Bolivar Pennisula Source: XXXXXXXX
Contents Acknowledgments............................................................................X
Introduction.......................................................X Context..................................................................................X
SSPEED Center Participants Faculty Dr. Philip B. Bedient, Director Mr. Jim B. Blackburn, Co-Director
Rice University Rice University
Dr. John B. Anderson
Rice University
Dr. Samuel P. Brody
Texas A&M University
Mr. Tom Colbert
University of Houston
Dr. Clint N. Dawson
University of Texas at Austin
Dr. Jennifer Proft
University of Texas at Austin
Dr. Jamie E. Padgett
Rice University
Dr. Hanadi Rifai
University of Houston
Dr. John Pardue
Louisiana State University
Dr. Zheng (Nick) Fang
University of Texas-Arlington
PhD Student Researchers Antonia Sebastian Rice University Jacob Torres Rice University Sabarethinam Kameshwar
Rice University
Jason A. Christian
Rice University
Wei Du
University of Texas at Austin
Russell Blessing Texas A&M University Daniel Burleson University of Houston
Contributing Authors Jacob Torres Rice University Benjamin Bass Rice University Nick Irza Rice University Courtney Hale Rice University
Missing Home on Bolivar Pennisula Source: XXXXXXXX
Executive Summary Since 2009, the SSPEED Center, with funding from the Houston Endowment, has focused on modeling, understanding, and mitigating hurricane storm surge. During Phase I and Phase II of the Houston Endowment-funded SSPPEED Center hurricane surge research efforts, two promising surge protection proposals were analyzed and are summarized in the 2014 SSPEED Center Report. The proposals developed during Phase I (2009-2011) and Phase II (2011-2014) of research are HSC gate and levee structure protecting the Houston Ship Channel, known as the Centennial Gate, and the Lone Star National Recreation Area (LSCNRA), which creates economic incentives for preserving the natural area along the coast via public and private partnerships.
Project Phases As part of the Houston Endowment funded research (Phases I and II), extensive computer modeling work has been completed by the research team led by Drs. Clint Dawson and Jennifer Proft at the Institute for Computational Engineering and Sciences, at the University of Texas at Austin. This team has developed the advanced capability, through the use of the Advanced Circulation (ADCIRC) model, to replicate storm surge from past events and to predict storm surge for hypothetical events occurring at various locations along the coast. PHASE I In the earlier phases of this project, the SSPEED research team tested eight hypothetical landfall locations along the upper Texas coast and found that Hurricane Ike making landfall near San Luis Pass, with the same angle of approach, would likely have generated a storm surge much greater than what occurred with the original Hurricane Ike landfall; had Hurricane Ike made landfall 30 miles southwest of its original landfall location, it would have generated up to 18 feet of surge in the Houston Ship Channel (HSC) and up to 15 feet of surge in the populated and industrialized areas on the west side of Galveston Bay. An increase in wind speed of the storm would have
Hurricane Ike in 2008 highlighted the vulnerability of the Houston-Galveston region to hurricane storm surge. also resulted in more significant surge heights at locations surrounding Galveston Bay and the HSC. These findings clarified the fact that the Houston-Galveston region, although faced with immense destruction following Ike, was spared the majority of damage due to the hurricane’s landfall location. This also points to the realization that the Houston Ship Channel and other areas surrounding Galveston Bay are at great risk to suffer worse damages during the next hurricane with the current hurricane protection strategy in place, a more comprehensive and strategic system is needed. Analyses within the SSPEED Center indicates that a surge protection gate at Highway 146 over the San Jacinto River can offer significant storm surge protection for the industrial facilities and residential communities located along the Houston Ship Channel at a high benefit-cost ratio to the region. Several simulations of Hurricane Ike were run through the model to simulate the actual hurricane landfall conditions as well as various other scenarios with increased wind field velocities. Under the various scenarios, inundation level and floodplain area across the HSC were reduced significantly with the addition of the gate and levees, up to 45% and up to 20%, respectively. Similarly, packaging the natural resources and features of the upper Texas coast
Baytown
Trinity Bay
225
La Porte
Houston Ship Channel East Bay
Kemah 146
Galveston Bay Bolivar Peninsula 45
Alvin
Texas City
SPEED
Galveston
Context Map The Houston=Galveston Area as shown in the Context Map is xx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
