Prioritizing Beach Restoration and Protection

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Feeder bluff.

This was a collaborative learning project that compared the physical and ecological functions of a range of sites targeted by the ESRP Beach Strategies project. We conducted field sampling throughout Puget Sound at the top prioritized restoration feeder bluffs, the top prioritized protection bluffs, and the lowest of each as well. This broad sampling allowed us to develop a ‘scale bar’ of localized beach functions, at sites being considered for capitol project implementation, and providing metrics for project success.

2023 Final Report[edit]

File:Functions of Feeder Bluffs in the Salish Sea.pdf

Also, see highlights from underwater GoPro videos during snorkel surveys, and a pdf of our final presentation: File:ESRP Feeder Bluff webinar Final.pdf

Link to recording of final project webinar on 12/13/2023.

Conceptual Basis[edit]

The Beach Strategies project aims to provide nearshore recovery practitioners with a suite of tools to guide their decision making, prioritizing restoration and conservation opportunities. We built on this opportunity, and connected geomorphology to ecological function at sites identified by the Beach Strategies project. The current priority framework is largely focused on habitat-forming processes such as sediment supply, and by adding additional data and outputs focused on the localized ecological function of beach/bluff systems, we can build a more holistic approach to developing management recommendations and thus increase the probability of optimal outcomes.

Abstract[edit]

Actively eroding coastal bluffs, known as feeder bluffs, are important sources of sediment for beaches in the Salish Sea. In Puget Sound, WA, 29% of the shoreline has artificial armor (i.e., seawall, bulkhead, rip-rap), which can disrupt natural beach processes, including sediment supply. The ESRP Beach Strategies Project generated a suite of management recommendations, based on geospatial data, to help prioritize beaches in Puget Sound according to shoreline degradation levels and potential benefit of restoration (armor removal) or protection (preventing armor construction) to nearshore sediment supply processes. We conducted field sampling at 20 beaches identified by Beach Strategies as the highest or lowest ranking feeder bluffs to restore or protect, so we could develop a more fine-tuned “scale bar” of local ecological beach function, and examine whether the prioritized sites have the highest realized functions, not just potential benefits. We sampled both ecological and physical parameters spanning zones from the top of the bluff to the low shore, for a total of 32 metrics of beach function including riparian vegetation, insect assemblages, logs, beach wrack, fish abundance and behavior, surface epifauna and algae, along with beach and bluff profiles and sediment size characteristics. We scaled each metric from 0 to 1 and calculated an average score of beach function among 5 replicate beaches for each of 4 treatments: “Protect High” (unarmored, ranked as high priority by Beach Strategies), “Protect Low” (unarmored, ranked low), “Restore High” (armored, ranked high), and “Restore Low” (armored, ranked low). Protect High and Low treatments were equivalent in our metrics of beach function, and both scored over twice as high as Restore treatments; Restore High scored only slightly higher than Restore Low. Statistical models revealed that beach function may be largely driven by strong responses of upper beach metrics including wrack, logs, and overhanging vegetation, while metrics for geomorphology and lower beach organisms were more variable, perhaps due to differences in geographical region and distance from the bluff. Upper beach metrics were also significantly influenced by amount of bluff or armor encroachment into the intertidal and upper beach slope. Our results suggest that beaches with natural unarmored bluffs have the highest level of localized ecological function regardless of potential sediment supply benefit predicted by Beach Strategies, and restoring sediment supply processes at beaches with armored bluffs could double their ecological function.

Map of Study Sites
A scale bar of our measured beach function at the four treatments. Values are averages of scaled metrics from 0 to 1, with higher values indicating greater beach function. Error bars are Standard Error.
Conceptual model of the relationship between natural (blue box) and armored (red box) feeder bluff features, shoreline structure, and localized beach ecosystem function (green box).