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Bromirski, PD, Cayan DR, Flick RE.  2005.  Wave spectral energy variability in the northeast Pacific. Journal of Geophysical Research-Oceans. 110   10.1029/2004jc002398   AbstractWebsite

The dominant characteristics of wave energy variability in the eastern North Pacific are described from NOAA National Data Buoy Center ( NDBC) buoy data collected from 1981 to 2003. Ten buoys at distributed locations were selected for comparison based on record duration and data continuity. Long- period ( LP) [ T > 12] s, intermediate- period [ 6 <= T <= 12] s, and short- period [ T < 6] s wave spectral energy components are considered separately. Empirical orthogonal function ( EOF) analyses of monthly wave energy anomalies reveal that all three wave energy components exhibit similar patterns of spatial variability. The dominant mode represents coherent heightened ( or diminished) wave energy along the West Coast from Alaska to southern California, as indicated by composites of the 700 hPa height field. The second EOF mode reveals a distinct El Nino-Southern Oscillation (ENSO)-associated spatial distribution of wave energy, which occurs when the North Pacific storm track is extended unusually far south or has receded to the north. Monthly means and principal components (PCs) of wave energy levels indicate that the 1997 - 1998 El Nino- winter had the highest basin- wide wave energy within this record, substantially higher than the 1982 - 1983 El Nino. An increasing trend in the dominant PC of LP wave energy suggests that storminess has increased in the northeast Pacific since 1980. This trend is emphasized at central eastern North Pacific locations. Patterns of storminess variability are consistent with increasing activity in the central North Pacific as well as the tendency for more extreme waves in the south during El Nino episodes and in the north during La Nina.

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Gallien, TW, Sanders BF, Flick RE.  2014.  Urban coastal flood prediction: Integrating wave overtopping, flood defenses and drainage. Coastal Engineering. 91:18-28.   10.1016/j.coastaleng.2014.04.007   AbstractWebsite

Flood extent field observations collected following a wave overtopping event are used to evaluate the accuracy of two urban flood prediction models: a static ('bathtub') model that simply compares water level to land elevation, and a hydrodynamic model that resolves embayment dynamics, overland flow, concrete flood walls, and drainage into the storm water system. Time-dependent overtopping rates were estimated using empirical models parameterized with survey data and local wave heights transformed to the nearshore using Simulating Waves Nearshore (SWAN) and subsequently input to the hydrodynamic model. The hydrodynamic model showed good agreement with field observations, whereas the static model substantially overpredicted flooding suggesting that urban backshore flood depths do not equilibrate with shoreline water levels in transient events. In the absence of a high backwater condition, storm system drainage attenuates wave overtopping flooding. Hydrodynamic model simulations suggest that bay side flood defenses may exacerbate flooding by restricting drainage and that temporary flood mitigation berms can significantly reduce backshore flooding. This study points to a promising urban coastal flood prediction and management framework. (C) 2014 Elsevier B.V. All rights reserved.

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Flick, RE, Murray JF, Ewing LC.  2003.  Trends in United States tidal datum statistics and tide range. Journal of Waterway Port Coastal and Ocean Engineering-Asce. 129:155-164.   10.1061/(asce)0733-950x(2003)129:4(155)   AbstractWebsite

Yearly tidal datum statistics and tide ranges for the National Oceanic and Atmospheric Administration/National Ocean Service long-term stations in the United States tide gauge network were compiled and used to calculate their trends and statistical significance. At many stations, significant changes in the tide range were found, either in the diurnal tide range [mean higher high water (MHHW)-mean lower low water (MLLW)], or mean tide range [mean high water (MHW)-mean low water (MLW)]. For example, at San Francisco, the diurnal tide range increased by 64 mm from 1900 to 1998, while at Wilmington, N.C., the mean tide range increased at a rate of 542 mm per century from 1935 to 1999. This analysis suggests that any studies concerned with present or future water levels should take into account more tidal datum statistics than just mean sea level (MSL). For example, coastal flooding and storm damage studies should consider trends in high water levels, since it is the peak values that cause flooding and determine the design of coastal structures. For habitat restoration planning, mean low water and tide range changes should be considered.