into a comprehensive ecotourism area, the Lone Star National Recreation Area (LSCNRA), was predicted to provide both economic benefits to the region and incentive to preserve and protect the undeveloped areas that help to buffer the region from storm surge. PHASE II Now in Phase III of the project, the SSPEED center has continued to develop the methodology formulated in the initial phases and build upon previous findings with new efforts to address a more regional protection system for the Houston-Galveston area. The SSPEED Center has developed and is analyzing a comprehensive plan for the Houston-Galveston region, known as the Houston-Galveston Area Protection System (H-GAPS). The regional surge mitigation strategy is focused on three primary areas of the HoustonGalveston region: the Houston Ship Channel, the west side of Galveston Bay, and Galveston Island. Additionally, the SSPEED Center is looking at the low-lying areas of Chambers, Galveston, Brazoria, and Matagorda Counties for participation in a novel ecosystem services exchange meant to help solidify and preserve the current surge risk reduction services and other ecosystem services provided by natural areas along the Texas coast. Various H-GAPS protection alternatives range in nature from structural to non-structural solutions including the following: Building gates and levees; Raising roadways;
Houston-Galveston Area Protection Strategies Various H-GAPS protection alternatives range in nature from structural to non-structural solutions including the following:
BUILDING GATES AND LEVEES
RAISING ROADWAYS
CONSTRUCTING BERMS
RESTORING OYSTER REEFS
Constructing enclosed dredge spoil berms; Restoring oyster reefs; and Developing the ecosystem services exchange platform mentioned above. The most promising structural alternatives have been analyzed using advanced storm surge and damage models customized for the region. Through these analyses, a comprehensive regional protection plan has been formulated and tested under various hurricane intensity and tract scenarios. This report summarizes the efforts conducted by the SSPEED Center over the past year and provides the region with a comparative analysis of all proposed regional surge protection strategies.
ECOSYSTEM SERVICES EXCHANGE
Ike’s Storm Surge on High Island Source: XXXXXXXX
10
Introduction
INTRODUC TION
One of the most important issues facing the Houston-Galveston region today is vulnerability from hurricane storm surge. The HoustonGalveston region is a heavily populated coastal region and remains a vital location for industries that provide economic value to the region and the United States. Although the wind and rainfall associated with hurricanes can generate significant damage, the Galveston Bay region is also particularly vulnerable to storm surge flooding due to the mild slope of the coastal shelf and the flat, low-lying areas onshore. Hurricane Ike hit Galveston and Houston in 2008 and generated over $25 billion in damages. For the last six years the Severe Storm Prediction Education and Evacuation from Disasters (SSPEED) Center at Rice University has worked with generous funding from the Houston Endowment to evaluate the potential impacts of storm surge and rainfall associated with severe hurricane events in the Houston-Galveston region. One of the primary goals of this work has been to develop structural and non-structural approaches to address storm surge flooding in vulnerable areas, particularly along the Houston Ship Channel and flood prone areas of Houston/ Galveston. At the conclusion of the Phase 1 and Phase II funded research efforts, the 2014 SSPEED report was released and summarized key findings of research and modeling efforts conducted from 2009 -2014. Now in Phase III of the project, the SSPEED center has continued to develop the methodology formulated in the initial phases and build upon previous findings with new efforts to address a more regional protection system for the Houston-Galveston area. This report summarizes the key findings of the SSPEED Center’s research over the first year of the Phase III effort (June 2014- June 2015) and outlines the future SSPEED Center work. 1.1 MOTIVATION FROM HURRICANE IKE In September 2008, Hurricane Ike made landfall just east of Bolivar Roads, north of Galveston Island, TX. Ike was a strong category 2 hurricane with maximum wind speeds of 109 miles per hour at landfall on the Texas coast; Ike passed over Bolivar Peninsula, covering most of the area
with at least 10 feet of water (not including wave heights), then traveled through Galveston Bay and hit landfall a second time east of Houston in Baytown, TX (Berg, 2009). Hurricane Ike was “only” a Category 2 storm, but due to its large wind field and relatively slow forward motion, it generated significant storm surge that flooded inland areas from Galveston Bay to Grand Isle in Louisiana, causing over $25 billion in damages (Figure 1.1). Heavy industrial damage occurred further east of landfall on the “dirty” side of the storm in areas near Beaumont and Orange approaching the Louisiana border where the surge extended north into Sabine Lake and the Sabine-Neches Waterway. The highest surge level was recorded in Chambers County where the surge nearly reached Interstate Highway 10, about 20 miles inland; that surge level was over 17 feet (Berg, 