event flows Qi

tfor i=1,nevents are summed to obtain the basin 

hydrograph. 

18
Table 5.3. USGS Runoff Characteristic Regression Equations from Liscum (2001). 

Region Equation R2

 (percent) 

1 QPEAK=312 DA 0.728 (13-BDF) -1.04 RTOT 0.984 RI 0.135 87 

2 QPEAK=312 DA 0.735 (13-BDF) -1.07 RTOT 0.837 RI 0.093 87 

1 RODUR=13.7 DA 0.199 (13-BDF) 0.227 RTOT 0.298 R85DUR 

0.154

67 

2 RODUR=10.7 SL 0.410 (13-BDF) 0.439 RTOT 0.274 R85DUR 

0.117

66 

1 TRISE=1.93 DA 0.199 RTOT 0.741 R60MAX –0.519 R85DUR 

0.255

55 

2 TRISE=1.63 DA 0.278 RTOT 0.501 R60MAX –0.357 R85DUR 

0.266

50 

1 Q75DUR=0.374 DA 0.294 (13-BDF) 0.678 RTOT 0.678

R60MAX –0.425

77 

2 Q75DUR=0.367 DA 0.274 (13-BDF) 0.646 RTOT 0.682

R60MAX –0.431

55 

1 Q50DUR=0.665 DA 0.287 (13-BDF) 0.723 RTOT 0.625

R60MAX –0.454

80 

2 Q50DUR=0.624 DA 0.271 (13-BDF) 0.711 RTOT 0.665

R60MAX –0.471

57 

1 TRECES=9.50 DA 0.223 (13-BDF) 0.337 RTOT 0.282 R85DUR 

0.084

62 

2 TRECES=9.17 SL 0.435 (13-BDF) 0.473 RTOT 0.314 RI 0.091 58 

1 BLAG=0.720 DA 0.333 (13-BDF) 0.781 RTOT 0.126 R85DUR 

0.106

77 

2 BLAG=0.693 SL 0.481 (13-BDF) 0.969 RTOT 0.296 RI 0.110 62 

To test the scheme, basin rainfall records were obtained from 3-12 June 2001 during 

Tropical Storm Allison from the Harris County Flood Control District. Computed 

average daily runoff flows using the above method were compared with the USGS 

records as shown in Table 5.4. 

Results given in Table 5.4 were computed by applying the reduction factors based on 

event rainfall totals to TRISE, TRECES, BLAG, Q50DUR, and Q75DUR given in Table 

5.3. This was necessary to improve the timing of the runoff flows, since the regression 

equations were developed for rainfall events of less than 5 inches. 

19
Table 5.4. Average Daily Flow (cfs) Comparison June 3-12, 2001 during Tropical Storm 

Allison. Note Pred=Prediction, Obs=Observation, and e following observation denotes an 

estimated value. 

Date 2001 Greens Bayou 

Pred Obs

Brays Bayou 

Pred 

Obs 

Sims Bayou 

Pred 

Obs 

Hunting Bayou 

Pred 

Obs 

June 3 0 - 0 

107 

0 

8.8 

0 

4.8 

June 4 0 - 0 

106 

0 

7.3 

0 

5.5 

June 5 0 

1110 

166 

3100 

32 

862 

0 

378 

June 6 6438 

13500 

4927 

960 

876 

809 

866 

1290 

June 7 5520 

2540 

2013 

5560 

476 

3210 

787 

332 

June 8 2938 

2380 

1001 

3000 

200 

939 

257 

601 

June 9 37609 

59300e 

12377 

14000e 

1021 

4650 

4172 

2950 

June 10 17886 

41100e 

4839 

530e 

358 

109 

405 

1320 

June 11 1240 

4240e 

210 

210 

110 

27 

17 

103 

June 12 54 

702 

9 

137 

5 

17 

1 

45 

Total 

Rainfall(in) 

34.07 21.07 12.90 24.11 

Total Pred 

Runoff (in) 

13.82 9.49 5.39 14.06 

Ratio 1 0.406 0.450 0.418 0.583 

Ratio 2 0.352 0.655 0.479 - 

Ratio 1== Total Predicted Runoff/Total Rainfall June 3-12, 2001; Ratio 2==Average 

Yearly Runoff/Average Yearly Rainfall with averages computed over 1965-1989. 

Table 5.5. Empirical Reductions Factors for Large Rainfall Events 

Rainfall total (in) 5 10 15 20 25 50 

Reduction factor 1. 0.5 0.25 0.33 0.29 0.2 

5.2. Overland Flooding Scheme 

The scheme was developed to supplement the drying/wetting scheme previously 

developed (Schmalz, 1998a; 2001). The original scheme allowed water areas to dry and 

subsequently wet (tidal flat problem) but did not allow land areas to flood. To 

accommodate this feature, a digital elevation model or test topography is used in which 

20
land elevations are set to a maximum of –1 m. Along the grid border, land elevations are 

set to –100m. Since it is necessary to perform computations over dry grid cells, a 

minimum water depth, dflood, is specified. Subsequent cell and cell face flags properly 

mask any undesired results. For surface temperature specification, a value tflood=29.5o

C 

is used for the overland flood cells. The flood scheme is actuated each internal mode time 

step and consists of the following check for a typical u-velocity face to see if it should be 

activated. Activation is based on the water level in the wet cell exceeding the dry cell bed 

elevation by a critical depth, dcrit, equal to 10dflood plus the depth needed to account for 

the water initially placed on the dry cell as given in the relation below, following 

Mellor’s (2003) notation: 

If , = 0, and , then we compute

.

If and then

 and the cell face is activated

and , , where 

dumi,j fsmi,j fsmi ,j

dil dflood*arti,j/arti ,j

eli ,j

m h

i,j dcrit dil di ,j

m dcrit

fsmi,j ioveri,j dumi,j

F

i,j,k

m F

i ,j,k

m F

i,j,k

m F

i ,j,k

m , k ,...kbm F (T,S,Q ,Q l)

= − =

= −

− +> + − >

= ==

= −

− = −

− = ==

0 1 1

1

1 1 2

1

1

1

1

1 1 1 2 2

 (5.2) 

A similar procedure is used for the case, dumi,j=0, fsmi,j=1, and fsmi-1,j=0 and for the vcell face. Once both u and v faces have been activated, the potential exists on a u-face for 

both fsmi,j=fsmi-1,j=1 with dumi,j=0. If this occurs, the average u-cell face water depth, 

dbar, is computed as If dbar > dcrit + dflood

then dum

dbar eli j

m eli j

m h

i j hi j = + − + + − 0 5 1 . ( , ,, ). 1,

i,j=1. An analogous procedure is used for the v-face. To monitor the 

computations and determine the areal extent of overland flooding, the following 

procedures were implemented. First an additional cell mask, imaski,j, was created and set 

to 1. If the cell bed elevation becomes negative, imaski,j=-1. If overland flooding occurs, 

ioveri,j=1 and imaski,j=0. This allows water depths over the complete water area, or over 

just the overland flooded portions of the grid, to be printed/plotted. 

Two test applications were employed in which dflood=25mm and dcrit=25cm. In the first 

application a test topography was specified based on the cell’s distance from mid-Bay as 

given in Table 5.6. In the second application, the USGS 3-arc second DEM for HoustonWest and Houston-East was used to specify the overland topography. In both 

applications, the 8 Sept 1999 JD 251 24-hour nowcast cycle (249.75-250.75) was 

simulated with the test surge given in Table 5.7 imposed. Model mean water surface 

elevations at three locations are given in Table 5.8 for each case. While the model mean 

and maximum water surface elevations were very close at the stations in Table 5.8, the 

areal extent of the flooding was vastly different. For the test topography, only order 10 

grid cells in the lower eastern portion of the Bay mean sea level boundary were inundated 

with flood depth levels of order 0.5m. For the DEM topography, order 1000 grid cells 

over major portions of the Bay east and west mean sea level boundaries were inundated 

with flood depth levels of order 2.2m. The river input flow cells were surrounded by 

floodwater. 

21
One should also note that salinity computations are performed over the flooded areas and 

as the water recede the flooded cells become inactive (they do no communicate with the 

Bay grid cells) and retain the values of salinity that were present when they were active 

during the surge propagation phase of the storm. 

Table 5.6. Test Topography based on Cell-Centered Distance from mid-Bay 

 (29.4o

N, 95.0oW). 

Distance (km) 0 5 10 15 20 25 30 35 40 45 50 

Bed elevation (m) -2. –2.5 -3.0 -4.0 -5.0 -6.0 -7.0 -8.0 -10.0 -12.0 -15.0 

Table 5.7. Test Storm Surge Specification based upon Hurricane Carla and Alicia surge 

levels. 

Elapsed Time (Hours) 0 6 12 48 72 

Surge Level (m) 0. 2.5 3.5 2.0 1.0 

Table 5.8. Simulated Mean Water Surface Elevation (m) JD 249.75-250.75 Nowcast 

Cycle with Test Storm Surge. 

Case Galveston Pleasure 

Pier 

Port Bolivar Galveston Pier 21 

Test Topography 3.07 2.23 2.60 

DEM Topography 3.05 2.51 2.66 

5.3. Hurricane Windfield and Atmospheric Pressure Algorithms 

Initially, the work of Schmalz (1986a,b,c) was reviewed to consider the Standard Project 

Hurricane (SPH) and the Tetra Tech (1979) models. A more recent parametric model 

developed by Holland (1980) and further modified by Sinha and Mandal (1999) was also 

considered. Each is outlined below and was studied using a hypothetical storm track and 

parameter set (R= radius to maximum winds, Po=far field atmospheric pressure, and ΔP= 

atmospheric pressure deficit). Each approach uses an inflow angle, α, as given by 

Graham and Nunn (1959) in the following relationship: 

 (5.3) α =

≤

+ − <<

≥

⎧

⎨

⎪

⎩

⎪

⎫

⎬

⎪

⎭

⎪

10

10 15 12 12

25 12

d R d R

dR R Rd R

d R

/

( )/ . .

.

where d=Distance from the storm center 

 

Each approach also uses the Schwerdt et al. (1979) asymmetry factor to account for storm 

forward speed as follows:

22
θ θ α

θ θθ

θ

max

max

. . cos

= ++

= −

=

h

a s

V

a

V f a

90

15 163

 

 (5.4) 

where 

θh=Storm direction bearing θmax=Bearing of maximum wind 

α=Inflow angle θa=Asymmetry angle 

θs=Storm center bearing Va=Asymmetry speed adjustment 

Vf=Storm forward speed 

For the Standard Project Hurricane (SPH), the maximum gradient windspeed is 

determined from the following relation: 

V P (5.5) gx = − 67 1800 1 2 Δ / ΩR

R

where 

ΔP=Central pressure deficit 

Ω=Earth rotation 

The maximum sustained windspeed at 10m, is then determined by Vmax=0.9Vgx. 

Next a reduction factor, fr is determined by fits to observed radial wind profiles in 

Schwerdt et al. (1979) and is given by: 

f (5.6) dR d R

e d r d R = ≤>

⎧

⎨

⎩

⎫

⎬

⎭ − +

(/)

(/ /)

3

7 17

where d and R are as previously defined. The complete windspeed, V, including 

asymmetry effects and Schloemer (1954) pressure profile, P, are given by: 

V fV V

P P Pe

r a

R d

= +

=+ − −

max

/ ( ) 0 Δ 1 (5.7) 

where quantities on the right hand sides have been previously defined. 

For the Tetra Tech approach, the algorithm is the same as the SPH algorithm with the 

exception of the relation for fr, which is replaced by the following relation developed by 

Collins and Viehman (1971). 

f

d R

dR R d R

cd R cd d R

r

k m

=

< ≤

− <

>

⎧

⎨

⎪

⎩

⎪

⎫

⎬

⎪

⎭

⎪

0 0

32 13 3

1 1 2

/

/( / /) /

/ log( / )

≤

3

 (5.8) 

where x cc k m 1 2

3 = = =− = 3354 1265 10 015128 1607 − ., . , . , ..

For the Holland approach, the storm category, kcat, is first determined based on the central 

pressure deficit using the following relation: 

23
k (5.9) 

P

P

P

P

cat =

≤

< ≤

< ≤

>

⎧

⎨

⎪

⎪

⎩

⎪

⎪

⎫

⎬

⎪

⎪

⎭

⎪

⎪

1 3

2 30

3 50

4 7

Δ

Δ

Δ

Δ

0

50

70

0

.

. (5.10) 

RRR R

bb b b

pf pf pf

mmm m

123 4

12 3 4

12 3

28 26 22 18

10 11 12 13

16 31 13

=== =

=== =

== =

...

...

...

 

 

 

Next the Coriolis parameter, f, is determined based on the hurricane latitude, λh, by: 

f

a Rb

h

kcat kcat

=

=

2Ωsin λ

(5.11) 

Note akcat is determined from bkcat rather than independently specified. 

The complete windfield and pressure description is then determined as: 

 (5.12) 

V a b Pe d d f df

f pf e

P P Pe

gx kcat kcat

a d

air

b

r

p f R R pf R R

a d

kcat

bkcat kcat

kcat

m

kcat

m

kcat

bkcat

= −

= +

=+ −

−

− +

−

( // )

.

( )

/ /

( / /)

/

Δ

Δ

ρ 2 2 12

1

0

4 2

0 65

1

2 3

− /

The three approaches are contrasted in Table 5.9 for a storm moving due North over 

(29.4o

N, 95oW) with a constant radius to maximum winds of 25 nm and central pressure 

deficit of 25 mb.

Table 5.9. Hurricane Wind and Pressure Fields for an Arbitrary Storm based on SPH, 

Tetra Tech, and Holland Methods. Note longitude of the storm track is constant at 95o

W, 

radius to maximum winds is 25nm, and central pressure deficit is 25mb with a far field 

pressure of 1013mb. Note f=all weather nowcast/forecast system, 1=SPH, 2=Tetra Tech, 

and 3=Holland. 

