George M. Kaminsky

Seasonal to Interannual Morphodynamics along a High-Energy Dissipative Littoral Cell

Abstract A beach morphology monitoring program was initiated during summer 1997 along the Columbia River littoral cell (CRLC) on the coasts of northwest Oregon and southwest Washington, USA. This field program documents the seasonal through interannual morphological variability of these high-energy dissipative beaches over a variety of spatial scales. Following the installation of a dense network of geodetic control monuments, a nested sampling scheme consisting of cross-shore topographic beach profiles, three-dimensional topographic beach surface maps, nearshore bathymetric surveys, and sediment size distribution analyses was initiated. Beach monitoring is being conducted with state-of-the-art real-time kinematic differential global positioning system survey methods that combine both high accuracy and speed of measurement. Sampling methods resolve variability in beach morphology at alongshore length scales of approximately 10 meters to approximately 100 kilometers and cross-shore length scales of approximately 1 meter to approximately 2 kilometers. During the winter of 1997/1998, coastal change in the US Pacific Northwest was greatly influenced by one of the strongest El Niño events on record. Steeper than typical southerly wave angles resulted in alongshore sediment transport gradients and shoreline reorientation on a regional scale. The La Niña of 1998/1999, dominated by cross-shore processes associated with the largest recorded wave year in the region, resulted in net beach erosion along much of the littoral cell. The monitoring program successfully documented the morphological response to these interannual forcing anomalies as well as the subsequent beach recovery associated with three consecutive moderate wave years. These morphological observations within the CRLC can be generalized to explain overall system patterns; however, distinct differences in large-scale coastal behavior (e.g., foredune ridge morphology, sandbar mor-phometrics, and nearshore beach slopes) are not readily explained or understood.

Shoreface Sand Supply to Beaches

The possibility of sand supply from the shoreface to beaches was evaluated based on a variety of methods involving field data and modeling results obtained from five coasts on three continents representing a wide range of coastal environments. The field data include wave-current measurements, historical seabed soundings and geological surveys. Cross-shore transport estimates from modeling on the annual time scale were compared against scaled-down inferences from the seabed-change and geological data. The results are all consistent with there being net onshore transport over the long term from the lower shoreface to beaches in each of the environments. These environments typify settings that occur commonly (probably predominantly) along the worlds coasts. So net shoreface sand supply to beaches may be a widespread and common but little appreciated factor in coastal stability. The effect of this net supply is to offset other factors causing shoreline recession, such as positive gradients in littoral transport Moreover, shoreline progradation occurs if sand supply from the shoreface dominates over littoral sediment losses. Implications are clearly significant for coastal engineering and coastal management, despite the processes not being immediately apparent: long-term shoreface sand supply to beaches is masked by more rapid cyclical changes. Rates of shoreface sand supply to beaches indicated from various lines of evidence are typically on the order of 10 0 m 3 a –1 per meter of shoreline. This volume corresponds to a lowering of the shoreface by only a few grain diameters per year.

Extreme oceanographic forcing and coastal response due to the 2015–2016 El Niño

The El Niño-Southern Oscillation is the dominant mode of interannual climate variability across the Pacific Ocean basin, with influence on the global climate. The two end members of the cycle, El Niño and La Niña, force anomalous oceanographic conditions and coastal response along the Pacific margin, exposing many heavily populated regions to increased coastal flooding and erosion hazards. However, a quantitative record of coastal impacts is spatially limited and temporally restricted to only the most recent events. Here we report on the oceanographic forcing and coastal response of the 2015–2016 El Niño, one of the strongest of the last 145 years. We show that winter wave energy equalled or exceeded measured historical maxima across the US West Coast, corresponding to anomalously large beach erosion across the region. Shorelines in many areas retreated beyond previously measured landward extremes, particularly along the sediment-starved California coast.

Predicting Shoreline Change at Decadal Scale in the Pacific Northwest, USA

This paper presents the approach taken to model and predict decadal scale shoreline change in the Columbia River littoral cell along the coast of southwest Washington and northwest Oregon. This work is a principal component of the Southwest Washington Coastal Erosion Study, a research program directed by the Washington Department of Ecology and the US Geological Survey. A primary goal of the study is understanding and predicting coastal change at a management scale of tens of kilometers and decades. Historical morphological changes are viewed in context with coastal change over several centuries prior to human influence as well as with recent data collected by beach monitoring that quantifies morphologic response to forcing conditions. These multi-scale data sets are being used to inform process-based modeling that simulates historical changes and predicts the evolution of the coast several decades into the future. The initial shoreline change predictions mostly depend on extrapolation of historical sediment budgets. The example predictions of shoreline change to 2020 presented in this paper suggest the sensitivity of the present shoreline configuration to potential reductions in sediment supply. The results emphasize the significance of the sediment budget estimates used to predict the shoreline position in future decades.

