The Design, Feasibility and Cost Analysis of Sea
Barrier Systems in Norfolk, Virginia and the
Comparative Cost of Shoreline Barriers
by
Charles H. Hasenbank
Submitted to the Department of Mechanical Engineering
in partial fulfillment of the requirements for the degrees of
Naval Engineer
and
Master of Science in Mechanical Engineering
at the
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
May 2020
© Massachusetts Institute of Technology 2020. All rights reserved.
Author . . . .
Department of Mechanical Engineering
May 15, 2020
Certified by. . . .
Daniel Frey
Professor of Mechanical Engineering
Thesis Supervisor
Accepted by . . . .
Nicolas Hadjiconstantinou
Chairman, Department Committee on Graduate Theses
The Design, Feasibility and Cost Analysis of Sea Barrier
Systems in Norfolk, Virginia and the Comparative Cost of
Shoreline Barriers
by
Charles H. Hasenbank
Submitted to the Department of Mechanical Engineering on May 15, 2020, in partial fulfillment of the
requirements for the degrees of Naval Engineer
and
Master of Science in Mechanical Engineering
Abstract
Protecting a coastline from the damage of a storm surge, or tidal flooding associ-ated with sea level rise, is a challenging and costly engineering endeavor. Low lying properties located directly on an ocean coastline are limited in protective solutions to include constructing shoreline barriers, increasing building elevations, or relocation. However, shoreline properties on an estuary are afforded the additional protective option of a dynamic sea barrier spanning the mouth of the bay or river.
The Delta Works projects in the Netherlands pioneered the design and construc-tion of large scale dynamic sea barriers. Although similar projects have been built or proposed, the high costs have minimized wide spread implementation. Even with positive benefit-cost ratios of prevented property damage to sea barrier cost, the will-ingness to fund these multi-billion dollar projects is reduced when the probability of extreme coastal flooding is associated with 100 to 1000 year storms. However, if sea level rise shifts the flooding probability to include king tides and annual storms, the perspective regarding the relative cost of a sea barrier system may soon change.
This study serves as a design, feasibility and cost analysis of potential sea barrier systems in the Chesapeake Bay near Norfolk, Virginia. Several sea barrier concept designs were proposed, and analyzed against intermediate sea level rise scenarios for the year 2100, to determine feasibility based on topography and projected tide levels. The cost and performance of the design concepts were then examined to determine an optimal design. Finally, the cost of the optimal sea barrier system was compared to the notional cost of installing shoreline barriers along the extent of the estuary, to determine the most cost effective method of coastal flooding protection.
Thesis Supervisor: Daniel Frey
Acknowledgments
Dating back to my undergraduate studies as an Ocean Engineer, I have always enjoyed exploring the topics associated with coastline flooding protection and mitigation. In a era when sea level rise has the potential of severely disrupting coastal communities on a scale and frequency not previously imaginable, this field of study has become increasingly important. With that in mind, I want to thank Professor Daniel Frey, of the Mechanical Engineering Department at MIT, for supporting me as I studied this topic and for granting me the leeway to establish the bounds of the thesis topic. Additionally, I would like to thank Professor David Kriebel of the Naval Architecture and Ocean Engineering Department at USNA, for providing guidance throughout the course of study as a subject matter expert in this field of study. Lastly, I would like to thank my family for their consistent support throughout my time at MIT.
Contents
1 Introduction 15
1.1 Project Background and Rationale . . . 16
1.2 Sea Level Rise Trends and Projections . . . 21
1.3 Mitigation Projects and Proposals . . . 29
1.4 Thesis Contributions . . . 33
2 Sea Barrier Feasibility Analysis 35 2.1 Study Locations . . . 35
2.2 Tidal Data and Sea Level Projections . . . 38
2.3 High Water Analysis . . . 42
2.3.1 Naval Station Norfolk Projected High Water Analysis . . . 42
2.3.2 Norfolk Naval Shipyard Projected High Water Analysis . . . . 44
2.4 Low Water and Mean Sea Level Analysis . . . 47
2.4.1 Naval Station Norfolk Projected Low Water Analysis . . . 48
2.4.2 Norfolk Naval Shipyard Projected Low Water Analysis . . . . 49
2.5 Norfolk, VA Storm Flooding Comparison . . . 50
3 Sea Barrier Concept Designs 51 3.1 Sea Barrier Concept Design One . . . 54
3.2 Sea Barrier Concept Design Two . . . 56
3.3 Sea Barrier Concept Design Three . . . 58
3.4 Sea Barrier Design Four . . . 60
3.6 Sea Barrier Design Six . . . 62
4 Sea Barrier Performance Analysis 63 4.1 OMOE: Project Scale Analysis . . . 67
4.2 OMOE: Protection Area Analysis . . . 69
4.3 OMOE: Perimeter Flooding Analysis . . . 70
4.4 OMOE: Frequency of Operation Analysis . . . 72
4.5 OMOE: Maritime Traffic Impact Analysis . . . 73
4.6 OMOE: Environmental Impact Analysis . . . 75
4.7 OMOE Results . . . 76
5 Sea Barrier Cost Analysis 79 5.1 Cost Model . . . 88
5.2 Cost Analysis . . . 92
6 Sea Barrier Selection and Analysis 97 6.1 Cost vs Performance Analysis . . . 97
7 Shoreline Infrastructure Analysis 101 7.1 Shoreline Barrier System Cost Factors . . . 103
7.2 Shoreline Infrastructure Cost Analysis . . . 106
7.3 Hybrid Shoreline Barrier Cost Analysis . . . 110
8 Conclusion 117 8.1 Project Accomplishments and Findings . . . 117
8.2 Areas for Further Work . . . 124
A Sea Barrier Cost Model 125
B Sea Barrier Cost Analysis 139
C Shoreline Barrier Cost Model 145
List of Figures
1-1 High Tide Nuisance Flooding . . . 16
1-2 Nuisance Flooding Frequency at USNA . . . 17
1-3 Sewells Point Tide Station Flood Stage Events (1930s-2010s) . . . 18
1-4 Hampton Roads and Major Maritime Facilities . . . 20
1-5 Topographic Map of Norfolk, VA with Shoreline Elevations . . . 21
1-6 NOAA Extreme Water Levels for Norfolk, VA . . . 22
1-7 NOAA Sea Level Rise Trends for Norfolk, VA . . . 22
1-8 Sea Level Rise and Norfolk, VA . . . 23
1-9 Global Sea Level Rise Overview . . . 24
1-10 Regional Sea Level Rise Overview . . . 25
1-11 Sea Level Rise Projection Types . . . 26
1-12 Sea Level Rise Scenario Curves . . . 27
1-13 National Climate Assessment GMSL Scenarios Overview . . . 28
1-14 Flood Management Feasibility and Mitigation Studies . . . 30
2-1 Study Location One (Naval Station Norfolk) . . . 36
2-2 Study Location Two (Norfolk Naval Shipyard) . . . 37
2-3 Naval Station Norfolk Tidal and Extreme Water Data . . . 38
2-4 Norfolk Naval Shipyard Tidal and Extreme Water Data . . . 38
2-5 Naval Station Norfolk Sea Level Projections . . . 39
2-6 Norfolk Naval Shipyard Sea Level Projections . . . 39
2-7 NOAA Sea Level Rise Viewer . . . 41
2-9 Naval Station Norfolk 1-YR Storm Projection (Year 2100) . . . 43
2-10 Naval Station Norfolk 10-YR Storm Projection (Year 2100) . . . 43
2-11 Naval Station Norfolk 100-YR Storm Projection (Year 2100) . . . 44
2-12 Norfolk Naval Shipyard MHHW Tidal Projection (Year 2100) . . . . 45
2-13 Norfolk Naval Shipyard 1-YR Storm Projection (Year 2100) . . . 45
2-14 Norfolk Naval Shipyard 10-YR Storm Projection (Year 2100) . . . 46