2009). Damage along the west side of Galveston Bay was primarily caused by counterclockwise winds blowing from east to west on the “clean” side of the storm causing water to build up along the northwest shoreline of near Shore Acres and La Porte, as well as in the Bacliff and San Leon areas. The surge level in west Galveston Bay reached and in the Houston Ship Channel reached about 13 feet. Early results from SSPEED indicate that if Hurricane Ike had made landfall at San Luis Pass, where it was originally predicted to be, storm surge levels and damages would have been much worse across the more populated and industrial areas of Galveston Island, Texas City, and the Houston Ship Channel (Figure 1.2, Sebastian et al. 2014). The realization that the majority of potential damage from Ike was avoided due to the path the storm actually took has caused discomfort over the fact that the region is gravely at risk from probable future events, especially if future storms impact the area more directly than Ike. With over 1.6 million people today, and over 2.4 million residents predicted to live in the Hurricane Evacuation Zones surrounding Galveston Bay in the next two decades, future hurricane surge impacts in the Houston-Galveston region have the potential to damage millions of homes and livelihoods (Sebastian 2014). The Port of Houston is the second largest port of the U.S. and the Houston Ship Channel (HSC) is the largest petrochemical complex in the U.S.; both
11 Figure 1-1, Galveston Island after Hurricane Ike, September 13, 2008 Source: U.S. Air Force photo by Staff Sgt. James L. Harper Jr.
INTRODUC TION
Future hurricane surge impacts in the Houston-Galveston region have the potential to damage millions of homes and livelihoods.
are located in Galveston Bay (Port of Houston Authority, 2012). Along the Houston Ship Channel, industrial facilities are to be protected pursuant to Federal Emergency Management Agency (FEMA) mandate and other federal regulatory requirements from flooding up to the 100-year FEMA floodplain of about 13 to 14 feet. Surge levels along the HSC during Hurricane Ike never exceeded 13 feet, due primarily to Ike’s track and landfall location; had the storm taken a more southerly path to landfall, significant damage to industrial facilities and hazardous material storage tanks would have likely occurred, crippling the region (Fig. 1.2). In the earlier phases of this project, the SSPEED research team tested eight hypothetical landfall locations along the upper Texas coast and found that Hurricane Ike making landfall near San Luis Pass, with the same angle of approach, would likely have generated such a scenario. Had Hurricane Ike made landfall 30 miles southwest of its original landfall location (shown as Landfall Point 7 in Figure 1.2), it would have generated up
12 Figure 1-2, Surge Generated by Hurricane Ike making Landfall at Point 7, near San Luis Pass Source: Rice University
INTRODUC TION
Had Hurricane Ike made landfall 30 miles southwest of its original landfall location (shown as Landfall Point 7 in Figure 1.2), it would have generated up to 18 feet of surge in the Houston Ship Channel and up to 15 feet of surge in the populated and industrialized areas on the west side of Galveston Bay.
to 18 feet of surge in the Houston Ship Channel and up to 15 feet of surge in the populated and industrialized areas on the west side of Galveston Bay. An increase in wind speed of the storm would have also resulted in more significant surge levels at locations surrounding Galveston Bay and the HSC (Sebastian et al. 2014). Our earlier research into evaluating the change in surge impacts resulting from altering the landfall point of the storm did not include any analysis of storms with varying approach angles and forward motion regimes (Sebastian et al. 2014). Such research would provide further evaluation of the severe vulnerability of the Houston-Galveston Bay region if exposed to different hurricane patterns.
Based on historical storm surge records in the Gulf of Mexico, the Upper Texas coast has the third highest hurricane surge probability. Needham at LSU calculated that the 100-year recurrence surge level for the upper Texas coast is approximately 21 feet at the coastline (Needham et al, 2012). Similarly, FEMA recently released preliminary floodplain maps showing an expected 100-year storm surge level of 19 feet along the coast at Galveston. These levels are higher than what occurred during Hurricane Ike and point to the likelihood of the Houston-Galveston region experiencing a more significant hurricane surge scenario in the future. Storms larger than Ike are both probable and likely. When a future storm hits our region, if the Houston-Galveston area has failed to protect critical infrastructure and vulnerable populations against a 20 to 25ft surge, the economy of the Houston region and likely the U.S. economy would be severely impacted. In addition to economic disaster, such a surge would likely inflict massive environmental damage if the hazardous materials and oil presently stored adjacent to the ship channel were to spill into neighboring communities and Galveston Bay.
