Project Title: Ultra-High Resolution and High-Frequency Change-Detection of Beach Face and Coastal Sea-Cliffs
Mendenhall Fellow: Brian D. Collins, (650) 329-5546, firstname.lastname@example.org
Duty Station: Menlo Park, CA
Start Date: January 23, 2006
Education: Ph.D. (Civil Engineering), University of California, Berkeley, 2004
Research Advisor: Robert Kayen, (650) 329-4195, email@example.com
Project Description: Rapid sea-cliff retreat along distinct portions of the U.S. Pacific coastline occurs frequently during each year’s winter storm season (Gerstal and others, 1998; Griggs and Savoy 1985; Komar and Shih 1993). Given the close proximity of many of these areas to highly developed portions of the U.S. west coast (fig. 1) and to key transportation routes along the coast, there is an urgent need to be able to understand and identify failure prone areas in danger of affecting human life and property.
Figure 1. Highly developed portions of the U.S. west coast located near areas of actively eroding sea cliffs. (A) San Francisco area. (B) San Diego area. (Photos are copyright © 2002-2005 Kenneth & Gabrielle Adelman, California Coastal Records Project, http://www.californiacoastline.org/)
Prediction of these events is difficult, owing to the ever-changing beach face and cliff morphology and the interaction between cliff material strength and the various failure mechanisms, including wave action and precipitation induced seepage. In many cases, sea cliff retreat can be linked directly to dramatic changes to the beach face, when periods of high wave energy both lower and reconfigure the near shore zone to allow direct exposure of sea cliffs to severe wave action. In other cases, precipitation and artificially induced groundwater seepage is responsible for cliff retreat through soil strength loss and development of seepage pressures within the cliff sediments. While there have been numerous efforts to identify the predominant failure mechanisms for particular stretches of sea cliff (e.g. Hampton 2002; Lajoie and Mathieson 1985 in the San Francisco, California area), there has yet to be attempted a comprehensive short term prediction of future cliff retreat in these and other highly active areas.
Given the introduction of new, state of the art technologies for performing change detection (3D laser scanning) (fig. 2), the availability of real-time data sets of climatic conditions (wave-tide recorders, buoys, and rain gauges), and the capability of powerful geotechnical modeling programs (finite element software packages), all the elements for developing reliable empirical correlations and analytical models, and obtaining predictions of future sea cliff change are now available.
Figure 2. 3D laser scanning (A) equipment and (B) surface models showing retrogressive sea cliff failures (from Collins, 2004).
The major goal of this project is to collect high resolution/high frequency data sets of beach and sea cliff change and to use these data sets as a basis for understanding the geotechnical behavior of steep sea cliffs under the influence of both wave action and precipitation induced seepage effects (fig. 3). From these studies, analytical and empirical models will then be developed for predicting beach change and sea cliff failure.
Figure 3. Geotechnical models of common failure modes in sea-cliffs (from Collins, 2004).
Among the scientific questions to be answered from this research are:
- What are the relationships between off- and near-shore wave climate and beach change and what are their effects on sea cliff failures?
- How does sea-cliff morphology relate to the evolution of sea cliff failures and can failure be predicted based on quantitative factors provided by high resolution topographical datasets?
- Can short-term, definitive predictions of sea cliff failures from large storm events be made using the combined effort of wave climate modeling, precipitation induced seepage indicators, beach and sea cliff characterization, and geotechnical modeling?
- What are the short and long term effects of sea level rise on the empirical and analytical models resulting from the research characterization? What are the future implications for land loss and societal endangerment?
Collins, B. D. (2004). "Failure Mechanics of Weakly Lithified Sand Coastal Bluff Deposits," University of California, Berkeley, Dissertation, 278p.
Gerstal, W. J., Brunengo, M. J., Lingley Jr., W. S., Logan, R. L., Shipman, H., and Walsh, T. J., 1998, Puget Sound Bluffs: The where, why, and when of landslides following the holiday 1996/97 storms: Washington Geology, vol. 6, no. 1, p. 17-31.
Griggs, G. B., and Savoy, L., 1985, Living with the California Coast: Durham, N.C., Duke University Press.
Hampton, M., 2002, Gravitational failure of sea cliffs in weakly lithified sediment: Environmental and Engineering Geoscience, vol. 8, no. 3, p. 175-192.
Komar, P. D., and Shih, S.-M., 1993, Cliff erosion along the Oregon coast: A tectonic-sea level imprint plus local controls by beach processes: Journal of Coastal Research, vol. 9, no. 3, p. 747-765.
Lajoie, K. R., and Mathieson, S. A., 1985, San Francisco to Ano Nuevo, in Griggs, G. B,. and Savoy, L,. eds., Living with the California Coast: Durham, N.C., Duke University Press, p. 140-177.
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