2-15 Norfolk Naval Shipyard 100-YR Storm Projection (Year 2100) . . . . 46
2-16 Naval Station Norfolk MLLW Tidal Projection (Year 2100) . . . 48
2-17 Naval Station Norfolk LMSL Tidal Projection (Year 2100) . . . 48
2-18 Norfolk Naval Shipyard MLLW Tidal Projection (Year 2100) . . . 49
2-19 Norfolk Naval Shipyard LMSL Tidal Projection (Year 2100) . . . 49
2-20 Norfolk, VA Study Area Storm Surge Flooding Comparison . . . 50
3-1 Arthur Kill Barrier Concept in the Greater New York City Area . . . 52
3-2 Jamaica Bay Barrier Concept in the Greater New York City Area . . 53
3-3 Sea Barrier Concept Design One Chart View . . . 54
3-4 Sea Barrier Concept Design One Satellite View . . . 55
3-5 Sea Barrier Concept Design Two Chart View . . . 56
3-6 Sea Barrier Concept Design Two Satellite View . . . 57
3-7 Sea Barrier Concept Design Three Chart View . . . 58
3-8 Sea Barrier Concept Design Three Satellite View . . . 59
3-9 Sea Barrier Concept Design Four Chart View . . . 60
3-10 Sea Barrier Concept Design Four Satellite View . . . 60
3-11 Sea Barrier Concept Design Five Satellite View . . . 61
3-12 Sea Barrier Concept Design Six Satellite View . . . 62
4-1 Delta Works: Maeslantkering Sector Gate . . . 64
4-2 Delta Works: Eastern Scheldt Surge Barrier . . . 64
4-3 Chesapeake Bay Region DOD Installations . . . 69
4-4 Areas of Probable Perimeter Flooding . . . 71
4-6 Norfolk, Virginia Port Facilities . . . 74
4-7 Environmental Impact Areas . . . 75
4-8 OMOE Results Table . . . 77
4-9 FOM Comparison Graph . . . 77
4-10 Weighted Sum Comparison Graph . . . 77
4-11 Sea Barrier Concept Five Overview . . . 78
5-1 Delta Works Barrier Overview . . . 79
5-2 Hurricane and Storm Damage Risk Reduction System (HSDRRS) . . 80
5-3 GCCPRD Storm Surge Suppression Study . . . 80
5-4 USACE Coastal Texas Protection and Restoration Study . . . 81
5-5 USACE Norfolk Coastal Risk Management Study . . . 82
5-6 USACE New York and New Jersey Harbor and Tributaries Study . . 83
5-7 HSDRRS: Seabrook (Top) and West Closure (Bottom) . . . 85
5-8 USACE Coastal Texas Study Preliminary Cost Ranges . . . 85
5-9 USACE Norfolk Coastal Risk Management Study Cost Data . . . 86
5-10 GCCPRD Storm Surge Suppression Study Cost Data . . . 86
5-11 Sea Barrier Reference Data for the USACE NY-NJ Study . . . 87
5-12 USACE NY-NJ Study Verrazano Narrows Sea Barrier Section Plan . 88 5-13 USACE NY-NJ Study Regression Formula and Data Plot . . . 89
5-14 Reference Sea Barrier Data Table . . . 90
5-15 Minitab Fitted Regression Model Summary . . . 90
5-16 Minitab Fitted Regression Line Plot . . . 91
5-17 Sea Barrier Design Concept One Diagram . . . 92
5-18 Sea Barrier Design Concept Two Diagram . . . 93
5-19 Sea Barrier Design Concept Three Diagram . . . 94
5-20 Sea Barrier Design Concept Four Diagram . . . 94
5-21 Sea Barrier Design Concept Five Diagram . . . 95
5-22 Sea Barrier Design Concept Six Diagram . . . 96
6-2 Cost vs Performance Analysis for the Sea Barrier Concepts . . . 98
6-3 Optimal Design: Sea Barrier Concept Five . . . 99
6-4 Sea Barrier Concept Five Design Specifications . . . 100
6-5 Sea Barrier Concept Five Inner and Outer Barrier . . . 100
7-1 City of Chesapeake, Virginia Tidal Shoreline Overview . . . 102
7-2 Shoreline Infrastructure Cost Factors (FY19 USD/LF) . . . 103
7-3 Shoreline Analysis One: Barrier Types and Cost Factors . . . 104
7-4 Shoreline Analysis Two: Shoreline Barrier Cost Factors . . . 106
7-5 VIMS Shoreline Data Sets (Denoted with Blue Stars) . . . 107
7-6 Shoreline Infrastructure Analysis Area . . . 108
7-7 Shoreline Infrastructure Cost Analysis Results . . . 109
7-8 Hybrid Shoreline Barrier Design . . . 110
7-9 Hybrid Shoreline Barrier Section Overview . . . 111
7-10 Norfolk Shoreline Barrier Design Comparison . . . 112
7-11 Waterfront Layout of the Elizabeth River Shipyards . . . 113
7-12 Hybrid Shoreline Barrier Cost Analysis Overview . . . 114
8-1 Hurricane Isabel Surge Levels (Norfolk, VA) . . . 118
8-2 Flooding Analysis at NSN and NNSY in 2100 . . . 118
8-3 Recommended Sea Barrier Concept . . . 119
8-4 Sea Barrier Concept Overview . . . 120
8-5 Category Four Hurricane Surge Projections . . . 123
8-6 Comparable Study Location: San Francisco Bay . . . 124
B-1 Chesapeake Bay Chart . . . 139
C-1 Shoreline Infrastructure Cost Factors (FY19 USD/LF) . . . 145
D-1 Shoreline Analysis One: Shoreline Infrastructure . . . 149
List of Tables
1.1 Norfolk, VA Tidal Datum Changes . . . 29
2.1 Naval Station Norfolk 2020 and 2100 Tidal Data Comparison . . . 40
2.2 Norfolk Naval Shipyard 2020 and 2100 Tidal Data Comparison . . . . 40
2.3 Projected Tidal Data Above Year 2020 MHHW . . . 41
2.4 Norfolk, VA Tidal Projections Above Year 2020 MHHW . . . 41
4.1 OMOE Performance Category Weight Factors . . . 66
4.2 Navigable Section Comparison . . . 67
4.3 Auxiliary Section Comparison . . . 67
4.4 Static Section Comparison . . . 68
4.5 FOM: Project Scale . . . 68
4.6 FOM: Protection Area . . . 69
4.7 FOM: Perimeter Flooding . . . 71
4.8 FOM: Frequency of Operation . . . 72
4.9 FOM: Maritime Traffic Impact . . . 73
4.10 FOM: Maritime Traffic Impact . . . 74
4.11 FOM: Environmental Impact . . . 76
4.12 Sea Barrier Concept Five Specifications . . . 78
5.1 Sea Barrier Design Concept One Cost Estimates . . . 92
5.2 Sea Barrier Design Concept Two Cost Estimates . . . 93
5.3 Sea Barrier Design Concept Three Cost Estimates . . . 93
5.5 Sea Barrier Design Concept Five Cost Estimates . . . 95
5.6 Sea Barrier Design Concept Six Cost Estimates . . . 95
5.7 Sea Barrier Design Concept Cost Comparisons . . . 96
6.1 Sea Barrier Design Concept Five Overview . . . 99
7.1 Barrier Cost Estimates for Shoreline Facilities . . . 116
Chapter 1
Introduction
In response to the North Sea Flood of 1953, a commission in the Netherlands, des-ignated as the Delta Committee, developed the framework for what would become the pioneering Delta Works flood control system [Watersnood Museum, 2020]. The construction of this elaborate system of flood protection barriers spanned from 1954 to 1997, with a design threshold as stringent as a 1/10,000 year storm for portions of the system [Watersnood Museum, 2020, Bouwer and Vellinga, 2007]. These mar-vels of engineering have become benchmarks for flood protection systems around the world, but the Delta Works design is being revisited to ensure the current flood bar-riers, and their successors, adequately address the growing threat of sea level rise [Delta Commission, 2008]. Referencing the bold scale of the Delta Works, and the proactive initiatives set forth by a second Delta Committee to address sea level rise, this thesis will examine the potential for a similar approach within the United States. Specifically, this study will conduct a design, feasibility and cost analysis of large scale sea barrier systems, similar to aspects of the Delta Works, for the greater Norfolk, Virginia area. Norfolk is located near the mouth of the Chesapeake Bay in a region known as Hampton Roads, named for the waterway that is situated at the confluence of the James and Elizabeth Rivers. The sea barrier system selected as the optimal design will be compared to the alternative option of constructing shoreline infrastruc-ture throughout Hampton Roads, to determine the most cost effective approach for regional flood management with reference to the impending threat of sea level rise.
