Abstract Title

Session S-06H: Puget Sound Shorelines and the Impacts of Armoring: State of the Science 2014

Presenter/Author Information

Andrea Ogston, University of WashingtonFollow

Keywords

Shorelines

Start Date

1-5-2014 5:00 PM

End Date

1-5-2014 6:30 PM

Description

Shore armoring is ubiquitous on Puget Sound’s mixed sand and gravel beaches and around our nation’s shorelines. On sandy beaches the relationships between slope, grain size and wave energy have been established and therefore the impacts of armoring on these relationships can be predicted. In contrast, the dynamics of mixed sand and gravel beaches are less well understood, and subsequently the impacts of armoring on these beaches are under debate. This study of paired unarmored/armored beaches in south-central Puget Sound examines beach profile, grain size, and wave energy relationships of mixed sand and gravel beaches, and evaluates the observable impacts of armoring on these geomorphic features. Beaches within Puget Sound have highly variable morphology, but generally have mixed grain size and relatively steep upper foreshores. Due to the mixed semidiurnal tide, the water level spends a significant proportion of time on the upper foreshore, where most beaches show evidence of active sediment motion. Generally within our study beaches, data suggests that seawall armoring is associated with steepening within this zone. However, factors within the beach pairs associated with the antecedent geology (e.g., local changes in bluff composition, bed rock morphology and accommodation) made direct observation at individual pairs highly variable, and more detailed effects of seawall armoring difficult to elucidate. For example, no clear effects of armoring on sediment grain sizes were found. Although we could extract only limited relationships from our morphological data, we found clear evidence that armored beaches enhance the nearshore wave energy. Waves were found to increase in wave height close to the armored sections by a factor of ~15% relative to the unarmored sections. Morphological impacts of shoreline armoring are not constrained to specific armored sites, as transport dynamics act to smear the effects to nearby unarmored controls.

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May 1st, 5:00 PM May 1st, 6:30 PM

Impacts of armoring on physical properties of south-central Puget Sound beaches

Room 6C

Shore armoring is ubiquitous on Puget Sound’s mixed sand and gravel beaches and around our nation’s shorelines. On sandy beaches the relationships between slope, grain size and wave energy have been established and therefore the impacts of armoring on these relationships can be predicted. In contrast, the dynamics of mixed sand and gravel beaches are less well understood, and subsequently the impacts of armoring on these beaches are under debate. This study of paired unarmored/armored beaches in south-central Puget Sound examines beach profile, grain size, and wave energy relationships of mixed sand and gravel beaches, and evaluates the observable impacts of armoring on these geomorphic features. Beaches within Puget Sound have highly variable morphology, but generally have mixed grain size and relatively steep upper foreshores. Due to the mixed semidiurnal tide, the water level spends a significant proportion of time on the upper foreshore, where most beaches show evidence of active sediment motion. Generally within our study beaches, data suggests that seawall armoring is associated with steepening within this zone. However, factors within the beach pairs associated with the antecedent geology (e.g., local changes in bluff composition, bed rock morphology and accommodation) made direct observation at individual pairs highly variable, and more detailed effects of seawall armoring difficult to elucidate. For example, no clear effects of armoring on sediment grain sizes were found. Although we could extract only limited relationships from our morphological data, we found clear evidence that armored beaches enhance the nearshore wave energy. Waves were found to increase in wave height close to the armored sections by a factor of ~15% relative to the unarmored sections. Morphological impacts of shoreline armoring are not constrained to specific armored sites, as transport dynamics act to smear the effects to nearby unarmored controls.