An interview with Lesley Ewing, P.E., M.ASCE
Waterways: The earth has gone through various periods of sea level rise and decline. What is unique about current trends in sea level rise?
Lesley Ewing: It’s true that global sea level has been mostly rising since the end of the last ice age about 18,000 years ago. The rate of rise has varied and for short periods of time, such as the Little Ice Age, sea level has even dropped. What is of concern now is the acceleration in sea level rise that started around 1850 with the dawn of the industrial revolution and its steadily increasing emission of greenhouse gasses. The Intergovernmental Panel on Climate Change (IPCC) documents in its Fourth Assessment Report (2007) that the rate of sea level rise for the 3000 years before the industrial revolution averaged only between 0.1 and 0.2 mm/yr, while the rate has increased to 1.8 ± 0.5 mm/yr when averaged over the more recent period from 1961 to 2003.
WW: Can you tell us more about future trends in sea level?
L.E.: Over the past century, global temperature has increased about 0.6oC and mean sea level has risen by 15 to 18 cm globally. State-of-the-art climate models predict that global temperature may rise by 1 to 5oC over the next 100 years. There is a large uncertainty in these estimates and even greater uncertainty about the sea level response; however, there is strong certainty that a future rise in global temperature will be accompanied by a rise in sea level. Future changes in global sea level will depend, among other factors, upon: future global temperature; lag between atmospheric changes and oceanic reactions; thermal expansion of water; and, effects of atmospheric temperature on changes in Antarctica, Greenland and other glaciers. The IPCC projects that mean sea levels will rise by between 0.2 and 0.6 meters during this century.
WW: What are the consequences of sea-level rise?
L.E.: The most obvious consequence of a large rise in sea level will be changes in areas that are submerged. Lands that now are only wet at high tide could be wet most of the day. Structures that are built above the water, like docks and piers, will be closer to the water, or eventually submerged. A second consequence will be an increase in wave energy since wave energy is a function of the square of wave height and wave height is strongly influenced by water depth.
WW: How should we respond to sea level rises?
L.E.: The responses to a rise in sea level will vary. It is likely that rises will necessitate both hard-engineering and soft-engineering solutions. Hard-engineering solutions such as seawalls, revetments, breakwaters and levees would likely be applied to individual properties. Soft-engineering solutions such as beach nourishment, vegetated buffers, accommodation and adaptation strategies and retreat are likely to be used on larger, multi-lot scale.
WW: How, specifically, are states addressing sea-level rise?
L.E.: Few states have passed special regulations to address sea level rise. Instead, most states have coastal programs that address sea level rise as an ongoing coastal condition and they modify or adapt current regulatory mechanisms to cover the effects of sea level rise. Texas has a rolling easement program that relocates the public land boundary to the current line of vegetation. States like South and North Carolina and Massachusetts have prohibited the construction of any hard shoreline armoring. This limits the responses that can be used to address sea level rise to soft engineering, accommodation and retreat. Maine has regulations that prohibit rebuilding structures that have been damaged by storms if the new structure could reasonably be expected to be damaged within the next 100 years. This regulation covers damage from sea level rise or other hazards.
WW: What role do you see for coastal engineers and planners in addressing sea-level rise?
L.E.: Sustainability and integrated coastal management are part of a new trend in coastal management that offer opportunities to address many future coastal concerns, especially sea-level rise. Engineering and planning solutions that are based upon any fixed water level will have great difficulty maintaining effectiveness during a period of rising sea level. The principles of sustainability and reliance upon multiple adaptive responses to the array of changing coastal conditions can provide many useful approaches for dealing with future changes in sea level. Coastal engineers and planners will increasingly need to do their work within, and be leaders of, such integrated, sustainable and holistic efforts.
Lesley Ewing, P.E., M.ASCE, serves as the ASCE representative on the COPRI Board of Governors. She is an engineer for the California Coastal Commission and is enrolled in a graduate program at the University of Southern California. Her research of sea level rise was recently contributed to the World Scientific Handbook on Coastal and Ocean Engineering. The handbook, edited by Dr. Young C. Kim, P.E., PhD, M.ASCE, is currently under review.