Trac

k 

Inde

x 

Location 

(lat o

N) 

Distanc

e 

(nm) 

Forward 

Speed 

(kts) 

 Windspeed 

 (kts) 

 Method 

 f 1 2 3 

Wind 

Direction 

(oT) 

Sea Level 

Pressure 

(mb) 

1 28.0 84 3.5 32.5 30.1 30.7 21.7 -115 1007.7 

2 28.35 63 3.5 36.9 35.2 34.9 27.7 -115 1006.2 

3 28.7 42 3.5 42.4 41.2 40.2 36.1 -115 1003.5 

4 29.05 21 3.5 50.8 48.8 48.2 49.8 -101 997.6 

5 29.4 0 3.5 3.3 3.3 3.3 3.3 0 988.0 

6 29.65 15 3.25 33.2 21.4 31.5 55.1 83 994.6 

7 29.9 30 3.0 49.0 47.6 46.6 45.3 65 1000.8 

8 30.15 45 2.75 45.1 42.8 41.9 37.0 65 1004.0 

9 30.4 60 2.5 40.1 38.5 38.1 30.8 65 1005.9 

24
A slightly modified approach was selected for incorporation within the all weather 

nowcast/forecast system in which for the Holland method, Vgx is evaluated for d=R and fr

is based on the Collins and Viehman (1971) method used by Tetra Tech (1979) to 

determine the reduction factor. The Holland (1980) pressure profile is used. 

5.4. Wave Algorithms 

The previously described algorithm used in the tracer studies is a robust and 

computationally efficient scheme, which can also be extended to hurricane conditions 

with minor modification. At present no distinction is made between a flooded cell and a 

cell which is always wet in the wave computation method. It should be noted that in the 

present approach wave conditions are computed for all water cells using the same 

method. The same curvilinear grid used by the Galveston Bay circulation model and the 

same windfield are used. 

The algorithm has been incorporated as a separate subroutine within the circulation 

model as was done by Schmalz (1986) for Lake Okeechobee, which allowed for further 

experimentation with wave-current interaction in the tracer studies. This has not been 

pursued in the storm surge studies. 

Since no wave data are available during historical hindcasts, the following relations were 

used to specify representative wave conditions along the open boundary: 

)0.4(0.5.315

0.42.1

)0.1,5.0max(

−+=

+=

= +

wl

HT

H wl

S

S S

S

θ

 (5.13) 

Where HS, TS, θS, and wl represent significant wave height (m), significant wave period 

(s), significant wave direction (deg T), and observed water level at Galveston Pleasure 

Pier (ft relative to MLLW). 

Data resources are required on nowcast and forecast. For the nowcast, data from NDBC 

Buoy 42035 may be obtained from the Texas Automated Buoy System (TABS) Project 

sponsored by the Texas General Land Office (TGLO) at: 

http://tabs.gerg.tamu.edu /Tglo/DailyData/Data/42035_met.shtml. 

For the forecast, the NWS Wavewatch III model forecast results at 42035 can be utilized 

at: ftp://polar.wwb.noaa.gov/pub/waves/latest_run/wna.42035.bull 

Note with the present three-dimensional long wave modeling approach, the effect of 

return flows can be simulated and the potential exists for more accurate surge prediction 

with the wave effects included as well. Since in the present experimental 

nowcast/forecast system both GBM and HSCM are executed, we have also performed 

wave computations using the HSCM with the GBM results providing boundary 

conditions. 

25
5.5. Design of the All Weather Nowcast/Forecast System 

The NOS experimental all weather nowcast/forecast system uses the separate 

nowcast/forecast set-up program to establish hydrodynamic model nowcast and forecast 

inputs with minor modifications (indicated by * and italics in the list below). The 

modified set-up program utilizes the following twelve-step procedure, where the steps 1-

10 constitute the original procedure: 

 *1) Setup 24 hour nowcast and 36 hour forecast time periods and grid parameters, 

 2) Predict astronomical tide, 

 3) Predict astronomical currents, 

 4) Read PUFFF files and develop station time series, 

 5) Develop GBM subtidal water level signal, 

 6) Assimilate PORTS salinity and temperature data into GBM and HSCM initial 

 conditions, 

*7) Establish GBM and HSCM salinity and temperature boundary conditions, 

 8) Establish GBM and HSCM SST forcing, 

 *9) Establish USGS observed and NWS/WGRFC forecast freshwater inflows, 

*10) Establish PORTS based and NWS/Aviation Model wind and pressure fields, 

11) Establish rainfall/runoff for City of Houston inflows, and 

12) Establish wave swell characteristics

Step 1 was modified to include the grid modifications to incorporate the four additional 

City of Houston inflows. Step 7 was modified to include salinity and temperature 

specification for these inflows. Step 9 was modified to set the City of Houston inflows to 

zero for no rainfall/runoff. Note if rainfall/runoff occurs (storm track file specified) these 

flows are determined in Step 11. In Step 10, hurricane wind and pressure fields are 

developed if the storm track file exists. If a storm track file does not exist, the set-up 

program skips to Step 12. Otherwise, the wind and pressure fields are then blended into 

the NWS Aviation Model (now called the Global Forecast System Model) far fields over 

a distance from the storm center of five times the radius to maximum winds. In Step 11, 

the rainfall/runoff is developed if a storm track file is present. A 2-5 day antecedent 

rainfall description is used to determine the rainfall moisture index. A Quantitative 

Precipitation Forecast (QPF) will be used to provide the rainfall input over the forecast 

period. In Step 12, the open boundary wave swell height, direction, and period are 

specified based on measurements at Buoy 42035 and the NCEP Wavewatch forecast at 

Buoy 42035. 

The GBM is modified to incorporate the overland flooding algorithm and includes the 

four additional freshwater inflows. The combined parametric wave model is included as a 

subroutine and uses the same wind fields. An open boundary swell condition is applied to 

incorporate Gulf of Mexico wave swell conditions. The fetch along the HSCM boundary 

is written to a transfer file for input to the HSCM. The HSCM modifications are similar. 

The overland flooding algorithm is included and the wave algorithm appears as a separate 

subroutine. The fetch from the GBM boundary and additional fetch specification within 

26
the Port of Houston is interpolated over the grid for input to the wave subroutine. The 

City of Houston inflows are incorporated as in the GBM. 

5.6. Additional Hydrodynamic Model Considerations 

To isolate the standard freshwater inflows from flooding, it was necessary to extend the 

river channels to the grid boundary and to further surround them with a land elevation of 

100m. In addition four other inflow channels were inserted in both the GBM and HSCM 

grids to model the Greens, Brays, Sims, and Hunting Bayou inflows. These inflow 

channels were extended to the grid boundaries as was done for the standard inflows. Note 

the Galveston sea wall was not directly included in the computations. 

Additional modifications were required in the restart mechanics to allow for the 

continuation of overland flood events during restarts between subsequent 

nowcast/forecast cycles. The status of the flooded cells needed to be retained from 

simulation to simulation. Additional modifications to the IDL field plot programs were 

required to allow for the moving land/water boundaries.

5.7. Simulation Objectives 

The storms shown in Table 5.10 are used to test the all-weather nowcast/forecast system 

first on a hindcast basis for two historical hurricanes and then on a nowcast/forecast cycle 

basis for Tropical Storm Allison. Separate storm track files were constructed and the 

modified set-up program exercised to provide forcing for the hydrodynamic models. Both 

long wave and short wave hydrodynamic computations were made using the GBM as 

well as the HSCM. The wave-current option outlined in Chapter 4 was not used in these 

initial computations. 

 Table 5.10. Major Storm Characteristics for Galveston Bay, Texas. 

Storm/ 

Source 

Central 

Pressure 

 (mb) 

Windspeed 

(kts) 

Radius to 

Max Winds 

(nm) 

Rainfall 

(in) 

Storm Surge 

(ft) 

Carla 3-15 

Sept 1961/ 

Dunn and 

staff (1962) 

970-975 75-80 30 5.0-10.0 8.8-9.3 

Alicia 15-21 

Aug 1983/ 

Case and 

Gerrish 

(1984) 

963-965 80-100 30 7.8-10.7 8.9 

Allison 9-11 

June 2000/ 

NWS(2001); 

Stewart 

(2002) 

990 20-30 30 9.8-35.1 1.8-2.1 

27
Hurricanes Carla and Alicia were simulated and wind and water level validation were 

performed to assess the ability to replicate the effects of severe storms. The focus is not 

only on peak storm surge prediction ability but also on the complete hydrograph. 

Inundation statistics are computed to assess overland flooding. To utilize the threedimensional capability, salinity and temperature responses will also be addressed. 

Tropical Storm Allison is simulated using the experimental nowcast/forecast system. 

During the rainfall/runoff event, water level and current predictions will be compared to 

available data to assess the impact of including additional rainfall/runoff flows from the 

City of Houston. 

While no short wave data are available to compare with simulation results, significant 

wave height and period are assessed for representativeness of hurricane conditions 

assuming no wave-current interaction. 

28
6. HURRICANE CARLA (1961) SIMULATION 

Three 24-hour hindcasts for September 9-11, 1961 were performed with the calculations 

restarted after each daily hindcast. No NCEP forecasts of surface winds and pressure 

fields or of storm surge were available. In experiment one, no wind and atmospheric 

pressure forcing were used while the open boundary storm surge was based on the 

nontidal water level at Galveston Pleasure. In experiment two, the parametric hurricane 

wind and atmospheric pressure forcing were applied with the same open boundary surge 

as in experiment one. The wind and atmospheric pressure forcing were mild over the 

Galveston Bay region, since the track of Hurricane Carla was well to the south of 

Galveston Bay (see Figure 6.1). As a result the results from experiment one and two are 

very similar with the results of experiment one presented below. Long wave results are 

given in terms of water surface elevation, prediction depth current (4.57m below 

MLLW), near surface salinity, and near surface temperature time series as well as field 

plots of water surface elevation and salinity. Short wave results are given in terms of 

significant wave height, period, and direction as well as field plots of significant wave 

height and period. Summary statistics are presented for flood inundation, maximum water 

surface elevation and maximum significant wave height. 

6.1. Storm Characteristics 

The track of Hurricane Carla is shown in Figure 6.1 with storm parameters given in Table 

6.1. The storm made landfall at Port O’Connor, Texas at 1400 CST on the afternoon of 

September 11.

Figure 6.1. Hurricane Carla (1961) Storm Track 3-16 September.

29
Table 6.1. Hurricane Carla Storm Characteristics 3-16 September 1961.

ADV LAT LON TIME WIND PR STAT 

 Deg N Deg W GMT MPH MB Saffir-Simpson Scale 

 1 12.50 -77.00 09/03/12Z 25 - TROPICAL DEPRESSION 

 2 12.90 -78.00 09/03/18Z 25 - TROPICAL DEPRESSION 

 3 13.30 -78.80 09/04/00Z 25 - TROPICAL DEPRESSION 

 4 13.70 -79.50 09/04/06Z 25 1007 TROPICAL DEPRESSION 

 5 14.20 -80.10 09/04/12Z 25 1006 TROPICAL DEPRESSION 

 6 14.90 -80.70 09/04/18Z 25 1005 TROPICAL DEPRESSION 

 7 15.50 -81.40 09/05/00Z 30 1002 TROPICAL DEPRESSION 

 8 15.90 -82.10 09/05/06Z 30 999 TROPICAL DEPRESSION 

 9 16.30 -82.70 09/05/12Z 40 997 TROPICAL STORM 

 10 16.90 -83.10 09/05/18Z 45 993 TROPICAL STORM 

 11 17.40 -83.60 09/06/00Z 50 990 TROPICAL STORM 

 12 18.10 -84.30 09/06/06Z 55 987 TROPICAL STORM 

 13 18.80 -85.10 09/06/12Z 65 984 HURRICANE-1 

 14 19.10 -85.60 09/06/18Z 70 981 HURRICANE-1 

 15 19.50 -85.90 09/07/00Z 75 978 HURRICANE-1 

 16 20.20 -86.00 09/07/06Z 80 975 HURRICANE-1 

 17 20.90 -86.00 09/07/12Z 85 973 HURRICANE-2 

 18 21.70 -86.30 09/07/18Z 95 970 HURRICANE-2 

 19 22.30 -87.30 09/08/00Z 100 968 HURRICANE-3 

 20 22.80 -87.80 09/08/06Z 105 966 HURRICANE-3 

 21 23.10 -88.30 09/08/12Z 110 965 HURRICANE-3 

 22 23.40 -89.20 09/08/18Z 110 962 HURRICANE-3 

 23 23.70 -89.80 09/09/00Z 110 959 HURRICANE-3 

 24 24.00 -90.20 09/09/06Z 110 956 HURRICANE-3 

 25 24.60 -91.00 09/09/12Z 110 953 HURRICANE-3 

 26 24.90 -91.80 09/09/18Z 110 948 HURRICANE-3 

 27 25.60 -92.60 09/10/00Z 110 944 HURRICANE-3 

 28 26.10 -93.30 09/10/06Z 115 940 HURRICANE-4 

 29 26.30 -93.90 09/10/12Z 120 937 HURRICANE-4 

 30 26.70 -94.50 09/10/18Z 130 936 HURRICANE-4 

 31 27.00 -95.00 09/11/00Z 140 936 HURRICANE-5 

 32 27.20 -95.70 09/11/06Z 150 936 HURRICANE-5 

 33 27.60 -96.20 09/11/12Z 145 935 HURRICANE-5 

 34 28.00 -96.40 09/11/18Z 125 931 HURRICANE-4---Landfall 21z 

 35 28.60 -96.80 09/12/00Z 100 940 HURRICANE-3 

 36 29.50 -97.20 09/12/06Z 80 955 HURRICANE-1 

 37 30.50 -97.40 09/12/12Z 60 975 TROPICAL STORM 

 38 31.80 -97.40 09/12/18Z 45 979 TROPICAL STORM 

 39 32.80 -97.20 09/13/00Z 40 980 TROPICAL STORM 

 40 33.50 -97.00 09/13/06Z 35 - TROPICAL STORM 

 41 34.30 -96.80 09/13/12Z 30 - EXTRATROPICAL DEPRESSION 

 42 36.20 -94.00 09/13/18Z 30 - EXTRATROPICAL DEPRESSION 

 43 38.00 -90.50 09/14/00Z 30 - EXTRATROPICAL DEPRESSION 

 44 42.10 -87.10 09/14/06Z 30 - EXTRATROPICAL DEPRESSION 

 45 46.30 -83.80 09/14/12Z 30 - EXTRATROPICAL DEPRESSION 

 46 47.50 -80.70 09/14/18Z 30 - EXTRATROPICAL DEPRESSION 

 47 48.70 -78.00 09/15/00Z 30 - EXTRATROPICAL DEPRESSION 

 48 51.20 -72.70 09/15/06Z 30 - EXTRATROPICAL DEPRESSION 

 49 53.70 -67.50 09/15/12Z 30 - EXTRATROPICAL DEPRESSION 

 50 56.80 -66.20 09/15/18Z 30 - EXTRATROPICAL DEPRESSION 

 51 60.00 -65.00 09/16/00Z 30 - EXTRATROPICAL DEPRESSION 

30
In the simulations, the radius to maximum winds was estimated at approximately 15 nm 

around the time of landfall and subsequently increased to 25 nm over the next 12 hours. 

