Significant Wave Height and Dynamic Water Level Analysis at NOAA Tide Gauges

The combined effects of mean water level and waves are important to consider for a range of processes including overtopping and inundation. However, despite the broad coverage of water level observations from National Oceanic and Atmospheric Administration (NOAA) tide gauges (over 200 throughout the coastal U.S.), co-located shallow water wave observations are uncommon. Here we expand upon previous work by Park et al. (2014) and Sweet et al. (2015) to show how 6-minute water level standard deviation (sigma, σ) measurements can be used as a proxy for significant wave height (H_m0), enabling both mean water level and wave height to be observed simultaneously using a single gauge. The NOAA 6-minute acoustic water level observations at the Duck, North Carolina tide gauge are compared to two nearby Nortek Acoustic Waves and Currents (AWAC) stations operated by the U.S. Army Corp of Engineers. Calibration parameters are calculated to adjust tide gauge derived H_m0 to best fit AWAC measured H_m0 and error is quantified for both calibrated and uncalibrated tide gauge H_m0 estimates. The quality control processes, correlation, and respective error between sigma and significant wave height found in this analysis can ultimately be used at other NOAA acoustic water level stations to derive historic (1996 - present) and real-time estimated wave heights. Additionally, the dynamic water level (DWL) defined by Sweet et al. (2015) as DWL = water level ± 2σ, is calculated for the entire historical timeseries (Jan. 1, 1996 – Dec. 31, 2016) for three different gauges along the U.S. East Coast (Duck, NC. Lewes, DE, and Cape May, NJ). The DWL is calculated using both the still water level and the non-tidal residual, defined as the observed water level minus the predicted water level. The analysis of DWL is used to better understand climatological trends related to storm events, wave setup, and coastal flooding events.