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1 May 2005 Cumulative Patterns and Controls of Seawall Construction, Thurston County, Washington
Anthony O. Gabriel, Thomas A. Terich
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This paper develops and applies techniques to describe and analyze spatial patterns and controls of seawall construction on Puget Sound Lowland shores, Washington State. The main objectives are: (1) to further develop a methodology that statistically differentiates between sequential, clustered, or random patterns of seawall installation; (2) to apply the cumulative pattern assessment methodology to three drift cells in Thurston County that are representative of those typically found along the Puget Sound; and (3) to identify physical and human controls of seawall construction and patterns by analyzing differences for 109 properties in a variety of relevant drift-cell factors, including direction of sediment transport, slope stability, vegetative cover, land use, and property owner experiences and motives. Property-level information was gathered using a combination of on-site field surveys, property assessment records, aerial photograph/map analysis, and property owner questionnaires. The aerial photo analysis showed that shore protection has greatly increased in each drift cell over the last 33–45 years, increasing from 4–15% to 71–83%. Dates of bulkhead installation, as well as the direction and distance of protected sites relative to the first protected sites within each drift cell, were analyzed using a Spearman rank correlation coefficient. Additional statistical analyses did not identify many significant differences in shoreline characteristics or hazard experiences between shoreline reaches that might help explain patterns in seawall installation, with some exceptions, such as differences in shore protection, erosion experiences, and beach types. Similarly, statistical analyses comparing protected and unprotected properties identified few significant differences or associations, primarily related to improved acreage, backshore uses, historic slumping and recent slope failure, and upland/slope vegetation types.

Anthony O. Gabriel and Thomas A. Terich "Cumulative Patterns and Controls of Seawall Construction, Thurston County, Washington," Journal of Coastal Research 2005(213), 430-440, (1 May 2005).
Received: 24 June 2003; Accepted: 1 July 2004; Published: 1 May 2005

beach erosion
cumulative effects
Puget Sound
shore protection
Washington State
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