REDUCING THE RISK FROM COASTAL GEOLOGIC HAZARDS El Niño Storms Erode Beaches on ,

s recently as 1998, storms Agenerated by El Niños se- verely eroded beaches along Monterey Bay, California. To better understand the effects of such storms, United States Geo- logical Survey (USGS) scien- tists, in cooperation with the California Department of Parks and Recreation, have been ac- tively monitoring changes in the foreshore since the mid-1980’s. The results of this study will help protect coastal residents, property, and environments and are being used by the State of California in guiding the manag- Waves generated by severe winter storms ement of public beaches. during the 1982-83 El Niño destroyed the wooden seawall at on California’s Monterey Bay. The barrier of large stones that had been emplaced Intense storms often produce abnor- seaward of the wall was also scattered by mally high waves and elevated sea level, the waves (photo above). The photo at causing extensive beach erosion and right, taken 2 years after these storms, shows the replacement seawall and rebuilt shoreline retreat. The worst erosion gener- beach. This seawall remained intact during ally occurs when multiple storms hit dur- the 1997-98 El Niño. ing periods of especially high tides. Sev- eral years may pass between storms of it along the northern, most populated normal wave activity deposited sand, re- intense enough to cause shoreline erosion part of the bay. To better understand the building the beaches. However, there is no that results in significant widespread dam- effects of such storms, United States Geo- way of knowing whether the beaches re- age. Although waves rebuild beaches after logical Survey (USGS) scientists, in coop- turned to near their pre-El Niño states, be- such storms, this seaward accretion may eration with the California Department of cause no data had been collected on their not return a beach to its pre-storm position, Parks and Recreation (DPR), began ac- profiles before 1983. In succeeding years, requiring coastal-zone managers to consider tively monitoring changes at nine Califor- the beaches went through several erosional whether to take remedial measures. nia State Beaches on Monterey Bay in and depositional cycles. From 1985 During the winters of 1982-83 and 1983 and at four additional ones in 1985. through September 1997, all but two 1997-98, two of the most severe El Niños The extent of beach erosion or accretion Monterey Bay beaches remained stable of the 20th century produced intense is measured by landward or seaward shifts except for normal seasonal fluctuations. storms that pounded central California. in the position of the shoreline at mean sea During the 1997-98 El Niño, several in- These storms followed more southerly level (MSL). Storm waves during the tense winter storms from the south struck tracks than usual and combined with peri- 1982-83 El Niño had stripped large vol- the Monterey Bay coastline. However, ods of high tides to intensify the normal umes of sand from Monterey Bay beaches, beach erosion along the bay was less than winter erosional cycle, causing tens of leaving beachfront homes and coastal in the 1982-83 El Niño, and not a single millions of dollars in damage along the cliffs and exposed to direct wave at- Monterey Bay beach was eroded so se- central California coast. On Monterey tack. By the end of the 1982-83 El Niño verely in 1997-98. For example, at Bay, coastal cliffs, dunes, and manmade storms, Monterey Bay beaches were dis- Seacliff State Beach on the northeast structures suffered serious damage, much tinctly narrower than before. For 2 years, coast of the bay, which is most susceptible

U.S. Department of the Interior USGS Fact Sheet 026-00 U.S. Geological Survey 2000 MONTEREY BAY STATE BEACHES AND THE EXTENT OF EROSION AND ACCRETION DURING 1983 TO 1998 Monterey Bay 0 5 MILES State Beaches New Brighton Seacliff State Beach (see map for locations) SANTA State Beach CRUZ 11 1 0 5 KILOMETERS 9 Pt Santa Cruz 2 8 M O N 7 T 3 E R E 6 Y 12 4 5 100 m

Eroding landward Salinas River 4 500 m 5 YON State Beach (north) Building seaward CAN 3 EY B TER 6 N A MO Salinas River SHORELINE SHIFT AT MEAN SEA LEVEL SHORELINE SHIFT AT Y State Beach (mouth) 2 10 1 CALIFORNIA 100 METERS 7 Beach

1984 1986 1988 1990 1992 1994 1996 1998 Area Pt Piños YEAR 8 of map Sand City Beach The extent of beach erosion or accretion is measured MONTEREY 9 13 Del Monte Beach by landward or seaward shifts in the position of the shoreline at mean sea level (MSL). Storm waves during First surveyed 2/83 the 1982-83 El Niño had 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 storms, Monterey Bay beaches were distinctly narrower than before. U.S. Geological Survey scientists, in cooperation with the California Department of Parks and Recreation, began actively monitoring changes at nine Monterey Bay beaches in February 1983 and at four additional beaches along the bay in 1985. During the 1997-98 El Niño, several intense winter storms eroded beaches along the bay, though not as severely as the 1982-83 El Niño storms.

Profiles of Seacliff State Beach 1983 to 1998 to waves from the south, erosion during DPR to help guide the management of pub- Mean sea level the 1997-98 El Niño was no more severe lic beaches along Monterey Bay. They will Top of rebuilt stairs than during some non-El Niño years. also provide new insights into how beach Only two beaches appear to have under- erosion occurs in other coastal areas. To im- gone net retreat since 1983. One, Moss prove that understanding further, the USGS Landing State Beach, is adjacent to the will continue to collect and analyze data head of Monterey Submarine Canyon, a from these beaches. The work of USGS sci- 3/10/98 factor that complicates interpretations of entists in the area of Monterey Bay is only long-term shoreline retreat because sand part of the USGS Coastal and Marine Geol- 9/9/97 eroded from the beach may move down ogy Program’s ongoing efforts to protect the canyon and be lost to the deep sea. The people’s lives and property from geologic other, Fort Ord Beach, is narrow and backed and environmental hazards in the coastal by a high, but easily eroded, cliff. In most zones of the United States. 3/28/95 years, winter storm waves erode the beach John R. Dingler to the extent that they can attack the cliff. 2 6/26/86 Graphic design by

Consequently, the shoreline has retreated an Susan Mayfield and Sara Boore METERS 0 50 METERS 2/3/83 average of 1 to 2 yards (meters) per year since USGS monitoring began in 1983. During 1982-83 El Niño storms, Seacliff State COOPERATING ORGANIZATION However, the summer beach continues to Beach on California’s Monterey Bay was se- California Department of verely eroded. Cross-shore profiles obtained by maintain nearly the same shape and width as Parks and Recreation U.S. Geological Survey scientists show that it migrates landward. normal wave activity in succeeding years The cooperative efforts of USGS scien- deposited sand, rebuilding the beach. The first For more information contact: profile (February 1983) was made at the same tists and the DPR at Monterey Bay’s U.S. Geological Survey, MS-999 time as the photograph on the front of this 345 Middlefield Road sheet. Wave conditions governed the depth to beaches have led to a better understanding Menlo Park, CA 94025 of how these beaches change during both El (650) 329-5042 which the profiles extend below mean sea level http://marine.usgs.gov/ (MSL). Erosion at Seacliff State Beach during Niño and non-El Niño years. The results of See also El Niño Sea-Level Rise Wreaks Havoc in California’s the 1997-98 El Niño was no more severe than these ongoing studies are being used by the San Francisco Bay Region (USGS Fact Sheet 175-99) during some non-El Niño years.

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