1.1
Project Background and Rationale
While living in Annapolis, Maryland, I witnessed a troubling trend regarding tidal flooding in low-lying areas at the United States Naval Academy (USNA) and through-out the surrounding community. These flooding events, although usually minor, ap-peared to be happening more frequently, and apart from storm systems that would have historically been the primary cause of coastal flooding. As I would come to learn, this tidal flooding was not a localized event, but rather an increasingly frequent trend throughout the Chesapeake Bay region, as well as along portions of the East Coast and Gulf Coast of the United States, as outlined in Figure 1-1.
Figure 1-1: High Tide Nuisance Flooding [NOAA, 2018]
As described in Figure 1-1, the cause of these higher tides is sea level rise, and the most frequent result, is localized flooding in low-lying areas during the highest of spring tides. The trend has been coined nuisance flooding because it tends to cause more of an inconvenience than substantial damage [NOAA, 2018]. However, the underlying concern associated with this trend is the increase of the local mean sea level (LMSL). The higher LMSL produces a corresponding increase to the high water levels expected during storm events, in which the damaging storm surges historically associated with 1/100 year storms or greater, begin to occur more frequently.
In response to the increased rate of tidal flooding in Annapolis, the Naval Academy formed a Sea Level Rise Advisory Council to examine the issue, and establish mit-igation recommendations. In a 2019 report, the council provided data illustrating nuisance flooding occurrences at USNA over the past 90 years, with a near exponen-tial increase in the number of flooding events since the turn of the century as shown in Figure 1-2 [USNA Sea Level Rise Advisory Council, 2019].
Figure 1-2: Nuisance Flooding Frequency at USNA [USNA Sea Level Rise Advisory Council, 2019]
The graphical analysis shown in Figure 1-2 confirms that I really had witnessed a substantial number of tidal flooding events while living in Annapolis, with year over year increases peaking in 2011 with nearly 30 nuisance floods. After departing Annapolis, I would witness the same trend 150 miles to the south while stationed in Norfolk, Virginia. Utilizing National Weather Service (NWS) data of flood stage events recorded at the Sewells Point tide station on Pier 6 of Naval Station Norfolk, Figure 1-3 outlines the number of floods per decade from the 1930s through the 2010s. As established by the NWS, flood stage at this location is 4.5ft above mean lower low water (MLLW) for a minor flood. A moderate flood occurs at 5.5ft above MLLW and a major flood at 6.5ft above MLLW [NWS, 2020]. Similar to the USNA data, the number of minor flooding events in the Norfolk, VA area increased dramatically in recent years with 31 of the 52 recorded floods taking place since 2015 [NWS, 2020]. Based on my experience of working at the naval station during this time period, these
minor flood stage events did not impact daily operations, and only produced minor pooling in low-lying, non-developed areas. However, as with the Annapolis data, the primary concern is the underlying cause which points toward an increase in LMSL, and the potential for future storm events to have substantially higher surge levels.
Figure 1-3: Sewells Point Tide Station Flood Stage Events (1930s-2010s) As illustrated in Figures 1-2 and 1-3, the increased number of tidal flooding events in Annapolis, MD and Norfolk, VA is significant, and has a clear upward trend. Witnessing the frequency of these flooding occurrences first hand, even with the vast majority only being nuisance floods, provided the background interest for this thesis, and the desire to examine the threat of sea level rise, as well as the potential for mitigation efforts in the Chesapeake Bay region.
In addition to witnessing the coastal flooding trends while living in Norfolk, Vir-ginia area, I also became acutely aware of the vital importance of this region in supporting United States Navy (USN) operations. Naval Station Norfolk (NSN) is the largest naval complex in the world with approximately 4,600 acres, 4,000 build-ings, 14 piers and an airfield [NAVFAC, 2020a]. The base serves as the homeport for approximately 60 ships with over 3,100 ship movements annually [NAVFAC, 2020a,
NAVSHIPSO, 2020]. Just a few miles away, on the Elizabeth River, is Norfolk Naval Shipyard (NNSY), one of four public shipyards operated by the USN with over 800 acres and five dry docks. NNSY is the sole public maintenance yard for aircraft carriers on the East Coast, as well as one of the primary submarine maintenance yards [NAVFAC, 2020b]. Across the Elizabeth River from NNSY are multiple pri-vate shipyards that fulfill a substantial portion of the surface combatant maintenance requirements for the USN. Across the Hampton Roads waterway is Newport News Shipbuilding, a private shipyard owned by Huntington Ingalls Industries. This fa-cility spans 2.5 miles of waterfront along the James River, with four dry docks and over 550 acres. Newport News Shipbuilding is the only building and refueling yard for aircraft carriers, and one of two shipyards that construct submarines for the USN [Huntington Ingalls Industries, 2020]. Several other Department of Defense (DOD) facilities are spread throughout the Hampton Roads region to include Joint Base Langley-Eustis, Joint Expeditionary Base Little Creek-Fort Story, Naval Air Station Oceana, Naval Medical Center Portsmouth, Craney Island Fuel Depot, and Naval Support Activity Hampton Roads, which houses the NATO Allied Command Trans-formation, the only U.S. based NATO command [Hampton Roads Chamber, 2020]. This concentration of military related facilities in the greater Norfolk area makes safeguarding the region a vital priority with respect to the threat of sea level rise.
In addition to the DOD related facilities, the Port of Virginia has six termi-nals spanning 1,864 acres with 19,885 linear feet of berth space. The port is the deepest on the East Coast and the sixth largest container port in the United States [Virginia Port Authority, 2020]. The four facilities in the immediate Norfolk area are Norfolk International Terminal, Virginia International Gateway, Portsmouth Marine Terminal and Newport News Marine Terminal. Additionally, a port expansion has been approved for a marine terminal on Craney Island that would significantly ex-pand the container capacity [Virginia Port Authority, 2020]. Protecting these port facilities from the increased likelihood of flooding related to sea level rise, while also maintaining functionality, are two aspects that will be explored in this study. The locations of the major maritime facilities outlined above are shown in Figure 1-4
Figure 1-4: Hampton Roads and Major Maritime Facilities
Based on the concentration of maritime facilities and topography of Hampton Roads, the greater Norfolk, Virginia region was selected as the study area for this thesis. In regard to the major maritime installations, which include Naval Station Norfolk, Norfolk Naval Shipyard, Newport News Shipbuilding, the maintenance ship-yards and the Port of Virginia terminals, failing to maintain the operational capacity of these facilities could have far reaching impacts ranging from national security to re-gional economic stability. With respect to topography, the vast majority of the greater Norfolk area has an elevation of less than 15ft in reference to the North American Vertical Datum of 1988 (NAVD88), and as a result, is susceptible to tidal flooding [USACE Norfolk District, 2018]. Figure 1-5 shows the shoreline heights for the City of Norfolk with 146 of 161 miles of shoreline within zero to five feet of present day sea level [Virginia Institute of Marine Science, 2020]. However, the general layout of the region, to include relatively narrow waterway access points, provides the possibility
of utilizing dynamic sea barriers to isolate waterways such as the Elizabeth or James Rivers from extreme tides or storm surges. The combination of the concentration of vital shoreline facilities, the regions susceptibility to tidal flooding, and topography of the local waterways establishes the greater Norfolk, VA area as a prime study location for a sea barrier design, feasibility and cost analysis.
Figure 1-5: Topographic Map of Norfolk, VA with Shoreline Elevations [Virginia Institute of Marine Science, 2020]
1.2
Sea Level Rise Trends and Projections
An analysis of the historical data pertaining to extreme water levels and sea level rise trends for Norfolk, VA, as shown in Figures 1-6 and 1-7, indicate a significant increase in LMSL, consistent with the nuisance flooding trend discussed in the previous section. As indicated in Figure 1-7, an analysis of sea level trend data from 1927 through 2019 is equivalent to a 1.54ft increase in LMSL over a 100 year period [NOAA, 2020c]. This increase in LMSL is nearly a foot higher than the global mean sea level (GMSL) rise since 1900 of 0.63ft [Sweet et al., 2017], indicating an accelerated risk for coastal flooding, and associated damage, in the Norfolk, Virginia region.
