Impacts of armoring on physical properties of south-central Puget Sound beaches
Presentation Abstract
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.
Session Title
Session S-06H: Puget Sound Shorelines and the Impacts of Armoring: State of the Science 2014
Conference Track
Shorelines
Conference Name
Salish Sea Ecosystem Conference (2014 : Seattle, Wash.)
Document Type
Event
Start Date
1-5-2014 5:00 PM
End Date
1-5-2014 6:30 PM
Location
Room 6C
Genre/Form
conference proceedings; presentations (communicative events)
Contributing Repository
Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.
Subjects – Topical (LCSH)
Shore protection--Environmental aspects--Washington (State)--Puget Sound; Coastal zone management--Washington (State)--Puget Sound
Geographic Coverage
Salish Sea (B.C. and Wash.); Puget Sound (Wash.)
Rights
This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.
Type
Text
Language
English
Format
application/pdf
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.