Hourly rainfall information was obtained at Station 413430 Galveston, Texas for use in 

the rainfall/runoff computations and totaled 16.23 inches. Cooperman and Sumner (1961) 

note that the crest elevation of the barrier islands from Port Aransas to Galveston is 

generally less than 10 feet MSL and for much of the distance it is less than 5 feet. Since 

the peak surge elevation at Galveston Pleasure Pier was 9.3 feet relative to NGVD 1929 

(which differs by a few tenths of a foot from local MSL), much of the barrier islands 

were inundated. 

6.2 Simulation Set-up Procedures 

The first hindcast covers the period June 9 18:00 CST to June 10 18:00 CST. Water 

surface elevations and velocities are started from rest. The initial salinity and temperature 

fields are determined based on climatology. Since no PORTS data are available, no 

adjustment of these fields is made. Open boundary conditions for the GBM for water 

surface elevation are computed by adding the observed nontidal water level at Galveston 

Pleasure Pier to the predicted astronomical tide. Salinity and temperature values along the 

open boundary are based on climatology. Sea surface temperature is specified by using 

the top layer of the temperature field and is held constant in time. River inflows for the 

San Jacinto, Buffalo Bayou, and Trinity Rivers are based on USGS daily observed 

values. Since no wave data are available, the relationships used in Equation 6.13 were 

used to prescribe the wave conditions along the GBM open boundary. 

For the subsequent two daily hindcasts over the periods June 10 18:00 CST to June 11 

18:00 CST and June 11 18:00 CST to June 12 18:00 CST, conditions are restarted from 

the end of the previous hindcast. No adjustment of the salinity and temperature fields is 

made. Boundary forcing and river inflows are set up the same way as aforementioned. 

Note the HSCM is directly driven from information saved from the GBM in a one-way 

coupling scheme. See Schmalz (2000c; 2001) for details. 

Two experiments are run using the above conditions but with different meteorological 

forcing. In experiment one, the observed surge level at Galveston Pleasure Pier is 

propagated into the Bay and the water level, current, and density response is investigated 

in the absence of wind and atmospheric pressure forcing. Results are presented for both 

the long wave and short surface gravity wave cases. Experiment two results with the 

parametric hurricane model wind and atmospheric pressure field forcing applied are next 

presented and contrasted. 

31
6.3 Experiment One Long Wave Results 

Simulated water surface elevations for each of the three hindcasts are shown for 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 6.2–6.4. GBM 

simulated water levels are in excellent agreement (order 35 cm maximum discrepancy) 

with the observations at Galveston Pleasure Pier and at Galveston Pier 21. One notes the 

prolonged duration of elevated water levels and the potential for overland flooding and 

overtopping of the barrier islands. In Figures 6.5–6.7, HSCM simulated water surface 

elevations are shown for each hindcast for Eagle Point and Morgans Point. Unfortunately, 

no water level gages were in operation during this storm at these locations. In the third 

panel of these figures, the water level residual (surge at Galveston Pleasure Pier) is given. 

This water level residual is applied uniformly in space over the entire GBM open water 

boundary. The storm surge at Freeport was order 3.3m, which is considerably larger than 

the surge at Galveston Pleasure Pier. Since Freeport is immediately south of the lower 

boundary, it may be more appropriate to use the Freeport surge level along a portion of 

the lower GBM open boundary. This suggests that for the storm surge case, Freeport, 

Galveston Pleasure Pier, and Sabine Pass water level residuals be examined and that a 

procedure using all three of these residuals be developed for the GBM open boundary 

nontidal water level specification. However, in this case, since the water level stations are 

near Galveston Pleasure Pier, using the Galveston Pleasure Pier value only, results in 

good water level comparisons at these two stations. 

Simulated currents are examined in three panel figures for current speed, current 

direction, and principal component direction with flood considered positive. Simulated 

Bolivar Roads currents are shown in Figures 6.8- 6.10 for each hindcast. One notes the 

complete absence of ebb flow until near the end of the second hindcast period around 

10:45 CST on September 11. This ebb flow is followed by only a four hour duration 

flood and then a prolonged ebb flow over most of the third hindcast. Peak current 

strengths on both flood and ebb are order 150 cm/s (~3 kts). Simulated currents at 

Redfish Bar, mid-way up the Bay, show a similar behavior in the ebb-flood structure to 

simulated currents at Bolivar Roads; however, the peak current strengths are reduced to 

order 75 cm/s (~1.5 kts). At Morgans Point, the simulated currents in Figures 6.11- 6.13, 

exhibit a similar ebb-flood structure, but a second flood current is present during the third 

hindcast. The peak current strengths on ebb and flood are on the order of 50 cm/s (~1 kt). 

Additional rainfall/runoff flows have not been included and inflows from the Buffalo 

Bayou, San Jacinto River, and Trinity River were negligible. 

Simulated surface temperature, temperature stratification (absolute difference between 

simulated surface and bottom temperatures) and surface salinity are examined in three 

panels at Bolivar Roads in Figures 6.14-6.16 and at Morgans Point in Figures 6.17-6.19, 

respectively. One notes the increase in salinity at Bolivar Roads from 30 to 35 psu during 

the surge propagation phase during hindcasts one and two and subsequent gradual 

decrease to 30 psu over the third hindcast during which the surge recedes. While the 

simulated surface temperature remains constant, there is an increase in stratification to 

order 2.5 o

C as the cooler shelf water moves in over the bottom layers during the surge 

propagation phase of the storm. At Eagle Point the simulated surface salinity increases 

32
from 17 psu to a maximum of 32 psu and then returns to 22.5 psu. The maximum 

simulated temperature stratification is over 5 o

C during the initial phase of the third 

hindcast. At Morgans Point the simulated surface salinity increase is less dramatic than at 

Eagle Point going from 18 psu to 24 psu and then returning to 18 psu. The maximum 

simulated temperature stratification is order 2.5 o

C as noted in hindcast three. 

GBM simulated water surface elevation contours relative to MTL model datum at the end 

of hindcast two in Figure 6.20 and at the end of hindcast three in Figure 6.21 Water 

surface elevations are initiated at rest. One day later at the end of the first hindcast the 

barrier islands have been overtopped and flooding has occurred. At the end of the second 

hindcast in Figure 6.20, the flooding has progressed further inland, while at the end of the 

third hindcast in Figure 6.21, some of the flooded areas have dried. It should be noted 

that in the present flooding algorithm, no drainage or seepage flows are computed and as 

result, there is no mechanism for the water to be removed from the majority of flooded 

grid cells. 

Next GBM simulated near surface and near bottom salinity contours are shown at the end 

of hindcast three in Figures 6.22 and 6.23. One notes the penetration of the shelf salinity 

into the Bay during the surge propagation phase in both the surface and bottom layers and 

the subsequent relaxation and seaward propagation of the increased salinity levels in the 

surface layer during the third hindcast. Note the simulated bottom layer salinity is still 

elevated and has not returned to prestorm values at the end of the third hindcast. One 

should also note that salinity computations are performed over the flooded areas and as 

the water recedes the flooded cells become inactive (they do no communicate with the 

Bay grid cells) and retain the values of salinity that were present when they were active 

during the surge propagation phase of the storm. As a result, there are discontinuities in 

salinity levels between active Bay cells and inactive previously flooded cells as noted at 

the end of the third hindcast. 

Since in the present experimental nowcast/forecast system both GBM and HSCM are 

executed, we have also performed storm surge computations using the HSCM with the 

GBM results providing boundary conditions. One should note that the areas, over which 

the water may flood in the HSCM are limited to the upstream reaches above Morgans 

Point and to the barrier island system, which is fictitiously extended to regions beyond 

the jetties extending into the Gulf. HSCM simulated water surface elevation contours 

relative to MTL model datum are shown at the end of hindcast two in Figure 6.24 and at 

the end of hindcast three in Figure 6.25. Again water surface elevations are initiated at 

rest. One day later at the end of the first hindcast the barrier islands have been overtopped 

and flooding has occurred. At the end of the second hindcast in Figure 6.24, the flooding 

has progressed further inland, while at the end of the third hindcast in Figure 6.25, some 

of the flooded areas have dried. It should be noted that also in the HSCM, no drainage or 

seepage flows are computed and as result, there is no mechanism for the water to be 

removed from the majority of flooded grid cells. 

Next HSCM simulated near surface and near bottom salinity contours are shown in 

Figures 6.26 and 6.27 at the end of hindcast three. One notes the penetration of the shelf 

33
salinity up the Houston Ship Channel during the surge propagation phase in both the 

surface and bottom layers and the subsequent relaxation and seaward propagation of the 

salinity in the surface layer during the third hindcast. Note the simulated bottom layer 

salinity is still elevated and has not returned to prestorm values at the end of the third 

hindcast. One should also note that similarly in the HSCM salinity computations are 

performed over the flooded areas and as the water recedes the flooded cells become 

inactive and retain the values of salinity that were present when they were active during 

the surge propagation phase of the storm. As a result, there are discontinuities in salinity 

levels between active cells and inactive previously flooded cells as noted at the end of the 

third hindcast. 

34
Figure 6.2. Hurricane Carla GBM Water Levels Experiment One: 9-10 September 1961

35
Figure 6.3. Hurricane Carla GBM Water Levels Experiment One: 10-11 September 1961

36
Figure 6.4. Hurricane Carla GBM Water Levels Experiment One: 11-12 September 1961

37
Figure 6.5. Hurricane Carla HSCM Water Levels and GBM Water Level Residual 

Experiment One: 9-10 September 1961

38
Figure 6.6. Hurricane Carla HSCM Water Levels and GBM Water Level Residual 

Experiment One: 10-11 September 1961

39
Figure 6.7. Hurricane Carla HSCM Water Levels and GBM Water Level Residual 

Experiment One: 11-12 September 1961

40
Figure 6.8. Hurricane Carla GBM Bolivar Roads Currents Experiment One: 9-10 

September 1961

41
Figure 6.9. Hurricane Carla GBM Bolivar Roads Currents Experiment One: 10-11 

September 1961

42
Figure 6.10. Hurricane Carla GBM Bolivar Roads Currents Experiment One: 11-12 

September 1961

43
Figure 6.11. Hurricane Carla GBM Morgans Point Currents Experiment One: 9-10 

September 1961

44
Figure 6.12. Hurricane Carla GBM Morgans Point Currents Experiment One: 10-11 

September 1961

45
Figure 6.13. Hurricane Carla GBM Morgans Point Currents Experiment One: 11-12 

September 1961

46
Figure 6.14. Hurricane Carla GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 9-10 September 1961

47
Figure 6.15. Hurricane Carla GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 10-11 September 1961

48
Figure 6.16. Hurricane Carla GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 11-12 September 1961

49
Figure 6.17. Hurricane Carla HSCM Eagle Point Temperature and Salinity 

 Experiment One: 9-10 September 1961

50
Figure 6.18. Hurricane Carla HSCM Eagle Point Temperature and Salinity 

 Experiment One: 10-11 September 1961

51
Figure 6.19. Hurricane Carla HSCM Eagle Point Temperature and Salinity 

 Experiment One: 11-12 September 1961

52
Figure 6.20. Hurricane Carla GBM Water Surface Elevation Field 

 Experiment One: 11 September 1961 18:00 CST 

53
Figure 6.21. Hurricane Carla GBM Water Surface Elevation Field 

 Experiment One: 12 September 1961 18:00 CST 

54
Figure 6.22. Hurricane Carla GBM Near Surface Salinity Field 

 Experiment One: 12 September 1961 18:00 CST 

55
Figure 6.23. Hurricane Carla GBM Near Bottom Salinity Field 

 Experiment One: 12 September 1961 18:00 CST 

56
Figure 6.24. Hurricane Carla HSCM Water Surface Elevation Field 

 Experiment One: 11 September 1961 18:00 CST 

57
Figure 6.25. Hurricane Carla HSCM Water Surface Elevation Field 

 Experiment One: 12 September 1961 18:00 CST 

58
Figure 6.26. Hurricane Carla HSCM Near Surface Salinity Field 

 Experiment One: 12 September 1961 18:00 CST 

59
Figure 6.27. Hurricane Carla HSCM Near Bottom Salinity Field 

 Experiment One: 12 September 1961 18:00 CST 

60
6.4. Experiment One Short Wave Results 

Unfortunately, no wave information was available and the results must be judged as 

being representative of hurricane wave conditions. Since in this experiment, no wind 

forcing was applied, the results contain no wind generation effects and only use an 

empirical reduction formula to reduce the offshore boundary wave condition generated 

using Equation 5.13. 

Simulated significant wave height for each of the three hindcasts is shown at Galveston 

Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 6.28 – 6.30. One notes the 

prolonged duration of elevated simulated wave heights on top of the simulated elevated 

water levels noted in the long wave results and the potential for overland flooding and 

overtopping of the barrier islands with accompanying large waves order 5m. In Figures 

6.31 – 6.33, HSCM simulated significant wave heights are shown for each hindcast at 

Eagle Point and Morgans Point with maximum significant wave heights of 2.7m and 

2.5m, respectively. In the third panel of these figures, the simulated significant wave 

height at NDBC buoy 42035 is given, which represents the GBM open boundary wave 

condition. This significant wave height is applied uniformly in space over the entire 

GBM open water boundary. Note the maximum simulated significant wave heights are 

order 10m. 

Simulated significant wave direction for each of the three hindcasts were considered at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in the GBM and for the 

HSCM at Eagle Point and Morgans Point, respectively. The simulated significant wave 

direction at NDBC buoy 42035 represents the GBM open boundary wave condition. This 

significant wave direction is applied uniformly in space over the entire GBM open water 

boundary. Note in the case of no wind generation, the significant wave direction is equal 

to the offshore boundary condition in all interior grid cells and varies in time based on the 

relation given in Equation 5.13. As a result, wave directions are the same for all of the 

above stations and are near 315 degrees True. 