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Bromirski, PD, Flick RE, Cayan DR.  2003.  Storminess variability along the California coast: 1858-2000. Journal of Climate. 16:982-993.   10.1175/1520-0442(2003)016<0982:svatcc>2.0.co;2   AbstractWebsite

The longest available hourly tide gauge record along the West Coast (U. S.) at San Francisco yields meteorologically forced nontide residuals (NTR), providing an estimate of the variation in "storminess'' from 1858 to 2000. Mean monthly positive NTR (associated with low sea level pressure) show no substantial change along the central California coast since 1858 or over the last 50 years. However, in contrast, the highest 2% of extreme winter NTR levels exhibit a significant increasing trend since about 1950. Extreme winter NTR also show pronounced quasi-periodic decadal-scale variability that is relatively consistent over the last 140 years. Atmospheric sea level pressure anomalies (associated with years having high winter NTR) take the form of a distinct, large-scale atmospheric circulation pattern, with intense storminess associated with a broad, southeasterly displaced, deep Aleutian low that directs storm tracks toward the California coast.

Bromirski, PD, Flick RE.  2008.  Storm surge in the San Francisco Bay/Delta and nearby coastal locations. Shore & Beach. 76:29-37. Abstract

California’s San Francisco Bay/Sacramento-San Joaquin Delta (bay/delta) estuary system is subject to externally forced storm surge propagating from the open ocean. In the lower reaches of the delta, storm surge dominates water level extremes and can have a significant impact on wetlands, freshwater aquifers, levees, and ecosys- tems. The magnitude and distribution of open-ocean tide generated storm surge throughout the bay/delta are described by a network of stations within the bay/delta system and along the California coast. Correlation of non-tide water levels between stations in the network indicates that peak storm surge fluctuations propagate into the bay/delta system from outside the Golden Gate. The initial peak surge propa- gates from the open ocean inland, while a trailing (smaller amplitude) secondary peak is associated with river discharge. Extreme non-tide water levels are generally associated with extreme Sacramento-San Joaquin river flows, underscoring the po- tential impact of sea level rise on the delta levees and bay/delta ecosystem.

Bromirski, PD, Flick RE, Miller AJ.  2017.  Storm surge along the Pacific coast of North America. Journal of Geophysical Research-Oceans. 122:441-457.   10.1002/2016jc012178   AbstractWebsite

Storm surge is an important factor that contributes to coastal flooding and erosion. Storm surge magnitude along eastern North Pacific coasts results primarily from low sea level pressure (SLP). Thus, coastal regions where high surge occurs identify the dominant locations where intense storms make landfall, controlled by storm track across the North Pacific. Here storm surge variability along the Pacific coast of North America is characterized by positive nontide residuals at a network of tide gauge stations from southern California to Alaska. The magnitudes of mean and extreme storm surge generally increase from south to north, with typically high amplitude surge north of Cape Mendocino and lower surge to the south. Correlation of mode 1 nontide principal component (PC1) during winter months (December-February) with anomalous SLP over the northeast Pacific indicates that the dominant storm landfall region is along the Cascadia/British Columbia coast. Although empirical orthogonal function spatial patterns show substantial interannual variability, similar correlation patterns of nontide PC1 over the 1948-1975 and 1983-2014 epochs with anomalous SLP suggest that, when considering decadal-scale time periods, storm surge and associated tracks have generally not changed appreciably since 1948. Nontide PC1 is well correlated with PC1 of both anomalous SLP and modeled wave height near the tide gauge stations, reflecting the interrelationship between storms, surge, and waves. Weaker surge south of Cape Mendocino during the 2015-2016 El Nino compared with 1982-1983 may result from changes in Hadley circulation. Importantly from a coastal impacts perspective, extreme storm surge events are often accompanied by high waves.

