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Assessing Coastal Hazards: Investigating the Linkages Between Nearshore Bathymetry and Shoreline Change: Peter Ruggiero

Project Title: Assessing Coastal Hazards: Investigating the Linkages Between Nearshore Bathymetry and Shoreline Change
Mendenhall Fellow: Peter Ruggiero, (650) 329-5433, pruggiero@usgs.gov
Duty Station: Menlo Park
Start Date: July 9, 2001
Education: Ph.D. (Civil Engineering), Oregon State University, 1997
Research Advisors: Guy R. Gelfenbaum, (650) 329-5483, ggelfenbaum@usgs.gov; Christopher R. Sherwood, (508) 457-2269, csherwood@usgs.gov
Project Description: Due to the great societal impact of coastal hazards, it is becoming increasingly important to develop a predictive capability with which to determine both the magnitude and frequency of coastal erosion along our shorelines. The socially relevant scales for these predictions range temporally from individual storm events to decadal-scale shoreline change and spatially from hundreds of meters to hundreds of kilometers. The goal of my Mendenhall Postdoctoral research is to evaluate and improve upon our existing predictive capabilities for nearshore morphology and shoreline change over this continuum of socially relevant scales. This will be accomplished using both existing data sets and state of the art numerical models. Achieving this goal will demonstrate improved understanding of coastal processes and morphodynamics along rapidly changing coastlines, leading to a better ability to assess the vulnerabilities of the coast to erosion, flooding and other natural hazards.

The large-scale behaviour (both in space and time) of nearshore morphology (such as sandbars) is just beginning to be understood. The few data sets presently available reveal increasingly more complex behaviour than originally thought to exist. For example, analyses of nearshore bathymetric data sets have demonstrated that interannual change contributes significantly to the overall nearshore bathymetric variability via slow cross-shore migration of bars. These observations force us to conclude that many existing descriptive and predictive models, which assume that beach response occurs at a time scale corresponding to changes in the incident wave climate, are inconsistent with a significant fraction of nearshore morphologic variance. This shortcoming is particularly serious because an understanding of inter-annual and decadal time scale response is most relevant to societal decisions regarding human response to the dynamic nearshore environment.

In this study, existing models will be tested with field measurements in order to improve our ability to predict coastal profile and shoreline change at event, seasonal, and interannual time scales.

Major Science Questions:
It is hypothesized that variability in nearshore morphology, that is, position, height and volume of sandbars has a first order affect on the position and variability of the shoreline at a variety of time scales. During individual storm events, sandbars store sediment eroded from the sub-aerial beach and provide a buffer against further erosion. In a recent study of kilometer-scale shoreline response to storms at Duck, N.C., erosion occurred at non-uniform locations or "hotspots." Since bars dissipate wave energy and protect the sub-aerial beach, alongshore gradients in offshore bar position and geometry may create such regions of relative vulnerability or resilience along the coast. However, the North Carolina data set only contains shoreline position change and lacks the nearshore bathymetry needed to test the above hypothesis. The aim of the research proposed here is to test this hypothesis using existing models and the few relevant data sets that merge topographic with nearshore bathymetric change.

The primary research objectives for the present study include:

  1. Use existing models to investigate the processes responsible for the highly variable nearshore morphology observed along the coastline.

  2. Quantify the relationships between nearshore morphometric parameters (number of bars in the cross-shore, bar height, cross-shore position of bars etc.) and shoreline variability, that is, beach erosion, accretion, and dynamic stability.

  3. Assess the ability of existing models, for example, UNIBEST-TC , to predict profile evolution and shoreline change at event, seasonal, and inter-annual time scales.

Publications:
Buijsman, M.C., Ruggiero, P., and Kaminsky, G., 2001, Sensitivity of shoreline change predictions to wave climate variability along the Southwest Washington coast, USA: Coastal Dynamics 2001, Lund Sweden, p. 617-626.

Ruggiero, P., Gelfenbaum, G., Thompson, D., and Kaminsky, G., 2001, Exploring the relationship between nearshore morphology and shoreline change: Coastal Dynamics 2001, Lund Sweden, p. 627-636.

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