ADVANCING COASTAL ENGINEERING IN US HIGHWAYS

ROADS AND BEACHES Two of America’s great emotional love affairs are with roads and with beaches. Coastal highways are part of the fabric of society from California’s Route 1 to Florida’s A1A. It is estimated that there are roughly 60,000 miles of roadways in the 100-year coastal storm surge floodplain and over 1,000 bridges exposed to storm surge conditions with the present-day sea levels. This paper and presentation will summarize Federal Highway Administration (FHWA) efforts related to the issues this exposure presents. A primary goal is improved integration of coastal engineering principles and practices in the planning and design of coastal highways.


ROADS AND BEACHES
Two of America's great emotional love affairs are with roads and with beaches.Coastal highways are part of the fabric of society from California's Route 1 to Florida's A1A.It is estimated that there are roughly 60,000 miles of roadways in the 100-year coastal storm surge floodplain and over 1,000 bridges exposed to storm surge conditions with the present-day sea levels.This paper and presentation will summarize Federal Highway Administration (FHWA) efforts related to the issues this exposure presents.A primary goal is improved integration of coastal engineering principles and practices in the planning and design of coastal highways.Recent, related research on how to adapt to rising sea levels includes the interesting finding that one major US bridge may have already been destroyed by the increase in wave-induced loads due to the sea level rise which occurred during the life of the structure (FHWA 2016a).Sea level rise occurring between the time of the original design of the I-10 bridge near Pensacola Florida and the day that it was severely damaged during Hurricane Ivan, increased the wave-induced loads by roughly 70 kips; enough to lead to the catastrophic failure.In other words, if sea levels had not risen for the four decades prior to that storm, the bridge may have survived.Another finding is that most of the countermeasures suggested to increase bridge resilience to storm damage may not provide much actual benefit.Strengthening the connections between the decks and the substructure, which typically fail, will just lead to another failure mechanism slightly later in major storms -negative bending of the girders and decks due to the extreme, wave-induced uplift loads.
In many cases, coastal engineering works to protect roads and makes good economic sense with today's sea level.The economic argument is even stronger when considering sea level rise projections (FHWA 2016b).
It is clear that "adaptations" for climate resilience will be similar to engineering required for improving infrastructure resilience to extreme events with today's sea levels, i.e. existing, proven coastal engineering approaches including nature-based solutions (FHWA 2016c).
FHWA is developing other technical assistance for transportation agencies in related coastal engineering areas.For the FHWA, authors developed a "primer" on coastal modeling as an introduction to coastal hydrodynamic modeling for transportation engineering professionals (Webb 2017).Also, some of the authors produced a "white paper" describing the current state of practice regarding the use of natural and nature-based features to protect coastal roads (Webb, et al 2018).Finally, FHWA is conducting two separate series of "peer exchanges" to investigate and draw upon the knowledge of coastal transportation practitioners in the areas of natured-based infrastructure approaches and coastal nuisance flooding.
UNIQUE COASTAL ENGINEERING TOOLS Particular coastal engineering approaches/tools and findings that have been developed through the efforts described above include guidance and findings on: As mentioned above, FHWA has engaged the authors to revise HEC-25 to combine the two existing volumes (see Figure 1) into a single third edition.The revision will update all of the current material and also include significant expansions/additions in several areas:  , 2008).This traveling course has been taught at locations from Hawaii to New England to hundreds of state and federal transportation agency staff and their consultants over the past decade.As an adult education, continuing education course, the focus is on active, "hands-on," learning and includes the use of a portable wave flume (see Figure 2) for participant exercises on wave mechanics, rock revetment design and to investigate and understand how waves on storm surge can impact bridge decks.

Figure 1 .
Figure 1.HEC-25: Highways in the Coastal Environment is FHWA's technical guidance manual for coastal highways and bridges.This manual presently is being revised to combine and update the two existing volumes into a single 3 rd edition.

Figure 2 .
Figure 2. A portable wave flume being used by participants during a 3-day professional training course.