Cardiff Beach Erosion & Inundation

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The beach width (average distance from highway 101 shoulder to mean sea level contour) at Cardiff  State Beach, CA.

The minimum average beach width (about 22 m) was during the 2010/11 El Nino. The maximum beach width  (about 63m) was immediately after a 2013 beach nourishment.  In mid-January 2016, the beach is the narrowest since 2012, before the nourishment. The width is the distance from the backbeach (e.g. rocks bordering HWY 101, seawall, parking lot edge) to MSL (mean sea level) beach elevation. The width is averaged over 1.7 km of coastline, and some locations are relatively wide or narrow. The beach is widest in late summer when waves are small, and narrowest in late winter, after erosive storms. At the end of summer 2012, the beach was about 10 m wider than the typical annual prenourishment maximum (dashed horizontal line). Then, in October of 2012, an additional ~50,000 m^3 of sand was mechanically placed on the beach, increasing the beach width even more, and potentially helping to maintain the wide beach in the following years. The recent July 2015 width is about 40m more than the maximum erosion in Feb 2010 (the last El Nino).

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Width of six southern California beaches (see legend) versus time. The width, the distance from the backbeach to MSL (mean sea level) beach elevation, is averaged over a few km alongshore at each beach, and the mean removed. All beaches are widest in late summer when waves are low, and narrowest in late winter, after erosive storms. Beaches were narrowest in Feb 2010 (the last El Nino).

UPDATE: Go to the latest 2012-13 update section

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Project Goals

image004.jpg  Coastal inundation on the U.S. west coast is often caused by the co-occurrence of high tides and energetic ocean waves. During storms, wave runup can reach several meters above tide level. Existing simple inundation models yield qualitative general information but not the information most valuable for issuing site-specific warnings for highway closures and sand-bagging. Quantitative inundation observations are critically needed to improve model accuracy. With rising sea levels and El Niño winters, it is crucial that a West Coast inundation model be developed for future safety and protection of coastal communities.

The goal of the Cardiff Beach Erosion and Inundation Project is to develop field-validated, site-specific inundation models for use in providing real-time warnings of wave and tide-induced coastal inundation. Groups interested in inundation information include lifeguards, the National Weather Service and Emergency Alert Network, recreational beachgoers, US Army Corps of Engineers, California Department of Transportation, California Coastal Commission, as well as regional city and county governments. Real-time users (e.g. highway departments) have indicated a willingness to work cooperatively to improve the warnings by providing information on when highways flood during storm events.

Experiment Description

A Cardiff Beach inundation model will be developed using existing models for offshore wave conditions and tides and field observations of nearshore water levels, runup, and sand levels during winter storms. Wave conditions will be estimated using a network of directional wave buoys and from the global NOAA Wave Models. Water levels will be estimated with nearby NOAA tide gages. Runup heights and inundation will be measured using pressure sensors, video cameras, and visual observations. Sand levels on beaches fronting the inundated areas will be surveyed before, during, and after storms, and on a regularly monthly basis.

The inundation model will be calibrated with field observations of water levels acquired during winter storms. Field observations will show the importance of local details (e.g., beach face profile, presence of rip-rap and structures, etc...) on shoreline run-up and inundation. After a reliable model is developed, inundation warnings will be disseminated to users via the Internet and/or automated phone calls. Model predictions will improve with additional observations and feedback on the accuracy of the inundation warnings from end-users.

Experiment Site

The experiment site is the 1.5 km stretch of Cardiff State Beach between Seaside (South Cardiff State Beach) to the south and the San Elijo Lagoon Inlet to the north. The site was selected for ease of access, logistical support from local agencies, and history of wave inundation. Cardiff State Beach is also an existing Scripps Institution of Oceanography beach processes focus area and monthly sand level surveys have been collected at this site for the past 3 years. Waves and the beach vary alongshore (e.g.. sandy at the North end and rip-rap in the South) allowing observations of a range of environmental conditions.
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Experiment Schedule

The experiment will take place from November 16, 2010 through April 15, 2011. Pressure sensors were buried on November 16 and will remain in place until mid-April 2011.

Data Collection

Water level, runup, and survey instrumentation and measuring techniques are described below.

