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El Niño and Coastal Protection

The recent Ocean Health Index study of the U.S. West Coast revealed relatively low scores for Coastal Protection provided by natural habitats. The scores reflect loss of dunes, salt marshes, and sea grasses along the entire coast, especially in California. National Oceanic Atmospheric Administration’s (NOAA) recent prediction that 2014 will be the start of an El Niño event with the potential of high sea-levels, kelvin waves, and storms with heavy precipitation causes us to both worry and feel the loss of these protective habitats more keenly.

El Niño and Rising Sea-levels

Wind-driven waves and extremely high sea-levels in the winter of 1997- 1998 left hundreds of millions of dollars in storm and flood damage in the San Francisco Bay area. Later the U.S. Geological Survey (USGS) confirmed that the abnormally high sea-levels were a direct result of that year’s El Niño. The study reported that “the Pacific Ocean surged over parking lots and the coastal highway at San Francisco’s Ocean Beach, and whitecaps up to 6 feet high splashed over the city’s waterfront Embarcadero for the first time in recent memory. …the Golden Gate Bridge was flooded by as much as 5 feet of water… and other low-lying areas around the bay were also swamped, forcing hundreds of people to flee their homes.” (USGS, 1999)  

Copyright: Vince Streano/CORBIS Rights Managed.

Recent reports from NOAA indicate that we will probably have an El Niño event in 2014 (NOAA, 2014). ‘ El Niño ‘ describes an episodic warming of the equatorial Pacific Ocean that occurs irregularly every 3 to 7 years and leads to significant changes in global weather patterns. The name, which means ‘the child’, was coined by fishermen in Peru, because El Niño events typically began there around Christmas time.

In the U.S. West Coast, it is very common that El Niño events cause a southerly shift in the jet stream and result in more precipitation, a series of waves from a more southerly or westerly direction, active winter storms and a sea-level rise of 15-30 cm (6-12 inches) (Commission, 2006; National Research Council, 2012; Bernard, et al., 2011). A very strong El Niño with these characteristics was a large part of the storms and flooding that caused so much damage in the San Francisco area in 1998.

The El Niño predicted to begin in 2014 may or may not cause this kind of damage. However, the impact of global warming has made the storms and sea level rise of El Niño more worrisome. 

California’s sea-level rose approximately 18 cm (7 inches) in the past century (Commission, 2006; National Research Council, 2012). For the last two decades there has been a slight decline in rate of sea-level rise along this coast, but it is considered a temporary variation within a long-term pattern of gradual sea-level elevation (National Research Council, 2012). The sea-level record from Fort Point, San Francisco provides a clear record of steady sea level rise and the spikes caused by El Niño events:

Source: US Geological Survey, 1999. USGS Library Call Number: (200) F327 no. 99-175.

When these data were reviewed by US Geological Survey scientists they cited four key factors causing sea-level changes at Fort Point:  daily tides, annual sea-level cycles, a long-term trend of slowly rising sea-level (red line on the chart) largely caused by thermal warming and melting of glaciers and ice caps world wide, and the occurrence of atmospheric events like Los Niños and Las Niñas. The largest rise in tides occurs along the West Coast in the winter and summer (National Research Council, 2012).

The elevated sea-levels enhanced by El Niño events are caused by solar heating of the surface waters of the western Pacific Ocean. Warm water expands. Continued heating produces an extensive ‘hill’ of warm water up to a meter higher than normal sea level. At a certain point oceanographic forces can no longer sustain the ‘hill’ and it breaks as a very long, low ‘Kelvin’ wave of warm water that moves eastward along the equator. It is estimated that these waves are about 6,000 miles long, measure about 10 inches high and travel at about 5 miles an hour. When a Kelvin wave hits South America, part of it is driven south and part of it north along the coast, causing sea-level to rise. These waves also cause local water temperature to increase, expand thermally and add to the sea-level rise (USGS, 1999).

Winter storms in California tend to mean high rainfall, low atmospheric pressure and strong winds. The low pressure allows the ocean water to expand even more. Strong storm winds from the south combine with the Coriolis effect to push water toward the coast, raising sea-levels even further (USGS, 1999). Winter storms also overlap with the period of some of the highest annual tides so sea-level elevation can be significant.

