Presentation Title

Statistical trend analysis of long-term nearshore monitoring data, Swinomish Indian Reservation

Session Title

Long term studies reveal the complex dynamics and interconnectivity of the physical, geomorphic, biological systems of Salish Sea shorelines and how these systems interact with social and political systems

Conference Track

Shorelines

Conference Name

Salish Sea Ecosystem Conference (2016 : Vancouver, B.C.)

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type of Presentation

Oral

Abstract

The Swinomish Indian Tribal Community has had long-standing concerns about the stability of Reservation shorelines. The Swinomish Indian Reservation, located in Northwest Washington about 40 miles south of the US/Canada Border, is about 90% bounded by saltwater and much of that boundary is modified by dikes, bulkheads, or other structures that affect nearshore processes.

The Swinomish Water Resources Program began monitoring elevation, substrate character, and vegetation at seven transects perpendicular to the western Reservation shoreline in 2002, and continued monitoring with monthly to quarterly frequency through 2011, and periodically thereafter. Elevation is measured using laser level and surveyed benchmarks at regular intervals between a fixed upper origin and the lowest accessible point along each transect. Substrate sediment texture is characterized at each elevation point using visual estimation methods and a 0.25 m2 quadrat grid. Type and abundance of vegetation based on field identification in each quadrat was also cataloged during surveys from 2002 to 2011. Repeat elevation surveys at these transects showed little to no change over the period of record when visualized as standard profiles. It was similarly difficult to visualize temporal trends in substrate character or vegetation distribution using graphical methods. The “noise” within the data set (seasonality, natural variability, etc.) overwhelmed any trend signal.

Statistical trend testing, particularly Mann-Kendall and seasonal Mann-Kendall testing, provide more robust analysis of temporal variability in the data. Seasonal Mann-Kendall testing compensates for seasonal variability in the data to evaluate overall trends, while standard Mann-Kendall testing can be applied to the separate “seasons” to identify trends within seasonal subsets. Application of these statistical tools has helped us identify specific locations at which change is more likely occurring, guides further work to link the changes to nearshore processes, and informs potential restoration or mitigation actions.

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.

Language

English

Format

application/pdf

Type

Text

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Statistical trend analysis of long-term nearshore monitoring data, Swinomish Indian Reservation

2016SSEC

The Swinomish Indian Tribal Community has had long-standing concerns about the stability of Reservation shorelines. The Swinomish Indian Reservation, located in Northwest Washington about 40 miles south of the US/Canada Border, is about 90% bounded by saltwater and much of that boundary is modified by dikes, bulkheads, or other structures that affect nearshore processes.

The Swinomish Water Resources Program began monitoring elevation, substrate character, and vegetation at seven transects perpendicular to the western Reservation shoreline in 2002, and continued monitoring with monthly to quarterly frequency through 2011, and periodically thereafter. Elevation is measured using laser level and surveyed benchmarks at regular intervals between a fixed upper origin and the lowest accessible point along each transect. Substrate sediment texture is characterized at each elevation point using visual estimation methods and a 0.25 m2 quadrat grid. Type and abundance of vegetation based on field identification in each quadrat was also cataloged during surveys from 2002 to 2011. Repeat elevation surveys at these transects showed little to no change over the period of record when visualized as standard profiles. It was similarly difficult to visualize temporal trends in substrate character or vegetation distribution using graphical methods. The “noise” within the data set (seasonality, natural variability, etc.) overwhelmed any trend signal.

Statistical trend testing, particularly Mann-Kendall and seasonal Mann-Kendall testing, provide more robust analysis of temporal variability in the data. Seasonal Mann-Kendall testing compensates for seasonal variability in the data to evaluate overall trends, while standard Mann-Kendall testing can be applied to the separate “seasons” to identify trends within seasonal subsets. Application of these statistical tools has helped us identify specific locations at which change is more likely occurring, guides further work to link the changes to nearshore processes, and informs potential restoration or mitigation actions.