13
There is existing levee infrastructure for surge protection in the Galveston Bay region, albeit limited. Texas City is protected by an existing levee system to a height of about 15-20 feet. Freeport and Lake Jackson are also protected by a similar structure. The City of Galveston is protected by a 17-foot seawall constructed after the 1900 Galveston Hurricane. The existing infrastructure in the Houston-Galveston region is shown in Figure 1.3.
The existing levee infrastructure includes:
DIKES
These levee systems have been adequate to date, but are inadequate to protect against a future disastrous surge, or even the 100-year surge, discussed previously. Anecdotal evidence indicates that the debris during Hurricane Ike reached the top of the Texas City Levee, demonstrating that it was nearly breached in certain low areas. Likewise, the Freeport Levee protected the Freeport and Lake Jackson area,
TEXAS CITY, FREEPORT AND LAKE JACKSON
CITY OF GALVESTON SEAWALL
Figure 1-3, Map Showing the Existing Storm Surge Protection Infrastructure and 10- and 20-foot Elevation Contours Source: Rice University
Texas City
Galveston
Freeport
Storm protection infrastructure includes the Freeport Levee, Texas City Levee, and Galveston Seawall.
INTRODUC TION
Existing Levee Infrastructure
1.2 EXISTING PROTECTION SYSTEM LIMITED
14
INTRODUC TION
Storms larger than Ike are both probable and likely.
Galveston Seawall
Source: XXXXXXXXXXXXXXXXXXXXXXX
15
An Aerial View of the Texas City Dike in 2010
Source: U.S. Army Corps of Engineers, Galveston District
INTRODUC TION
but concern exists about its height. The City of Galveston suffered significant flooding during Hurricane Ike, but it was not due to a failure in the structural stability or height of the seawall. Instead, Galveston flooded from the backside, as the surge in the Bay rose and counter-clockwise hurricane winds pushed water towards the south end of Galveston Bay. This bay-side vulnerability is a significant risk for the City of Galveston and island development. This is one issue that our current phase of research aims to address.  
These levee systems have been adequate to date, but are inadequate to protect against a future disastrous surge.
16
2. Review of Findings from Previous SSPEED Efforts (2009-2014) Hurricane Ike in 2008 highlighted the vulnerability of the Houston-Galveston region to hurricane storm surge. Since 2009, the SSPEED Center, with funding from the Houston Endowment, has focused on modeling, understanding, and mitigating hurricane storm surge. During Phase I and Phase II of the Houston Endowmentfunded SSPPEED Center hurricane surge research efforts, two promising surge protection proposals were analyzed and are summarized in the 2014 SSPEED Center Report. The proposals developed during Phase I (2009-2011) and Phase II (2011-2014) of research are the HSC gate and levee structure protecting the Houston Ship Channel, known as the Centennial Gate, and the Lone Star National Recreation Area (LSCNRA), which creates economic incentives for preserving the natural area along the coast via public and private partnerships. As part of the Houston Endowment funded research (Phases I and II), extensive computer modeling work has been completed by the research team led by Drs. Clint Dawson and Jennifer Proft at the Institute for Computational Engineering and Sciences, at the University of Texas at Austin. This team has developed the advanced capability, through the use of the Advanced Circulation (ADCIRC) model, to replicate storm surge from past events and to
predict storm surge for hypothetical events occurring at various locations along the coast. Analyses within the SSPEED Center indicate that the HSC gate can offer significant storm surge protection for the industrial facilities and residential communities located along the Houston Ship Channel at a high benefit-cost ratio to the region. A recent paper published by Natural Hazards Review in 2014 discusses the research conducted by Christian et al. and the SSPEED Center on the proposed HSC gate protection system through modeling the hydraulic effectiveness of the gate to reduce inland surge flooding impacts in the Houston Ship Channel. Using a coupled riverinecoastal hydraulic model to simulate the effects of storm surge propagation from Galveston Bay into the HSC with effects of upstream rainfall/ runoff during a hurricane event, the research was able to show that locating a moveable gate structure across the San Jacinto River near the State Highway 146 bridge and a levee protection system extending west and east of the gate effectively reduced surge inundation depths and the overall flood extent within the HSC area and upstream in the San Jacinto River basin. The moveable gate structure is conceptually designed to be closed during high surge risk events but would otherwise be left open to allow for normal use of the waterway (Figure 2.1). The gate would also be opened at the point when upland runoff flooding behind the gate reaches
Figure 2-2, Inundation maps showing the results of the SSPEED Centennial Gate Study
REVIEW OF FINDINGS FROM PREVIOUS EFFORTS
Source: Rice University
The Centennial Gate significantly reduces depth and extent of flooding in the HSC.
