Orange County Branch Newsletter
Sea-Level Rise in Orange County: Designing for Resilience
by Nathan Chase, PE, ENV SP, LEED AP ND, Project Engineer at URS Corporation
Along its 42-mile coastline, Orange County boasts some of the nation’s most visited and economically important beach communities and a full suite of infrastructure to support them. However, the 128,849 residents living below an elevation of 10 feet face the threat of coastal flooding due to the sea-level rise and increased severity of storm events brought on by climate change (see map below).
Inundation map showing areas in Orange County lower than 10 feet above average local high tide (Source: http://sealevel.climatecentral.org; affected population based on 2010 Census).
The latest sea-level rise projections from the National Research Council (2012) indicate that, from a year 2000 baseline, by 2100 mean sea level will have risen 1.4 to 5.5 feet (0.42 to 1.67 meters) for the Orange County Coast (NRC 2012). Coupled with a 100-year coastal flood, a 4.6-foot (1.4-meter) sea-level rise in Orange County would make major infrastructure vulnerable to flooding damage, including 540 miles of roadways, power plants with a combined output of 922 MW (including the AES Huntington Beach plant), OCSD’s 168 MGD wastewater treatment plant No. 2, and $17 billion dollars value of buildings and their contents (Pacific Institute 2009). Impacts to natural resources will also be dramatic, including loss of beaches, wetlands, and habitat for commercial fish species.
For engineers designing projects within the influence area of sea-level rise, the following guidance is available increase resilience to the storms ahead:
- California Coastal Commission Draft Sea-Level Rise Policy Guidance (2013), which provides a step-by-step process for incorporating sea-level rise and adaptation planning into Local Coastal Programs.
- U.S. Army Corps of Engineers (USACE) Regulation ER 1100-2-8162, Incorporating Sea Level Change in Civil Works Programs (2013), which provides an online sea-level change calculator to determine local sea-level rise under three scenarios (low, intermediate, and high rate of local mean sea-level change). This Regulation also provides guidance
- EnvisionTM includes credits under the Climate and Risk category (e.g., CR2.3 Prepare for Long-Term Adaptability) that can help project proponents and engineers design more resilient and adaptive infrastructure.
Output from the USACE online sea-level change calculator for the Los Angeles NOAA gauge station (Source: http://www.corpsclimate.us/ccaceslcurves.cfm).
In some locations the effects of sea-level rise on storm heights may be more pronounced than what would result from simply adding the incremental projected sea-level rise value to a given design water level. For example, by examining historical NOAA gauge records for Los Angeles, researchers have observed a correlation between increasing water depths and increased variability in tidal ranges. This is thought to be due to a compounding effect of deeper water on high tide levels.
To organize the available state-of-the-science information into a format that is readily usable for engineers and designers, ASCE Coasts, Oceans, Ports and Rivers Institute (COPRI) has created a Sea-Level Change committee that is developing a best practice manual on sea-level change considerations for marine/coastal projects. The forthcoming manual will include recommendations on providing context to project stakeholders, determining local sea-level change and other factors (e.g., land subsidence, local wave climate, tidal fluctuations), and implementing adaptive measures suited to the criticality of the structure in question and its risks of failure. 
While climate science is a continually advancing field, there is a clear consensus around the direction of sea-level change and increase in coastal flooding risks over the course of this century and beyond. The resources highlighted here are a good starting point for use by engineers to improve outcomes for projects in the coastal zone that are being designed or retrofitted to last 25, 50, or 100 years—well into the timeframe when the magnitude of likely sea-level change will have significant impacts in Orange County and around the world.