Figure 1-6: NOAA Extreme Water Levels for Norfolk, VA [NOAA, 2020c]
Figure 1-7: NOAA Sea Level Rise Trends for Norfolk, VA [NOAA, 2020c]
Based on these significant LMSL trends, Norfolk is consistently highlighted as an area of concern for sea level rise as shown in Figure 1-8. These spotlight reports are
helpful in highlighting the general issue, but conventionally provide only broad esti-mations, such as the 2.5ft to 11.5ft LMSL projection range listed in the introductory chapter of the Fourth National Climate Assessment, Volume II [Jay et al., 2018].
Figure 1-8: Sea Level Rise and Norfolk, VA [Jay et al., 2018, Kusnetz, 2018]
The LMSL trends, and broad range sea level rise projections, discussed above firmly establish that there is a significant risk for increased coastal flooding in the Norfolk, VA area. However, these data points do not provide a specific sea level rise scenario that can be utilized for a design and feasibility analysis of sea barrier systems. As such, additional research was required to determine the most likely LMSL scenario for the year 2100 in Norfolk, VA. This sea level scenario would, in turn, be established as the LMSL design threshold for a conceptual sea barrier system. The primary documents referenced for this portion of the thesis were the 2016 SERDP Regional Sea Level Scenarios for Coastal Risk Management [Hall et al., 2016] and the 2017 Fourth National Climate Assessment, Volume I [Sweet et al., 2017]. A brief overview of some of the key findings from these reports is outlined below.
The 2016 SERDP report provided an overview of the primary causes of global and regional sea level rise. Conceptualizing these large and small scale catalysts for sea level rise provides for a better understanding why a region such as Norfolk, VA may witness accelerated LMSL trends. The three primary causes of global sea level change are identified as thermal expansion, land-based ice melting, and land water storage changes as shown in Figure 1-9 [Hall et al., 2016].
Figure 1-9: Global Sea Level Rise Overview [Hall et al., 2016]
The National Climate Assessment outlines the same causes for global sea level rise with ice melting identified as the dominant factor (50%), followed by thermal expan-sion (37%) and land water storage (13%) [Sweet et al., 2017]. Figure 1-10 outlines the primary causes of local sea level changes, which are vertical land movement, ice melt effects, and dynamic sea level changes. The vertical land movement, also known as subsidence, and the effects of the ice melt, which alters the gravitational attraction associated with land masses, are cited as the primary causes for accelerated sea level rise in the Mid-Atlantic region near Norfolk, VA [Hall et al., 2016, Sweet et al., 2017].
Figure 1-10: Regional Sea Level Rise Overview [Hall et al., 2016]
The next aspect of the SERDP report that applied directly to this thesis was the description of different approaches to sea level rise estimation. These approaches were identified as deterministic, probabilistic, and scenario-based, as illustrated in Figure 1-11 [Hall et al., 2016]. This thesis will focus on establishing the most likely projection for the Norfolk, VA study area. Utilizing this scenario based approach, and focusing on the most likely projection, is in line with the recommendation of the 2017 NAVFAC Climate Change Installation Adaptation and Resilience Planning Hand-book [NAVFAC, 2017]. Referencing the SERDP report, the NAVFAC HandHand-book also states that considering less likely, but more conservative, scenarios is acceptable
for installations of high value and low risk tolerance. Additionally, the handbook recommends focusing on longer time periods, such as the year 2100, and considering less severe but more frequent storm events as design benchmarks [NAVFAC, 2017]. These SERDP and NAVFAC recommendations will be referenced when selecting the sea level rise projection and design threshold for the Norfolk, VA study area.
Figure 1-11: Sea Level Rise Projection Types [Hall et al., 2016]
Lastly, the SERDP report established five global sea level rise scenarios, ranging from 0.2m to 2.0m as shown in Figure 1-11 [Hall et al., 2016]. These GMSL projec-tions were then tailored to individual DOD facilities based on regional trends, with the approximate projection range for the Norfolk, VA region being 2ft to 9ft by the year 2100 [Hall et al., 2016]. With reference to this model, the deterministic projec-tion of the most likely scenario would indicate approximately a 5ft increase in LMSL for the Norfolk, VA study area. A similar set of sea level rise scenarios was provided in the National Climate Assessment. The only significant deviation from the SERDP report was the addition of a sixth scenario of a 2.5m global sea level rise based on extreme levels of ice melt [Sweet et al., 2017].
Figure 1-12: Sea Level Rise Scenario Curves [Hall et al., 2016]
Two central aspects of the sea level rise chapter of the Fourth National Climate Assessment, Volume I will be outlined below, to include the key findings of the report, and the sea level rise scenarios. The key findings of very high to high confidence from the National Climate Assessment are listed below [Sweet et al., 2017]:
• LMSL along portions of the East Coast and Gulf Coast are likely to be higher than the GMSL.
• LMSL rates are increasing in over 25 U.S. cities situated on the Atlantic Ocean and Gulf of Mexico. Based on this trend, tidal flooding will increase in breath, depth and frequency over the next century.
• LMSL rise will increase the frequency and scope of flooding associated with coastal storms such as a hurricane or nor’easter.
As previously discussed, the National Climate Assessment added an Extreme Sea Level Rise projection for a total of six scenarios as shown in Figure 1-13.
Figure 1-13: National Climate Assessment GMSL Scenarios Overview [Sweet et al., 2017]
As outlined in Figure 1-13, the sea level rise scenarios were compared to Ra-diative Concentration Pathways (RCP), which are atmospheric carbon concentra-tion trajectories. The probabilities listed are the likelihood of GMSL exceeding the projection of a given sea level rise scenario based on the associated RCP. The or-ange box indicates the scenarios identified for this thesis as having acceptable
de-grees of risk associated with GMSL exceeding a scenario projection. On the other hand, the intermediate-low scenario is based on a 2050 stabilized global emissions rate. Based on this being an ambitious emissions forecast, and the presence of a lag between emission reductions and atmospheric concentrations decreasing, the risk of global sea levels exceeding the projections of this scenario are much higher [Sweet et al., 2017]. Based on this information, the intermediate sea level rise sce-nario was selected for this thesis as the most likely projection that also appropriately manages the associated risks of the study area. The decision to reference the interme-diate sea level rise scenario aligns with the recommendation of the USNA Sea Level Rise Advisory Council which is using the same projection adjusted for Annapolis [USNA Sea Level Rise Advisory Council, 2019].
Based on the intermediate scenario, a 4.39ft sea level increase, in reference to NAVD88, is projected at the Sewells Point in Norfolk, VA [USACE, 2020]. Table 1.1 outlines the projected shift in water levels and the associated datums in Norfolk, VA between 2020 and 2100 in reference to NAVD88.
Table 1.1: Norfolk, VA Tidal Datum Changes
Datum (Reference: NAVD88) 2020 Level (ft) 2100 Level (ft)
NAVD88 0.00 0.00 MLLW -1.61 2.78 LMSL -0.25 4.14 MHHW 1.15 5.54 1-YR 2.59 6.98 10-YR 4.81 9.20 50-YR 6.15 10.54 100-YR 6.79 11.18
1.3
Mitigation Projects and Proposals
Over the course of this thesis, four studies were identified as having related objectives, to included flood barrier design, or the location of the study area. These included the U.S. Army Corps of Engineers (USACE) Norfolk Coastal Storm Risk Management
Study, the USACE New York-New Jersey Harbor and Tributaries Coastal Storm Risk Management Feasibility Study, the USACE Coastal Texas Protection and Restoration Feasibility Study and the Naval Facilities Engineering Command (NAVFAC) Mid-Atlantic NNSY Small Docks Flood Mitigation Study as shown in Figure 1-14.
Figure 1-14: Flood Management Feasibility and Mitigation Studies [USACE Norfolk District, 2018, NAVFAC MID-ATLANTIC, 2015, USACE Galveston District, 2018, USACE New York District, 2019]
An overview of these reports is outlined below, to include the key data points referenced for this thesis.