17 Figure 2-1, Conceptual Rendering of the Centennial Gate near Highway 146 across the San Jacinto River Source: Rice University
REVIEW OF FINDINGS FROM PREVIOUS EFFORTS
The perspective of the photo is looking upstream into the HSC.
the surge elevation in front of the gate within the bay to prevent propagated inland flooding from the river collecting runoff during intense rainfall associated with the hurricane event. Several simulations of Hurricane Ike were run through the model to simulate the actual hurricane landfall conditions as well as various other scenarios with increased wind field velocities. Under the various scenarios, inundation levels and floodplain areas across the HSC were reduced significantly with the addition of the gate and levees, up to 45% and up to 20%, respectively. Surge scenarios of greater magnitude provided greater storm surge reduction benefit; in other words, the worse the storm, the greater the benefit the gate and levee system provided (Christian et al. 2014). The HSC Gate proposal proved, through our modeling efforts, to greatly increase protection for the Houston Ship Channel from devastating economic and environmental impacts resulting from hurricane surge (Figure 2.2).
Similarly, packaging the natural resources and features of the upper Texas coast into a comprehensive ecotourism area, the Lone Star Coastal National Recreation Area (LSCNRA), was predicted to provide both economic benefits to the region and incentive to preserve and protect the undeveloped areas that help to buffer the region from storm surge. The LSCNRA has been developed as a proposal by a coalition of local partners and a steering committee. This includes leadership by former Secretary of State James Baker, Houston businessman John Nau and Galvestonian Doug McLeod, as facilitated by the National Parks Conservation Association (NPCA). Over the past several months, a series of meetings have occurred with potential partners in the formation of this National Recreation Area which would be operated as a unit of the National Park System. An economic study commissioned by NPCA and SSPEED Center found that such an eco-tourism facility could generate upwards of
18 Figure 2-3, Proposed Lone Star Coastal National Recreation Area Source: National Parks Conservation Association
The LSCNRA includes flood mitigation, land conservation, economic development and outdoor recreation.
REVIEW OF FINDINGS FROM PREVIOUS EFFORTS
5,000 jobs and add about $200 million to the local economy annually?. This park system would be a network of existing public and non-governmental organization protected lands (Figure 2.3). The governance of the LSCNRA will be by agreement among the partners who will be authorized to develop a plan that will set forth the principles for management of the recreation area. This concept for governing a national park has been implemented successfully in the past by the National Park Service in Boston Harbor Islands NRA and Santa Monica Mountains NRA, as well in other similar applications by the United States Fish and Wildlife Service. The LSCNRA has garnered support from residents, government leaders, businesses and conservation organizations. The LSCNRA is an exciting idea
that includes flood mitigation, land conservation, economic development and outdoor recreation. It has been designed with Texas concepts of private property and the federal government in mind. In many ways, it provides one approach that could emerge as key in the future of the National Park System - to become a provider of important outdoor opportunities and enjoyment adjacent to major urban areas. More information can be found in the 2014 SSPEED report.
19
REVIEW OF FINDINGS FROM PREVIOUS EFFORTS
An economic study commissioned by NPCA and SSPEED Center found that an ecosystem tourism facility could generate upwards of 5,000 jobs and add $20 million to the local economy (annually?).
