Evaluating Puget Sound Beach Services for Protection and Restoration

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This project conducted by the Washington State Department of Ecology Coastal Monitoring & Analysis Program (CMAP) will advance ESRP’s understanding of beach processes, the impact of shoreline armor, and relative benefits of restoration measures in the Puget Sound region by comparing beach features between armored and adjacent unarmored shorelines. Existing boat-based LiDAR collected between 2015 and 2021 as part of the Mapping Bluffs and Beaches to Quantify Sediment Supply effort, will be used to create a robust dataset of key physical indicators of beach health extracted along cross-shore profiles from ~25 pairs of armored and unarmored shoreline. The results from analysis are intended to generate guidance for strategic prioritization and planning of recovery projects to maximize ecological lift objectives.

The impacts of shoreline armoring to the nearshore habitat have been observed throughout the Puget Sound region, however an inadequate understanding of the relationship between physical and ecological beach features makes it difficult to prioritize restoration sites and assess the effectiveness of recovery projects. As shoreline restoration and soft-shore protection efforts increase, it is essential to gain a strong understanding of beach characteristics on a natural beach and how they compare to armored beaches in order to make the best use of restoration and protection resources.

This project will use existing high-resolution boat-based lidar collected between 2015 and 2021 from ~25 pairs of armored and adjacent unarmored reaches of shoreline. Beach characteristics including beach width, slope, backshore width, large woody debris area, vegetation coverage, and bluff or armor toe elevation will be extracted from 1-m spaced cross-shore transects and averaged within 10-m alongshore intervals. This high spatial-resolution sampling strategy will ensure robust statistics and allow us to observe alongshore trends that may reveal any edge effects of shoreline armor.

Outcomes from the project are intended to inform management and planning of recovery projects. High-resolution baseline conditions of unarmored shorelines can function as target conditions for restoration and protection measures. Determining the quantitative impacts of armoring based on encroachment within the context of shore type, sediment supply, and drift cell setting, can offer guidance for prioritization in order to achieve maximum ecological lift. These data may also be applied to improve the guidance around soft-shore approaches to shoreline protection such as beach nourishment, gravel berms, and installation of large wood and riparian vegetation.

Site Selection[edit]

Sites were selected using a combination of qualitative and quantitative parameters describing the feasibility and geomorphic setting. The following criteria were considered:

  • ~500-meter stretch of shoreline with roughly 50% armored and 50% unarmored
  • Geographic and geomorphic distribution
  • Drift cells with mapped drift direction and apparent sediment source
  • Availability of high-resolution boat-based lidar data for analysis, with preference given to sites with two or more lidar datasets for temporal analysis

In some instances, more than one site was identified within a drift cell, which may offer insights on beach metric alongshore variability.

Key Physical Indicators[edit]

Physical indicators of ecological function were identified for analysis based on a literature review and the ability to map using existing boat-based lidar. Beach metrics include backshore width, foreshore width, foreshore slope, bluff or armor toe elevation, and relative vertical and horizontal encroachment. Habitat metrics include area of large woody debris, riparian vegetation, and overhanging vegetation. Cross-shore variability and alongshore trends will also be considered while interpreting results.