Young, AP, Flick RE, Gallien TW, Giddings SN, Guza RT, Harvey M, Lenain L, Ludka BC, Melville WK, O'Reilly WC.  2018.  Southern California coastal response to the 2015-2016 El Niño. Journal of Geophysical Research Earth Surface. 123   10.1029/2018JF004771  
Rasmussen, L, Bromirski PD, Miller AJ, Arcas D, Flick RE, Hendershott MC.  2015.  Source location impact on relative tsunami strength along the US West Coast. Journal of Geophysical Research-Oceans. 120:4945-4961.   10.1002/2015jc010718   AbstractWebsite

Tsunami propagation simulations are used to identify which tsunami source locations would produce the highest amplitude waves on approach to key population centers along the U.S. West Coast. The reasons for preferential influence of certain remote excitation sites are explored by examining model time sequences of tsunami wave patterns emanating from the source. Distant bathymetric features in the West and Central Pacific can redirect tsunami energy into narrow paths with anomalously large wave height that have disproportionate impact on small areas of coastline. The source region generating the waves can be as little as 100 km along a subduction zone, resulting in distinct source-target pairs with sharply amplified wave energy at the target. Tsunami spectral ratios examined for transects near the source, after crossing the West Pacific, and on approach to the coast illustrate how prominent bathymetric features alter wave spectral distributions, and relate to both the timing and magnitude of waves approaching shore. To contextualize the potential impact of tsunamis from high-amplitude source-target pairs, the source characteristics of major historical earthquakes and tsunamis in 1960, 1964, and 2011 are used to generate comparable events originating at the highest-amplitude source locations for each coastal target. This creates a type of ``worst-case scenario,'' a replicate of each region's historically largest earthquake positioned at the fault segment that would produce the most incoming tsunami energy at each target port. An amplification factor provides a measure of how the incoming wave height from the worst-case source compares to the historical event.

Ludka, BC, Guza RT, O'Reilly WC, Merrifield MA, Flick RE, Bak AS, Hesser T, Bucciarelli R, Olfe C, Woodward B, Boyd W, Smith K, Okihiro M, Grenzeback R, Parry L, Boyd G.  2019.  Sixteen years of bathymetry and waves at San Diego beaches. Scientific Data. 6   10.1038/s41597-019-0167-6   AbstractWebsite

Sustained, quantitative observations of nearshore waves and sand levels are essential for testing beach evolution models, but comprehensive datasets are relatively rare. We document beach profiles and concurrent waves monitored at three southern California beaches during 2001-2016. The beaches include offshore reefs, lagoon mouths, hard substrates, and cobble and sandy (medium-grained) sediments. The data span two energetic El Nino winters and four beach nourishments. Quarterly surveys of 165 total cross-shore transects (all sites) at 100 m alongshore spacing were made from the backbeach to 8 m depth. Monthly surveys of the subaerial beach were obtained at alongshore-oriented transects. The resulting dataset consists of (1) raw sand elevation data, (2) gridded elevations, (3) interpolated elevation maps with error estimates, (4) beach widths, subaerial and total sand volumes, (5) locations of hard substrate and beach nourishments, (6) water levels from a NOAA tide gauge (7) wave conditions from a buoy-driven regional wave model, and (8) time periods and reaches with alongshore uniform bathymetry, suitable for testing 1-dimensional beach profile change models.

Young, AP, Guza RT, O'Reilly WC, Flick RE, Gutierrez R.  2011.  Short-term retreat statistics of a slowly eroding coastal cliff. Natural Hazards and Earth System Sciences. 11:205-217.   10.5194/nhess-11-205-2011   AbstractWebsite

The frequency, spatial distribution, and dimensions of coastal cliff retreats, a basic statistic underlying cliff top hazard assessment, are presented for 7.1 km of unprotected and slowly retreating coastal cliffs near Point Loma in San Diego, California, US. Using 8 airborne light detection and ranging (lidar) surveys collected over 5.5 years, 130 individual cliff edge failures (primarily rockfalls, block falls, and topples) were detected. Footprint areas varied from 3 to 268 m(2), maximum landward retreats from 0.8 to 10 m, and alongshore lengths from 2 to 68 m. The failures with the largest landward retreats were also relatively long, and 13% of the slides accounted for 50% of the lost cliff area over the study period. On this short (5.5 years) time scale, "no change" was the most common observation (84% of the cliff edge). Probability distributions of non-zero cliff retreat during each time interval usually had a single peak between 1 and 2.5 m. Intervals with high mean retreat had elevated numbers of failure in all class sizes, and also contained the largest individual retreats. Small and medium slides tended to reoccur preferentially (relative to randomly) near previous small and medium slides, forming short-term hot spots, while large slides were less likely to reoccur near previous large slides. Cumulative distributions of landslide failure parameters (area, mean retreat, maximum retreat, and length) follow an inverse power-law for medium to large size events, similar to previously reported distributions of coastal and inland landsliding.

