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USGS Mendenhall Postdoctoral  Research Fellowship Program

16-37. Coastal response under rising sea levels – how sediment budgets influence shoreline change

The predicted future acceleration in sea-level rise and changes in storm patterns poses the question: how will the coast respond in the next century? Changes in coastal morphology can be expected and many studies predict large-scale coastal erosion. However, future shoreline predictions are often based on the application of Bruun Rule-type models that employ a simple relationship between sea-level rise and shoreline retreat, without taking into account the dynamic response of the sedimentary coastal system. On the other hand, resolving the coastal dynamics on the storm-event time scale is complex, computationally expensive, and difficult to upscale. Predicting the cumulative long-term effect of climate change on sandy coasts requires taking into account possible changes in storm magnitude and frequency and changes in sediment budget, including sources such as rivers and cliffs and sinks such as tidal deltas, estuaries, and barriers, and how they are influenced by changes in sea level.

Our hypothesis is that the net supply of sediment will govern the dynamic response of the coastal system, both in the short and long term. In the present-day sea level high-stand situation, most marine sediment sources that fed the building of coastal systems during the Late Holocene are depleted. That means that the present-day net sediment supply is coming from rivers (many of which are dammed), local cliff erosion, and reworking of sediment bodies in the coastal zone. A recent United Nations Environmental Program (UNEP) report (UNEP GEAS, 2014) describes the decline of the sediment supplied to the coast. It states that sand and gravel account for the largest volume of solid material extracted globally, that the rate of extraction is far greater than the renewal, and that the amount being mined from rivers, coasts and the sea-bed is increasing exponentially. A conservative estimate for the world consumption of aggregates exceeds 40 billion tons a year, which is twice the amount of sediment supplied by all the rivers in the world (UNEP GEAS, 2014). This will have a serious impact on rivers, deltas and coastal and marine ecosystems and result in a decreased sediment supply and loss of land through river and coastal erosion. Local coastal erosion problems are in many cases caused by interference with the natural sediment fluxes. For example, in California damming has reduced sediment supply to the coast by 23% (Slagel and Griggs, 2008) and damming on the Nile River has resulted in long-term delta shoreline retreat of more than 100 m/yr (Frihy and Komar, 1993). Sustainable solutions for coastal erosion due to climate change will have to consider not only sea-level rise and storm patterns, but also the sediment budget of the coastal system.

The geological study of coastal systems shows that the sediment budget is crucial for the response of these systems to sea-level rise, both on short and long time scales. The balance between increased accommodation space for sediment along the coast and in the coastal plain caused by the rise in sea level, and the supply of sediment to fill that space determines the long-term coastal evolution. Essentially, this is a ‘demand’ versus ‘supply’ relationship. If the supply outruns the demand, the shoreline will be stable or prograde seaward. If the supply is too limited, the coast will erode and the shoreline will recede landward. Therefore, it is critical to include sediment budgets in any model projecting future coastal response to sea-level rise and climate change.

We seek a Mendenhall Fellow to make a fundamental scientific contribution to the coastal research community that results in more sophisticated and accurate predictions of the coastal response to climate change. Specifically, the aim of this opportunity is to build a quantitative model based on the hypothesis that sediment supply is a dominant driver in determining the dynamic response of a coastal system to sea-level rise and climate change. This model should be a general tool that builds on previous barrier or shoreline evolution model approaches (e.g., Cowell et al., 2003; Lorenzo-Trueba and Ashton, 2014) by adding longshore sediment transport processes to the existing cross-shore balance. The overall goal of research under this Opportunity is to quantify the balance between accommodation space and sediment supply to assess and predict future coastal response at decadal to century time scales. This tool needs to be tested and validated against data sets of long-term coastal evolution. The extensive data sets of the Late Holocene evolution of the Dutch North Sea coast (Beets & van der Spek, 2000) and the historical evolution of the Columbia River littoral cell along the US Pacific Northwest coast (Kaminsky et al., 2010) are readily available for this exercise. Moreover, the model can be tested against data on decadal coastal evolution as well. The changes in development of the Dutch coast since the introduction of a large-scale sand nourishment scheme suggest that the supply-demand model is valid for these shorter time scales too. The final model should be applicable to any sedimentary coastal system on time scales from decades to centuries.

REFERENCES

Beets & van der Spek, 2000. The Holocene evolution of the barrier and the back-barrier basins of Belgium and the Netherlands as a function of late Weichselian morphology, relative sea-level rise and sediment supply. Netherlands Journal of Geosciences, 79 (1), 3-16.

Cowell, Stive, Niederoda, Swift, de Vriend, Buijsman, Nicholls, Roy, Kaminsky, Cleveringa, Reed & de Boer, 2003. The Coastal-Tract (part 2): Applications of aggregated modeling of low-order coastal change. Journal of Coastal Research, 19 (4), 828-848.

Frihy, O.E., Komar, P.D., 1993. Long-term shoreline changes and the concentration of heavy minerals in beach sands of the Nile-delta, Egypt. Marine Geology 115 (3–4), 253–261.

Kaminsky, Ruggiero, Buijsman, McCandless & Gelfenbaum, 2010. Historical evolution of the Columbia River littoral cell. Marine Geology, 273, 96-126.

Lorenzo-Trueba, J., and A. D. Ashton, 2014. Rollover, drowning, and discontinuous retreat: Distinct modes of barrier response to sea-level rise arising from a simple morphodynamic model, J. Geophys. Res. Earth Surf., 119, 779–801, doi:10.1002/2013JF002941.

Slagel and Griggs, 2008. Cumulative Losses of Sand to the California Coast by Dam Impoundment, JCR Volume 24 (3), p. 571-584.

UNEP GEAS, 2014. Sand, rarer than one thinks. Publication United Nations Environmental Program – Global Environmental Alert Service, March 2014, 15pp.

Proposed Duty Station: Santa Cruz, CA

Areas of Ph.D.: Oceanography, geology, or coastal engineering (candidates holding a Ph.D. in other disciplines but with knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet one of the following qualifications - Research Oceanographer, Research Geologist, Research Physical Scientist, or Research Engineer (This type of research is performed by those who have backgrounds for the occupations stated above. However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Research Advisor(s): Guy Gelfenbaum, (831) 460-7417, ggelfenbaum@usgs.gov; Ad van der Spek (Deltares USA), Ad.vanderSpek@deltares.nl; Patrick Barnard, (831) 460-7556, pbarnard@usgs.gov; Edwin Elias, (831) 460-7573, epelias@usgs.gov; George Kaminsky (Washington Department of Ecology), (360) 407-6797, GKAM461@ecy.wa.gov; Peter Ruggiero (Oregon State U), (541) 737-1239, pruggier@coas.oregonstate.edu.

Human Resources Office Contact: Paul Rawlins, (916) 278-9388, prawlins@usgs.gov.


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U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/opps/2016/round16/16-37 Gelfenbaum.htm
Direct inquiries to Rama K. Kotra at rkotra@usgs.gov
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