Cardiff Beach Erosion & Inundation

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 run-up can reach several meters above the 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 or 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 gauges. 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 regular 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, the 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.

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, run up, and survey instrumentation and measuring techniques are described below.

 

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 help and dolly-mounted portable GPS instruments will be used to locate and monitor the extent of inundation at the site. 

 

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.

 

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.  Additionally, 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 waterline will be conducted at each low tide.  Cross-shore survey lines will be spaced 50 m apart.  

All Terrain Vehicle Surveys

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

A Jetski equipped with a GPS and Sonic Depth Finder will be used to survey the underwater bathymetry seaward of the surf zone 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 Erosion in Southern California

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 yd3 of sand from offshore were placed on San Diego beaches at an estimated cost of $28M.  A 50-yr, $200M plan to nourish San Diego area beaches has been proposed.  Potential impacts of beach nourishment (or a lack of beach nourishment) include effects on lobster and other biotas, surfing, cliffs, tourism, Hwy 101, and the Amtrak rails.  Our understanding of nearshore sand transport, and ability to estimate future waves and water levels are 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 1).  Beach widths (Figure 2) were minimum in the recent El Nino at all sites and maximum at the recently nourished sites.  Monitoring is ongoing and beach widths are updated approximately monthly.

Figure 1: (Left) Beach survey sites are within a larger area infrequently surveyed with airborne Lidar. (Right) Cardiff and Solana Beaches were nourished in 2012

Figure 2: Alongshore averaged beach width (mean removed) versus time. Each dot is one beach survey.