Salt Marsh Wetlands
Source: Earl Nottingham, TPWD
CONSIDER ATIONS FOR A REGIONAL APPROACH
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3. Considerations for a Regional Approach (H-GAPS) (2014-2015)
Building gates and levees
At the beginning of 2014, the Houston-Galveston region found itself in a difficult situation. Six years after Hurricane Ike, a lack of unified leadership and public consensus slowed progress in determining how the region proposes to address hurricane surge flooding. Generally speaking, the landscape-scale green space solutions (LSCNRA) proposed by the SSPEED Center have been well accepted by governmental and business interests throughout the region, but the situation becomes much more difficult when considering structural alternatives within the currently developed portions of the region. The HSC Gate is an excellent project that has a useful price tag and has the ability to be constructed relatively quickly. However, it does not address the surge vulnerability of the communities south of the gate, such as along the west side of Galveston Bay, the City of Galveston or the West End of Galveston Island. Local business and governmental leaders called for a more regional approach to hurricane surge risk management that addresses surge vulnerability in the greater region of Galveston Bay, not just protecting the Houston Ship Channel. The SSPEED Center has spent the past year addressing these regional concerns in detail.
Restoring oyster reefs
With Phase III funding from the Houston Endowment starting in June 2014, the SSPEED Center has developed and is analyzing a comprehensive plan for the Houston-Galveston region, known as the Houston-Galveston Area Protection System (H-GAPS). The regional surge mitigation strategy is focused on three primary areas of the Houston-Galveston region: the Houston Ship Channel, the west side of Galveston Bay, and Galveston Island. Additionally, the SSPEED Center is looking at the low-lying areas of Chambers, Galveston, Brazoria, and Matagorda Counties for participation in a novel ecosystem services exchange meant to help solidify and preserve the current surge risk reduction services and other ecosystem services provided by natural areas along the Texas coast (see Chapter 7). Various H-GAPS protection alternatives range in nature from structural to non-structural solutions including the following:
Raising roadways Constructing enclosed dredge spoil berms Developing the ecosystem services exchange platform mentioned above The various structural alternatives are displayed in Figure 3-1and form what we generally refer to as the Houston-Galveston Area Protection System (H-GAPS). Details of the H-GAPS alternatives are discussed in Chapter 4. The most promising structural alternatives have been analyzed using advanced storm surge and damage models customized for the region. Through these analyses, three comprehensive regional protection plans have been formulated and tested under various hurricane intensity and tract scenarios. This report summarizes the efforts conducted by the SSPEED Center over the past year and provides the region with a comparative analysis of all proposed regional surge protection strategies. The SSPEED Center at Rice University and Texas A&M University at Galveston, with their respective research teams, have been studying strategies for surge suppression for the Galveston Bay Region. SSPEED had been concentrating its efforts on suppressing surge using barriers internal to the Bay system and non-structural alternatives, while Texas A&M Galveston has concentrated on methods to stop the surge at the coast using a continuous coastal barrier - the “Ike Dike” concept. Both Texas A&M Galveston and the SSPEED Center are now coordinating their research efforts with an eye towards ultimately combining their various strategies into a single surge reduction plan having “Multiple Lines of Defense” to achieve the best overall solution for the region from an economic, environmental and social perspective. The SSPEED Center and Texas A&M University at Galveston will continue to coordinate their modeling work and analyses so that the knowledge gained by all efforts can be shared and utilized to more efficiently and effectively reach the development of a regional surge reduction plan for the entire HoustonGalveston area. Each institution is committed to finding the best overall solution for the entirety of Galveston Bay and will work together to achieve that result.
Figure 3-1, H-GAPS Proposed Regional Storm Surge Protection Alternatives
CONSIDER ATIONS FOR A REGIONAL APPROACH
PLACEHOLDER U C
E M D
F
I
2
L
SPEED
J 11 - GALVESTON SEAWALL 2 TEXAS CITY LEVEE 2-
1
H
C HIGHWAY 146 C-
DD - OYSTER REEFS EE - DREDGE SPOILS FF - RAISED HIGHWAY 87 GG - RAISED FM 3005
G
HH - GALVESTON LEVEE II - RAISING TEXAS CITY DIKE JJ - RAISING JETTIES JL - BOLIVAR ROADS GATE N
0
MILES
5
21
JM- MID-BAY GATE JU - HOUSTON SHIP CHANNEL GATE
22
4. H-GAPS Evaluation Process
Insert Figure 4-1
Over the course of funding from the Houston Endowment, the SSPEED Center has worked vigorously on developing the appropriate methodology for analyzing the HoustonGalveston region’s surge risk. There are many components involved in our analysis that we describe in the following sections. Additionally, the results of our evaluation of the current state of protection for the region, a description of the various alternative protection systems we have developed and evaluated, and a discussion on the evaluation results of those alternatives, are all presented in the following sections.