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Ewing, L, Flick RE, Synolakis CE.  2010.  A review of coastal community vulnerabilities toward resilience benefits from disaster reduction measures. Environmental Hazards-Human and Policy Dimensions. 9:222-232.   10.3763/ehaz.2010.0050   AbstractWebsite

The coast has always been an area of significant hazards. In situations of community self-sufficiency, consequences of coastal hazards might be isolated to regions directly affected by the hazard. But, in the current global economy, fewer and fewer communities are isolated; damage to one location frequently has consequences around the globe and coastal community resilience can have broad-reaching benefits. Hazard responses for the built coastal environment have typically been resistance: constructing stronger buildings, enhancing natural barriers or creating artificial barriers. These approaches to hazard reduction through coastal engineering and shoreline defence efforts have been crucial to sustained coastal development. However, as coastal forces continue or magnify and resources become scarcer, resistance alone may be less effective or even unsustainable, and interest in resilience has grown. Resilience is a community's ability either to absorb destructive forces without loss of service or function, or to recover quickly from disasters. Community resilience encompasses multiple elements, ranging from governance to structural design, risk knowledge, prevention, warning systems and recovery. This paper focuses on hazards of coastal communities, and provides a review of some recent engineering efforts to improve the resilience elements of risk knowledge and disaster warnings for coastal disaster reduction.

Sanford, TB, Flick RE.  1975.  Relationship between Transport and Motional Electric Potentials in Broad, Shallow Currents. Journal of Marine Research. 33:123-139. AbstractWebsite
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Elwany, MHS, Flick RE.  1996.  Relationship between kelp beds and beach width in Southern California. Journal of Waterway Port Coastal and Ocean Engineering-Asce. 122:34-37.   10.1061/(asce)0733-950x(1996)122:1(34)   AbstractWebsite

The relationship between the width of kelp beds and the width of the beaches inshore was examined in the San Diego region of Southern California. Two statistical approaches were used. The first simply determined the correlation between kelp-bed width and adjacent-beach width. A small (0.3), but statistically significant, positive correlation was found in the 20% of shoreline that had both a nonzero beach width and an offshore kelp bed; however, no correlation was found when the entire shoreline was considered. The second method examined differences in width between beaches inshore of the kelp beds and those immediately to the north and south. No statistically significant differences were found. The overall conclusion is that there is no clear correlation or consistent pattern indicating that offshore kelp beds have any direct influence on adjacent-beach width.

Young, AP, Guza RT, Flick RE, O'Reilly WC, Gutierrez R.  2009.  Rain, waves, and short-term evolution of composite seacliffs in southern California. Marine Geology. 267:1-7.   10.1016/j.margeo.2009.08.008   AbstractWebsite

A four-year time series of nine airborne LiDAR surveys were used to assess the roles of wave attack and rainfall on the erosion of 42 km of southern California seacliffs. Nine continuous seacliff sections, separated by coastal lagoon mouths, all show maximum seacliff erosion in the rainiest time period (when wave energy was not particularly elevated), and in most sections the squared correlations between rainfall and erosion time series exceeded 0.8. Although rain and associated subaerial mechanisms such as groundwater seepage triggered most of the observed seacliff failures, wave attack accelerated seacliff erosion, with erosion rates of cliffs exposed to wave attack five times higher than at adjacent cliffs not exposed to waves. The results demonstrate the importance of both waves and rain in the erosion of southern California seacliffs and suggest that the combined influences of marine and subaerial processes accelerate the erosion rate through positive feedbacks. (C) 2009 Elsevier B.V. All rights reserved.

