Wave Run-Up and Sea-Cliff Erosion

Shih, S.-M.; Komar, P. D.; Tillotson, Kenneth J.; McDougal, W. G.; Ruggiero, P.

doi:10.1061/9780784400890.158

Cited by 12 publications

(14 citation statements)

References 2 publications

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“…Total water level (TWL) is the sum of the observed water level at the Los Angeles tide gage (station 9410660) and the vertical height of wave runup (Ruggiero et al, ; Shih et al, ). Vertical wave runup was approximated as the level exceeded by 2% of wave uprushes (Stockdon et al, , equation (18)).…”

Section: Methodsmentioning

confidence: 99%

Southern California Coastal Response to the 2015–2016 El Niño

et al. 2018

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Widespread erosion associated with energetic waves of the strong 2015–2016 El Niño on the U.S. West Coast has been reported widely. However, Southern California was often sheltered from the northerly approach direction of the offshore waves. The few large swells that reached Southern California were not synchronous with the highest tides. Although west coast‐wide tidal anomalies were relatively large in 2015–2016, in Southern California, total water levels (sum of tides, anomalies, and wave superelevation) were lower than during the 1997–1998 Niño, and comparable to the 2009–2010 Niño. Airborne lidar surveys spanning 300 km of Southern California coast show the beach response varied from considerable erosion to accretion. On average, the shoreline moved landward 10 m, similar to the 2009–2010 El Niño. Some San Diego county beaches were narrower in the 1997–1998 El Niño than in 2015–2016, consistent with the higher erosion potential in 1997–1998. Beach retreat exceeded 80 m at a few locations. However, 27% of the shoreline accreted, often in pocket beaches, or near jetties. While adjacent beaches eroded, estuary mouths accreted slightly, and several estuaries remained or became closed during the study period. Only 12% of cliffs eroded (mostly at the base), and the average cliff face retreat was markedly less than historical values. Only two cliff‐top areas retreated significantly. Although some areas experienced significant change, the potential for coastal erosion and damage in Southern California was reduced compared to the 1997–1998 El Niño, because of low rainfall, a northerly swell approach, and relatively limited total high‐water levels.

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Section: Methodsmentioning

confidence: 99%

Southern California Coastal Response to the 2015–2016 El Niño

et al. 2018

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“…4) is the sum of tides and the vertical height of wave runup (Shih et al, 1994;Kirk et al, 2000;Ruggiero et al, 2001;Collins and Sitar, 2008). Tidal fluctuations are more than 2 m during spring tides, so large swells arriving during relatively low tide may not even reach the cliffs, whereas moderate swell arriving during high tide can have significant impact duration.…”

Section: Waves and Runupmentioning

confidence: 97%

Rain, waves, and short-term evolution of composite seacliffs in southern California

et al. 2009

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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.

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“…Evidence from experiments and fieldwork indicates that moderately cohesive sediments, such as underlie most of our study sites, erode with relative ease (Shih et al 1994). Furthermore, erosion of such sediments in low‐energy environments occurs only at tides above the mean high spring tide (MHST) with some minimum wind speed to produce waves up to the riser base, and such episodes of erosion are relatively infrequent (<20 events yr −1 ) (McGreal 1979).…”

Section: Raised Shoreline Data and Error Analysismentioning

confidence: 99%

Rapid uplift of southern Alaska caused by recent ice loss

Larsen

Motyka

Freymueller

et al. 2004

Geophysical Journal International

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S U M M A R Y Extreme uplift rates and sea level changes in southern Alaska have been documented by GlobalPositioning System (GPS) surveys, tide gauge measurements and studies of raised shorelines. The movements detected in a network of 45 GPS survey points describe a broad pattern of rapid regional uplift. The majority of the study area is uplifting at a rate faster than 10 mm yr −1 , with several sites uplifting more rapidly than 25 mm yr −1 . New tide gauge data presented here consist of repeat occupations of 18 temporary gauge sites. Sea level rates at these sites agree with similar measurements in southern Alaska taken ∼50 yr earlier, and also with the pattern of uplift derived from the GPS data. Raised shoreline studies at 14 sites document total sea level change, with a maximum change in sea level of −5.7 m found in upper Lynn Canal. The start of the ongoing uplift episode that raised these shorelines has been dated with dendrochronology and found to be coincident with the start of the collapse of the Glacier Bay Icefield, at ca. 1750 AD. The pattern of total sea level change is in general agreement with upliftrate measurements, with greater sea level change found at the sites closest to the peak uplift rates in upper Glacier Bay. We use a viscoelastic earth model subjected to an ice load history built upon observations of glacial change to predict uplift rates at the tide gauge and GPS sites as well as the total uplift at the raised shoreline sites. Our modelling exercises are limited to an ice load model based on independent studies of the region's glacial history over the past 1.7 kyr, to evaluate whether the uplift observations can be explained by simple earth models subjected to this load history. Two-layer earth models, consisting of an elastic crust and a low-viscosity upper mantle half-space, can be adjusted to fit either the raised shoreline data or the combined GPS and tide gauge uplift-rate data, but cannot fit all the data with a single set of earth model parameters. However, all three data sets are consistent with an approximated three-layer earth model. The combined model is constrained by a total of 77 uplift measurements, which at the 95 per cent confidence level require a low-viscosity asthenosphere [η A = (1.4 ± 0.3) × 10 19 Pa s and thickness 110 +20 −15 km] beneath a 50 +30 −25 km thick elastic lithosphere and overlying an upper mantle half-space with a viscosity of 4 × 10 20 Pa s. This earth model achieves a low degree of misfit with the observations (reduced chi-square value of χ 2 ν = 2.5), suggesting that glacial isostatic rebound associated with post-Little Ice Age melting can entirely account for the rapid uplift of southern Alaska over the last ∼250 yr.

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Wave Run-Up and Sea-Cliff Erosion

Cited by 12 publications

References 2 publications

Southern California Coastal Response to the 2015–2016 El Niño

Southern California Coastal Response to the 2015–2016 El Niño

Rain, waves, and short-term evolution of composite seacliffs in southern California

Rapid uplift of southern Alaska caused by recent ice loss

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