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 for future safety and protection of coastal communities.

Project Description

During 2018-19, we used observations of coastal runup, offshore waves, and beach morphology at Imperial Beach, Cardiff, and Coronado to examine empirical relationships of runup for use in a planned product set of extreme water levels based on CDIP nowcasts and hindcasts of waves and water level. A standard parameterization of runup (Stockdon et al., 2006), that has been used in CDIP total water level estimates, was found to be insufficient based on the field data comparisons, and so our work plan for the past year was altered as we sought to develop an improved parameterization. We are in the final stages of testing a new runup parameterization that incorporates more information from the full incident wave spectrum, available from CDIP products. Once that runup estimate is finalized, we will complete our deconstruction of extreme total water level events during 2019-20, quantifying relative contributions from the tide, nontidal residual sea level, and wave runup at Cardiff, Coronado, and Imperial Beach. The product will provide an ongoing assessment of how various processes combine to cause coastal flooding. The information will be used to develop extreme water level statistics and return periods specific to each site. In addition, the seasonality of total water levels will be specified, with a depiction of tidal, wave, and water level contributions in each season. The influence of sea-level rise on extreme water level statistics will be evaluated, providing the public with a understanding of what causes high water level events today, with impacts on beach erosion and coastal flooding, and how the probability of occurrence of extreme water levels is likely to change in the future.

During the past year, websites have been developed for Cardiff and Imperial Beach. These websites will be expanded in the coming year to include the new coastal runup and extreme water level products, as well as a beach profile viewer that is in the final stages of development. During 2019-2020, we will develop coastal hazard websites at Coronado and Huntington Beach (based on previously collected field observations at both sites, which is critical for tuning of the runup parameterization). In collaboration with a proposed State Parks funded project, new field data will be obtained at a site in the northern SCCOOS region (likely Malibu or Santa Monica). Once those data are available, we will develop a webpage for this site based on the Cardiff and Imperial Beach templates. Given the need for field validation data, we will delay our proposed product development in Santa Barbara County until a field deployment can be arranged.

Stockdon, H. F., R. A. Holman, and A. H. Sallenger, Jr. (2006), Empirical parameterization of setup, swash, and runup, Coastal Eng., 53, 573-588.

Observations

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.

Applications

2. Coastal Hazards:

To provide accurate, validated inundation models and information with the long-term goal of improving coastal safety.

Principal Investigators

  1. Mark Merrifield, UCSD - mamerrifield@ucsd.edu
  2. Falk Feddersen, UCSD - ffeddersen@ucsd.edu

Publications