Sea-Level Rise for the Coasts of California, Oregon, and Washington Past, Present, and Future (2012) / Chapter Skim
Currently Skimming:
6 Responses of the Natural Shoreline to Sea-Level Rise
6 Responses of the Natural Shoreline to Sea-Level Rise
Pages 109-136
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From page 109... ...
Cliffs and bluffs are dominant features along the The distribution and character of coastal habitats west coast of the United States, and they have been and geomorphic environments varies along the Cali- retreating for thousands of years. The rate of coastal fornia, Oregon, and Washington coasts, as does their cliff and bluff retreat is controlled by the properties of response to sea-level rise.
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From page 110... ...
Some evidence suggests that waves have been increasing in height off the west coast. SOURCE: Courtesy of Erica Harris, Oregon State University.
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From page 111... ...
Approximately one-third of the Puget them as waves and littoral currents easily move the Sound shoreline is now armored (Shipman et al., sand. Along the west coast, beaches change seasonally 2010)
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From page 112... ...
SOURCE: Copyright 20022012 Kenneth & Gabrielle Adelman, California Coastal Records Project, |
From page 113... ...
Over the long that 28 dams and more than 150 debris basins in the term, rising sea level will cause landward migration water sheds of eight major rivers in southern California or retreat of beaches. The retreat is caused partly by have impounded more than 4 million m3 yr-1 of sand.
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From page 114... ...
of sea-level rise, all west coast beaches with hardened or constrained back beach edges will gradually be COASTAL DUNES inundated. Only a few studies have quantified rates of change Cooper (1958, 1967)
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From page 115... ...
. Many of the dune to the beach, is an ephemeral and unstable feature areas exposed along and inland from the west coast (e.g., McHarg, 1969)
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From page 116... ...
(Left) Homes in central Monterey Bay were threatened by erosion during the high tides, elevated sea levels, and large storm wave of the 1983 El Niño.
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From page 117... ...
Such uncertainties in land losses, combined with uncer tainties in exactly how sandy shorelines with back beach barriers or armor will respond to sea-level rise and with uncertainties in rates of future sea-level rise, make precise projections of future beach retreat or erosion in these areas problematic. Wave Energy and Coastal Erosion Wave-induced cliff and shoreline erosion is a sig nificant problem along the west coast of the United States, and an increase in wave energy will only in crease the rates of retreat.
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From page 118... ...
. The first lidar topographic survey of the California coast was flown in October 1997 as a large El Niño event was approaching the west coast.
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From page 119... ...
. Large storm waves occurring during Diego County, California, found significant variation high tide or times of elevated sea level are particularly in the rate of erosion, as well as in intrinsic proper
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From page 120... ...
0 25 50 100 150 200 1.4m by 2100 FIGURE 6.12 Variability in the distances coastal cliffs along the central and northern California coast are projected to erode under sea-level rise of 1.0 and 1.4 m by 2100 relative to 2000. Bar charts along the coast show average and maximum erosion distances between the 1.0 and 1.4 m sea-level rise scenarios.
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From page 121... ...
The largest estuaries along the west coast of Living with the Changing California Coast (Griggs the United States include Puget Sound, the Columbia et al., 2005) provides a different approach for assessing River Estuary, and the San Francisco Bay-Delta.
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From page 122... ...
. Extensive tidal marshes also existed historically within the deltas of major rivers flowing into Puget Sound, such as the Nisqually and Skagit rivers.
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From page 123... ...
If tolerance Important west coast marsh species in high-salinity limits of the vegetation are exceeded, abrupt transitions habitats include Spartina foliosa (from Bodega Bay could occur.
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From page 124... ...
The efficacy of some west coast are a product of their sea level and tectonic Spartina species in trapping suspended sediments has histories, which control the position of the sea relabeen demonstrated in many areas, especially where in- tive to valleys and coastal embayments and influence vasive species have quickly covered large intertidal areas sediment delivery from adjacent steep watersheds. San and raised elevations.
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From page 125... ...
. The cross-profile shape Slough Watershed, the relationship between estuarine of intertidal flats in southern San Francisco Bay, an marshes and adjacent uplands varies according to the important determinant of their role in wave attenua- changing nature of watershed inputs (Byrd and Kelly, tion, is influenced by sediment deposition, tidal range, 2006)
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From page 126... ...
they cannot maintain their relative elevation. Although The response of coastal marshes to sea-level rise is the figure shows an idealized uniform slope, many influenced by changes in sediment dynamics, mediated west coast shorelines steepen abruptly landward of the by physical forcing, biotic factors, and plant growth.
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From page 127... ...
Fully assessing the fate of west coast marshes under climate change, including sea-level rise, is further hampered by the lack of long-term data on many west coast marshes and the differences in species composition compared to other more-studied systems. Response of Mudflats and Marshes to Future SeaLevel Rise and Storms The regional projections presented in Chapter 5 show substantial differences in the magnitude of sealevel change along the west coast.
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From page 128... ...
(2011) , who examined the of high sediment supply, the opportunity for sediment fate of San Francisco Bay marshes under varying rates deposition increases.
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From page 129... ...
ments. The depth of flooding and its interaction with If the highest estimates of sea-level rise are realized for plant stems and leaves is yet another nonlinear relationthis part of the coast, only marshes in areas with a high ship as field studies of wave attenuation in seagrass beds local sediment supply (e.g., at the mouth of major river have demonstrated (e.g., Koch et al., 2009)
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From page 130... ...
Many land surfaces within the As shown above, the response of marshes to future delta are currently on the order of 35 m below water sea-level rise and storminess along the west coast of levels. Data from interferometric synthetic aperture the United States depends on local conditions.
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From page 131... ...
late 1990s may have enabled higher accretion rates in restored marshes in the past than would be possible Effect of Restored Marshes on Wave and Storm in the future. Transport of sediment from adjacent Attenuation intertidal and subtidal flats into relatively quiescent restored areas where it cannot be readily suspended The Golden Gate carries storm surges from the would promote accretion in restored marshes at the open coastal Pacific into San Francisco Bay and expense of the erodible sediment pool.
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From page 132... ...
. Whether vertical land movements enhance or counterCase Study on the Puget Sound act the effects of regional sea-level rise has important implications for existing coastal habitats, the viability Puget Sound includes more than 8,000 square of future restoration, and the potential of these habitats kilometers of marine waters and nearshore environ to help mitigate the effects of future storms.
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From page 133... ...
Tidal hydrology and sediment delivery, combined with general trends in sediment input affect many delta processes, including vertical land motion, can be used to identify areas where distributary channel migration, tidal channel formation restored coastal marshes would most likely survive and maintenance, sediment retention, and exchange of future sea-level rise. In general, areas with high fluvial aquatic organisms.
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From page 134... ...
found an sea-level rise for 2030 and 2050. Under the highest overall success rate of 1380 percent, concluding that sea-level projections for 2100, a high sediment supply eelgrass transplantation cannot yet be used reliably for and uplift may not be enough for restoration to succeed, mitigation in Puget Sound.
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From page 135... ...
bed currents, turbulence, and drag in the San Juan Rising sea levels and increasing wave heights will archipelago of Puget Sound. Zostera marina grows exacerbate coastal erosion and shoreline retreat in at water depths less than 5 m relative to mean lower all geomorphic environments along the west coast.
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From page 136... ...
For A detailed assessment of the response of west coast 2100, marshes will need room to migrate, a high sedimarshes to sea-level rise is hampered by the lack of ment supply, and uplift or low subsidence to survive long-term and/or comparable data and by the variety projected sea-level rise. of geological (e.g., vertical land motion, sediment
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