What’s problematic is that all of these factors for sea level rise are additive, meaning that we could see record-breaking water levels during a strong El Niño event. Short-term rises in sea-level caused by El Niño events and seasonal high tides are critical to coastal planners. Storm surges and wind-driven waves cause most of the erosion and flooding damage along the coasts of California, Washington, and Oregon (National Research Council, 2012; Armstrong et. al., 1989; Domurat, et. al., 1989, Allen and Komar 2006).

The impact of El Niño in elevating sea-level occurs along the entire West Coast during winter months and is especially significant along the California coast (National Research Council 2012; Seager et al., 2010). The National Academy report on sea level rise in California, Washington and Oregon finds: ‘Historically, most coastal damage has occurred when storm surges and large waves coincided with high astronomical tides and El Niños—a combination that can raise short-term sea level above sea levels projected for 2100.’

It is hard to estimate how high sea-level will rise during this century because different models produce different results. The 2001 Intergovernmental Panel on Climate Change (IPCC) report produced a range of sea-level change predictions ranging from 70 cm (~28 inches) to almost 180 cm (~71 inches). IPCC 2007 used new methods that resulted in lower estimates. The 2012 National Academy report on sea level rise reviewed various methodologies and developed a new estimate for the year 2100 for 48 cm (~19 inches) to 140 cm (~55 inches) (National Research Council, 2005).


Source: Revell et. al., 2011.

What's at Risk?

A study from the California Department of Energy attempted to evaluate the risk if sea-levels rise to 140 cm (~55 inches) and estimate the impact of a 100-year flood occurring. The study area spans 1,100 miles covering the entire California coastline and the perimeter of the San Francisco Bay and evaluates only coastal flooding and coastal erosion.

The results are enough to make us all gulp. In California, if sea-levels rose 140 cm, 480,000 people would be at risk of disruption due to evacuations, displacement from homes that have been destroyed or damaged with the possibility of injury or loss of life from flooding in a 100-year storm.

$100 billion of property (in 2000 dollars) would be at risk from flooding. It is estimated that accelerated erosion would result in a loss of 41 square miles of California’s coast. In addition key infrastructure like roads, hospitals, wastewater treatment plants, power plants, airports and wetlands are vulnerable. Twenty-eight wastewater treatment plants; both the San Francisco and Oakland Airports; 3500 miles of roadways; Thirty coastal power plants; and major ports at Oakland, Los Angeles, and Long Beach are at risk of flooding in a 100-year storm (24).

The study also estimates the threat to coastal wetlands. The value of the ecological services of the 550 square miles of coastal wetlands in California was estimated to be worth from $1.8 billion to $70 billion. Almost every county on the California coast has large wetland areas with the majority of them in the San Francisco Bay and the Sacramento-San Joaquin Delta. Wetlands provide services such as flood protection, water purification, wildlife habitat, recreational opportunities and carbon sequestration (24). 

With rising sea level it will be necessary to provide approximately 150 square miles of designated accommodation space located near the existing wetlands. This is land where the wetlands vegetation can migrate to survive a sea-level rise of 140 cm. Of that space only 55% is viable for wetland habitat. 15% more is viable for wetlands but would cause some loss of value including parks, orchards and agricultural land. The remaining 30% of the space is unsuitable for wetland migration. This would require protecting this land for the gradual migration of these wetlands (24).

We use California only as an example of the potential risk of sea-level rise and storms to the coastline.  Washington and Oregon impacts will differ but the rising sea levels and increasing wave heights will cause more coastal erosion and shoreline retreat along every section of the West Coast of the USA. Using projections based on historical data only, it is estimated that cliff erosion will be 10-30 meters of retreat along the West Coast by 2100 (Bernard, 2011).

Ocean Health Index Scores for Coastal Protection

Dunes, salt marshes, and sea grasses can play an important role in reducing flood and erosion damage caused by sea level rise and winter storms. During the past 100 years there has been significant loss of these habitats, leaving many coastlines more vulnerable. 