Figure 4-1, Surge and Storm Tide Concept Source: NOAA
4.1 HURRICANE SURGE MODELING The following paragraphs describe the basis for the modeling of the different surge scenarios that are presented in this report. Storm surge is a very complex issue, especially along the coastline of Texas and Louisiana due to the very mildly sloping bathymetry, presence of local bays, low-lying coastal areas, and the potential for devastating winds from hurricanes. The modelers at University of Texas are some of the best experts for handling these complex assignments, and Hurricane Ike is actually one of the best-monitored and bestmodeled hurricanes in history. For a more indepth and technical discussion of the ADCIRC model and the methodology of our research, see Appendix A.
H - GAPS EVALUATION
4.1.1 UNDERSTANDING HURRICANE STORM SURGE The water level generated by a hurricane as it approaches the shoreline and subsequently moves inland is sometimes referred to as the “surge” (Figure 4 1). However, the maximum water level generated by a hurricane is actually a combination of various water levels, such as that generated by (1) the drop in atmospheric pressure, (1) the forward movement of the storm, (3) the wind set-up, (4) the wave set-up and (5) waves. The major factors that contribute to determining the magnitude of a hurricane’s maximum water level are (1) wind speed, (2) radius to maximum winds, (3) forward speed of the storm, and (4) bathymetry. Of course, the maximum surge occurs on the “dirty side” of the hurricane, which is usually the eastern side of the
eye of the hurricane in the Gulf of Mexico, due to the maximum winds occurring on that side of the eye before being dampened as they pass over land (Figure 4 2). 4.1.2
MODELING STORM SURGE
The SWAN+ADCIRC model predicts storm surge levels, water velocities and wave characteristics in the near-shore and far inland resulting from hurricane activity. It can be an extremely useful tool to indicate which communities are most at risk in an impending storm, and to analyze the potential effectiveness of various proposed mitigation strategies. For example, such strategies have been implemented by modifying the underlying model to include levees, gates and raised roadways in the region of interest. The Advanced CIRCulation (ADCIRC) and Simulating WAves Nearshore (SWAN) computer models have been used to model the hurricane wind fields and resulting surge levels, including waves, in and around Galveston Bay. The SWAN model was developed by Delft University of Technology (TU-Delft) to simulate wind-generated waves during a hurricane. SWAN and ADCIRC can be coupled and run on the same system, simultaneously. The coupling of the ADCIRC and SWAN models, referred to collectively as SWAN + ADCIRC, utilizes a flexible computational mesh of triangular elements to compute and simulate
23
H - GAPS EVALUATION
Insert Figure 4-2
Figure 4-2, Hydraulic Forcing Functions Influencing Combined Water Levels of Semi-Enclosed Bays During Hurricanes Figure Courtesy of Jacob Torres
the surge caused by a hurricane’s specific characteristics and location (Figure 4 3). This complex model was verified for Hurricane Ike, as well as many other historical hurricane events such as Katrina, Rita, and Gustav. We generally refer to the SWAN+ADCIRC model simply as ADCIRC, but it is important to note that the modeled surge levels from our studies do include wave heights. For these reasons, the UT-Austin research effort has centered on the application and continued development of the SWAN+ADCIRC model for simulating hurricane storm surge and wave setup within the Gulf of Mexico, Galveston Bay, and the HSC. The SWAN+ADCIRC model is currently calibrated to predict storm surge levels, water velocities and wave characteristics in the near-shore and far inland resulting from hurricane activity. The model can be an extremely useful tool to indicate which communities are most at risk in an impending storm, and to analyze the potential effectiveness of various proposed mitigation strategies. For example, such strategies have been implemented by modifying the underlying model to include levees, gates and raised roadways in the region of interest. As this is an active area of research, improvements and new features are constantly being included in the software, and it must be continuously analyzed and validated. Recently, a high resolution finite element mesh was developed for the Texas coast that can not only produce more accurate solutions but also drastically decrease the time to