The USACE Norfolk Study conducted a design analysis of multiple flood barrier systems to mitigate coastal flooding in the City of Norfolk. The estimated cost of the recommended solution is $1.6B (FY18), which includes barrier systems spanning Pretty Lake, the Lafayette River, the Hague and Broad Creek. Portions of these barriers are dynamic, in order to maintain tidal flow, as well as support the transit of small vessels. The largest of these dynamic structures is a 150ft wide sector gate across a shallow channel on the Lafayette River. Additionally, a seawall, constructed near the shoreline, protects the majority of downtown Norfolk. The average design height of the barrier system is 15.5ft above NAVD88, indicating that these struc-tures can continue providing flood protection in 2100 for water levels up to 100 year storms, based on the projections shown in Table 1.1 [USACE Norfolk District, 2018]. Although the dynamic barrier system spanning the Lafayette River is complex and costly, it is likely more affordable and functional than installing shoreline barriers along the entire river. This design trade-off between a dynamic barrier, and shore-line infrastructure, is one of the central themes of this thesis, only on a larger scale. Overall, the proposals outlined in the Norfolk Study are an essential first step in pro-tecting this region from coastal flooding. However, the study is limited in scope to the municipal boundaries of Norfolk, excluding surrounding cities, as well as federal and state facilities such as Naval Station Norfolk and Norfolk International Terminal. The study discusses eliminating the consideration of larger sea barrier systems, that would span waterways such as the Elizabeth River, because of the higher costs, and requirement for regional coordination [USACE Norfolk District, 2018]. This decision points to another theme of this thesis regarding the cost comparison of large sea barriers to regional shoreline barrier systems designed to protect equivalent areas.
The NAVFAC NNSY Study examines structural mitigation options to address the flood risks associated with the four smaller dry docks. As outlined in a 2017 Naval Shipyards Government Accountability Office (GAO) report, four of five dry docks are at risk of flooding, with three of the dry docks reaching a flood condition at the
present day 10 year storm water levels. Additionally, portions of the shipyard expe-rience one major flood event on average per year [GAO, 2017]. The NAVFAC report recommended a system of seawalls protecting dry docks two through four, which are the docks with the lowest risk tolerance based on the type of platforms maintained in these facilities. With substantial consideration to maintaining functionality around the dry docks, the seawall height was designed to a 500 year storm threshold at present day water levels. This equates to a barrier height of 10ft above NAVD88. Total project costs were projected at approximately $70M (FY15) [NAVFAC, 2017]. Expanding the scope of the seawall system, or raising the design height would have caused considerable disruptions to the functionality of the shipyard. However, based on the sea level projections discussed in the previous section, these proposed seawalls will likely be overtopped at 50 year storm water levels in the year 2100 as shown in Table 1.1. Overall, the mitigation proposals outlined in the NAVFAC NNSY report are an affordable solution to the near term flooding risks. However, additional flood barrier systems will be required to sufficiently protect the entire shipyard, based on sea level rise projections. The design decisions associated with balancing the installa-tion of a flood barrier systems, with the requirement for maintaining the funcinstalla-tionality of a shoreline facility, will be referenced throughout this thesis.
The USACE NY-NJ and TX studies have similar scales and design types. Both studies are in early stages, but provide invaluable design insights and cost data for this thesis. The NY-NJ Study is examining five design alternatives ranging from the exclusive use of shoreline barriers, stationed at the areas of greatest flooding risk, to a sea barrier system spanning the 6 mile wide harbor entrance from Sandy Hook to Breezy Point. This large scale sea barrier concept consists of 30 miles of structure, and an estimated construction cost of $36.5B (FY19) before contingency adjustments [USACE New York District, 2019]. In order to compare the wide range of alternatives in this study, the USACE New York District established a cost model for sea barriers that will be referenced throughout this thesis. The USACE TX study is similar in that it is also considering a range of options along the coastline. The most complex portion of the project focuses on the Houston Ship Channel near Galveston, TX.
At this location, the proposed barrier would include 70 miles of coastal structure to include a dynamic system spanning the 2.5 mile harbor entrance. This dynamic structure would include large environmental sluice gates to promote tidal flow, and a 1200ft wide sector gate across the 60ft deep channel. Early project cost estimates range from $23B to $32B (FY18) [USACE Galveston District, 2018]. The cost data from this report, as well as from a Gulf Coast Community Protection and Recovery District (GCCPRD) report that preceded the USACE TX Study [GCCPRD, 2018], was utilized to supplement the USACE NY-NJ Study cost model.
1.4
Thesis Contributions
The contributions of this thesis are twofold. First, this thesis conducted a design, feasibility and cost analysis of potential sea barrier systems for the greater Norfolk, Virginia area. The Norfolk area was selected as the study location because of its high risk to the impacts of sea level rise, the potential for the local topography to support the installation of a sea barrier system, and due to the regions vital importance to both the Commonwealth of Virginia and the federal government. With the substantial concentration of military facilities, shipyards and port terminals, storm surge related damages could have far reaching, and long standing impacts, ranging from disruptions to the regional economy and trade network, to significant risks to infrastructure and industries supporting national security.
Harnessing the topography of the region, this study proposed six potential sea barrier systems with protection zones ranging in size from the entire Chesapeake Bay, to the Southern and Eastern Branches of the Elizabeth River. A feasibility study was conducted to determine if a sea barrier system, conventionally utilized for storm surge protection, could also be utilized to safeguard shorelines from high tide flooding. The feasibility criteria was straightforward: if substantial flooding was projected at low tide or mean sea level, based on an intermediate sea level rise scenario in the year 2100, then a sea barrier system alone, could not be used to safeguard the Norfolk, VA region. However, if minimal flooding was projected at these lower water levels, it
was established that a sea barrier system could potentially replace the requirement for extensive shoreline barrier infrastructure. In order to examine the six sea barrier concepts, an Overall Measure of Effectiveness (OMOE) analysis was conducted with performance criteria ranging from the scale and associated protection area of the design concept, to the maritime traffic and environmental impacts of the proposed sea barrier system. A cost analysis was then conducted on all six design concepts utilizing a storm surge barrier cost model developed by the USACE New York District in 2019 as part of the NY-NJ Harbor and Tributaries Coastal Storm Risk Management Feasibility Study [USACE New York District, 2019]. This cost model was analyzed with respect to other ongoing USACE studies for Norfolk, VA and the Texas Gulf Coast to establish the consistency of the formula in estimating construction cost of sea barrier systems. With the OMOE and cost analyses completed, a cost versus performance plot was created to determine the optimal sea barrier concept design for the greater Norfolk, VA area.
The second aspect of the thesis was a comparative cost analysis of the recom-mended sea barrier design, to the alternative option of a shoreline barrier system that provided equivalent protection. Shoreline barriers were separated into two cate-gories for the cost analysis, shore based infrastructure, and a hybrid shoreline barrier system incorporating shore based infrastructure and shallow water dynamic barriers. Both types of shoreline barriers were analyzed to determine a notional cost that could be compared to the sea barrier system selected as the optimal concept.
In total, this thesis provided a notional sea barrier design, selected as the optimal concept from six designs, with the ability to safeguard a region with vital coastal facilities and industries from the ever increasing risks associated with sea level rise. Additionally, this thesis provided a cost comparison of a sea barrier system to equiv-alent shoreline infrastructure, with the goal of determining the most cost effective approach for protecting an expansive estuary. Although every location requires dif-ferent design considerations, the comparison of these two large scale coastal flood protection approaches provided some relevant conclusions for future coastal protec-tion design studies.
Chapter 2
Sea Barrier Feasibility Analysis
Determining the notional feasibility of a sea barrier system for the Norfolk, Virginia region required an analysis of the projected rise in sea levels, and the associated im-pacts to coastal properties, to include several major maritime facilities. This baseline feasibility analysis had two objectives. First, the analysis created a comparative illus-tration of the impacts of sea level rise over a range of elevated tides to include mean higher high water (MHHW) and storm surge conditions. This part of the analysis provided the illustrative data necessary to determine if a large scale sea barrier sys-tem was practical and warranted based on local topography, and the projected sea levels in the year 2100. Second, the analysis provided important insights into coastal conditions, and the associated functionality of coastal facilities, at lower tidal levels ranging from mean lower low water (MLLW) to mean sea level (MSL). A dynamic sea barrier designed to be activated during elevated tide levels would be impractical if significant coastal flooding was already occurring during low tide or at mean sea level. In the case of extensive low tide flooding, a robust network of shoreline seawalls and infrastructure elevation would be the only viable solution, short of facility relocation.