The Ocean Health Index recently published a report on the US West Coast. The study included an assessment of the coastal protection provided by certain natural habitats. Coastal Protection scores for the states of Washington, Oregon, and California averaged 58 out of 100, significantly lower than the score of 80 for the entire USA Exclusive Economic Zone (EEZ) as reported in the global Ocean Health Index (Halpern, et al., 2012). While the two studies are not truly comparable because they used different databases and reference points, the difference in the scores point towards potential problems or lost opportunities for the West coast. When examining the 5 regions on the West Coast we see that only Oregon scores above 60 out of 100.

These scores are calculated partially based on current status measuring the extent and/or condition of 3 habitats – sand dunes, salt marshes, and sea grasses. The criteria for a score of 100 is based on the following targets:

-Sand Dunes 100% of habitat extent in 1960.

-Salt Marshes 50% of habitat extent in 1850s.

-Sea Grasses Zero pressure to coastal waters from nutrient input (Halpern et al., 2012).

The protective habitat ranking of each habitat is factored in as well.  The protective habitat ranking comes from the Natural Capital Project (Tallis, H. T. et. al, 2011), which ranks the coastal protective ability of salt marshes as 3, sand dunes as 2 and sea grasses as 1.  Finally the 5-year trend for each habitat and selected pressures and resilience factors were part of the calculation (Halpern et al., 2012).

Dunes, salt marshes and sea grasses were selected because they provide the most significant and measurable biological coastal protection. The study does not evaluate protection provided by human-made or geological features. 

Natural Protection

Coastal erosion from wave energy is a significant issue on the West Coast. Wave energy is determined by wave height, sea level and the profile and width of the beach (National Research Council, 2012). Salt marshes significantly dissipate wave energy that contributes to erosion, transport of sediment, and flooding (Möller et al., 1999). Salt marshes are particularly effective with low long wave energy. Salt marshes and eelgrass can both be very effective at reducing currents, turbulence and drag.  When velocity profiles up to 1.5 m above the sea floor over a spring-neap tidal cycle were measured, it was found that eelgrass slowed currents by 40-70 percent. (National Research Council, 2012; Lacy, J.R. and S. Wyllie-Echeverria, 2011).

 The coastal damage anticipated from the rise of sea-level and increased storminess may be lessened in some areas by coastal mudflats and marshes. These habitats buffer inland areas to various degrees from flooding and wave damage. (Bernard, David et al., 2011.)

Dunes provide coastal defense against high sea levels, high tides, and to some degree waves from storms. Waves can reach the dune front and draw sand onto the beach to form a storm beach profile. Later the dune is replenished by sand blown onto it from the beach.  Much of dune’s effectiveness depends on the vegetation growing on them because the plant roots hold the sand in place and then later trap sand blown up from the beach that rebuilds dunes (FAO, 2007).  

Photos by: Keith Ellenbogen

Loss of Natural Protection

The U.S. West Coast’s low scores for Coastal Protection are largely driven by the loss of salt marsh habitats. Salt marsh habitat has been lost throughout the U.S. west coast, but it has been most severe in California.  Washington and Oregon have lost about 35% of the 3.6 million acres of wetlands that existed there in the 1780's (Dahl, Thomas, 1990). 

The California Department of Fish and Game (2001) estimates that California has lost 91% of the historic wetland acreage present before 1850, a total loss of 5 million acres.  By contrast, historical maps showed that the coast of New England, which has a much longer settlement history, has lost an estimated 37% of its historical salt marsh coverage, with higher amounts for the state of Rhode Island, which lost 55% since 1832; Massachusetts, which lost 41% since 1777. 

Most losses were attributable to urban growth (Natural Resources Agency, State of California, 2010).   As of 2001, the extent of California’s remaining salt marshes was estimated to be 31,300 acres along the North Coast, 3,800 acres along the Central Coast, 93,000 out of an original 200,000 in San Francisco Bay (54% loss) and 13,000 out of an original 53,000 in Southern California (75% loss). 

The main causes for salt marsh loss have been residential, commercial, industrial or urban development; diking, filling, draining, pad building for oil exploration, road building, draining for mosquito control or livestock grazing, contamination, introduction of exotic species, sea level rise and excessive level of nutrient run-off from land.  An example of the extent of historical loss can be seen on these maps that focus the San Francisco Bay region.

Setula et. al., 2008.

