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IMPACTS DUE TO ENGINEERING PROJECTS (i.e. CHANNELS, JETTIES, etc.)

Shoreline impacts (accretion and erosion) due to an engineering project constructed along or perpendicular to the shoreline are often evaluated using historical shoreline maps or profile information. The investigation of historical (and probable future) shoreline impact trends is necessary for Section 111 studies or litigation studies where quantification of project impact is required.

A common analysis procedure used for quantification of shoreline project impact is "even-odd analysis" as popularized by Berek and Dean(1982) and Dean and Work(1993). In this approach, the total shoreline change signal is separated into an "even" and an "odd" shoreline change signal. Typically, the "odd" component of shoreline change signal is noted to reflect accretion/erosion changes due to effects of longshore barriers (natural or man-made) impeding the littoral sediment transport. The "even" component of shoreline change signal may reflect offshore/onshore sediment transport patterns existing naturally or caused by man-made structures.

An example scenario from one U.S. East Coast location is shown below:

Figure(1a) The "total" shoreline change signal and the "odd" component of the "total" shoreline change signal are shown here. The distance along the shoreline is shown as the ordinate scale (where x=0 is the location of the project in question, in this case a navigation channel and jetties). As the interest is primarily on the adjacent shoreline effects of the project, the area between the jetties is not represented in this plot. The abscissa scale measures the shoreline change occurring between two different (historical) times for any given x location. The "odd" function portion of the total shoreline change signal represents (in part) the "longshore sediment transport" effects of the navigation entrance and jetties with accretion on the left side of the figure and erosion on the right.
Figure(1b) The "total" shoreline change signal and the "even" component of the "total" shoreline change signal are shown here. Ordinate and Abscissa scales are as in the previous figure. This "even" component of the total shoreline change pattern represents effects of channel dredging, onshore/offshore sediment transport, sediment sources or sinks, etc.

Additional information can be obtained by combining the approach utilized above along with analytical shoreline modeling techniques to better understand the shore processes and sediment transport rates at the site.

In many situations measurement noise in the data or (natural or man-made) rhythmic patterns inherent in the shoreline may mask important shoreline trends. In such cases further data analysis may be needed beyond even-odd shoreline change analysis discussed above. Methods to reduce measurement noise and improve the "true" shoreline change trends are provided in Walton(1998, 1999a, 1999b) where optimal least squares filtering, K-L techniques, and spatial correlation techniques,have been utilized to improve the understanding of the shoreline trend patterns.

Should you have any specific project needs for these types of data analysis please call: Todd Walton, Ph.D., P.E. (850-644-2847).

REFERENCES:

Berek, E.P., and Dean, R.G. (1982). "Field Investigation of Longshore Transport Distribution.", Proc. 18th Coastal Engineering Conference, ASCE, 1620-1638.

Dean, R.G. and Work, P.A.(1993). "Interaction of Navigational Entrances with Adjacent Shorelines," Journal of Coastal Research 18: 91-110.

Walton, T.L. Jr.(1996). "Effects of Port Canaveral Harbor on Downdrift Shoreline," unpublished summary report of findings.

Walton, T.L. Jr.(1998). "Least Squares Filtering to Assess Shoreline Change Signatures," Journal of Coastal Research, Vol.14, No. 4, 1225-1230.

Walton, T.L. Jr.(1999a). "Separation of Shoreline Change Signal from Random Noise," Ocean Engineering, Vol.27, No.2000, 77-86.

Walton, T.L. Jr.(1999b). "Shoreline Rhythmic Pattern Analysis," Journal of Coastal Research, Vol.15, No.2, 379-387.




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