Sensitivity of Shoreline Change Predictions to Wave Climate Variability along the Southwest Washington Coast, USA

A processes-based shoreline change model is applied to simulate historical shoreline behaviour and predict future change along a 40-km stretch of coast in the US Pacific Northwest. The sensitivity of the modeled shoreline change to different schematizations of the wave climatology is examined. The modeling results are most sensitive to directional changes in the incident waves as well as to the anomalous wave climatology associated with the 1997-1998 El Nifio. The sensitivity of shoreline change to a future climatology based on a trend of increasing significant wave height and peak period, was minimal. The impact of the 1997-1998 El Nifio was compared to 1999-2000, a more typical wave year, suggesting that on annual time-scales cross-shore transport processes dominate over alongshore processes. INTRODUCTION Following the construction of jetties at the Columbia River entrance in the late 1800s and early 1900s, the morphology of the Columbia River entrance and adjacent coasts has undergone significant change (Gelfenbaum et al, , 1999, Kaminsky et al. , 1999, and Kaminsky e t al, , 2001). As a result of this redistribution of sand, the Long Beach Peninsula, a 44-krn long barrier beach north of the Columbia River entrance (Figure 1), has accreted significantly during the last century, O(I0 m/yr). This trend of accretion has slowed in recent decades, and future erosion along southern Long Beach is now a possibility. Predicting shoreline change is a principal component of the Southwest Washington Coastal Erosion Study (SWCES), a goal of which is to understand the decadalscale coastal behaviour of the Columbia River Littoral Cell (CRLC). The one-line shoreline change model UNIBEST (WLIDelft Hydraulics, 1994) is being applied to simulate and understand historical (1955-1995) and to predict future (1995-2020) shoreline behaviour along the coast of Long Beach. 1) Washington Department of Ecology, Coastal Monitoring & Analysis Program, P.O. Box 47600 Olympia, WA 98504-7600 USA, mbui461 @ecy.wa.gov

Coastal sedimentary research examines critical issues of national and global priority

An international conference was held recently in Honolulu, Hawaii, to examine and plan for coastal sedimentary research in the United States and globally. Participants agreed that sedimentary coastal environments constitute a critical national and global resource that suffers widespread degradation due to human impacts. Moreover, human population growth and inappropriate development in the coastal zone are escalating public asset losses due to coastal hazards and placing large numbers of communities at growing risk (Figure 1).

COASTAL MORPHOLOGIC VARIABILITY OF HIGH ENERGY DISSIPATIVE BEACHES

Detailed studies have been undertaken to assist in the design of major extensions to the port of Haifa. Both numerical and physical model studies were done to optimise the mooring conditions vis a vis the harbour approach and entrance layout. The adopted layout deviates from the normal straight approach to the harbour entrance. This layout, together with suitable aids to navigation, was found to be nautically acceptable, and generally better with regard to mooring conditions, on the basis of extensive nautical design studies.Hwa-Lian Harbour is located at the north-eastern coast of Taiwan, where is relatively exposed to the threat of typhoon waves from the Pacific Ocean. In the summer season, harbour resonance caused by typhoon waves which generated at the eastern ocean of the Philippine. In order to obtain a better understanding of the existing problem and find out a feasible solution to improve harbour instability. Typhoon waves measurement, wave characteristics analysis, down-time evaluation for harbour operation, hydraulic model tests are carried out in this program. Under the action of typhoon waves, the wave spectra show that inside the harbors short period energy component has been damped by breakwater, but the long period energy increased by resonance hundred times. The hydraulic model test can reproduce the prototype phenomena successfully. The result of model tests indicate that by constructing a jetty at the harbour entrance or building a short groin at the corner of terminal #25, the long period wave height amplification agitated by typhoon waves can be eliminated about 50%. The width of harbour basin 800m is about one half of wave length in the basin for period 140sec which occurs the maximum wave amplification.Two-stage methodology of shoreline prediction for long coastal segments is presented in the study. About 30-km stretch of seaward coast of the Hel Peninsula was selected for the analysis. In 1st stage the shoreline evolution was assessed ignoring local effects of man-made structures. Those calculations allowed the identification of potentially eroding spots and the explanation of causes of erosion. In 2nd stage a 2-km eroding sub-segment of the Peninsula in the vicinity of existing harbour was thoroughly examined including local man-induced effects. The computations properly reproduced the shoreline evolution along this sub-segment over a long period between 1934 and 1997.In connection with the dredging and reclamation works at the Oresund Link Project between Denmark and Sweden carried out by the Contractor, Oresund Marine Joint Venture (OMJV), an intensive spill monitoring campaign has been performed in order to fulfil the environmental requirements set by the Danish and Swedish Authorities. Spill in this context is defined as the overall amount of suspended sediment originating from dredging and reclamation activities leaving the working zone. The maximum spill limit is set to 5% of the dredged material, which has to be monitored, analysed and calculated within 25% accuracy. Velocity data are measured by means of a broad band ADCP and turbidity data by four OBS probes (output in FTU). The FTUs are converted into sediment content in mg/1 by water samples. The analyses carried out, results in high acceptance levels for the conversion to be implemented as a linear relation which can be forced through the origin. Furthermore analyses verifies that the applied setup with a 4-point turbidity profile is a reasonable approximation to the true turbidity profile. Finally the maximum turbidity is on average located at a distance 30-40% from the seabed.