These losses are significant considering the many benefits of that wetlands provide.  A 2008 report by Setula et al., on the Status of Perennial Estuarine Wetlands in California summarizes this point saying ‘Estuarine wetlands are highly valued for many reasons (Day et al. 1989, Mitsch and Gosselink 2000). They serve as nurseries for commercial fisheries, including salmon, crab, and shellfish. They shelter and feed millions of migratory shorebirds and waterfowl. They serve as critical habitat for most of the coastal threatened and endangered species. Estuarine wetlands filter contaminants from surface water, absorb flood waters, dissipate storm surges, and stabilize shorelines, and trap carbon (Chmura et al. 2003).’

It is clear that maintaining and restoring natural habitats to protect shorelines from storms and rising sea levels is important, but it has not been an easy task. California has invested billions of dollars to protect and restore wetlands and riparian areas. As an example, the Southern California Wetlands Recovery Project acquired 6,603 acres and restored 2,161 acres of wetlands at a cost of $430 million (Ambrose, R.F, et al., 2006).

Nevertheless the Ocean Health Index reveals there are continued losses of marine habitats today.  The trend for the status of salt marsh wetlands was nearly neutral in Washington and Oregon (-0.00 for both), but slightly negative for northern (-0.03), central (-0.02) and southern (-0.02) California.

Washington shows a positive trend (+.10) for seagrasses while the trend in the other regions is slightly negative and strongly negative in northern California (-0.41).

 The trend for the status of sand dunes was strongly negative in all areas: -0.14 in Oregon, -0.21 in Washington and -0.17, -0.19 and -0.21 for northern, central and southern California, respectively.

Longer-term data available for the U.S. West Coast showed that the status of these habitat-based goals and sub-goals has declined over the decade from 2000-2010.  The California findings are somewhat surprising because the state has had a “no net loss” policy for Wetlands since 1983. 

California has had a “no net loss” policy for wetlands since 1983. In keeping with that policy there has been an effort to assure that there is compensatory replacement of wetlands acreage that has to be destroyed for purposes allowed under the Clean Water Act and other regulations. In fact records from 2007 to 2009 show that 300 – 400 acres have been impacted each year but the compensatory mitigation provides a greater than 1:1 replacement of acreage for impacted habitats, often 3:1 (Hebeger et al., 2009).

This seems like good news.  Unfortunately a study done in California in 2007 (Ambrose, R.F., et al., 2006) found that most mitigation projects, while meeting their acreage goals, were not meeting their performance goals.  In fact only 19% of the mitigation wetlands were considered ecologically successful, and 27% did not meet the federal definition of wetland. In essence the study found that the primary state and federal wetland protection programs have been generating more wetlands of lower quality than the wetlands they allowed to be destroyed (Hebeger et al., 2009).

Degradation of sand dunes is largely due to human development. Despite well-know hazards of building on frontal dunes (Mc Harg, 1969) many housing developments in all 3 states are built on dunes and consequently are threatened or damaged periodically (National Research Council, 2012). Beach vehicles, construction, and destruction of vegetation reduce the viability of dunes. Storms, tides, and currents also cause temporary or permanent degradation.  Sand dunes are unstable and accrete or expand during storms and winds.  

Photo courtesy of Gary Griggs, University of California, Santa Cruz

Overall, California, Washington and Oregon have made great progress over the past 10 years to protect and restore wetlands. The Ocean Health Index recognizes the progress, and despite these trends, near-term (5 year) future scores indicate that the status of salt marshes, sand dunes and sea grass is likely to improve owing to more effective management actions and other resilience measures.   

In Closing

Dunes, salt marshes, and sea grasses are natural buffers that reduce wave impact and flooding.  The lack of these natural lines of protection can be somewhat remediated by restoration and providing room for landward migration as sea level rise causes some areas to become inhospitable to these habitats.

The Ocean Health Index’s regional assessment of Coastal Protection on the West Coast of the United States measures the extensive and continuing loss of dunes, salt marshes, and sea grasses in California, Oregon and Washington.

Winter storms and sea level rise may well accompany this year’s El Niño and will add to the sea level rise from global warming, making coast lines vulnerable to flooding and erosion. 

Dunes, salt marshes, and sea grasses are natural buffers that reduce wave impact and flooding.  The lack of these natural lines of protection can be somewhat remediated by restoration and providing room for migration that will be necessary when as level rise causes some areas to become inhospitable to these habitats.