Sea-Level Change

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. These tools are described briefly below:

Sea Level Analysis Tool

The Sea Level Analysis Tool (SLAT) is a user-friendly web application that enables users to visualize observed sea level data, compare observations to projected sea level change, and estimate when tidal and extreme water levels will intersect with elevation thresholds related to local infrastructure (e.g., roads, power generating facilities, dunes).  SLAT facilitates the application of United States Army Corps of Engineers (USACE) Engineer Regulation 1100-2-8162 and Engineering Pamphlet 1100-2-1, which provide guidance for incorporating sea level change into USACE projects.

SLAT allows users to:

  • Visualize observed water levels from over 140 NOAA tide gauges
  • Calculate trends and moving averages for observed water levels
  • Generate sea level change projections for tidal stations or gridded points using a variety of authoritative sources, including the scenarios from ER 1100-2-8162 and the 2022 NOAA Interagency Sea Level Rise Technical Report
  • Estimate when various water levels may cross elevation thresholds relevant to local infrastructure (e.g., critical access roads, dunes, sea walls)
  • Export visualizations and data from the tool as downloadable files

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 Analysis Tool does not yet 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.