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Sensitivity Matrix

I(a) Waves and Storm Surge - Summary

Asset Categories   Waves and Storm Surge - Summary
Mode Sub-Mode Important Impact-Asset Relationships Threshold Mobile-Specific Detail Potential Indicators of Sensitivity
Bridges Bridge (Superstructure) When storm surge raises the elevation of waves to the height of the bridge superstructure, strong horizontal loadings are applied which the bridge has often not been designed to withstand, resulting heavy damage. Powerful storm waves stress both the superstructure and the substructure of the bridge, particularly when the wave crest is elevated due to storm surge and is able to directly hit the bridge superstructure. Stress may damage or destroy the connection between the bridge's superstructure and substructure, leading to the bridge span being shifted or even unseated completely. The shifting of the spans causes additional damage to other parts of the bridge, including: abutments, bent caps, and girders. [21, 50, 51] In addition to directly stressing the bridge structure, rising storm surge elevation can trap air beneath the bridge deck, increasing the stress on the bridge deck and contributing to unseating or shifting of bridge spans or damage to bridge deck. [21] While damage to the bridge can begin when the wave crest elevation is below the bridge's low-chord elevation, damage increases substantially when the storm surge elevation is near the low-chord bridge elevation. [13, 21, 22] For more information, see the AASHTO Bridge Specifications and Vessel Collision guidance. While the lateral forces of wave impacts generally cause the most direct damage to bridge decks during storms, when the storm surge elevation (water level) is at or above the low-chord elevation of the bridge, trapped air can significantly increase the stress on the bridge (at least double the wave-induced load). [21, 22] Due to multiple factors, including the existing elevations of Gulf Coast bridges, during Hurricane Katrina damage to the bridge spans in terms of shifting or unseating did not tend to occur until the surge reached elevations of approximately 10 ft. Nearly 80% of the shifted or unseated spans occurred at surge elevations of 16 feet or less. There was extensive damage to an on-ramp from a lower elevation highway (US 90/98) up to the elevated interstate. Only the lowest five simply-supported spans moved, while the spans with higher elevations were not moved. The sixth span up the ramp was the first one not damaged; it had an estimated 1.4 feet of clearance between the low-chord elevation and the surge elevation. [21, 50, 51, 59] - Low-chord elevation of bridge
- Prestressed concrete beams [72]
- Prefabricated components (such as prestressed concrete beams) [72]
- Lack of continuity (continuity can help spans of multiple span superstructure resist loadings) [72]
- Diaphragm and girder designs which trap air under the bridge during a storm (i.e. girder depth, girder shape, presence of holes in the lateral diaphragms) Douglass et al. (2008) analyzed the effect of diaphragms (structures that connect the girders under the bridge) on uplift loads of bridges. They found that diaphragms can double the uplift loads for some water levels since the structures trap air pockets under the bridge. [21]
- Location near barges, oil rigs, tug boats, and other types of items which may become dislodged during a storm
- Presence and exposure of electrical equipment needed to operate bridge (movable bridges) [72]
- Age [72]
- Assets in areas designed as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion are particularly vulnerable [68]
Bridge (Substructure) Storm surge can wash away large pieces of debris, such as oil rigs or barges, which can then crash into bridges, damaging bridge components such as the girders, piers, bent caps, and bridge parapets. The extent of the damage depends on the nature of the impact. In addition, on the side of the pier facing an incoming wave, the wave hits the pier and then is channeled down to the base of the pier, where it may gradually erode the base of the pier.

Storm surge can result in scour and erosion damage to the abutment, slope failure, and undermining of the approach, resulting in failure of the bridge's substructure. [50, 51]
AASHTO LRFD specifications require that the acceptable annual frequency of bridge collapse due to Vessel Collision is 0.001 for critical bridges and 0.001 for other bridges. Design return period for vessel collisions is 1 year. [73] See also the AASHTO Bridge Specifications and Vessel Collision guidance.