Simulated significant wave period for each of the three hindcasts are shown at Galveston 

Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 6.34–6.36. In Figures 

6.37-6.39, HSCM simulated significant wave periods are shown for each hindcast at 

Eagle Point and Morgans Point, respectively. In the third panel of these figures, the 

simulated significant wave period at NDBC buoy 42035 is given, which represents the 

GBM open boundary wave condition. This significant wave period is applied uniformly 

in space over the entire GBM open water boundary. Note in the case of no wind 

generation, the significant wave period as given in Equation 5.13 is a function of 

significant wave height, which is based on empirical reduction. As a result, wave periods 

are the similar in form for all of the above stations. Note the maximum simulated 

significant wave periods are order 18s. 

GBM simulated significant wave height and direction vectors are shown at the end of 

hindcast two in Figure 6.40. At the end of the first hindcast the barrier islands have been 

61
overtopped and that flooding has occurred and wave computations have been performed 

over the flooded cells. At present no distinction is made between a flooded cell and a cell 

which is always wet in the wave computation method. At the end of the second hindcast 

in Figure 6.40, the flooding has progressed further inland, while at the end of the third 

hindcast some of the flooded areas have dried. It should be noted that in the present 

model, no drainage or seepage flows are computed and as result, there is no mechanism 

for the water to be removed from the majority of flooded grid cells. For all water cells, 

wave conditions are computed. Simulated significant wave heights are in the range from 

1 m in upper Trinity Bay to 10m near the offshore boundary. Note in the present case of 

no wind generation, simulated significant wave directions are near 315 deg True for all 

grid cells. 

Next GBM simulated significant wave period contours are shown in Figure 6.41 at the 

end of hindcast two. One should note that wave computations are performed over the 

flooded areas and as the water recedes, while the flooded cells become inactive in the 

long wave computations, wave computations continue to be performed over these grid 

cells. Simulated significant wave periods range from below 1s in upper Trinity Bay to 

over 14s near the offshore boundary. 

HSCM simulated significant wave height and direction at the end of hindcast two in 

Figure 6.42. Simulated significant wave heights are in the range of 1 to 5 m consistent 

with those computed in the GBM. Note in the present case of no wind generation, 

significant wave directions are near 315 deg True for all grid cells as determined in the 

GBM. 

Next HSCM simulated significant wave period contours are shown in Figure 6.43 at the 

end of hindcast two. One should note that wave computations are performed over the 

flooded areas and as the water recedes, while the flooded cells become inactive in the 

long wave computations, wave computations continue to be performed over these grid 

cells. Simulated significant wave periods are in the range of 1 to 7s consistent with those 

computed over the GBM. 

62
Figure 6.28. Hurricane Carla GBM Significant Wave Height Experiment One: 

9-10 September 1961

63
Figure 6.29. Hurricane Carla GBM Significant Wave Height Experiment One: 

10-11 September 1961

64
Figure 6.30. Hurricane Carla GBM Significant Wave Height Experiment One: 

11-12 September 1961

65
Figure 6.31. Hurricane Carla HSCM and GBM 42035 Significant Wave Height 

Experiment One: 9-10 September 1961

66
Figure 6.32. Hurricane Carla HSCM and GBM 42035 Significant Wave Height 

Experiment One: 10-11 September 1961

67
Figure 6.33. Hurricane Carla HSCM and GBM 42035 Significant Wave Height 

Experiment One: 11-12 September 1961

68
Figure 6.34. Hurricane Carla GBM Significant Wave Period Experiment One: 

9-10 September 1961

69
Figure 6.35. Hurricane Carla GBM Significant Wave Period Experiment One: 

10-11 September 1961

70
Figure 6.36. Hurricane Carla GBM Significant Wave Period Experiment One: 

11-12 September 1961

71
Figure 6.37. Hurricane Carla HSCM and GBM 42035 Significant Wave Period 

Experiment One: 9-10 September 1961

72
Figure 6.38. Hurricane Carla HSCM and GBM 42035 Significant Wave Period 

Experiment One: 10-11 September 1961

73
Figure 6.39. Hurricane Carla HSCM and GBM 42035 Significant Wave Period 

Experiment One: 11-12 September 1961

74
Figure 6.40. Hurricane Carla GBM Significant Wave Height and Direction 

Experiment One: 11 September 1961 18:00 CST 

75
Figure 6.41. Hurricane Carla GBM Significant Wave Period Experiment One: 

11 September 1961 18:00 CST 

76
Figure 6.42. Hurricane Carla HSCM Significant Wave Height and Direction 

Experiment One: 11 September 1961 18:00 CST 

77
Figure 6.43. Hurricane Carla HSCM Significant Wave Period Experiment One: 

11 September 1961 18:00 CST 

78
6.5. Experiment Two Long and Short Wave Results 

In this experiment, the parametric hurricane wind and atmospheric pressure algorithm in 

Section 5.3 is used to provide the meteorological forcing. It should be noted that the 

present procedure does not allow for a reduction of windspeed due to overland friction 

effects directly. The central pressure deficit of the storm is reduced based on observed 

overland weakening, but the windfields computed based on the reduced pressure deficit 

are not further reduced. 

GBM simulated water surface elevations for each of the three hindcasts at Galveston 

Pleasure Pier, Bolivar Roads, and Galveston Pier 21 and HSCM simulated water surface 

elevations at Eagle Point and Morgans Point are in good agreement with the available 

observations and are very near those obtained in experiment one. 

Simulated peak windspeeds are approximately 13 m/s at Galveston Pleasure Pier and 

Eagle Point, and are over 25 m/s at Morgans Point for a few hours during hindcast three. 

The simulated atmospheric pressure is constant at around 1010 mb at all three stations but 

drops to 1008 mb at Morgans Point during the period of maximum winds in hindcast 

three. The wind and atmospheric pressure forcing are from the far field of the hurricane. 

The simulated atmospheric pressure field snapshot on 11 September 1961 at 18:00 CST 

shown in Figure 6.44 indicates the radial structure of the hurricane atmospheric pressure 

field. The corresponding snapshots of the simulated windfield at the same time shown in 

Figure 6.45 show a slight tendency for outflow rather than inflow to the radial structure 

of the pressure field at the end of hindcast two. This result needs further investigation. 

In this experiment, simulated significant wave heights follow the same general pattern as 

in experiment one and are largely determined by the GBM offshore wave conditions. 

Wind generation increases wave heights by order 0.25m at all stations in each of the three 

hindcasts, except at Galveston Pier 21, which is sheltered and exhibits no wind 

generation growth. Wave directions are in the direction of the wind and move from near 

315 deg T to a range of 225 to 250 deg T at all stations during hindcast one, to near 0 deg 

T in the lower Bay to a range from 250 to 300 deg T at Eagle and Morgans Point during 

hindcast two, and to 45 to 135 deg T in the lower Bay to near 0 deg T in the upper Bay in 

hindcast three. 

In contrast to experiment one, simulated significant wave periods are reduced at 

Galveston Pleasure Pier from 7s to 5s during hindcast one and are slightly increased at 

the Bay by less than 1s. During hindcast two, simulated wave periods are reduced at 

Galveston Pleasure Pier from 8 to 6s, while at all Bay stations the differences in wave 

periods are less than 1s. During hindcast three, simulated wave periods are reduced at 

Galveston Pleasure Pier by at most 1.5s, while at the other Bay stations results are less 

than 1s from those obtained in experiment one. 

It should be noted that in experiment two for wind generation, the wave period is 

79
computed directly from the wind wave and the offshore swell period is not used in the 

wave period computations. This method yielded the best results for the limited one month 

calibration period for non-hurricane conditions. It might be useful to revisit this 

procedure for hurricane conditions. 

6.6. Wind and Water Surface Elevation Validation 

In Table 6.2 peak windspeeds over the GBM grid are compared with fastest mile 

observations reported by Cooperman and Cumner (1961). Wind speeds computed used 

the parametric hurricane model in Section 6.3 are in general agreement with these 

observations. 

Table 6.2. Hurricane Carla (1961) Windspeed Validation. Note simulated GBM peak 

corresponds to results obtained in Experiment Two with parametric hurricane model 

wind and atmospheric pressure forcing. 

Station Location ID Simulated 

GBM Peak (m/s) 

Observed 

 Fastest Mile (m/s) 

Galveston 12923 14.7 22.8 

Ellington AFB 12906 29.4 - 

Hobby Airport 12918 30.2 23.3 

In Table 6.3, GBM peak simulated water levels and simulated significant wave heights 

are compared with observed peak water levels reported by Dunn and staff (1961) and 

Cooperman and Cumner (1961). The observed peak water levels are reported with 

respect to NGVD-1929 whereas the GBM simulated water levels are with respect to the 

MTL model datum. Peak water levels from high water marks, particularly at Morgans 

Point may include surface gravity wave effects. One should note that at two Galveston 

water level gauges, the level of agreement shown in Figures 6.2-6.4 for experiment one 

are in close agreement and are both based on a MLLW datum. MSL stands 5 mm and 3 

mm lower than MTL at Galveston Pleasure Pier based on the 1960-1978 and 1983-2001 

tidal epochs, respectively. At Galveston Pier 21 MSL stands 4 mm and 3 mm higher than 

MTL for the corresponding tidal epochs. Therefore we can assume that MSL and MTL 

are approximately equivalent at the coast. At Morgan's Point, MSL is higher by 12 mm 

and 9 mm than MTL based on the above epochs, respectively. Therefore throughout 

Galveston Bay MSL and MTL are nearly equivalent differing by at most 1 cm. At 

Galveston Pleasure Pier and Galveston Pier 21, NGVD-29 stands .201m below MTL. 

The corrections at the inland stations in Table 6.3 are not known precisely but are 

probably larger due to subsidence effects induced by groundwater pumping and oil 

extraction. These effects would tend to elevate the observed peak water levels as would 

possible surface gravity wave effects in the high water marks, making the direct 

comparison at the inland stations more problematical. 

80
Table 6.3. Hurricane Carla (1961) GBM Storm Surge Validation. 

Note + indicates high water mark. Exp1==Experiment One with no wind and 

atmospheric forcing, while Exp 2==Experiment Two with parametric hurricane model 

wind and atmospheric pressure forcing. 

Station Location Simulated Peak 

 Water Level 

(m-MTL) 

Exp 1 Exp 2 

Simulated Peak 

Significant 

Wave Height (m) 

Exp 1 Exp2 

Observed Peak 

Water Level 

(m-NGVD-1929) 

Galveston Pl. Pier 2.43 2.44 4.95 5.23 2.8 

Galveston Pier 21 2.37 2.38 2.97 2.97 2.7 

Eagle Point 2.38 2.39 2.97 3.18 3.35+ 

Smith Point 2.36 2.39 2.97 3.16 4.27+ 

Morgans Point 2.39 2.44 1.98 2.25 4.51,5.0+ 

Round Point 2.39 2.49 0.99 1.13 3.51 + 

6.7. Surface Salinity, Surface Current, and Inundation Statistics 

In Table 6.4, GBM simulated surface minimum salinity and simulated maximum surface 

current strengths are given for stations proceeding northward up Galveston Bay are 

compared between experiment one and two. The added wind forcing adjust the salinity 

structure and increase the maximum currents only slightly, due to the distance to the 

center of the storm. 

Table 6.4. Hurricane Carla (1961) GBM Minimum Surface Salinity and Maximum 

Current Speeds. Exp1==Experiment One with no wind and atmospheric forcing, while 

Exp 2==Experiment Two with parametric hurricane model wind and atmospheric 

pressure forcing. 

Station Location Minimum Salinity (PSU) 

Exp 1 Exp 2 

Maximum Current (m/s) 

Exp 1 Exp 2 

Galveston Pl. Pier 33.7 33.6 0.23 0.56 

Galveston Pier 21 33.7 33.6 0.74 0.67 

Eagle Point 21.9 25.6 0.52 0.51 

Smith Point 28.7 28.4 0.57 0.43 

Morgans Point 21.5 21.7 0.44 0.30 

Round Point 11.1 11.1 0.23 0.37 

Inundation statistics for both experiments are presented in Table 6.5 in terms of the time 

and areal extent of the maximum flooding. Average and maximum flood depths are also 

determined. Experiment 2 values are slightly elevated over those of experiment 1 due the 

influence of the wind and atmospheric pressure forcing, which are modest due to the 

distance to the storm center. 

81
Table 6.5. Hurricane Carla (1961) Inundation Statistics. 

Note the first line corresponds to results from Experiment 1 with no wind and 

atmospheric pressure forcing. The second line presents results from Experiment 2 with 

parametric hurricane wind and atmospheric pressure forcing. 

Hindcast 

No. 

Simulation 

Dates 

Time of 

Maximum 

Flood (JD) 

Maximum 

Flooded 

Area (km2

) 

Average 

Flood Depth 

(m) 

Maximum 

Flood Depth 

(m) 

1 9/9-9/10 253.75 

253.75 

1113 

1117 

0.793 

0.813 

1.053 

1.052 

2 9/10-9/11 254.64 

254.50 

1463 

1462 

1.112 

1.044 

1.471 

1.605 

3 9/11-9/12 254.754 

255.483 

1463 

1463 

1.102 

0.402 

1.297 

1.525 

82
Figure 6.44. Hurricane Carla GBM Atmospheric Pressure Field Experiment Two: 

11 September 1961 18:00 CST 

83
Figure 6.45. Hurricane Carla GBM Wind Field Experiment Two: 

11 September 1961 18:00 CST 

84
7. HURRICANE ALICIA (1983) SIMULATION 

Two 24-hour hindcasts for August 16-18 were performed with the calculations restarted 

for the second daily hindcast from results at the end of the first hindcast. No NCEP 

forecasts of surface winds and atmospheric pressure fields or of storm surge were 

available. Two separate experiments were performed. In experiment one, no wind and 

atmospheric pressure forcing were used while the open boundary storm surge was based 

on the nontidal water level at Galveston Pleasure Pier. In experiment two, the parametric 

hurricane wind and atmospheric pressure forcing were applied with the same open 

boundary surge as in experiment one. The wind and atmospheric pressure forcing were 

severe over the Galveston Bay region, since the track of Hurricane Alicia passed just 

west of the City of Houston (see Figure 7.1). The results from experiment one are first 

presented below. Long wave results are given in terms of water surface elevation, current, 

salinity, and temperature time series as well as field plots of water surface elevation and 

salinity. Short wave results are given in terms of significant wave height, period, and 

direction as well as vector plots of significant wave height and direction and contour plots 

of significant wave period. Next, experiment two results are given in the same format. 

