Data related to "Free infragravity waves on the inner shelf: Observations and Parameterizations at two Southern California beaches"

Abstract: 

Co-located pressure and velocity observations in 10-15m depth are used to estimate the relative contribution of bound and free infragravity (IG) wave energy to the IG wave field. Shoreward and seaward going IG waves are analyzed separately.  At the Southern California sites, shoreward propagating IG waves are dominated by free waves, with the bound wave energy fraction <30% for moderate energy incident sea-swell and <10% for low energy incident sea-swell. Only the 5% of records with energetic long swell show primarily bound waves. Consistent with bound IG wave theory, the energy scales as the square (frequency integrated) sea-swell energy, with a higher correlation with swell than sea energy. Seaward and shoreward free IG energy is strongly tidally modulated. The ratio of free seaward to shoreward propagating IG energy suggests between 50-100% of the energy radiated offshore is trapped on the shelf seaward of 10-15m and redirected shoreward.  Remote sources of IG energy are small.The observed linear dependency of free seaward and shoreward IG energy on local sea-swell wave energy and tide are parameterized with good skill (R2 ~ 0.90).  Free (random phase) and bound (phase-coupled) IG waves are included in numerically simulated timeseries for shoreward IG waves that are used to initialize (~ 10m depth) the numerical nonlinear wave transformation SWASH. On the low slope study beach, wave runup is only weakly influenced by free shoreward propagating waves observed at the offshore boundary (foreshore slope = 0.02).  

Plain Language Summary:

Infragravity (IG) waves are long-period (every 25 sec to 2.5 min) waves that contribute to coastal flooding and beach erosion. IG waves, generated near the shoreline by short-period sea-swell (SS) wave groups (known by surfers as "sets"), have long wavelengths (100s of m) and do not curl and break like ordinary sea and swell waves. Instead, they can bounce off the beach face and propagate seaward. Our study concerns IG waves on the inner shelf (10-15m depth, ~ 500-700m offshore), seaward of the region of IG generation. Similar to previous observations in Hawai'i and North Carolina, we find most of the bounced, seaward going IG energy cannot reach deep water and is trapped on the continental shelf. We develop an observation-based estimate IG wave energy on the inner shelf as a function of SS wave energy and tide level. Finally. we show with a numerical model that IG wave runup at the shoreline is influenced only weakly by IG waves on the inner shelf. 

About the data: 

The PUV MATLAB data structure is saved in the .mat file provided. Data is aggregated from numerous deployments of Nortek Vectors (PUV) in San Diego County between 2019 and 2022, at Torrey Pines State Beach and Cardiff State Beach. This data was collected by the Coastal Processes Group at the Scripps Institution of Oceanography. 

2488 3 hour at 2Hz timeseries of pressure, cross-shore and alongshore velocity are provided. 

time is given in UTC time as a MATLAB datetime.

MOP is the location of the instrument for a specific timeseries given as a MOP number (corresponding to the MOP lines given in O'Reilly et al. (2016) and used by the Coastal Data Information Program (CDIP). The MOP number can be used to obtain shorenormal angle and location of the sensor from https://cdip.ucsd.edu/mops/.

depth is given as the mean depth over the 3h pressure records in meters and includes the mean tidal elevation.

P is the detrended pressure data in meters, detided and the mean depth removed.

U is the detrended cross-shore velocity data in meters/second, with the main tidal constituents M2, S2 and K1 and the mean depth removed, and rotated to be shorenormal according the the MOP angle (+x is onshore).

V is the detrended alongshore velocity data in meters/second, with the main tidal constituents M2, S2 and K1 and the mean depth removed, and rotated to be shorenormal according the the MOP angle (+y is north).

sensor_offsets includes both the sensor offset from the sea floor in meters of the pressure sensor and the current meter. These can be used to surface correct the timeseries.

The timeseries are grouped by instrument.