2.1
Study Locations
As part of the feasibility analysis, Naval Station Norfolk and Norfolk Naval Shipyard were selected as study locations within the greater Norfolk, Virginia study area. These
two naval installations were chosen because of their important roles as large scale shoreline facilities and due to their varying locations within the study area.
Naval Station Norfolk, located at Sewells Point near the mouth of the James and Elizabeth Rivers, is the largest coastal naval base in the world with over eight miles of shoreline and 4631 acres. The base houses an airfield and an extensive port facility with 11 miles of pier and wharf space [NAVFAC, 2020a, CNIC, 2020]. Figure 2-1 shows an aerial view and a boundary map of the base, as well as the location of Naval Station Norfolk relative to the greater Norfolk, Virginia region.
Figure 2-1: Study Location One (Naval Station Norfolk) [CNIC, 2020, NAVFAC, 2020a]
Norfolk Naval Shipyard (NNSY) is located in Portsmouth, Virginia on the south-ern branch of the Elizabeth River. Serving as the primary East Coast maintenance yard for aircraft carriers and a large percentage of submarines, the shipyard fills an invaluable role. NNSY has four miles of shoreline wharf and over 800 acres between the main facility and nearby annexes [NAVFAC, 2020b]. NNSY was selected as the second study location due to its inland location, 10 miles upriver from Naval Station Norfolk. Figure 2-2 shows shows an aerial view and a boundary map of the shipyard, as well as the location of NNSY relative to the greater Norfolk, Virginia region.
Figure 2-2: Study Location Two (Norfolk Naval Shipyard) [National Archives, 1995, NAVFAC, 2020b]
2.2
Tidal Data and Sea Level Projections
An analysis of projected sea levels was conducted for Naval Station Norfolk and Nor-folk Naval Shipyard utilizing a joint USACE and National Oceanic and Atmospheric Administration (NOAA) database [USACE, 2020]. The database provided tidal da-tums, extreme water levels and sea level rise projections for the NOAA measurement stations within the boundaries of both naval facilities. Figures 2-3 and 2-4 show the tidal datums and extreme water levels for Naval Station Norfolk (Sewells Point) and Norfolk Naval Shipyard respectively [USACE, 2020].
Figure 2-3: Naval Station Norfolk Tidal and Extreme Water Data
Utilizing the same USACE and NOAA database, sea level projections were ac-cessed for both study locations. Figures 2-5 and 2-6 show the sea level projections through the year 2100 in reference to local mean sea level (LMSL) with the interme-diate scenario selected for Naval Station Norfolk (Sewells Point) and Norfolk Naval Shipyard respectively [USACE, 2020].
Figure 2-5: Naval Station Norfolk Sea Level Projections
Figure 2-6: Norfolk Naval Shipyard Sea Level Projections
NOAA intermediate projections indicate a rise in LMSL of 4.65ft and 4.59ft for Naval Station Norfolk and Norfolk Naval Shipyard respectively by the year 2100.
Tables 2.1 and 2.2 compare present day (YR 2020) tidal data to projected (YR 2100) sea levels in reference to year 2020 LMSL.
Table 2.1: Naval Station Norfolk 2020 and 2100 Tidal Data Comparison
Datum (Units: FT, Reference: 2020 LMSL) YR 2020 YR 2100
North American Vertical Datum 1988 (NAVD88) 0.26 0.26
Mean Lower Low Water (MLLW) -1.35 3.30
Local Mean Sea Level (LMSL) 0.00 4.65
Mean Higher High Water (MHHW) 1.40 6.05
Annual Storm (1-YR) 2.85 7.50
Ten Year Storm (10-YR) 5.07 9.72
Hundred Year Storm (100-YR) 7.05 11.70
Table 2.2: Norfolk Naval Shipyard 2020 and 2100 Tidal Data Comparison
Datum (Units: FT, Reference: 2020 LMSL) YR 2020 YR 2100
North American Vertical Datum 1988 (NAVD88) 0.27 0.27
Mean Lower Low Water (MLLW) -1.52 3.07
Local Mean Sea Level (LMSL) 0.00 4.59
Mean Higher High Water (MHHW) 1.58 6.17
Annual Storm (1-YR) 3.06 7.65
Ten Year Storm (10-YR) 5.24 9.83
Hundred Year Storm (100-YR) 6.94 11.53
The sea level projections for Naval Station Norfolk and Norfolk Naval Shipyard were converted to reference year 2020 MHHW as outlined in Table 2.3. The average of both study locations was calculated for each datum, and rounded to the nearest one-foot interval as shown in Table 2.4. The sea level projections were converted to MHHW and rounded to the nearest foot in preparation for plotting the data in the NOAA Sea Level Rise Viewer [NOAA, 2020a]. A snapshot of the viewer, with the intermediate scenario selected for the year 2100, is shown in Figure 2-7. The viewer plots direct flooding, from seawater flowing over a shoreline, in light blue. Light green denotes low lying areas with a high probability of indirect flooding due to rainwater or seawater pooling as a result of tidal interactions with gravity drainage systems.
Table 2.3: Projected Tidal Data Above Year 2020 MHHW
Datum (FT +/- YR 2020 MHHW) Naval Station Naval Shipyard
NAVD88 -1.14 -1.31 MLLW 1.90 1.49 LMSL 3.25 3.01 MHHW 4.65 4.59 1-YR 6.10 6.07 10-YR 8.32 8.25 100-YR 10.30 9.95
Table 2.4: Norfolk, VA Tidal Projections Above Year 2020 MHHW
Datum (FT +/- YR 2020 MHHW) Average Value Rounded Value
NAVD88 -1.23 -1.0 MLLW 1.70 2.0 LMSL 3.13 3.0 MHHW 4.62 5.0 1-YR 6.09 6.0 10-YR 8.29 8.0 100-YR 10.13 10.0
2.3
High Water Analysis
As stated at the beginning of this chapter, the first objective of the feasibility analysis was to examine the study locations at elevated tidal values to include MHHW and storm conditions. This portion of the analysis provided a visualization of the impacts each of the high water levels would have on Naval Station Norfolk and Norfolk Naval Shipyard. In turn, the illustrative data assisted in determining if a large scale sea barrier system was warranted and practical. MHHW and water levels for an annual, ten year and one hundred year storm were plotted in the NOAA Sea Level Rise Viewer [NOAA, 2020a] for both naval facilities. Water levels were plotted in one-foot intervals above year 2020 MHHW as listed in Table 2.4.
2.3.1
Naval Station Norfolk Projected High Water Analysis
Figure 2-8: Naval Station Norfolk MHHW Tidal Projection (Year 2100) MHHW: 5ft above YR 2020 MHHW. Minor direct flooding occurred at four locations along the northern waterfront of the base. The potential for indirect flooding was significant, but mostly contained to areas nonessential to base operations.
Figure 2-9: Naval Station Norfolk 1-YR Storm Projection (Year 2100)
1-YR Storm: 6ft above YR 2020 MHHW. Direct flooding increased significantly to include an aircraft taxiway, roads, parking lots and a handful of buildings.
Figure 2-10: Naval Station Norfolk 10-YR Storm Projection (Year 2100) 10-YR Storm: 8ft above YR 2020 MHHW. Substantial direct flooding with upwards of 40 percent of the base nonoperational to include access to all warship berths.
Figure 2-11: Naval Station Norfolk 100-YR Storm Projection (Year 2100) 100-YR Storm: 10ft above YR 2020 MHHW. Debilitating direct flooding with over 75 percent of the base damaged and inaccessible.
The analysis of the effects of projected high water levels on Naval Station Norfolk indicated varied results ranging from minor nuisance flooding at MHHW to extreme base-wide flooding at the 100-YR storm levels. Overall, the high water analysis illustrated the need for large scale mitigating infrastructure such as a sea barrier to preserve the facilities and functionality of Naval Station Norfolk through storm surge conditions in the year 2100. Even the projected annual storm surge conditions of 6ft would cause disruptive flooding to the base on par with the year 2020 100-YR storm surge levels of 5.65ft above MHHW or 7.05ft above LMSL.