Wind and water surface elevation validation are presented followed by surface salinity, 

surface current, and inundation summary statistics. 

7.1. Storm Characteristics 

The track of Hurricane Alicia is shown in Figure 7.1 with storm parameters given in 

Figure 7.1. Hurricane Alicia (1983) Storm Track 15-21August. 

85
Table 7.1. The storm made landfall along the Texas coast 40 km southwest of Galveston 

at San Luis Pass, Texas at 0800 CST on the morning of August 18. 

In the simulations, the radius to maximum winds was estimated at approximately 18 nm 

around the time of landfall and subsequently increased to 31 nm over the next 12 hours. 

Hourly rainfall information was obtained at Station 414300 Houston International 

Airport, Texas for use in the rainfall/runoff computations and totaled over 17 inches. 

Case and Gerrish (1984) note that the peak water surface elevations relative to MSL 

range from 3.9 m at San Luis Pass to 2.7 m at Galveston Pleasure Pier and that peak 

water levels within Galveston Bay increase to 3.5 m at Morgans Point. 

 

Table 7.1. Hurricane Alicia Storm Characteristics 15-21 August 1983. 

ADV LAT LON TIME WIND PR STAT 

 1 28.30 -90.50 08/15/12Z 30 1009 TROPICAL DEPRESSION 

 2 28.20 -91.00 08/15/18Z 40 1006 TROPICAL STORM 

 3 28.10 -91.50 08/16/00Z 45 1005 TROPICAL STORM 

 4 28.00 -92.00 08/16/06Z 50 1004 TROPICAL STORM 

 5 28.10 -92.40 08/16/12Z 55 1002 TROPICAL STORM 

 6 28.30 -92.80 08/16/18Z 60 998 TROPICAL STORM 

 7 28.40 -93.30 08/17/00Z 65 991 HURRICANE-1 

 8 28.70 -93.70 08/17/06Z 70 987 HURRICANE-1 

 9 28.90 -94.20 08/17/12Z 75 983 HURRICANE-1 

 10 28.10 -94.50 08/17/18Z 90 974 HURRICANE-2 

 11 28.40 -94.80 08/18/00Z 95 969 HURRICANE-2 

 12 28.90 -95.00 08/18/06Z 100 963 HURRICANE-3 

 13 29.70 -95.50 08/18/12Z 80 965 HURRICANE-1 ----Landfall 15 GMT 

 14 30.50 -96.00 08/18/18Z 40 990 TROPICAL STORM 

 15 31.50 -96.70 08/19/00Z 35 998 TROPICAL STORM 

 16 32.40 -98.40 08/19/06Z 30 1003 TROPICAL DEPRESSION 

 17 33.30 -98.00 08/19/12Z 25 1006 TROPICAL DEPRESSION 

 18 34.40 -98.50 08/19/18Z 25 1009 TROPICAL DEPRESSION 

 19 35.40 -99.00 08/20/00Z 20 1010 TROPICAL DEPRESSION 

 20 36.50 -99.40 08/20/06Z 20 1011 EXTRATROPICAL DEPRESSION 

 21 38.60 -99.20 08/20/12Z 20 1011 EXTRATROPICAL DEPRESSION 

 22 38.90 -99.00 08/20/18Z 20 1011 EXTRATROPICAL DEPRESSION 

 23 40.00 -98.00 08/21/00Z 20 1010 EXTRATROPICAL DEPRESSION 

 24 41.20 -98.00 08/21/06Z 20 1010 EXTRATROPICAL DEPRESSION 

7.2. Simulation Set-up Procedures 

The first hindcast covers the period August 16 18:00 CST to August 17 18:00 CST. 

Water surface elevations and velocities are started from rest. The initial salinity and 

temperature fields are determined based on climatology. Since no PORTS data are 

available, no adjustment of these fields is made. Open boundary conditions for the GBM 

for water surface elevation are computed based on adding the observed nontidal water 

level at Galveston Pleasure Pier to the predicted astronomical tide. Salinity and 

temperature values along the open boundary are based on climatology. Sea surface 

temperature is specified by using the top level of the initial temperature field and is held 

constant in time. River inflows for the San Jacinto, Buffalo Bayou, and Trinity Rivers are 

based on USGS daily observed values. Since no available wave data are available, the 

86
relations in Equation 5.13 were used to specify representative wave conditions along the 

GBM open boundary. 

For the subsequent daily hindcast over the period August 17 18:00 CST to August 18 

18:00 CST, conditions are restarted from the end of the previous hindcast. No 

adjustments of the salinity and temperature fields are made. Open boundary conditions 

for water surface elevation, salinity, and temperature are specified using the same 

technique as described above for the first hindcast. Similarly, sea surface temperature, 

river inflows for the San Jacinto, Buffalo Bayou, and Trinity Rivers, and the wave 

conditions along the open boundary are specified as above. Note the HSCM is directly 

driven from information saved from the GBM using the same one-way coupling scheme 

mentioned previously. 

Two experiments are run using the above conditions but with different meteorological 

forcing. In experiment one, the observed surge level at Galveston Pleasure Pier is 

propagated into the Bay and the water level, current, and density response is investigated 

in the absence of wind and atmospheric pressure forcing. Results are presented for both 

the long wave and short surface gravity wave cases. Experiment two results with the 

parametric hurricane model wind and atmospheric pressure field forcing applied are next 

considered. 

7.3. Experiment One Long Wave Results 

Simulated water surface elevations for each of the two hindcasts are shown at Galveston 

Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 7.2–7.3. GBM simulated 

water levels are in excellent agreement with the observations at Galveston Pleasure Pier 

and at Galveston Pier 21. The maximum discrepancy is 35 cm. One notes the rapid rise in 

water levels and the potential for overland flooding and overtopping of the barrier islands 

during the second hindcast. In Figures 7.4–7.5, HSCM simulated water surface elevations 

are shown for each hindcast at Eagle Point and Morgans Point. Unfortunately, no water 

level gages were in operation during this storm at these locations. In the third panel of 

these figures, the water level residual (surge at Galveston Pleasure Pier) is given. This 

water level residual is applied uniformly in space over the entire GBM open water 

boundary. As noted previously, the storm surge at San Luis Pass was order 3.9 m, which 

is considerably larger that the surge at Galveston Pleasure Pier. Since San Luis Pass is at 

the lower boundary, it may be more appropriate to use the San Luis Pass surge level 

along a portion of the lower GBM open boundary. 

Simulated currents are examined in three-panel figures for current speed, current 

direction, and principal component direction with flood considered positive. Simulated 

Bolivar Roads currents are shown in Figures 7.6- 7.7 for each hindcast. One notes the 

strong persistent flood flow at the beginning of the first hindcast. This flood flow is 

followed by a weak ebb flow of 70 cm/s and then a very strong flood flow of over 200 

cm/s during the second hindcast. Simulated currents at Redfish Bar, mid-way up the Bay, 

show a similar behavior in the ebb-flood structure to simulated currents at Bolivar Roads; 

however, the peak flood current strength during the second hindcast is reduced to order 

87
125 cm/s. At Morgans Point, the simulated currents in Figures 7.8-7.9, exhibit a similar 

ebb-flood structure. The peak current strengths on ebb and flood are on the order of 70 

cm/s. Additional rainfall/runoff flows have not been included and inflows from the 

Buffalo Bayou, San Jacinto River, and Trinity River were small. 

Simulated surface temperature, temperature stratification (absolute difference between 

simulated surface and bottom temperatures) and surface salinity are examined in three 

panels at Bolivar Roads in Figures 7.10-7.11 and at Eagle Point in Figures 7.12-7.13, 

respectively. One notes the increase in salinity at Bolivar Roads from 30 to 34 psu during 

the surge propagation phase and gradual decrease to 30 psu in the second hindcast during 

which the surge recedes. While the simulated surface temperature remains constant, there 

is increase in stratification to order 0.75 o

C as the cooler shelf water moves in over the 

bottom layers during the surge propagation phase of the storm. At Eagle Point the 

simulated surface salinity increases from 17 psu to a maximum of 27 psu and then returns 

to 22.5 psu. The maximum simulated temperature stratification is only 0.5 o

C. At 

Morgans Point the surface salinity remains nearly constant at 20 psu with a maximum 

simulated temperature stratification of order 1.25 o

C. 

GBM simulated water surface elevation contours relative to MTL model datum are 

shown at the end of hindcast two in Figure 7.14. Water surface elevations are initiated at 

rest. One day later at the end of the first hindcast no flooding has occurred. At the end of 

the second hindcast in Figure 7.14, the barrier islands have been overtopped and areas 

have been flooded. 

Next GBM simulated near surface and near bottom salinity contours are shown in Figures 

7.15 and 7.16 at the end of hindcast two. One notes the penetration of the shelf salinity 

into the Bay during the surge propagation phase at both the surface and bottom. Note that 

both the surface and bottom layer simulated salinities are still elevated and have not 

returned to prestorm values at the end of the second hindcast. 

HSCM simulated water surface elevation contours relative to MTL model datum and 

simulated near surface and near bottom salinity contours are consistent with GBM results 

and are not shown here. 

88
Figure 7.2. Hurricane Alicia GBM Water Levels Experiment One: 16-17 August 1983 

September 1961

89
Figure 7.3. Hurricane Alicia GBM Water Levels Experiment One: 17-18 August 1983

90
Figure 7.4. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

Experiment One: 16-17 August 1983 

91
Figure 7.5. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

Experiment One: 17-18 August 1983 

92
Figure 7.6. Hurricane Alicia GBM Bolivar Roads Currents Experiment One: 16-17 

August 1983 

93
Figure 7.7. Hurricane Alicia GBM Bolivar Roads Currents Experiment One: 17-18 

August 1983 

94
Figure 7.8. Hurricane Alicia GBM Morgans Point Currents Experiment One: 16-17 

August 1983 

95
Figure 7.9. Hurricane Alicia GBM Morgans Point Currents Experiment One: 17-18 

August 1983 

96
Figure 7.10. Hurricane Alicia GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 16-17 August 1983 

97
Figure 7.11. Hurricane Alicia GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 17-18 August 1983 

98
Figure 7.12. Hurricane Alicia HSCM Eagle Point Temperature and Salinity 

 Experiment One: 16-17 August 1983 

99
Figure 7.13. Hurricane Alicia HSCM Eagle Point Temperature and Salinity 

 Experiment One: 17-18 August 1983 

100
Figure 7.14. Hurricane Alicia GBM Water Surface Elevation Field 

 Experiment One: 18 August 1983 18:00 CST 

101
Figure 7.15. Hurricane Alicia GBM Near Surface Salinity Field 

 Experiment One: 18 August 1983 18:00 CST 

102
Figure 7.16. Hurricane Alicia GBM Near Bottom Salinity Field 

 Experiment One: 18 August 1983 18:00 CST 

103
7.4. Experiment One Short Wave Results 

Unfortunately, no wave information was available and the results must be judged as 

being representative of hurricane wave conditions. In experiment one, no wind forcing 

was applied. An empirical reduction formula is used to reduce the offshore boundary 

wave condition generated using Equation 5.13 over the interior grid cells. 

Simulated significant wave height for each of the two hindcasts is shown at Galveston 

Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 7.17-7.18. One notes the 

period of elevated simulated wave heights on top of the elevated simulated water levels 

noted in the long wave results and the potential for overland flooding and overtopping of 

the barrier islands with accompanying large waves order 5m. In Figures 7.19-7.20, 

HSCM simulated significant wave heights are shown for each hindcast at Eagle Point and 

Morgans Point with maximum significant wave heights of 2.6m and 2.5m, respectively. 

In the third panel of these figures, the simulated significant wave height at NDBC buoy 

42035 is given, which represents the GBM open boundary wave condition. This 

significant wave height is applied uniformly in space over the entire GBM open water 

boundary. Note the maximum simulated significant wave heights are order 10m. 

Note in this experiment with no wind generation, the significant wave direction is equal 

to the offshore boundary swell condition in all interior grid cells and varies in time based 

on the relation given in Equation 5.13. As a result, wave directions are the same for all of 

the above stations and are near 315 degrees True. 

GBM simulated significant wave periods for each of the hindcasts are shown at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 7.21-7.22. In 

Figures 7.23-7.24, HSCM simulated significant wave periods are shown for each hindcast 

at Eagle Point and Morgans Point, respectively. Maximum simulated significant wave 

periods range from 4 to 8s. In the third panel of these figures, the simulated significant 

wave period range from 11 to 18s at NDBC buoy 42035, which represents the GBM open 

boundary wave condition. This significant wave period is applied uniformly in space over 

the entire GBM open water boundary. Note in the case of no wind generation, the 

significant wave period as given in Equation 5.13 is a function of significant wave height, 

which is based on empirical reduction. As a result, wave periods are the similar in form at 

all of the above stations. 

GBM simulated significant wave height and direction vectors are shown at the end of 

hindcast two in Figure 7.25. At the end of the second hindcast in Figure 7.25 one notes 

that the barrier islands have been overtopped and that flooding has occurred and that 

wave computations have been performed over the flooded cells. Simulated significant 

wave heights are in the range from 1 m in upper Trinity Bay to 10m near the offshore 

boundary. Note in the present case of no wind generation, simulated significant wave 

directions are near 315 deg True for all grid cells. 

104
Next GBM simulated significant wave period contours are shown in Figure 7.26 at the 

end of hindcast two. Simulated significant wave periods range from below 1s in upper 

Trinity Bay to over 10s near the offshore boundary. 

HSCM simulated significant wave height and direction vectors and wave period contours 

are consistent with those of the GBM. Simulated significant wave periods are in the range 

of 1 to 7s consistent with those computed over the GBM. 