AASHTO LRFD specifications require that scour at bridge foundations be designed for the 100-year flood storm surge tide or for the overtopping flood of lesser recurrence interval. The bridge should also be designed to withstand the "super flood" or the 500-year flood. The corresponding 100-year design scour depth at bridge foundations is estimated by using a procedure in HEC-18. [73]
Operator Houses (movable bridges) and electrical parts Storm surge can flood operator houses and/or mechanical rooms, causing the failure of electrical systems and jamming gear mechanisms. [50, 51] See Threshold for Damage to Entire Bridge. While none of the bridges damaged in Alabama during Hurricane Katrina were movable bridges, damage to electrical equipment substantially increased the cost of bridge repair in many cases. [50]
Roads and Highways Paved road surface Several mechanisms damage pavements exposed to overwash, including the direct wave attack on the seaward shoulder of the road, the water flow across the road and down the landward shoulder ("weir" flow), and the flow parallel to the road as the storm surge recedes and water settles on lower spots in the road. [63]   During Hurricane Frederic, Alabama highways suffered considerable damage from scour and erosion. Cedar Point in Mobile County (State Highway 163) had a section of road about 200 feet in length washed away. [59]During most large hurricanes, much of the damage to roads occurs on coastal roads that parallel the shore. For example, during Hurricane Ivan, the high water flow often damaged the northern side of the road (side furthest from the Gulf) and was particularly apparent in roads where the road crest was elevated relative to the adjacent ground. [22] - Elevation of road relative to adjacent ground
- Road parallel to coast
- Assets in areas designated as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion loss are particularly vulnerable. [68]
Road substructure (gravel base, substructure)  
unpaved roads Storm surge may wash out unpaved roads.   While storm surge could easily destroy a unpaved road, in Mobile County, unpaved roads occur primarily inland.
Stormwater drainage (culverts, side drains, etc) See section on the relationship between heavy precipitation and stormwater drainage. See section on the relationship between heavy precipitation and stormwater drainage. See section on the relationship between heavy precipitation and stormwater drainage.
Highway, road and street signs and traffic lights During storms, utility connections and exposed cables usually fail before systems do, causing traffic gates and lights (among other electrical traffic control components) to fail. [47] See also wind impacts on highway, road, and street signs and traffic lights.   Hurricane Katrina caused failure of traffic control devices such as traffic lights across the entire Gulf Coast region, which made driving conditions hazardous and delayed recovery. [47]
Highway and road traffic and service Storm surge impedes highway and road service in multiple ways. Most directly, storm surge can flood coastal and low lying routes, including evacuation routes. Storm surge and waves can render key bridges inoperable, while accompanying precipitation and wind lessen visibility and increase the risk of traveling. [36] Some damage occurs at all levels of storm surge. Despite a diversity of transportation modes, in Alabama the majority of the transportation within the state, both in terms of freight and persons moved, utilizes only a very small portion of the total roadway network and is thus vulnerable to disruptions with relief only available from a small number of primary roadways. [36]
Railroads Electrical Equipment (gates/flashers and signal bungalows) Storm surge can cause rail sensor failure. There is also potential corrosive damages from salt. [2, 49] Any above normal conditions, depending on railbed height. [49]   - Presence of the high shear blocks (15 in.) at the end of the pier cap beams can limit damage.
