MBNMS Ecosystem Observations 2001: Beach Systems

El Niño Storms Erode Monterey Bay Beaches

Intense storms often produce especially high waves and elevated sea level, causing extensive beach erosion and dramatic shoreline retreat. The worst erosion usually occurs when multiple storms strike the coast during the highest tides. Several years can pass between stormy seasons intense enough to cause enough shoreline erosion to produce widespread damage to coastal land and structures. Although waves rebuild beaches after such storms, this seaward accretion may not return a beach to its pre-storm position, requiring coastal zone managers to consider whether to take long-term remedial measures.

During the winters of 1982-83 and 1997-98, two of the most severe El Niños of the twentieth century produced intense storms along the central California coast. These storms followed more southerly storm tracks than do non-El Niño storms. The southerly storms, combined with periods of high tides, intensify the normal winter erosional cycle. Coastal cliffs, dunes, and man-made structures along Monterey Bay suffered serious damage, much of it along the northern, most populated, part of the bay. To understand the effects of such storms better, United States Geological Survey (USGS) scientists, in cooperation with the California Department of Parks and Recreation, began a monitoring program at nine Monterey Bay beaches in the midst of the 1982-83 El Niño and four other beaches in 1985.

Figure 1: February 1983 photograph of the remains of a wooden seawall at Seacliff State Beach. Waves generated by the 1982-83 El Niño destroyed the seawall and scattered the large stones that had been emplaced seaward of the wall. Insert: April 1985 photograph of the replacement seawall and rebuilt beach. That seawall remained intact through the 1997-98 El Niño. photo John Dingler

Landward or seaward shifts in the position of the shoreline at mean sea level (MSL) are a measure of the extent of beach erosion (loss) or accretion (growth), respectively. During the 1982-83 El Niño, storm waves stripped large volumes of sand from Monterey Bay beaches, leaving beachfront homes and coastal cliffs and dunes exposed to direct wave attack. By the end of the 1982-83 El Niño, Monterey Bay beaches had dramatically eroded. For example, Figure 1 shows beach conditions at Seacliff State Beach, on the northeast coast of the bay, at the end of the 1982-83 El Niño. During the ensuing two years, normal wave activity returned sand to the beaches, resulting in net accretion (see insert to Figure 1). However, there is no way of knowing whether the beaches returned to near their pre-El Niño positions, because no profile data had been collected just preceding the El Niño. Between 1985 and September 1997, the beaches went through typical seasonal fluctuations (erosional and accretionary cycles).

During the 1997-98 El Niño, several intense winter storms from the south struck the Monterey Bay coastline. However, no Monterey Bay beach eroded as severely as during the 1982-83 El Niño. For example, at Seacliff State Beach, which is most susceptible to waves from the south, erosion during the 1997-98 El Niño was no more severe than during some non-El Niño years.

Only two beaches appear to have undergone net retreat since 1983. One, Moss Landing State Beach, is adjacent to the head of Monterey Canyon. This complicates interpretations of long-term shoreline retreat because sand eroded from the beach can wash into the canyon and be lost to the deep sea rather than being shifted onshore and offshore. Thus, the condition of Moss Landing State Beach also depends on the rate of longshore sand movement from the north. The other, Fort Ord Beach, is narrow and backed by a high cliff that is easily eroded. Even in most non-El Niño years, storm waves erode the beach enough to attack the cliff, which then fails. Consequently, the shoreline has retreated an average of one to two meters per year since monitoring began in 1983. However, the summer beach continues to return to the same shape and width as MSL moves landward.

The cooperative efforts of USGS scientists and the California Department of Parks and Recreation at Monterey Bay’s beaches have led to a better understanding of how these beaches change during both El Niño and non-El Niño years. The State of California Department of Parks and Recreation is using the results of this study to aid its development of long-term plans for managing its public beaches along Monterey Bay. This research will also provide new insights into how beach erosion occurs in other coastal areas in an ongoing effort to protect people’s lives and property from geologic and environmental hazards in the coastal zones of the United States. This study is part of the USGS research in the Monterey Bay National Marine Sanctuary, which will be published soon in a special volume of the journal Marine Geology.

John Dingler
United States Geological Survey

National Marine Sanctuaries | National Ocean Service | National Oceanic and Atmospheric Administration
U.S. Department of Commerce | NOAA Library

For Website comments/questions, contact the MBNMS Webmaster.
For programmatic comments/question, contact the appropriate MBNMS Staff

MBNMS Privacy Policy

This page last modified on: 12/26/04

URL: http://montereybay.noaa.gov/reports/2001/eco/beach.html