105
Figure 7.17. Hurricane Alicia GBM Significant Wave Height Experiment One: 

16-17 August 1983 

106
Figure 7.18. Hurricane Alicia GBM Significant Wave Height Experiment One: 

17-18 August 1983 

107
Figure 7.19. Hurricane Alicia HSCM and GBM 42035 Significant Wave Height 

Experiment One: 16-17 August 1983 

108
Figure 7.20. Hurricane Alicia HSCM and GBM 42035 Significant Wave Height 

Experiment One: 17-18 August 1983 

109
Figure 7.21. Hurricane Alicia GBM Significant Wave Period Experiment One: 

16-17 August 1983 

110
Figure 7.22. Hurricane Alicia GBM Significant Wave Period Experiment One: 

17-18 August 1983 

111
Figure 7.23. Hurricane Alicia HSCM and GBM 42035 Significant Wave Period 

Experiment One: 16-17 August 1983 

112
Figure 7.24. Hurricane Alicia HSCM and GBM 42035 Significant Wave Period 

Experiment One: 17-18 August 1983 

113
Figure 7.25. Hurricane Alicia GBM Significant Wave Height and Direction 

Experiment One: 18 August 1983 18:00 CST 

114
Figure 7.26. Hurricane Alicia GBM Significant Wave Period Experiment One: 

18 August 1983 18:00 CST 

115
7.5. Experiment Two Long and Short Wave Results 

In experiment two, the parametric hurricane wind and atmospheric pressure model is 

used to provide the meteorological forcing. It should be noted that the present procedure 

does not allow for a reduction of windspeed due to overland friction effects directly. The 

central pressure deficit of the storm is reduced based on observed overland weakening, 

but the windfields computed based on the reduced pressure deficit are not further 

reduced. 

GBM simulated water surface elevations for each of the two hindcasts are shown at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 7.27-7.28. In 

Figures 7.29-7.30, HSCM simulated water surface elevations are shown for each hindcast 

at Eagle Point and Morgans Point. Simulated water levels exceed those of experiment one 

and are above the available observations by over 1 m, indicating the influence of local 

wind and atmospheric pressure forcing. 

These forcing are shown in Figures 7.31-7.32 at Morgans Point. Simulated peak 

windspeeds are approximately 40 m/s at Galveston Pleasure Pier, Eagle Point, and 

Morgans Point. The simulated atmospheric pressure drops sharply from 1008 mb to 985 

mb at all three stations. The simulated wind and atmospheric pressure forcing are from 

the near field of the hurricane. 

Snapshots of the simulated atmospheric pressure fields using a 24 hour increment are 

shown in Figures 7.33-7.34, respectively, and indicate the radial structure of the hurricane 

atmospheric pressure field. Snapshots of the simulated windfields at the same times are 

shown in Figures 7.35-7.36, respectively and show a difference in wind direction over the 

Port of Houston and near the barrier islands. This result needs further investigation. 

In experiment two, simulated significant wave heights follow the same general pattern as 

in experiment one and are largely determined by the GBM offshore wave conditions. 

Wind generation increases wave heights by order 0.60 m at Galveston Pleasure Pier and 

at Port Bolivar and by order 0.25 m at Eagle and Morgans Point. Simulated wave 

directions are in the direction of the wind and move from near 270 deg T to 45 deg T at 

all stations during hindcast two. 

In contrast to experiment one results, simulated significant wave periods are reduced at 

Galveston Pleasure Pier from 7s to 5s during hindcast one and are slightly increased at 

the Bay by less than 1s. During hindcast two, wave periods are reduced at Galveston 

Pleasure Pier from 8 to 6s, while at all Bay stations the differences in wave periods are 

less than 1s. The wave period is computed directly from the wind wave and the offshore 

swell period is not used in the wave period computations. 

7.6. Wind and Water Surface Elevation Validation 

In Table 7.2 peak simulated windspeeds over the GBM grid are compared with fastest 

mile observations reported by Case and Gerrish (1984). Simulated wind speeds computed 

116
used the parametric hurricane model are in general agreement with these observations. 

Table 7.2. Hurricane Alicia (1983) Wind speed Validation. Note simulated GBM peak 

corresponds to results obtained in Experiment Two with parametric hurricane model 

wind and atmospheric pressure forcing. 

Station Location ID Simulated 

GBM Peak (m/s) 

Observed 

 Fastest Mile (m/s) 

Galveston 12923 41.8 27.-35. 

Ellington AFB 12906 38.5 25. 

Hobby Airport 12918 38.1 42. 

In Table 7.3, GBM peak simulated water levels and simulated significant wave heights 

are compared with observed peak water levels reported by Case and Gerrish (1984). The 

observed peak water levels are reported with respect to MSL whereas the GBM simulated 

water levels are with respect to the MTL model datum. As noted previously, MSL and 

MTL in Galveston Bay maximum differences are order 1 cm and therefore these two 

vertical datums are nearly equivalent. Peak water levels from high water marks, 

particularly at Seabrook and Baytown may include surface gravity wave effects making 

direct comparison more problematical. One should note that at the two Galveston water 

level gauges, the comparisons with simulation results shown in Figures 7.2-7.3 for 

experiment one and in Figures 7.27-7.28 for experiment two are made with respect to 

MLLW. 

Table 7.3. Hurricane Alicia (1983) GBM Storm Surge Validation. Note + indicates high 

water mark. Exp1==Experiment One with no wind and atmospheric forcing, while Exp 

2==Experiment Two with parametric hurricane model wind and atmospheric pressure 

forcing. Note *==Morgans Point value and #==Christmas Bay value. 

Station Location Simulated Peak 

 Water Level 

(m-MTL) 

Exp 1 Exp 2 

Simulated Peak 

Wave Height 

(m) 

Exp 1 Exp2 

Observed Peak 

Water Level 

(m-MSL) 

Galveston Pl. Pier 2.20 3.27 4.93 5.65 2.64 

Galveston Pier 21 1.77 2.75 2.96 2.96 1.71 

Seabrook 1.57* 3.85* 1.97* 2.72* 3.45+ 

Baytown 1.57* 3.85* 1.97 * 2.72* 3.24+ 

San Luis Pass 1.87# 2.23# 1.97# 1.97# 3.85+ 

7.7. Surface Salinity, Surface Current, and Inundation Statistics 

In Table 7.4, GBM simulated surface minimum salinity and simulated maximum surface 

current strengths for stations proceeding northward up Galveston Bay are compared 

between experiment one and two. The added wind forcing significantly adjust the salinity 

structure and increase the maximum currents, due to the proximity of the center of the 

storm. 

117
Inundation statistics for both experiments are presented in Table 7.5 in terms of the time 

and areal extent of the maximum flooding. Average and maximum flood depths are also 

determined. Experiment two values are significantly elevated over those of experiment 

one due the influence of the strong wind and atmospheric pressure forcing. 

Table 7.4. Hurricane Alicia (1983) GBM Minimum Surface Salinity and Maximum 

Current Speeds. Exp1==Experiment One with no wind and atmospheric forcing, while 

Exp 2==Experiment Two with parametric hurricane model wind and atmospheric 

pressure forcing. 

Station Location Minimum Salinity (PSU) 

Exp 1 Exp 2 

Maximum Current (m/s) 

Exp 1 Exp 2 

Galveston Pleasure Pier 33.4 34.6 0.55 1.62 

Galveston Pier 21 31.7 32.7 1.46 1.95 

Eagle Point 19.9 29.8 0.71 0.56 

Smith Point 24.6 13.0 0.67 1.94 

Morgans Point 19.4 18.4 0.33 1.19 

Round Point 10.8 7.9 0.14 0.57 

Table 7.5. Hurricane Alicia (1983) Inundation Statistics. Note the first line corresponds 

to results from Experiment 1 with no wind and atmospheric pressure forcing. The second 

line presents results from Experiment 2 with parametric hurricane wind and atmospheric 

pressure forcing. 

Hindcast 

No. 

Simulation 

Dates 

Time of 

Maximum 

Flood (JD) 

Maximum 

Flooded 

Area (km2

) 

Average 

Flood Depth 

(m) 

Maximum 

Flood Depth 

(m) 

1 8/16-8/17 - 

229.746 

- 

180 

- 

0.440 

- 

0.775 

2 8/17-8/18 230.413 

230.704 

980 

1476 

0.324 

0.590 

1.251 

3.612 

118
Figure 7.27. Hurricane Alicia GBM Water Levels Experiment Two: 

16-17 August 1983

119
Figure 7.28. Hurricane Alicia GBM Water Levels Experiment Two: 

17-18 August 1983 

120
Figure 7.29. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

Experiment Two: 16-17 August 1983 

121
Figure 7.30. Hurricane Alicia HSCM Water Levels and GBM Water Level Residual 

Experiment Two: 17-18 August 1983 

122
Figure 7.31. Hurricane Alicia Wind and Atmospheric Pressure at Morgans Point 

Experiment Two: 16-17 August 1983 

123
Figure 7.32. Hurricane Alicia Wind and Atmospheric Pressure at Morgans Point 

Experiment Two: 17-18 August 1983 

124
Figure 7.33. Hurricane Alicia GBM Atmospheric Pressure Field Experiment Two: 

17 August 1983 18:00 CST 

125
 

Figure 7.34. Hurricane Alicia GBM Atmospheric Pressure Field Experiment Two: 

18 August 1983 18:00 CST 

126
Figure 7.35. Hurricane Alicia GBM Wind Field Experiment Two: 

17 August 1983 18:00 CST 

127
Figure 7.36. Hurricane Alicia GBM Wind Field Experiment Two: 

18 August 1983 18:00 CST 

128
8. TROPICAL STORM ALLISON (2001) SIMULATIONS 

The complete All-Weather Nowcast/Forecast System is exercised for two separate events 

during Tropical Storm Allison: the surge event of 5-6 June 2001 and the rainfall/runoff 

event of 10-11 June. Nowcast/forecast cycle results are presented separately for each of 

these two events. The nowcast/forecast cycle consists of a 24-hour nowcast followed by a 

36-hour forecast. On the nowcast, PORTS met stations are used via Barnes interpolation 

to provide the meteorological forcing, while the open boundary storm surge was based on 

the nontidal water level at Galveston Pleasure Pier. River flows are based on USGS 

average daily flows. On the forecast, NWS/WGRFC flows for the San Jacinto and Trinity 

Rivers and a persisted USGS daily flow for Buffalo Bayou are used. NWS/GFS (formerly 

AVN) atmospheric model winds and sea level pressure and NWS/ETSS storm surge 

levels at Galveston Pleasure Pier are used for meteorological forcing and nontidal water 

level, respectively. 

For the surge event, two complete nowcast/forecast cycles for June 5 and 6 were 

performed with the calculations restarted for the second nowcast from results at the end 

of the first nowcast. Long wave results are given in terms of water surface elevation, 

current, salinity, and temperature time series. River flows and meteorological forcing are 

also shown. Short wave results are given in terms of significant wave height, period, and 

direction time series. No overland flooding occurred during the simulations and 

inundation statistics are not necessary. 

For the rainfall/runoff event, two complete nowcast/forecast cycles for June 10 and 11 

were performed with the calculations restarted for the second nowcast from results at the 

end of the first nowcast. Two separate experiments were performed. In experiment one, 

the standard inflows for the Trinity and San Jacinto Rivers and Buffalo Bayou are 

considered, while in experiment two additional inflows from Sims, Brays, Green, and 

Hunting Bayous within the City of Houston are also input. Long wave results are given in 

terms of water surface elevation, current, salinity, and temperature time series. River 

flows and meteorological forcing are also shown. Short wave results are given in terms of 

significant wave height, period, and direction time series. Salinity response is presented 

in terms of near surface and near bottom contour plots. No overland flooding occurred 

during the simulations and no inundation statistics are required. 

8.1. Coastal Surge Propagation Event Characteristics 

The track of Tropical Storm Allison is shown in Figure 8.1 with storm parameters given 

in Table 8.1. The storm made landfall along the Texas coast 50 km southwest of 

Galveston near Freeport, Texas at 1400 CST on the afternoon of June 5. 

In the simulations, the radius to maximum winds was estimated at approximately 30 nm 

around the time of landfall based on Stewart (email, 20 March 2003) and was held at this 

value. Stewart (2002) notes that the peak storm surges were mild ranging from 0.64 m at 

Galveston Pleasure Pier to only 0.37 m at Morgans Point. At the west end of Galveston 

Island, wave heights of up to 2.4 m were reported with order 1 m of surge. 

129
Figure 8.1. Tropical Storm Allison (2001) Storm Track 5-6 June. 

Table 8.1. Tropical Storm Allison Storm Characteristics: 5-6 June 2001. 

ADV LAT LON TIME WIND PR STAT 

 1 29.30 -94.70 06/05/19Z 50 1004 TROPICAL STORM 

 2 29.80 -95.10 06/05/21Z 50 1002 TROPICAL STORM--Landfall 21 GMT 

 3 29.10 -95.00 06/06/03Z 40 1003 TROPICAL STORM 

 3A 29.90 -95.30 06/06/06Z 35 1004 TROPICAL STORM 

 4 30.20 -95.30 06/06/09Z 30 1004 TROPICAL DEPRESSION 

8.2. Rainfall/Runoff Event Characteristics 

The track of Tropical Storm Allison shown in Figure 8.1 is only for the surge event 

portion of the storm. The storm then became stationary near Lufkin, Texas. On June 8 the 

storm proceeded southward entering the Gulf of Mexico on 17:00 CST on the afternoon 

of June 10 at nearly the same location that it had made landfall five days earlier. In the 

simulations, the radius to maximum winds was estimated at approximately 30 nm. Hourly 

rainfall information was obtained at Harris County Flood Control Station rain gages 1620 

for Greens Bayou, 0410 for Brays Bayou, 0370 for Sims Bayou, and 0830 for Hunting 

Bayou, repectively, for use in the rainfall/runoff computations. Rainfall totals exceeded 

over 35 inches for Greens Bayou. Average daily flows on the San Jacinto River exceeded 

130
100,000 cfs and even on Greens Bayou, a peak average daily flow of over 50,000 cfs was 

recorded. 

8.3. Coastal Surge Propagation Event Simulation Set-up Procedures 

The first nowcast covers the period June 3 18:00 CST to June 4 18:00 CST. Water 

surface elevations and velocities are started from rest. The initial salinity and temperature 

fields are determined based on climatology. PORTS data were used in the adjustment of 

these fields. Open boundary conditions for the GBM for water surface elevation are 

computed based on adding the observed nontidal water level at Galveston Pleasure Pier 

to the predicted astronomical tide. Salinity and temperature values along the open 

boundary are based on climatology. Sea surface temperature is specified by using the top 

level of the initial temperature field and is held constant in time. River inflows for the 

San Jacinto, Buffalo Bayou, and Trinity Rivers are based on USGS daily averaged 

values. During the 36 hour forecast out to June 6 06:00 CST, NWS GFS atmospheric 

model wind and sea level atmospheric pressure were used along with the NWS/ETSS 

storm surge forecast at Galveston Pleasure Pier. Wave data from NBDC 42035 buoy 

were used to specify the wave conditions along the GBM open boundary during both the 

nowcast and forecast period. 