- Assets in areas designated as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion loss are particularly vulnerable. [68]
Railroad Tracks, Ties, and Ballast Wave action can strip rail, ties, and ballast off of railroad bridges if they are exposed. Additionally, there may be rail damage from "line stretch". [49] Any above normal conditions, depending on railbed height. [49]  
Railroad services (i.e., operations) Storm surge can scour the railbed, derail rail cars, and damage railway bridges over streams, all of which can disrupt service. Increased risk of hazardous material spills (requiring monitoring, mitigation, and reporting) also a risk for service disruption. [47, 49] Any above normal conditions, depending on railbed height. [49] During Hurricane Katrina, storm surge impacts to railroad bridges were responsible for massive disruptions in railroad service. For example, in Pascagoula and St. Louis Bay, storm surge pushed the railroad bridge superstructures off of supporting piers, destroying the ties and tracks of the railroad bridges. Additionally, a CSX railroad bridge suffered relatively little damage, despite being low-water crossing and subjected to the same forces that destroyed the US-90 bridge slightly to its south. [47]
Airports/ Heliports Runway and navigational aids Storm surges may cause inundation of runway, resulting in damage to runway as well as flight cancellations and delays. [60] Dependent on elevation of airport, protective or preventative measures established, and proximity to coast. See "Mobile Specific Detail" column for thresholds for specific airports. Mobile Downtown Airport: Potential exposure to storm surge of 23 feet (7m).
Mobile Regional Airport: No exposure to storm surge.
Dauphin Island Airport: High potential exposure to storm surge.
St. Elmo Airport: No exposure to storm surge. [60]
- Proximity to coast and low elevation of runway
- Extent to which protective measures (e.g., dykes, retaining walls) have been developed
- Assets in areas designated as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion loss are particularly vulnerable. [68]
Aircraft No documented relationship. No documented relationship. No documented relationship.  
Airfield buildings and structures (e.g., terminal buildings, hangers, air traffic control tower) Storm surge and heavy precipitation can flood buildings, access roads, and disrupt fuel supply and storage. [37] Dependent on elevation of airport, protective or preventative measures established, and proximity to coast. See "Mobile Specific Detail" column for thresholds for specific airports. No documented relationship. - Proximity to coast and low elevation
- Extent to which protective measures (e.g., dykes, retaining walls) have been developed [6]
- Assets in areas designated as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion loss are particularly vulnerable. [68]
Services and airport/ heliport operations (e.g., flight departures and arrivals, baggage/cargo transfers, ground transportation) During a large storm event itself, airport services can be completely disrupted by high wind speeds, precipitation, flooding, electrical outages, and debris impacts. However, after the storm, limited airport services can often be opened relatively quickly in order to aid emergency relief efforts. Dependent on elevation of airport, protective or preventative measures established, and proximity to coast. See "Mobile Specific Detail" column for thresholds for specific airports. No documented relationship.  
Natural Oil and Gas Pipelines Pipelines, aboveground Waves and storm surge generally do not damage aboveground pipelines; however, damage has occurred from changes in water tables or soil stability due to sea level rise, increased risks from wave action and storm surge, particularly for submerged or low-elevation pipelines. One additional concern is the corrosion of pipes due to saltwater intrusion of groundwater. [60] No documented relationship. No documented relationship. Assets in areas designated as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion loss are particularly vulnerable. [68]
Pipelines, underground Waves and storm surge generally do not damage underground pipelines; however, damage has occurred from changes in water tables or soil stability due to sea level rise, increased risks from wave action and storm surge, particularly for submerged or low-elevation pipelines. One additional concern is the corrosion of pipes due to saltwater intrusion of groundwater. [60] Pipeline infrastructure is primarily buried three or more feet below ground; likely to be unaffected by storm surge. Sea level rise could affect water tables, soil stability. [52, 60] In the Gulf Coast, natural gas pipelines are generally below ground and do not suffer damage from storm surge. However, damage has occurred during severe Hurricanes, such as Andrew, Ivan, and Katrina. [47] Unknown.
