Beginning with coastal fortifications for national defense in the late 1700s, coastal engineers inside and outside the US Army Corps of Engineers (USACE) collected measurements of mean sea level, tides, surge, and other coastal water levels. In the 1960s, concerns about the effects of changing sea levels on coastal erosion spurred USACE to undertake the 1971 National Shoreline Study, which raised awareness inside the USACE about the potential threats changing sea level posed to missions and operations. A National Research Council (NRC) committee report in 1987 addressed the engineering implications of global sea level rise, concluding that “the most appropriate present engineering strategy is not to adopt one particular sea level rise scenario, but instead to be aware of the probability of increasing sea level and to keep all response options open” (NRC 1987, p. 4). This concept has formed the basis of USACE policy and technical guidance, beginning with a 1986 USACE guidance letter requiring consideration of sea level change (SLC) in the planning and design of coastal flood control and erosion protection projects.
Subsequent planning guidance in 1989 required that project plans be formulated based on the observed local relative rate of change (historic rate) and consider the consequences to the project of the full range of NRC scenarios. An update in 2000 (Appendix E, Section IV, paragraph E-24.k) of ER 1105-2-100 addressed sensitivity to the historic and NRC high rate scenario (equivalent to 1.5 m at 2100). More detailed planning and engineering policy in 2009 and 2011 was followed by the release of the current guidance, USACE 2013 that requires consideration of three scenarios. USACE coastal practitioners, however, also are allowed to consider a higher rate of sea-level change (for example, global rise of 2.0 m at 2100 global scenario) if justified by project conditions (USACE 2013). In addition, the flexibility to use even higher scenarios, when justified, can account for changes in statistically significant trends and new knowledge about SLC. In 2014, USACE published technical guidance for adaptation to SLC, including examples of how to incorporate the effects of sea-level change on coastal processes, project performance, and project response within a tiered, risk-based planning framework in Engineer Technical Letter (ETL) 1100-2-1. This ETL was updated in 2019 to a permanent continuing guidance in the form of Engineer Pamphlet 1100-2-1. All planning and engineering studies must follow this policy and technical guidance to incorporate, and adapt to, changing sea levels.
Moreover, web-based tools have been developed to automate the computation of SLC scenarios and provide consistency with repeatable analytical results. Two tools are described briefly below:
Sea Level Tracker
Sea level change and its impacts along vulnerable shorelines have generated more concern over the last couple of decades. The question is often asked, “What rate of change is currently being observed?” The Sea Level Tracker was developed to allow the user to compare observed sea level and trends for specific NOAA NWLON tide gauges with the USACE sea level change scenarios as described in ER 1100-2-8162, “Incorporating Sea Level Change in Civil Works Programs”, 31-Dec-2013. In addition, the Sea Level Tracker includes several alternative projections from national sources (e.g., NOAA) and local sources (e.g., NYC Part 490). For the observed data, a variety of monthly means can be visualized: highest, mean higher high water (MHHW), MSL, mean low water (MLW), mean lower low water (MLLW), and lowest . Historical data is represented by either 19-year or 5-year midpoint moving averages. Users can also visualize linear trends and extreme water levels. The visualizations from the tool can be combined into a downloadable report to support application of insights to USACE projects.
Sea-Level Change Curve Calculator
The sea-level calculator provides a way to visualize the USACE and other authoritative sea level rise scenarios for any tide gauge that is part of the NOAA National Water Level Observation Network (NWLON). Scenarios include those of the The West Coast National Research Council 2012 study, the New York State Department of Environmental Conservation 6 NYCRR Part 490 projections for New York City and Long Island (available when the NOAA gauge, "The Battery" or "Montauk Point" is selected), the New York City Panel on Climate Change 2013 and 2015 projections for The Battery (8518750), the Maryland Climate Change Commission 2013 Projections (available when selecting a gauge in Maryland), the CARSWG scenarios for developed for the 2016 CARSWG report, and the 2017 US Global Change Research Program scenarios. The User Manual includes a discussion of the technical concepts incorporated into the Sea Level Curve Calculator, and step-by-step instructions for using the on-line tool. The site also links to the superseded version of the tool and user manual.
Note that the key functionality of this tool has been integrated into the Sea Level Tracker. Accordingly, the Sea Level Change Curve Calculator will be deprecated at the end of the 2023 calendar year.
There is also a separate calculator for use in the high-subsidence environment of coastal Louisiana, based on long-term non-NOAA tide gauges. This tool will remain active, as the Sea Level Tracker does not include non-NOAA tide gauges.
The Atlas of Observed Sea Level Change (low-res file) / (high-res file) allows nontechnical users to easily view the results of the Sea Level Tracker through visualizations of results that are presented alphabetically by state.