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Zetler, BD, Flick RE.  1985.  Predicted Extreme High Tides for Mixed-Tide Regimes. Journal of Physical Oceanography. 15:357-359.   10.1175/1520-0485(1985)015<0357:pehtfm>2.0.co;2   AbstractWebsite
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Zetler, BD, Flick RE.  1985.  Predicted Extreme High Tides for California - 1983-2000. Journal of Waterway Port Coastal and Ocean Engineering-Asce. 111:758-765. AbstractWebsite
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Flick, RE, Guza RT.  1980.  Paddle Generated Waves in Laboratory Channels. Journal of the Waterway Port Coastal and Ocean Division-Asce. 106:79-97. AbstractWebsite
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Elwany, MHS, Flick RE, Aijaz S.  1998.  Opening and closure of a marginal southern California lagoon inlet. Estuaries. 21:246-254.   10.2307/1352472   AbstractWebsite

Over the past 50 yr, direct observations of the inlet status (open or closed) of San Dieguito Lagoon, a typical southern California lagoon located in Del Mar, California, have shown that river flooding is the major natural determinant of inlet conditions on time scales longer than a few years. River flooding is strongly dependent on rainfall in the San Dieguito River watershed and on the influences of two water storage reservoirs in the area. Rainfall fluctuates on yearly and longer time scales and undergoes cycles of wet and dry periods. Over short time periods, ranging from a few months to several years, inlet status is primarily determined by the available tidal prism and littoral sand transport. Recognition of these factors is crucial in order to correctly evaluate the probability that a small lagoon will remain open naturally. A probability approach is essential because the variables controlling inlet conditions are random in nature. The results of our study show that the inlet will remain open naturally 34% of the time. The tendency to remain open is vastly smaller during years of dry weather (12%) versus times of above-average rainfall (66%).

Bromirski, PD, Flick RE, Graham N.  1999.  Ocean wave height determined from inland seismometer data: Implications for investigating wave climate changes in the NE Pacific. Journal of Geophysical Research-Oceans. 104:20753-20766.   10.1029/1999jc900156   AbstractWebsite

Knowing the wave climate along the California coast is vital from the perspectives of climatological change and planning shore protection measures. Buoy data indicate that the wave climate is very similar along much of the California coast. We show that elements of the wave climate can be accurately reconstructed using near-coastal inland broadband seismometer data. Such reconstructions are possible because swell approaching the coast generates pressure fluctuations that are locally transformed into seismic waves at the seafloor that propagate inland and are detectable by land-based seismometers. Buoy and seismometer data show that most of the microseism energy recorded inland near the coast is generated from wave events at nearby coastal locations. A site-specific, empirically derived seismic-to-wave transfer function is demonstrated to be applicable to seismic data from the same location for any year. These results suggest that ocean wave heights estimated from near-coastal broadband seismometer data are sufficiently reliable for monitoring the coastal wave height when buoy data are unavailable, provided that adequate simultaneous nearby buoy measurements are available to calibrate the seismometer data. The methodology presented here provides an important tool that allows the investigation of potential wave climate changes from reconstructions using archived seismic data collected since the 1930s.

George, R, Flick RE, Guza RT.  1994.  Observations of Turbulence in the Surf Zone. Journal of Geophysical Research-Oceans. 99:801-810.   10.1029/93jc02717   AbstractWebsite

Turbulence generated by waves breaking on a natural beach is examined using hotfilm anemometer data. Turbulence intensity is estimated from dissipation rates determined from wavenumber spectra of short (1/8 s) hotfilm time series. The resulting Froude-scaled turbulence intensities are relatively uniform between the seabed and the wave trough level and are similar in vertical structure but lower in magnitude than in existing laboratory studies. The magnitudes of the turbulence intensities observed in both the field and laboratory are consistent with an existing macroscopic model of bore dissipation in the surf zone. Scaling by this bore model relates turbulence intensities generated by monochromatic waves in small-scale laboratory experiments to those generated by random waves in the natural surf zone.