2.3.2
Norfolk Naval Shipyard Projected High Water Analysis
The high water analysis for Norfolk Naval Shipyard was completed in the same man-ner as Naval Station Norfolk with an analysis of projected MHHW, 1-YR, 10-YR, and 100-YR water levels in the year 2100. With the location of the shipyard 10 miles up-river from the naval station, the analysis provided a secondary snapshot of projected impacts within the greater Norfolk, Virginia study area.
Figure 2-12: Norfolk Naval Shipyard MHHW Tidal Projection (Year 2100) MHHW: 5ft above YR 2020 MHHW. Significant flooding to a portion of the shipyard.
Figure 2-13: Norfolk Naval Shipyard 1-YR Storm Projection (Year 2100) 1-YR: 6ft above YR 2020 MHHW. Substantial flooding to most of the shipyard.
Figure 2-14: Norfolk Naval Shipyard 10-YR Storm Projection (Year 2100) 10-YR: 8ft above YR 2020 MHHW. Extensive flooding of the entire shipyard.
Figure 2-15: Norfolk Naval Shipyard 100-YR Storm Projection (Year 2100) 100-YR: 10ft above YR 2020 MHHW. Debilitating flooding of the entire shipyard.
The analysis of the impacts of projected high water levels on Norfolk Naval Ship-yard also illustrated varied results, but were more severe at MHHW and the 1-YR storm levels as compared to the impacts experienced at Norfolk Naval Station. Over-all, the high water analysis of Norfolk Naval Shipyard also illustrated the need for large scale mitigating infrastructure such as a sea barrier to preserve the facilities and functionality of the naval shipyard. However, the need for tidal flood protection upriver near Norfolk Naval Shipyard is even greater than that of Norfolk Naval Sta-tion because of the potential for daily flooding condiSta-tions brought about by MHHW levels. This projection will drive the design and analysis phase of this project in two ways. First, a shore based barrier system would require extensive infrastructure lining the entire bank of the Elizabeth River in low-lying areas to prevent the flanking of seawalls. Second, a sea gate at the mouth of the Elizabeth River, in the vicinity of Naval Station Norfolk, would be required to close up to twice daily due to the high tide flooding projections near the shipyard. In contrast, a sea gate only functioning to protect Naval Station Norfolk may only need to close during a King Tide, and during storm surge conditions.
2.4
Low Water and Mean Sea Level Analysis
The second objective of the feasibility analysis was to analyze the study locations at low tide and mean sea level in order to determine the condition of coastal facilities at these lower water levels. A dynamic sea barrier designed to be activated during elevated water levels would be impractical if significant coastal flooding also occurred during low tide or at mean sea level. MLLW and LMSL were plotted in the NOAA Sea Level Rise Viewer for both naval facilities [NOAA, 2020a]. Water levels were plotted in one-foot intervals above year 2020 MHHW as listed in Table 2.4. Figures 2-16-2-19 indicate that although the MLLW and LMSL water levels are projected to be much higher in 2100 as compared to the year 2020, the ongoing design studies for shoreline infrastructure improvements near downtown Norfolk and at Norfolk Naval Shipyard will be sufficient to prevent coastal flooding at the lower water levels.
2.4.1
Naval Station Norfolk Projected Low Water Analysis
Figure 2-16: Naval Station Norfolk MLLW Tidal Projection (Year 2100)
2.4.2
Norfolk Naval Shipyard Projected Low Water Analysis
Figure 2-18: Norfolk Naval Shipyard MLLW Tidal Projection (Year 2100)
2.5
Norfolk, VA Storm Flooding Comparison
Chapter 3
Sea Barrier Concept Designs
Six sea barrier concept designs were created to protect varying areas of the Chesapeake Bay and tributaries surrounding the greater Norfolk, Virginia study area. Each design included up to three different barrier types within the overall system to include static, auxiliary dynamic and navigable dynamic structures. The static portions of the sea barrier designs consist of seawalls that tie the system into high ground on shore, or span between dynamic sections of the system. The auxiliary dynamic sections of the system are designed to promote increased water flow through the barrier when the sea barrier system is open in order to minimize the environmental impacts associated with the movement of nutrients, sediment and sea life. The auxiliary dynamic sections utilize a series of miter or sluice gates to support water flow and can also serve as auxiliary passageways for small pleasure craft. The last barrier type is the navigable dynamic section of the system. This section consists of large sector gates that close to seal off the deep water navigation channels when the sea barrier system is activated. These three categories of sea barrier are exhibited in two concept designs from the preliminary USACE New York-New Jersey Harbor and Tributaries Feasibility Study [USACE New York District, 2019].
The Arthur Kill Barrier concept shown in Figure 3-1 has a central navigable section (labeled as B). This navigable section includes a sector gate which close to seal off the main channel, and the two artificial islands created to stow the sector gate arms when the barrier system is open. The navigable dynamic section is flanked by two smaller
auxiliary dynamic sections (labeled as A and C). These auxiliary sections have one sluice gate each which allow for additional water flow through the open sea barrier system, and function as auxiliary passageways for smaller vessels. The remainder of the sea barrier system is comprised of static seawalls spanning from the dynamic sections to high ground on both shorelines [USACE New York District, 2019].
Figure 3-1: Arthur Kill Barrier Concept in the Greater New York City Area [USACE New York District, 2019]
The Jamaica Bay Barrier concept shown in Figure 3-2 has a central navigable section (labeled as D). This navigable section includes two sector gates, and the associated stowage areas, which close to seal off an inbound and outbound
chan-nel. The navigable dynamic section is flanked by a series of sluice gates on both sides which form the auxiliary dynamic sections (labeled as A, B, C and E). The 15 sluice gates, which span the vast majority of the waterway, significantly increase the rate of water flow through the barrier system, and subsequently decrease the environmental impacts. The outermost sections of the sea barrier are comprised of static seawalls that serve as tie-ins from the dynamic sections to high ground [USACE New York District, 2019].
Figure 3-2: Jamaica Bay Barrier Concept in the Greater New York City Area [USACE New York District, 2019]
3.1
Sea Barrier Concept Design One
Sea Barrier One is located near the mouth of the Chesapeake Bay, and parallel to the Chesapeake Bay Bridge-Tunnel. This design concept consists of approximately 18.5 total miles of sea barrier structure, to include 10 miles of static seawall, 7.25 miles of auxiliary dynamic and 1.25 miles of navigable dynamic. Figures 3-3 and 3-4 illustrate the the design overlaid on a nautical chart and satellite image.
3.2
Sea Barrier Concept Design Two
Sea Barrier Two is located at the confluence of the James and Elizabeth Rivers, and parallel to the existing Hampton Roads Bridge-Tunnel. This design consists of approximately 4.5 miles of sea barrier structure, to include 2.5 miles of static seawall, 1.5 miles of auxiliary dynamic and 0.5 miles of navigable dynamic. Figures 3-5 and 3-6 illustrate the the design overlaid on a nautical chart and satellite image.
3.3
Sea Barrier Concept Design Three
Sea Barrier Three is located near the mouth of the Elizabeth River in the vicinity of Willoughby Bay and Naval Station Norfolk. This design consists of approximately 5.5 miles of sea barrier structure, to include 2.75 miles of static seawall, 2.25 miles of auxiliary dynamic and 0.5 miles of navigable dynamic. Figures 3-7 and 3-8 illustrate the the design overlaid on a nautical chart and satellite image.
3.4
Sea Barrier Design Four
Sea Barrier Four is located near Pinner Point and parallel to the Elizabeth River Tunnel. This design consists of approximately 0.5 miles of sea barrier structure with 0.3 miles of static seawall and a 0.2 mile navigable dynamic section. Figures 3-9 and 3-10 illustrate the the design proposal overlaid on a nautical chart and satellite image.
Figure 3-9: Sea Barrier Concept Design Four Chart View
3.5
Sea Barrier Design Five
Sea Barrier Five incorporates the designs concepts of Sea Barriers Two and Four. Figure 3-11 shows the combined design proposal superimposed on a satellite image.
3.6
Sea Barrier Design Six
Sea Barrier Six incorporates the designs concepts of Sea Barriers Three and Four. Figure 3-12 shows the combined design proposal superimposed on a satellite image.