Exploring the Relationship between Nearshore Morphology and Shoreline Change

Abatraot: Nearshore bathymetry data collected along the US Pacific Northwest is analyzed to determine relationships between nearshore morphology and shoreline change at a variety of spatial scaks. Sandbar properties are compared at three sites, locations separated by tens of kilometers but subject to similar hydrodynanuc forcing and having like sediment characteristics. These three sites, an accreting coast, an eroding coast, and a dynamically stable coast, are shown to exhibit different large-scale coastal hehaviour. The nearshore profile slopes at these locations are correlated with recent shoreline change history. Measurements have revealed offshore trending sandbars that are continuous over alongshore distances of tens of kilometers, hehavlour that spatially mimics the net offshore bar migration documented on several other coasts.

Spatial and Temporal Variability of Dissipative Dry Beach Profiles in the Pacific Northwest, U.S.A.

ABSTRACT Díez, J.; Cohn, N.; Kaminsky, G.M.; Medina, R., and Ruggiero, P., 2018. Spatial and temporal variability of dissipative dry beach profiles in the Pacific Northwest, U.S.A. Dissipative beaches in the U.S. Pacific Northwest are subject to a marked seasonality in wave climate and water levels, which leads to periodic oscillations in the morphology of the typically dry part of the beach profile. The back-and-forth, seasonal sediment exchange between the emerged and submerged parts of the beach system induces two main dry-beach profile-equilibrium configurations. During approximately 70% of the year, the dry beach adapts its configuration to a uniform positive slope from the mean high-water level to the dune toe. The remaining 30% of the time, typically corresponding to summer, the profile adopts a berm-like profile. These changes are quantified by studying intra-annual and interannual variations of the dry-beach profile shape. For intra-annual variations, a monthly profiling campaign between July 2014 and October 2015 from South Beach State Park (Oregon) was used. For interannual variations, 17 years (1997–2015) of quarterly beach profiles at 31 transects spread along the four subcells that constitute the Columbia River littoral cell were used. Several morphological phenomena have been identified via the application of two data-mining routines: the K-means clustering technique (KMA) and empirical orthogonal functions (EOFs). KMA clustering illustrates the main equilibrium configurations that the dry-beach profile experiences over time, whereas the EOF analysis explains the variability of the data in space and time. These analyses allow for examinations of berm formation and destruction as well as the shifting of the profile between summer/winter configurations—among other changes induced by the cross-shore sediment exchange, such as beachface and dune toe erosion and recovery.

New Insights on Coastal Foredune Growth: The Relative Contributions of Marine and Aeolian Processes

Coastal foredune growth is typically associated with aeolian sediment transport processes, while foredune erosion is associated with destructive marine processes. New data sets collected at a high energy, dissipative beach suggest that total water levels in the collision regime can cause dunes to accrete-requiring a paradigm shift away from considering collisional wave impacts as unconditionally erosional. From morphologic change data sets, it is estimated that marine processes explain between 9% and 38% of annual dune growth with aeolian processes accounting for the remaining 62% to 91%. The largest wind-driven dune growth occurs during the winter, in response to high wind velocities, but out of phase with summertime beach growth via intertidal sandbar welding. The lack of synchronization between maximum beach sediment supply and wind-driven dune growth indicates that aeolian transport at this site is primarily transport, rather than supply, limited, likely due to a lack of fetch limitations.