Pipelines, offshore Currents and waves generated by storms can damage offshore pipelines directly and indirectly. Often, the majority of damage to pipelines is caused by damage experienced by the platforms and risers. Storms can also directly cause damage to offshore pipelines, for example by removing covers and spans, thereby exposing the pipeline. [71] Pipeline infrastructure is generally built to withstand the 100-year storm. [71] - During Hurricanes Katrina and Rita, the majority of the offshore pipeline damages occurred at or near platform interfaces or as a result of an indirectly related force, such as platform failure, riser damage, or anchor dragging. Other damages due to loss of cover and movement of pipelines that are near shore and in shallow water. [71]
- Hurricane Andrew mainly damaged pipelines in the range of 2" to 6" diameter and in less than 100 ft. of water. [71]
- Offshore pipeline construction activities become dangerous with wave heights around 3-4 feet and are extremely dangerous at wave heights greater than 4 feet. [60]
- Location of pipeline in ultra-shallow water
- Location of pipeline in mudflow areas [71]
- Small diameter of pipe (4 in) [71]
- Age of platform [71]
- Older pipelines located in shallower water may be at increased risk [71]
Aboveground infrastructure (e.g., compressor stations, metering stations, other buildings, structures)        
Utilities for pipelines - electricity Damage during storms, flooding can cause power loss to pumping facilities and compressor stations can cause pipeline closures. [33, 60] Pipeline closures during Hurricane Katrina and Rita were due mainly to loss of power rather than physical damage to pipelines. [33, 60]    
Electric Power Systems Electric Power Systems Wind, storm surge, and waves damage essentially every component of electric power systems (transmission lines, towers, insulators, generating plants) through direct flooding impacts, damage from debris, and other effects such as salt spray contamination. Saltwater rapidly corrodes all electrical components. [33, 47] Unknown. During Hurricane Katrina, over one million distribution poles had to be replaced. [33] - High density coastal communities with aboveground power lines [75]
Marine Ports, Terminals, and Waterways Electrical Equipment Storm surge can flood and severely damage or destroy exposed electrical equipment. [2] If the storm surge overtops the elevation of the port, damage is likely to occur due to a combination of flooding and wave action. During Hurricane Katrina, most of the damage at the Port of Mobile was associated with submergence of electric motors on container cranes and coal dock loaders. [47]  
Terminal Buildings Storm surge and direct wave action can damage marine port buildings. [44]
If the storm surge overtops the elevation of the port, damage is likely to occur due to a combination of flooding and wave action. Major port facilities generally have economic design lives on the order of 50-80 years. Damages to the Port of Mobile:
- Hurricane Frederic: Over $11 million [59]
- Hurricane Ivan: $2.6 million (wind as primary cause of damage)
- Hurricane Katrina: $29 million (flooding as primary cause of damage) [31]
- Roll-up door openings [17]
Channels Storm surge can wash debris and sediment into the shipping channels, necessitating dredging following the storm. [48]   After Hurricane Katrina, Port of Mobile officials estimated that dredging expenses, including the removal of branches, sand, and silt from pier areas, would be more than $7.5 million. [31] Areas designated as Velocity (V) zones by the National Flood Insurance Program that experience significant flood-related and long-term erosion loss are particularly vulnerable. [68]
Piers, wharves, and berths - Strong waves can batter piers and scour pier supports.
- Storm surge can wash away fender system timbers, leaving berths inoperable.
- Storm surge can wash away asphalt paving. [48]
Harbor waves of under 3 feet (not including storm surge) are generally considered to result in little or no damage. [32] Hurricane Frederic damaged 6 piers and fender systems in the Port of Mobile. [59] - Floating piers versus fixed piers
- Freeboard elevation [32]
Port services (i.e., operations) Storms cause damage to marine port services by disrupting the power and communications networks, displacing port workers, washing away channel buoys, and submerging debris in ship channels. [17, 30] Since wind speed is correlated with wave height, see "Wind" matrix for more information on thresholds. During Hurricane Katrina, loose boats and other floating debris damaged piers and disrupted port services. Following the 2005 hurricane season, the Port of Mobile convened a task force to reorganize disaster planning to an all-hazards approach with improved communications between agencies involved. [31, 59] - Lack of a back-up communications plan to reach employees when phone lines, including cellular phones, are down
- Lack of a back-up power supply
Updated: 03/27/2014
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