1. The document discusses the need to update the US Coast Guard's bridge permitting guidelines to account for projected sea level rise of 2 feet by 2050 and 6.6 feet by 2100 in order to ensure the safe passage of vessels and sustain the lifespan of bridges. 2. Currently, the guidelines only recommend considering potential sea level rise as a side factor, but with nearly 2,300 miles of tidal shoreline in Florida, failing to incorporate projected increases could severely limit navigation in vulnerable waterways and cost billions in economic impacts. 3. Updating permitting to proactively require higher bridges based on sea level rise projections would reduce reactive alteration costs and prevent bridges from becoming obstacles much sooner than anticipated under current standards.

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Bridging the Gap: Sea Level Rise and Navigable Waterways
A white paper prepared for the United States Coast Guard.
Arthur R. Marshall Foundation for the Everglades
Mary Crider, Paul Boynton, Janna Ellis Kepley, Jessica Huffman,
Cheng-Tung Liu, Morgan Mooney, Nigel Woodfork.
1028 N. Federal Highway Lake Worth, FL 33460.
Phone: 561-233-9004 SIP@artmarshall.org
July 31, 2014
Issue:
With predicted sea level rise (SLR), the permitting guidelines for bridge dimensions will
have to be updated to accommodate the changing environment and allow the safe transit of
maritime vessels. Global SLR is projected to be approximately 2 feet by 2050 and 6.6 feet by
2100 (Parris, 2012). The low elevation and porous geology of Florida make it particularly
susceptible to the effects of SLR (Williams et al., 1999). Bridges that are built to existing
permitting standards that do not take into account SLR will obstruct vessels that were previously
able to navigate under them, severely limiting the capacity potential of affected waterways.
Larger cargo shipping vessels and passenger cruisers currently need to retract
smokestacks and remove antenna before fitting under bridges already significantly affected by
sea level rise (California Coastal Commission, 2013). Reactive alteration costs to structures
affected by SLR could be orders of magnitude greater than proactive alterations and could
shorten the overall lifespan of the bridge.
The United States Coast Guard Bridge Permit Program needs to be updated to reflect
rising sea levels in order to reduce future costs, sustain the lifespan of bridges that are to be built
or raised, and ensure continued safe navigation for vessels under bridges over navigable water.
Rule:
Currently the USCG Bridge Administration Manual (USCGBA, 2004) mentions sea level
rise only once as a potential factor that could affect the lifespan of bridge structures. The manual
recommends that sea level, among other factors, should be taken into consideration when
determining the vertical clearance requirement of proposed bridges to prevent them from
becoming obstacles and accommodate existing and prospective navigation. The 1972 Waterways
Safety Act mandates the establishment of bridge clearances with the USCG and these clearances
are such that the horizontal and vertical spacing available for navigation beneath bridges should
be sufficient to permit the safe transit of a vessel expected to use the waterway under normal
conditions (U.S. Army Corps of Engineers, 2006).
The vertical clearance under bridges should be the vertical height between the mean
water level during normal ship transits and the lowest part of the bridge. In tidal waterways, the
water level specified is the mean higher high spring tide elevation, also known as Mean Higher
High Water (MHHW) (U.S. Army Corps of Engineers, 2006).
Analysis:
As sea level rises, the established horizontal and vertical clearances of existing fixed
bridges will need to be updated. The unique geology and hydrologic regime of Florida make it
particularly susceptible to SLR. Projected SLR is an especially important issue to Florida since

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the state has nearly 2,276 miles of tidal shoreline, 2,100 miles of canals, and more than 19
million residents (U.S. Census, 2014; Englander, 2012). Three-fourths of the residents in
Florida’s coastal counties generate 79% of the state’s total annual economy (Florida Oceans and
Coastal Council, 2010). In 2012 Florida’s maritime shipping conducted $67 billion in trade, $28
billion in exports alone. This maritime shipping accounts for 9% of the U.S. total gross domestic
product (GDP) (Lambert, 2013). If bridge heights are not adequate for increasing sea level,
shipping and passenger vessels requiring higher clearances will have to consider leaving the
waterway and re-entering at non-optimal waterway or ports to reach their destination. Detours of
this manner represent potential for major economic detriment if the areas are forced to close to
larger commercial shipping vessels, passenger traffic, and military ships. The Tampa Port
Authority lists the height of the Skyway bridge as one of the port’s biggest weaknesses and a
limiting factor for future cruise ship operations (Norbridge, Inc, 2008).
Global SLR is projected at approximately 2 feet by 2050 and 6.6 feet by 2100 (Parris,
2012). Failing to address projected sea level rise on current waterway infrastructure will hinder
future navigation of vulnerable waterways. It is necessary that bridge specifications and
permitting requirements be altered to account for the more realistic scenario of 2 ft. by 2050 and
6.6 ft. rise in sea level by 2100.
As sea level in the waterways rises, the vertical clearance of the bridges will be reduced,
leading to increased risk of vessel protrusions (e.g. masts and radio antenna) colliding with
bridges. The vertical clearance requirement is a critical issue during project development and the
bridge permitting process in order to prevent bridges from becoming obstacles. The USCG
Bridge Administration Manual (2004) only recommends permit applicants conduct waterway
surveys to help determine vertical clearance requirements for prospective vessels that will use
the waterways in order to establish future vertical clearances. This recommendation lists
potential, rather than projected (p. 2-12) SLR as a side factor to consider.
The channel depth of waterways are expected to increase as sea levels rise (depending on
the configuration of each waterway) allowing larger vessels with deeper drafts to navigate them.
Waterways currently able to get advanced approval for permitting of bridges, defined by the
Bridge Administration Manual as “those waterways that are not actually navigated other than by
log rafts, rowboats, canoes, and small motorboats pursuant to 33 CFR 115.70” (USCGBA, 2004,
p. 4-9) must take this into consideration. In addition to sea level rise, ship sizes themselves are
continuing to increase, which amplifies the need for higher bridges (U.S. Army, Corps of
Engineers, 2006).
Conclusion:
Every effort should be made to reasonably accommodate current and future waterway
navigation by updating the permitting requirements to account for projected SLR. The USCG
bridge manual currently sets consideration of SLR on the permit applicant whereas it must be an
explicit requirement when determining vertical clearance. Specific language needs to be added
regarding vertical clearance requirements for fixed bridges to incorporate projected sea level rise
during the lifespan of a proposed bridge. Waiting to increase bridge permitting heights only
when the structure becomes an obstacle results in the need for short term reactive alterations that
are both costly and inefficient. Proactively updating permitting requirements of bridges sustains
the lifespan of the structure and reduces the overall cost of upkeep.

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Acknowledgements
This white paper was developed with support from the United States Coast Guard’s Seventh
District. Special thanks to Chief Paul Lehman, and Mr. Glenn Stratton, for providing us with
access to the USCG clearance guides and the USCG bridge Access database. This paper was
edited by staff of the Arthur R. Marshall Foundation for the Everglades, and particular thanks go
to Tara Bardi, lead scientist, and Rebecca Robin, for their insight and technical knowledge.
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