achieve results. These modifications to the model must undergo extensive testing before being put in “production” mode. The bathymetry of Galveston Bay and the Gulf of Mexico in the vicinity of the Bay are important in the resulting surge that occurs as a hurricane approaches the Galveston area. The ADCIRC model incorporates the bathymetry, or underwater topography, of the Bay using various sources of information. All of this data was obtained prior to Hurricane Ike. The SSPEED team obtained updated bathymetry information from the USACE for the Houston Ship Channel (HSC) dated 2010 and checked it against the existing data in the ADCIRC model to determine if there were any significant changes resulting from Hurricane Ike. The results showed that there were fairly insignificant changes in the bathymetry along the HSC, including in the Bolivar Roads area, between the two data sets (see Appendix 1). The various scenarios that were modeled in this study to simulate the resulting surge vary from altering the hurricane parameters such as landfall location, track, and wind speed, to altering the model’s mesh to include new features, such as gates, levees, or other barrier alternatives that we wish to evaluate surge reduction effects. A surge reduction alternative is simulated in the ADCIRC model by altering the topographic mesh to include a solid barrier of a designated height at specific locations, such as a 17 feet high wall along Bolivar Peninsula that represents the
24
Insert Figure 4-3
Figure 4-3, ADCIRC Computational Mesh Resolution for (a) full mesh, (b) Galveston Bay region, and (c) Galveston Island Source: Rice University
H - GAPS EVALUATION
Highway 87 levee. By running various scenarios, with altered meshes and hurricanes, we are able to investigate the surge reduction capabilities of the proposed alternatives for a variety of storm events. Moreover, the SWAN+ADCIRC model is a sophisticated computational tool that relies on the use of state-of-the-art large scale high performance platforms (supercomputers) to achieve results within a useful timeframe. The computational resources at the Texas Advanced Computing Center (TACC) are utilized for all hurricane simulations. SWAN+ADCIRC computations are executed using the Lonestar Linux cluster, consisting of 1,888 compute nodes, 22,656 164 processing cores, 44 terabytes of memory, and a peak performance of nearly 302 teraflops. 4.1.3 HURRICANE LANDFALL LOCATION AND TRACKS The location of the landfall of the hurricane determines where the maximum surge will most likely occur (i.e. on the dirty side or east side). SSPEED researchers utilized the ADCIRC model
to simulate inputted wind fields of a known hurricane, and produce the resulting surge levels. We then moved the location of landfall of those hurricanes to various spots along the coastline of Galveston to evaluate the differing surge levels computed in the area. Three landfall locations were eventually selected and generally used for this study (Figure 4 4): (1) San Luis Pass – “p7”, (2) the original landfall location of Hurricane Ike, Bolivar Roads – “p0”, and (3) Rollover Pass – “pR”. The landfall location that produced the greatest surge levels in the HSC was at San Luis Pass – p7 (see Figure 1-1). The landfall location that produced the greatest surge levels along the backside of Galveston was at Rollover Pass – pR. These differing landfall locations will be used to test the performance of any surge-reduction strategy or system that is to be considered for recommendation as the plan for implementation.
25
No. Hurricane
Year
Date of Landfall
U.S. SaffirRadius to Minimum Central Landfall Simpson Maximum Pressure (mb) Location Category Winds (mi)
Maximum Maximum Sustained Water Level Winds (mph) (ft)
1
Katrina
2005
Aug. 29
LA
3
920
29 to 35
127
28
2
Camille
1969
Aug. 18
MS
5
909
< 15
200
24.6
3
Carla
1961
Sept. 11
TX
3
931
40
115
18.5
4
Rita
2005
Sept. 24
TX
3
930
35 to 45
115
15
5
Ivan
2004
Sept. 16
AL/FL
3
943
46 to 58
121
10 to 15
6
Ike
2008
Sept. 13
TX
2
951
46
109
13
7
Gustav
2008
Sept. 1
LA
2
953
-
104
12 to 13
8
Isaac
2012
Aug. 29
LA
1
965
46 to 52
81
11
H - GAPS EVALUATION
TABLE 4-1 HISTORICAL GULF SYSTEM HURRICANE CHARACTERISTICS IN DECREASING ORDER OF MAXIMUM RECORDED WATER LEVEL