Chapter 4
Sea Barrier Performance Analysis
Following the development of the six sea barrier concepts, an overall measure of ef-fectiveness (OMOE) was conducted to analyze the performance of each design. The following OMOE performance categories were established to evaluate the design con-cepts: Project Scale, Protection Area, Perimeter Flooding, Frequency of Operation, Maritime Traffic Impact and Environmental Impact. A figure of merit (FOM), rang-ing from one to five, was assigned to each sea barrier concept for every performance category, with one being a low score and five being a high score. A description, and the associated weight factor, of each evaluation category is discussed below:
• Project Scale: The Maeslantkering and Eastern Scheldt surge barriers, both part of the Delta Works, were utilized as reference scales. Although both projects have been operational for over two decades, with Maeslantkering com-pleted in 1997 and Eastern Scheldt in 1986, these barrier systems remain bench-mark designs. Concept designs that were larger in scale than the reference projects received a lower FOM due to increased cost and complexity, while pro-posals that were on par or smaller in scale were assigned a higher FOM. Figure 4-1 depicts the navigable dynamic Maeslantkering sector gate which protects the 0.25 mile wide Port of Rotterdam channel. Figure 4-2 shows the Eastern Scheldt Surge Barrier which is a combination static seawall and auxiliary dynamic sluice gate system spanning five miles across an estuary [Watersnood Museum, 2020].
Figure 4-1: Delta Works: Maeslantkering Sector Gate [Higgins, 2012, Watersnood Museum, 2020]
Figure 4-2: Delta Works: Eastern Scheldt Surge Barrier [Watersnood Museum, 2020]
• Protection Area: Design proposals were evaluated based on the size and characteristics of the protection area situated behind the sea barrier. Protection area characteristics included the quantity of shoreline, and the number of large facilities vulnerable to coastal flooding such as DOD installations, shipyards and port terminals.
• Perimeter Flooding: As part of the feasibility analysis conducted in Chapter 2, several high water scenarios were analyzed to determine the extent of coastal flooding in the Norfolk, Virginia region. The most extreme of these scenar-ios was a 100 year storm in the year 2100 with a projected high water level of 10ft above present day MHHW. Each design concept was evaluated under this extreme condition to determine if flooding breached the desired perimeter established by the sea barrier due to flanking as a result of local topography. Examples of perimeter flooding include a storm surge advancing across low ly-ing areas from the Virginia Beach coastline, or flood waters backly-ing-up into the region from waterways leading from North Carolina such as the Dismal Swamp Canal. Design concepts that had minimal perimeter flooding received a higher FOM. Conversely, design proposals that required several additional bar-rier projects to prevent perimeter flooding were assigned a lower FOM. Shoreline infrastructure proposed in ongoing design studies such as the USACE Norfolk Study will be factored into the assigned FOM as a planned mitigation.
• Frequency of Operation: The frequency of operation of a design proposal was evaluated based on a projected five foot increase in MHHW by the year 2100 as outlined in Chapter 2. If significant flooding was indicated on the NOAA sea level rise viewer at MHHW based on present day land elevations and shoreline infrastructure, it was assumed that the proposed sea barrier would be activated to prevent the flooding. Design proposals that required high frequencies of operation to prevent flooding during daily high tides received a lower FOM. Design concepts that only required activation during elevated water levels such as a spring tide or annual storm were assigned a higher FOM.
• Maritime Traffic Impact: The locations associated with the design concepts affect varying densities of maritime traffic flow within the Chesapeake Bay and its tributaries. If a proposed sea barrier design was activated and closed due to elevated water levels, it was considered for this analysis that the Atlantic Ocean was inaccessible to inbound and outbound traffic. The inclusion of a lock system, to allow for continued traffic flow throughout a sea barrier closure period, could mitigate the traffic flow issue, but was not considered during this portion of the performance analysis. In this case, design proposals that impacted higher densities of maritime traffic received a lower FOM.
• Environmental Impact: Estuaries like the Chesapeake Bay, and the asso-ciated tidal tributaries, are dependent on the tide cycle to provide nutrient flows. Altering these environmental processes with the closure of a sea barrier, or merely the presence of the static portions of the structures, will alter water, sediment and nutrient flows throughout an estuary such as the Chesapeake Bay. For these reasons, design proposals with the largest environmental impact areas were assigned a lower FOM. In contrast, relatively small impact areas received a higher FOM.
Table 4.1 indicates the weight factor applied to each of the evaluation categories: Table 4.1: OMOE Performance Category Weight Factors
OMOE Performance Category Weight Factor
Project Scale 0.25
Protection Area 0.25
Perimeter Flooding 0.20
Frequency of Operation 0.10
Maritime Traffic Impact 0.10
Environmental Impact 0.10
The project scale, protection area and ability to prevent perimeter flooding were assigned the highest weight factors due to their direct association with the construc-tion cost, as well as the potential cost benefit of the proposal.
4.1
OMOE: Project Scale Analysis
The navigable, auxiliary and static components of each concept design were compared to the Delta Works reference projects to quantify the scale of the proposed design.
Table 4.2: Navigable Section Comparison
Design Gates Gate (mi) Stowage (mi) Total (mi) Comparison
Reference 1 0.24 0.26 0.50 -One 2 0.24/0.35 0.13/0.20 1.25 150% Two 1 0.24 0.26 0.50 0% Three 1 0.24 0.26 0.50 0% Four 1 0.10 0.10 0.20 -60% Five 2 0.24/0.10 0.13/0.10 0.70 40% Six 2 0.24/0.10 0.13/0.10 0.70 40%
Table 4.2 compares the number of gates, gate length, gate stowage area length, total length (gate lengths plus the stowage area lengths) and the percent difference of the total navigable length of the reference project and the concept designs.
Table 4.3: Auxiliary Section Comparison
Design Sections Total (mi) Comparison
Reference 3 2.00 -One 8 7.30 265% Two 3 1.50 -25% Three 3 2.25 13% Four 0 0.00 -100% Five 3 1.50 -25% Six 3 2.25 13%
Table 4.3 compares the number of auxiliary sections, total auxiliary length and the percent difference of the total auxiliary length of the reference and concept designs.
Table 4.4: Static Section Comparison
Design Sections Total (mi) Comparison
Reference 5 3.00 -One 11 10.05 235% Two 4 2.40 -20% Three 5 2.80 -7% Four 2 0.35 -88% Five 6 2.75 -8% Six 7 3.15 5%
Table 4.4 compares the number of static sections, total static length and the percent difference of the total static length of the reference and concept designs.
Table 4.5: FOM: Project Scale
Concept Total Project Scale Assigned Figure
Design Length (mi) Comparison of Merit (FOM)
Reference 5.50 - -One 18.60 238% 1.0 Two 4.40 -20% 4.5 Three 5.55 1% 3.0 Four 0.55 -90% 5.0 Five 4.95 -10% 4.0 Six 6.10 11% 2.0
Table 4.4 lists the total length of each design, the percent difference of the total length of the reference and concept designs, and the assigned FOM for each of the concept designs based on project scale. Concept Design Four received the highest FOM due to its smaller scale compared to the reference project.
4.2
OMOE: Protection Area Analysis
The design concept protection areas were analyzed and compared. Table 4.6 outlines the body of water and estimated length of tidal shoreline protected by each design [Virginia Institute of Marine Science, 2020]. Figure of merits were assigned based on the relative size of the protection area, with Design One receiving the highest FOM and Design Four receiving the lowest FOM. Figure 4-3 shows the Chesapeake Bay DOD installations with Design One protecting the largest number of facilities followed by Concepts Two and Five, Concepts Three and Six, and Concept Four respectively.
Table 4.6: FOM: Protection Area
Design Shoreline (mi) Body of Water FOM
One 11684 Chesapeake Bay & Tributaries 5.0
Two 2306 James & Elizabeth Rivers 4.0
Three 458 Elizabeth River (3 Branches) 3.0
Four 268 Elizabeth River (2 Branches) 1.0
Five 2306 James & Elizabeth Rivers 4.0
Six 458 Elizabeth River (3 Branches) 3.0
Figure 4-3: Chesapeake Bay Region DOD Installations [USGS, 2020]