Pressure Sensors:

Pressure sensors (photo below) will be used for continuous water level measurements and to monitor wave runup and overtopping.
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Buried Pressure Sensors:

Ten pressure sensors will be buried in the sand or cobble on the beach face (typically at or near the high water line) at various alongshore locations within the study area for the duration of the experiment. These fixed instruments are completely self-contained (power and data acquisition), have no moving parts, and are low power.

Mobile Pressure Sensors:

During storm events additional pressure sensors will be temporarily deployed within the rip-rap high on the beach face to measure wave overtopping and inundation water levels.

Video Cameras:

Three video cameras located at sites overlooking the study area will be used to visually monitor wave overtopping and inundation.

GPS-Equipped Instrumentation:

During storms, hand held and dolly-mounted portable GPS instruments will be used to locate and monitor the extent of inundation at the site.

Beach and Bathymetric surveys:

At Cardiff State Beach, monthly sand level surveys of the sub-aerial beach and quarterly surveys out to 8 m water depth using various GPS-equipped instrumentation are ongoing (since 2007) and will continue throughout the experiment. Additional, higher resolution surveys will be conducted to characterize sand level changes during winter storms. Just before and shortly after major storms, sand level changes will be measured out to 8 m water depth. During storms, sub-aerial beach sand level surveys from the back beach to the waterline will be conducted at each low tide. Cross-shore survey lines will be spaced 50 m apart.

Survey Instrumentation:

All Terrain Vehicle Surveys

image010.png  Sub-aerial beach sand level surveys will be conducted at low tide with a GPS-equipped all terrain vehicle (ATV). ATV surveys are made by driving parallel to the shoreline. ATV surveys need to be conducted at low tide, which may occur at night.

Jetski Surveys

image012.jpg  A Jetski equipped with a GPS and Sonic Depth Finder will be used to survey the underwater bathymetry seaward of the surfzone to about 8 m depths. Surveys will be conducted at high tide and are made by driving the Jetski on lines perpendicular to the shoreline. Jetski surveys are conducted when waves are low and are never conducted at night.

Dolly Surveys

Surveys of the beach from the waterline to about waist deep water are made using a hand-pushed GPS-equipped Dolly.

2013 Beach errosion in southern Califonia

Bob Guza, SIO

Wide beaches protect shoreline infrastructure and support recreation and tourism. Southern California beaches have been occasionally replenished with sand. In 2012, 1.5M cu yd of sand from offshore were placed on San Diego beaches at an estimated cost of 28M$ (Figure 1). A 50-yr, 200+M$ plan to nourish San Diego area beaches has been proposed. Potential impacts of beach nourishments (or a lack of beach nourishments) include effects on lobster and other biota, surfing, cliffs, tourism, Hwy 101, and the Amtrak rails. Our understanding of nearshore sand transport, and ability to estimate future waves and water levels, is so limited that the probability of negative environmental impacts from cannot be estimated reliably. How high on the beach does wave uprush reach, where does the nourishment sand go, and why does it go there? Our research objective is to understand the physics at work, and to thereby help answer relevant management questions.

Ongoing monitoring is building a database of sand level changes and waves at local beaches, including an El Nino and the recent 2012 nourishment at Solana-Cardiff beaches (Figure 2). Beach widths (Figure 3) were minimum in the recent ElNino at all sites, and maximum at the recently nourished sites. Monitoring is ongoing and beach widths are updated approximately monthly.

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Figure 1: (left) Sand from offshore was placed on San Diego County beaches in 2012. High tides and energetic waves can (center) flood coastal infrastructure and (right) damage coastal property.

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Figure 2: (Left) Beach survey “focus” sites are within a larger area infrequently surveyed with airborne Lidar. (Right) Cardiff and Solana Beaches were nourished in 2012

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Figure 3: Alongshore averaged beach width (mean removed) versus time. Each dot is one beach survey.

Contact Information

Logistics Coordinator:
Dr. Michele Okihiro
Scripps Institution of Oceanography
Coastal Data Information Program
9500 Gilman Drive
La Jolla, CA 92093-0214

mokihiro@ucsd.edu (email)
(858) 534-3032 (phone)

Principal Investigators:
Professor Robert Guza (rguza@ucsd.edu)
Dr. Adam Young (adyoung@ucsd.edu)
Dr. W. C. O'Reilly (woreilly@ucsd.edu)

 

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