Young, AP, Guza RT, O'Reilly WC, Burvingt O, Flick RE.  2016.  Observations of coastal cliff base waves, sand levels, and cliff top shaking. Earth Surface Processes and Landforms. 41:1564-1573.   10.1002/esp.3928   AbstractWebsite

Concurrent observations of waves at the base of a southern California coastal cliff and seismic cliff motion were used to explore wave-cliff interaction and test proxies for wave forcing on coastal cliffs. Time series of waves and sand levels at the cliff base were extracted from pressure sensor observations programmatically and used to compute various wave impact metrics (e.g. significant cliff base wave height). Wave-cliff interaction was controlled by tide, incident waves, and beach sand levels, and varied from low tides with no wave-cliff impacts, to high tides with continuous wave-cliff interaction. Observed cliff base wave heights differed from standard Normal and Rayleigh distributions. Cliff base wave spectra levels were elevated at sea swell and infragravity frequencies. Coastal cliff top response to wave impacts was characterized using microseismic shaking in a frequency band (20-45Hz) sensitive to wave breaking and cliff impacts. Response in the 20-45Hz band was well correlated with wave-cliff impact metrics including cliff base significant wave height and hourly maximum water depth at the cliff base (r(2) = 0.75). With site-specific calibration relating wave impacts and shaking, and acceptable anthropogenic (traffic) noise levels, cliff top seismic observations are a viable proxy for cliff base wave conditions. The methods presented here are applicable to other coastal settings and can provide coastal managers with real time coastal conditions. Copyright (C) 2016 John Wiley & Sons, Ltd.

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Graham, NE, Cayan DR, Bromirski PD, Flick RE.  2013.  Multi-model projections of twenty-first century North Pacific winter wave climate under the IPCC A2 scenario. Climate Dynamics. 40:1335-1360.   10.1007/s00382-012-1435-8   AbstractWebsite

A dynamical wave model implemented over the North Pacific Ocean was forced with winds from three coupled global climate models (CGCMs) run under a medium-to-high scenario for greenhouse gas emissions through the twenty-first century. The results are analyzed with respect to changes in upper quantiles of significant wave height (90th and 99th percentile H-S) during boreal winter. The three CGCMs produce surprisingly similar patterns of change in winter wave climate during the century, with waves becoming 10-15 % smaller over the lower mid-latitudes of the North Pacific, particularly in the central and western ocean. These decreases are closely associated with decreasing windspeeds along the southern flank of the main core of the westerlies. At higher latitudes, 99th percentile wave heights generally increase, though the patterns of change are less uniform than at lower latitudes. The increased wave heights at high latitudes appear to be due a variety of wind-related factors including both increased windspeeds and changes in the structure of the wind field, these varying from model to model. For one of the CGCMs, a commonly used statistical approach for estimating seasonal quantiles of H-S on the basis of seasonal mean sea level pressure (SLP) is used to develop a regression model from 60 years of twentieth century data as a training set, and then applied using twenty-first century SLP data. The statistical model reproduces the general pattern of decreasing twenty-first century wave heights south of similar to 40 N, but underestimates the magnitude of the changes by similar to 50-70 %, reflecting relatively weak coupling between sea level pressure and wave heights in the CGCM data and loss of variability in the statistically projected wave heights.

Flick, RE, Knuuti K, Gill SK.  2013.  Matching Mean Sea Level Rise Projections to Local Elevation Datums. Journal of Waterway Port Coastal and Ocean Engineering-Asce. 139:142-146.   10.1061/(asce)ww.1943-5460.0000145   AbstractWebsite

A method is presented to consistently tie future mean sea level rise (MSLR) scenario projections to local geodetic and tidal datums. This extends the U. S. Army Corps of Engineer (USACE) guidance for incorporating the effects of future MSLR into coastal projects. While USACE relies on the National Oceanic and Atmospheric Administration (NOAA) 19-year National Tidal Datum Epoch (NTDE) for its datum relationships, the approach proposed herein generalizes this guidance by choosing the appropriate 19-year epoch centered on the start year of the MSLR scenario under consideration. The procedure takes into account the local annual sea level variability, which confounds the matching to any given single year while generalizing and preserving the 19-year averaging long used by NOAA to calculate the NTDE. Examples of the MSLR scenario matching procedure are given using actual data and projections for La Jolla, California, and Sewells Point (Hampton Roads), Virginia. DOI: 10.1061/(ASCE)WW.1943-5460.0000145. (C) 2013 American Society of Civil Engineers.