For the subsequent daily nowcast over the period June 4 18:00 CST to June 5 18:00 CST, 

conditions are restarted from the end of the previous nowcast. PORTS data based 

adjustments of the salinity and temperature fields were made. Open boundary conditions 

for water surface elevation, salinity, and temperature are specified using the same 

technique as described above for the first nowcast. Similarly, sea surface temperature, 

river inflows for the San Jacinto, Buffalo Bayou, and Trinity Rivers, and the wave 

conditions along the open boundary are specified as above. During the 36 hour forecast 

out to June 7 06:00 CST, NWS GFS atmospheric model wind and sea level atmospheric 

pressure were used along with the NWS/ETSS storm surge forecast at Galveston Pleasure 

Pier. 

8.4. Rainfall/Runoff Event Simulation Set-up Procedures 

The first nowcast covers the period June 8 18:00 CST to June 9 18:00 CST. Water 

surface elevations and velocities are started from rest. The initial salinity and temperature 

fields are determined based on climatology. PORTS data were used in the adjustment of 

these fields. Open boundary conditions for the GBM for water surface elevation are 

computed based on adding the observed nontidal water level at Galveston Pleasure Pier 

to the predicted astronomical tide. Salinity and temperature values along the open 

boundary are based on climatology. Sea surface temperature is specified by using the top 

level of the initial temperature field and is held constant in time. River inflows for the 

San Jacinto, Buffalo Bayou, and Trinity Rivers are based on USGS daily averaged 

values. During the 36 hour forecast out to June 11 06:00 CST, NWS GFS atmospheric 

model wind and sea level atmospheric pressure were used along with the NWS/ETSS 

storm surge forecast at Galveston Pleasure Pier. NDBC 42035 buoy data were used to 

specify representative wave conditions along the GBM open boundary during both the 

nowcast and forecast period. 

131
For the subsequent daily nowcast over the period June 9 18:00 CST to June 10 18:00 

CST, conditions are restarted from the end of the previous nowcast. PORTS data based 

adjustments of the salinity and temperature fields were made. Open boundary conditions 

for water surface elevation, salinity, and temperature are specified using the same 

technique as described above for the first nowcast. Similarly, sea surface temperature, 

river inflows for the San Jacinto, Buffalo Bayou, and Trinity Rivers, and the wave 

conditions along the open boundary are specified as above. During the 36 hour forecast 

out to June 12 06:00 CST, NWS GFS atmospheric model wind and sea level atmospheric 

pressure were used along with the NWS/ETSS storm surge forecast at Galveston Pleasure 

Pier. 

Two experiments are run using the above conditions but with different freshwater 

inflows. In experiment one, the standard three inflows were used, while in the second 

experiment, four additional inflows from the City of Houston were included. Results are 

presented in separate sections for both experiments for the long wave computations with 

a particular emphasis on the comparison of the salinity decrease and water surface 

elevation increase at Morgans Point due to the additional inflows. Short period gravity 

wave results are shown for experiment one only, since results from experiment two with 

the additional inflows were nearly the same. 

8.5. Coastal Surge Propagation Event Long Wave Results 

Water surface elevations for each of the two nowcast/forecast cycles are shown at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 8.2 – 8.3. GBM 

simulated water levels are in excellent agreement with the observations at Galveston 

Pleasure Pier and at Galveston Pier 21. In Figures 8.4 – 8.5, HSCM simulated water 

surface elevations are shown for each nowcast/forecast cycle at Eagle Point and Morgans 

Point. HSCM simulated water levels are in excellent agreement with the observations at 

Eagle and Morgans Point. In the third panel of these figures, the water level residual 

(surge at Galveston Pleasure Pier) is given. This water level residual is applied uniformly 

in space over the entire GBM open water boundary. 

Simulated Bolivar Roads currents demonstrate no strong persistent of flood or ebb flow 

with maximum current strengths of 80 cm/s with the exception of a peak ebb flow of 125 

cm/s at the end of the first nowcast. Simulated currents at Redfish Bar, mid-way up the 

Bay have a similar behavior in their ebb-flood structure to simulated currents at Bolivar 

Roads; however, the peak ebb current strength at the end of the first nowcast is reduced 

to order 50 cm/s. At Morgans Point, the simulated currents exhibit a similar ebb-flood 

structure. The peak current strengths on ebb and flood are on the order of 35 cm/s with 

the exception of a peak ebb current of order 75 cm/s near the end of the first forecast. 

Additional rainfall/runoff flows have not been included and inflows from the Buffalo 

Bayou, San Jacinto River, and Trinity River were small. 

Simulated surface temperature, temperature stratification (absolute difference between 

132
simulated surface and bottom temperatures) and surface salinity are examined in three 

panels at Morgans Point in Figures 8.6-8.7. One notes the increase in simulated salinity at 

Bolivar Roads from 30 to 34 psu during the surge propagation phase. While the simulated 

surface temperature remains constant, there is mild stratification to order 0.75 o

C as the 

cooler shelf water moves in over the bottom layers during the surge propagation phase of 

the storm. No PORTS data were available at this station. At Eagle Point the simulated 

surface salinity increases from 22.5 psu to a maximum of 27 psu at the end of the first 

nowcast in general agreement with the PORTS data, but the large dip and rapid increase 

in observed salinity is not replicated in the simulation. The same behavior is observed 

during the second nowcast period. The maximum simulated temperature stratification is 

only 0.5 o

C. At Morgans Point the simulated surface salinity remains nearly constant at 

17.5 psu with a maximum simulated temperature stratification of order 0.5 o

C during the 

first nowcast with a similar behavior noted during the second nowcast. The large 

observed dip and increase in observed salinity at Morgans Point is not captured. This 

suggests that there are additional freshwater inflows effects which have not been 

accounted for in the simulation. 

Simulated wind speed and direction and atmospheric pressure are shown in Figures 8.8-

8.9 at Morgans Point. Maximum nowcast windspeeds at Bolivar Roads and Eagle Point 

are 12.5 m/s while at Morgans Point they are reduced to 6.3 m/s. Maximum forecast 

windspeeds are near are near 20 m/s at Bolivar Roads and Eagle Point. Nowcast and 

forecast atmospheric pressure is near 1010 mb at all stations. 

 

133
Figure 8.2. Tropical Storm Allison GBM Water Levels: 5 June 2001 Nowcast/Forecast 

Cycle 

134
Figure 8.3. Tropical Storm Allison GBM Water Levels: 6 June 2001 Nowcast/Forecast 

Cycle 

135
Figure 8.4. Tropical Storm Allison HSCM Water Levels 

and GBM Water Level Residual: 5 June 2001 Nowcast/Forecast Cycle 

136
Figure 8.5. Tropical Storm Allison HSCM Water Levels 

and GBM Water Level Residual: 6 June 2001 Nowcast/Forecast Cycle 

137
Figure 8. 6. Tropical Storm Allison HSCM Morgans Point Temperature 

 and Salinity: 5 June 2001 Nowcast/Forecast Cycle 

138
Figure 8.7. Tropical Storm Allison HSCM Morgans Point Temperature 

 and Salinity: 6 June 2001 Nowcast/Forecast Cycle 

139
Figure 8.8. Tropical Storm Allison HSCM Morgans Point Wind 

 and Atmospheric Pressure: 5 June 2001 Nowcast/Forecast Cycle 

140
Figure 8.9. Tropical Storm Allison HSCM Morgans Point Wind 

 and Atmospheric Pressure: 6 June 2001 Nowcast/Forecast Cycle 

141
8.6. Coastal Surge Propagation Event Short Wave Results 

Unfortunately, no wave information was available within the Bay for comparison. NBDC 

42035 buoy data were used to specify the offshore boundary wave condition during both 

nowcast and forecast, since the forecasts were run after the fact. 

Simulated significant wave height for each of the two nowcast/forecast cycles is shown at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 8.10-8.11. 

Maximum simulated wave heights are of order 2.6 m at Galvestion Pleasure Pier, 2.0m at 

Bolivar Roads, and 1.2m at Galveston Pier 21. HSCM simulated significant wave heights 

at Eagle Point and Morgans Point are order 1.25 m. The maximum simulated significant 

wave height at NDBC buoy 42035, which represents the GBM open boundary wave 

condition, exceeds 4m. Note in this experiment with wind generation, the significant 

wave direction is equal to the wind direction, which is near 315 deg T. 

GBM simulated significant wave periods for each of the nowcast/forecast cycles at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 are order 4s. HSCM 

simulated significant wave periods for each nowcast/forecast cycle at Eagle Point and 

Morgans Point are also order 2s. The simulated significant wave period ranges from 5 to 

7s at NDBC buoy 42035, which represents the GBM open boundary wave condition. 

This significant wave period is applied uniformly in space over the entire GBM open 

water boundary. 

142
Figure 8.10. Tropical Storm Allison GBM Significant Wave Height: 

5 June 2001 Nowcast/Forecast Cycle 

143
Figure 8.11. Tropical Storm Allison HSCM and GBM 42035 Significant Wave 

 Height: 5 June 2001 Nowcast/Forecast Cycle 

144
8.7. Rainfall/Runoff Event Experiment One Long Wave Results 

Tropical Storm Allison standard inflows for the Trinity, San Jacinto, and Buffalo Bayou 

inflows are shown for both nowcast/forecast cycles in Figures 8.12 and 8.13. Note the 

forecast and subsequent nowcast flow of over 100000 cfs for the San Jacinto River. 

Trinity and Buffalo Bayou inflows are order 35,000 cfs and less than 8000 cfs, 

respectively. 

Water surface elevations for each of the two nowcast/forecast cycles are shown for 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 in Figures 8.14-8.15. 

GBM simulated water levels are in excellent agreement with the observations at 

Galveston Pleasure Pier and at Galveston Pier 21. In Figures 8.16-8.17, HSCM simulated 

water surface elevations are shown for each nowcast/forecast cycle at Eagle Point and 

Morgans Point. HSCM simulated water levels are below the observations at Eagle and 

Morgans Point during the second nowcast by order 25 cm. In the third panel of these 

figures, the water level residual (surge at Galveston Pleasure Pier) is given. This water 

level residual is applied uniformly in space over the entire GBM open water boundary. 

Simulated currents are examined in three panel figures for current speed, current 

direction, and principal component direction with flood considered positive. Simulated 

Bolivar Roads currents are shown in Figures 8.18-8.19 for each nowcast/forecast cycle. 

One notes no strong persistent flood or ebb flow with peak current strengths of order 100 

cm/s during both nowcast/forecast cycles. Simulated currents at Redfish Bar, mid-way up 

the Bay, are shown in Figures 8.20-8.21 for each nowcast/forecast cycle. One notes a 

similar behavior in the ebb-flood structure to simulated currents at Bolivar Roads; 

however, the peak flood current strengths are reduced to order 50 cm/s. At Morgans 

Point, the simulated currents in Figures 8.22-8.23, exhibit a much different ebb-flood 

structure, with ebb dominance occurring during the first forecast and throughout both the 

second nowcast/forecast cycle. Ebb current strengths are in the range of 70-100 cm/s. 

Simulated surface temperature, temperature stratification (absolute difference between 

surface and bottom temperatures) and surface salinity are examined in three panels at 

Bolivar Roads in Figures 8.24-8.25, at Eagle Point in Figures 8.26-8.27, and at Morgans 

Point in Figures 8.28-8.29, respectively. One notes the sinusoidal character of the 

simulated salinity at Bolivar Roads with amplitude order 2.5 psu. While the simulated 

surface temperature remains constant, there is a mild simulated stratification to order 0.5 o

C. At Eagle Point the simulated surface salinity remains constant near 15 psu and does 

not follow the decrease in observed salinity from 15 to 5 psu during the first nowcast. 

The maximum simulated temperature stratification is only 0.5 o

C. At Morgans Point the 

surface salinity remains nearly constant at 12 psu and does not follow the decrease from 

12 to 4 psu during the first nowcast. During the second nowcast, the simulated salinity is 

in closer agreement with the observations. The maximum simulated temperature 

stratification is 1.5 o

C. 

145
Wind speed and direction and atmospheric pressure are in Figures 8.30-8.31 at Morgans 

Point. Maximum nowcast windspeeds at Bolivar Roads and Eagle Point are 12.5 m/s at 

all three stations. Maximum forecast windspeeds are less than maximum nowcast 

windspeeds. Nowcast and forecast atmospheric pressure is near 1010 mb at all stations. 

HSCM simulated near surface and near bottom salinity contours are shown at the end of 

the second nowcast and forecast in Figures 8.32-8.33 and in Figures 8.34-8.35, 

respectively. One notes the propagation of the freshwater effects on salinity down the 

estuary in both the surface and bottom waters due to the large flows in the San Jacinto 

River. 

