New ways to measure waves and their effects at NOAA tide gauges: A Hawaiian‐network perspective

Abstract

We use the standard deviation (sigma) of continuous 1 s water level sampling at 46 U.S. NOAA tide gauges available since 1996 as a high‐frequency variance measure. Sigma estimates local infragravity and incident wave band variability, is significantly correlated (r = 0.5–0.9) to significant wave height (Hs), and scales linearly to local observations and output from the global ocean wave reanalysis at most ocean‐exposed and harbor‐sheltered locations. Empirical orthogonal functions of daily mean sigma from six Hawaii tide gauges distinguish northerly and southerly modes that closely match local Hs observations. Depending on tide gauge location, the 99% of daily maxima sigma can be as large as or larger than the nontidal residual component of the water level sample. Our findings provide new uses of land‐based tide gauge data to estimate significant wave heights and dynamic water levels to better monitor for local conditions leading to impacts.

Usable Science for Managing the Risks of Sea‐Level Rise

“…They can (1) provide predictions for locations where there are no tide gauges, (2) better resolve rare‐event probabilities and overcome record length limitations by simulating large numbers of synthetic storms under a specified climatology (Haigh et al, ; Lin et al, ), and (3) physically account for non‐stationarity associated with climate variability and climate change. Dynamic simulations can also incorporate high‐frequency wave effects (Vitousek et al, ; Vousdoukas et al, ), which have not traditionally been measured by tide gauge records (but see Sweet et al, ) but are of particular concern in areas where erosion is primarily driven by waves rather than by surge, as along the U.S. West Coast (Serafin et al, ; Sweet et al, ). On the other hand, dynamic simulations are subject to the limitations of the driving reanalysis data sets and ultimately must rely on tide‐gauge observations for validation.…”

What's streamflow got to do with it? A probabilistic simulation of the competing oceanographic and fluvial processes driving extreme along-river water levels

“…Around river mouths, the elevation of the water level measured by tide gauges, or the still water level (SWL), varies depending on the mean sea level, tidal stage, and the nontidal residual contributors which may include the following forcings: storm surge, seasonally induced thermal expansion (Tsimplis and Woodworth, 1994), the geostrophic effects of currents (Chelton and Enfield, 1986), wave setup (Sweet et al, 2015;Vetter et al, 2010), and river discharge. Most commonly, estimates of nontidal residuals are determined by subtracting predicted tides from the measured wa-ter levels.…”

Key Internet Connections and Locations are at Risk from Rising Seas

“…Changes in nearly instantaneous water level (for safe navigation, storm-surge preparedness and other commerce-supporting activities) and in RSL (including VLM effects) are measured by tide gauges at the land-ocean interface. However, it should be noted that, in the discussion of the consequences of RSL rise on tidal flood frequencies (see section 6), waves and their high-frequency (seconds to minutes) dynamical effects are not considered; we refer to 'still water levels' instead of a more 'total water level' (Hall et al, 2016) as operationally reported by tide gauges due to the mechanical low-pass filtering associated with their protective wells, multi-minute averaging scheme and general placement in protected waters (Sweet et al, 2015). Also, for context, the term 'sea level' is distinguished from 'water level' in that the former is generally considered to represent monthly and longer-scale variability; when discussing spatial scales, responses locally refer loosely to scales upwards of about tens of kilometers and regionally to scales upwards of about hundreds of kilometers.…”

“…Figure 15c shows the water level heights with a 20% annual chance of occurrence (5-year recurrence interval) for a set of NOAA tide gauges with more than 20 years of hourly observations. The 20% annual chance flood levels range from about 0.3 m (~1 foot), such as where narrow and deep continental shelves bathymetrically constrain the magnitude of storm surges (e.g., along the West Coast and Islands where wave runup and/or dynamic water levels [Stockdon et al, 2006;Sweet et al, 2015] can be larger than storm surge [Hoeke et al, 2013;Ruggiero, 2013;Serafin and Ruggiero, 2014]) to 0.9 m or more at higher latitudes, where powerful extratropical storms and wide continental shelves allow larger surges to build (Tebaldi et al, 2012;Hall et al, 2016;Merrifield et al, 2015Merrifield et al, , 2016. The median of the 20% annual chance flood in Figure 15c is about 0.8 m (ranging from about 0.3 m to 1.8 m) above MHHW, which is nearly the same as the National Weather Service's empirically derived elevations used to define 'moderate' flooding at dozens of NOAA tide gauges (~0.8 m and ranging from about 0.5 m to 1.8 m; http://water.weather.gov/ahps).…”