 

146
Figure 8.12. Tropical Storm Allison Standard Inflows 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle 

147
Figure 8.13. Tropical Storm Allison Standard Inflows Experiment One: 11 June 2001 

Nowcast/Forecast Cycle

148
Figure 8.14. Tropical Storm Allison GBM Water Levels Experiment One: 10 June 2001 

Nowcast/Forecast Cycle 

149
Figure 8.15. Tropical Storm Allison GBM Water Levels Experiment One: 11 June 2001 

Nowcast/Forecast Cycle 

150
Figure 8.16. Tropical Storm Allison HSCM Water Levels and GBM Water Level 

Residual Experiment One: 10 June 2001 Nowcast/Forecast Cycle 

151
Figure 8.17. Tropical Storm Allison HSCM Water Levels and GBM Water Level 

Residual Experiment One: 11 June 2001 Nowcast/Forecast Cycle 

152
Figure 8.18. Tropical Storm Allison GBM Bolivar Roads Currents Experiment One: 10 

June 2001 Nowcast/Forecast Cycle 

153
Figure 8.19. Tropical Storm Allison GBM Bolivar Roads Currents Experiment One: 11 

June 2001 Nowcast/Forecast Cycle 

154
Figure 8.20. Tropical Storm Allison GBM Redfish Bar Currents Experiment One: 10 

June 2001 Nowcast/Forecast Cycle 

155
Figure 8.21. Tropical Storm Allison GBM Redfish Bar Currents Experiment One: 11 

June 2001 Nowcast/Forecast Cycle 

156
Figure 8.22. Tropical Storm Allison GBM Morgans Point Currents Experiment One: 10 

June 2001 Nowcast/Forecast Cycle 

157
Figure 8.23. Tropical Storm Allison GBM Morgans Point Currents Experiment One: 11 

June 2001 Nowcast/Forecast Cycle 

158
Figure 8.24. Tropical Storm Allison GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle 

159
Figure 8.25. Tropical Storm Allison GBM Bolivar Roads Temperature and Salinity 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle 

160
Figure 8.26. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle 

161
Figure 8.27. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle 

162
Figure 8.28. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment One: 10 June 2001 Nowcast/Forecast Cycle 

163
Figure 8.29. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment One: 11 June 2001 Nowcast/Forecast Cycle 

164
Figure 8.30. Tropical Storm Allison Wind and Atmospheric Pressure at Morgans Point 

Experiment One: 10 June 2001 Nowcast/Forecast Cycle 

165
Figure 8.31. Tropical Storm Allison Wind and Atmospheric Pressure at Morgans Point 

Experiment One: 11 June 2001 Nowcast/Forecast Cycle 

166
Figure 8.32. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment One: 11 June 2001 Nowcast End 

167
Figure 8.33. Tropical Storm Allison GBM Near Bottom Salinity Field 

 Experiment One: 11 June 2001 Nowcast End 

168
Figure 8.34. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment One: 11 June 2001 Forecast End 

169
Figure 8.35. Tropical Storm Allison HSCM Near Bottom Salinity Field 

 Experiment One: 11 June 2001 Forecast End 

170
8.8. Rainfall/Runoff Event Experiment Two Long Wave Results 

Tropical Storm Allison standard inflows for the Trinity, San Jacinto, and Buffalo Bayou 

inflows were shown for both nowcast/forecast cycles in Figures 8.12 and 8.13, where we 

noted the forecast and subsequent nowcast flow of over 100000 cfs for the San Jacinto 

River. Here additional inflows are shown for flow set one in Figures 8.36-8.37, and in 

Figures 8.38-8.39 for flow set two. Note in the third panel of these figures, the Buffalo 

Bayou inflow is shown as a reference comparison flow. One notes the Greens Bayou 

forecast and nowcast flows exceed 50,000 cfs, while the other inflows are order those of 

Buffalo Bayou inflow. 

In response to this additional inflow, the HSCM simulated water surface elevations are 

shown in Figures 8.40-8.41 for each nowcast/forecast cycle at Eagle Point and Morgans 

Point. These results are to be compared with experiment one HSCM simulated water 

levels shown in Figures 8.16-8.17. One notes similar results except at Morgans Point 

where water surface elevations in experiment two are elevated by order 10-15 cm above 

experiment one levels during the second nowcast/forecast cycle. 

HSCM simulated currents are examined in three panel figures for current speed, current 

direction, and principal component direction with flood considered positive at Morgans 

Point in Figures 8.42-8.43, and exhibit peak current speeds of 125 cm/s. These results are 

to be compared with the experiment one results given in Figures 8.22-8.23. One notes a 

similar ebb dominance but with current strengths reduced by 25 cm/s in experiment one. 

 

HSCM simulated surface temperature, temperature stratification (absolute difference 

between surface and bottom temperatures) and surface salinity are examined in three 

panels at Eagle Point in Figures 8.44-8.45, and at Morgans Point in Figures 8.46-8.47, 

respectively. From experiment one results at Eagle Point both the salinity and 

temperature responses are nearly identical for both experiments. From experiment one 

results at Morgans Point the simulated surface salinity and temperature responses are 

nearly the same but with the degree of temperature stratification reduced by 0.6 o

C. 

HSCM simulated near surface and near bottom salinity contours are shown at the end of 

the second nowcast and forecast are shown in Figures 8.48-8.49 (see experiment one 

results in Figures 8.32-8.33) and in Figures 8.50-8.51 (see experiment one results in 

Figures 8.34-8.35), respectively. Via the figure comparisons, one notes the greater area of 

propagation of the freshwater effects on salinity down the estuary in both the surface and 

bottom waters in experiment two relative to experiment one due to the additional Greens 

Bayou inflows of experiment two. 

 

 

171
Figure 8.36. Tropical Storm Allison City of Houston Inflow Set One 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle 

172
Figure 8.37. Tropical Storm Allison City of Houston Inflow Set One 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle 

173
Figure 8.38. Tropical Storm Allison City of Houston Inflow Set Two 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle 

174
Figure 8.39. Tropical Storm Allison City of Houston Inflow Set Two 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle 

175
Figure 8.40. Tropical Storm Allison HSCM Water Levels and GBM Water Level 

Residual Experiment Two: 10 June 2001 Nowcast/Forecast Cycle 

176
Figure 8.41. Tropical Storm Allison HSCM Water Levels and GBM Water Level 

Residual Experiment Two: 11 June 2001 Nowcast/Forecast Cycle 

177
Figure 8.42. Tropical Storm Allison HSCM Morgans Point Currents Experiment Two: 

10 June 2001 Nowcast/Forecast Cycle 

178
Figure 8.43. Tropical Storm Allison HSCM Morgans Point Currents Experiment Two: 

11 June 2001 Nowcast/Forecast Cycle 

179
Figure 8.44. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle 

180
Figure 8.45. Tropical Storm Allison HSCM Eagle Point Temperature and Salinity 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle 

181
Figure 8.46. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment Two: 10 June 2001 Nowcast/Forecast Cycle 

182
Figure 8.47. Tropical Storm Allison HSCM Morgans Point Temperature and Salinity 

 Experiment Two: 11 June 2001 Nowcast/Forecast Cycle 

183
Figure 8.48. Tropical Storm Allison HSCM Near Surface Salinity Field 

 Experiment Two: 10 June 2001 Nowcast End 

184
Figure 8.49. Tropical Storm Allison HSCM Near Bottom Salinity Field 

 Experiment Two: 10 June 2001 Nowcast End 

185
Figure 8.50. Tropical Storm Allison GBM Near Surface Salinity Field 

 Experiment Two: 11 June 2001 Forecast End 

186
Figure 8.51. Tropical Storm Allison GBM Near Bottom Salinity Field 

 Experiment Two: 11 June 2001 Forecast End 

187
8.9. Rainfall/Runoff Event Short Wave Results 

Unfortunately, no wave information was available within the Bay for comparison. NBDC 

42035 buoy data were used to specify the offshore boundary wave condition during both 

nowcast and forecast, since the forecasts were run after the fact. Results are given for 

experiment one, since the results for experiment two are nearly identical. 

Maximum simulated wave heights are of order 1.0 m at Galvestion Pleasure Pier, 0.75m 

at Bolivar Roads, and 0.5 m at Galveston Pier 21. HSCM simulated significant wave 

heights at Eagle Point and Morgans Point are order 0.5 m. The simulated significant wave 

height at NDBC buoy 42035, which represents the GBM open boundary wave condition, 

exceeds 1.75 m. 

GBM simulated significant wave periods for each of the nowcast/forecast cycles at 

Galveston Pleasure Pier, Bolivar Roads, and Galveston Pier 21 are order 4s. HSCM 

simulated significant wave periods at Eagle Point and Morgans Point are order 2s. The 

simulated significant wave period ranges from 5 to 7s at NDBC buoy 42035, which 

represents the GBM open boundary wave condition. Note in this experiment with wind 

generation, the significant wave direction is equal to the wind direction, which ranges 

from 135 to 315 deg T. 

188
9. OPERATIONAL CONSIDERATIONS 

Prior to implementation in the operational setting, it would be advantageous to implement 

the surface wave and all-weather algorithms in a quasi-operational setting with the NOS 

Galveston Bay Experimental Nowcast/Forecast System. Approaches towards achieving 

this goal are outlined. 

The most immediate step would be to implement the surface gravity wave algorithms 

within the present experimental nowcast/forecast system. What is needed are the linkages 

from ODAAS for the wavewatch 3 wave model forecasts at Galveston Pleasure Pier and 

the real-time acquisition of NBDC 42035 buoy wave and wind conditions. The present 

CSDL website would then be updated to provide the wave products, which have been 

demonstrated in this work; e.g., time series of significant wave height, direction, and 

period as well as field plots of wave height and direction. 

An all-weather capability has been demonstrated here and should be implemented in the 

experimental system to further gain insight on computational requirements. When a storm 

is predicted to influence the Galveston region, a storm track file is created defining the 

storm path and intensity. If the track file is present, the system operates in the all-weather 

mode. Note rainfall predictions are also necessary over the four major drainage areas 

within the City of Houston. Based on storm intensity it would be necessary to potentially 

modify hydrodynamic model time steps and the computational burdens would be 

accordingly increased. Some indication of these requirements is discernable in Tables 

9.1-9.4, which present the computational requirements for the simulations reported. 

Table 9.1. Hurricane Carla (1961) Long and Short Wave Computational Time. Note the 

computations were performed on a 4 CPU SGI Origin 3000. Note the two entries are for 

experiment one and two, respectively. 

GBM Real Time (min:sec) HSCM Real Time (hr:min:sec)

Time Steps 

(External, Internal) 

(5s,30s) (0.5s,3s) 

9/11 24 hr Hindcast 7:51.9 7:54.2 1:14:15.0 1:17:50.1 

9/12 24 hr Hindcast 9:05.5 9:14.5 1:19:40.0 1:17:13.9 

9/13 24 hr Hindcast 7:52.8 7.56.9 1:16:41.4 1:16:19.1 

Table 9.2. Hurricane Alicia (1983) Long and Short Wave Computational Time. Note the 

computations were performed on a 4 CPU SGI Origin 3000. Note the two entries are for 

experiment one and two, respectively. 

GBM Real Time (min:sec) HSCM Real Time (hr:min:sec)

Time Steps 

(External, Internal) 

(5s,30s) (0.5s,3s) 

8/18 24 hr Hindcast 7:48.9 8:00.1 1:18:28.5 1:14:25.7 

8/19 24 hr Hindcast 7:51.9 8:01.0 1:15:46.6 1:36:39.8 

189
Table 9.3. Tropical Storm Allison (2001) Coastal Surge Propagation Event Long and 

Short Wave Computational Time. Note the computations were performed on a 4 CPU 

SGI Origin 3000. Note no experiment two was performed. 

GBM Real Time (min:sec) HSCM Real Time (hr:min:sec)

Time Steps 

(External, Internal) 

(10s,60s) (2s,10s) 

6/5 

24 hr Hindcast/36 hr Forecast 

9:51.1 1:00:26.6 

6/6 

 24 hr Hindcast/36 hr Forecast 

11:25.5 1:03:1.0 

Table 9.4. Tropical Storm Allison (2001) Rainfall/Runoff Event Long and Short Wave 

Computational Time. Note the computations were performed on a 4 CPU SGI Origin 

3000. Note the two entries are for experiment one and two, respectively. Note the third 

entry was used to achieve stability in the additional inflow case of experiment two. 

GBM Real Time (min:sec) HSCM Real Time (hr:min:sec)

Time Steps 

(External, Internal) 

 (10s,60s) (5s,30s) (2s,10s) (0.5s,3s) (0.2s,1s) 

6/10 

24 hr Hindcast/36 hr Forecast 

 9:46.9 19:44.4 1:03:45.1 3:18:55.6 - 

6/11 

 24 hr Hindcast/36 hr Forecast 

 9:54.4 21:19.7 1:05:05.0 3:13:37.5 8:45:53.1

Note the computational requirements of each model for different time steps are given. 

While the computational times for the GBM are modest, the HSCM computational 

requirements for the high flow case are intensive. 

For the present grids, an accurate prediction of coastal storm surge is required as the 

offshore boundary condition and this must be supplied from either NWS/ETSS or another 

basin scale model. It is possible to further explore the extension of the GBM to deeper 

waters and allow a direct computation of the storm surge over the extended grid. This 

would suggest a separate model grid for storm surge which would be run on a 

nowcast/forecast system basis by the National Hurricane Center (NHC). CO-OPS would 

provide the NHC with the latest nowcast/forecast cycle restart prior to the storm track 

input and the NHC would use the system to provide additional model guidance. The 

impacts on wetlands and the ecological response to the storm could be studied to allow 

for enhanced wetland and estuarine resource planning.

190
10. CONCLUSIONS AND FUTURE WORK

The algorithms developed for rainfall/runoff, overland flooding, surface gravity waves, 

and for the hurricane wind and atmospheric pressure fields, have been adopted within the 

NOS Galveston Bay Experimental Nowcast/Forecast System. Their effectiveness in 

replicating the storm surge has been demonstrated for Hurricanes Carla (1961) and Alicia 

(1983), and Tropical Storm Allison (2001). The effectiveness of a modular nested grid 

approach; e.g., the GBM to the HSCM one-way coupling has been demonstrated. 

To further improve results during high flow events, hourly discharges should be used. 

Additional combined sewer overflows and municipal treatment plant flows should also be 

specified. While the effects of runoff from the Houston metroplex have been considered, 

the properties of the other drainage areas surrounding Galveston Bay need further 

consideration. In particular, marsh hydrodynamics should be considered. Within the 

present simulations, drainage and seepage of flooded areas is not considered. These might 

be used as inputs to marsh hydrodynamic simulations. More work on the wave-current 

interaction effects needs to be considered. The issues of sediment transport and 

morphological change prediction should also be considered. In this instance, it will be 

necessary to consider moveable bed hydrodynamics. 

To further validate the algorithms developed additional field data are required. Detailed 

inundation mapping based on overflights of the flooded areas needs to be performed for 

each major hurricane. Post event high water marks are not sufficient. Improvements in 

wind and water level instrumentation to withstand hurricane conditions would enable 

additional validation data to be collected. Salinity, turbidity, and chlorophyll-a fields need 

to be measured on a daily basis over the next month following storm passage to assess 

storm ecological impacts. 

ACKNOWLEDGMENTS

The storm surge model work has been carried out in the Coast Survey Development 

Laboratory (CSDL) of NOS’s Office of Coast Survey with the encouragement from the 

Chief of CSDL’s Marine Modeling and Analysis Programs, Dr. Frank Aikman. Dr. Frank 

Aikman also provided further information on the Coastal Storms Initiative. Philip H. 

Richardson assisted in a review of recent storm surge modeling and the application of the 

wave algorithms to the January 25-30, 1997 period. 

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