Feeder bluffs play a critical role in maintaining the ecological health and sediment balance of Puget Sound shorelines. A fully functional feeder bluff in Puget Sound is one that actively erodes and contributes sediment to the shoreline system without significant human alteration. These bluffs, typically composed of unconsolidated glacial sediments, are shaped by natural processes such as wave action and precipitation-induced landslides. Through ongoing erosion and mass wasting, feeder bluffs contribute approximately 90 percent of the sediment that maintains beaches, spits, and estuarine habitats (Keuler 1988). Feeder bluffs classified as “exceptional” are particularly important due to their high erosion rates and the large volumes of sediment they deliver to the nearshore. These bluffs, in turn, support ecologically important areas such as forage fish spawning grounds and juvenile salmon habitat.

Preserving the function of feeder bluffs requires avoiding shoreline armoring or development, such as bulkheads, seawalls, fill, and overwater structures, that impounds or “locks up” sediment and disrupts natural coastal processes. Fully functioning feeder bluffs also maintain natural drainage and vegetation patterns, which help regulate slope stability and erosion rates. Restoration actions such as removing shoreline armor at historically active feeder bluff sites are considered key strategies for reestablishing natural sediment input and enhancing nearshore habitat complexity. These actions allow for gradual erosion and support a more resilient and dynamic shoreline system. Compiled mapping data (this study and Beach Strategies) indicates that approximately 34% of feeder bluffs in Puget Sound—about 223 miles—have impaired function over historic conditions due to shoreline armor (Coastal Geologic Services 2017; Natural Systems Design, 2025) (Figure 2).

• Just over one third (34%) or 223 miles of Puget Sound feeder bluffs have impaired function due to shoreline armor. 
• There has been no significant change or improvement in feeder bluff function in the last few decades (based on a subsampling of 32% of feeder bluff length in the region).  
• The highest levels of feeder bluff impairment are concentrated in South Central and South Puget Sound, whereas the Strait of Juan de Fuca and North Central Puget Sound retain the most functional feeder bluffs.
• The majority of armor was categorized as in “OK” condition, substantially reducing the ability of feeder bluffs to deliver sediment to nearshore ecosystems.
• Armor removal efforts have led to notable improvements of feeder bluff function in localized areas.

The function of feeder bluffs across Puget Sound varies based on geographic region, feeder bluff type, and drift cell. Geographic patterns reveal that South Central Puget Sound has the highest percentage of non-functional feeder bluffs, followed closely by South Puget Sound (Figure 3). These areas are among the most heavily developed in the region, with residential properties and other infrastructure often situated extremely close to the shoreline. In contrast, North Central Puget Sound and the Strait of Juan de Fuca have the lowest percentages of impaired feeder bluffs. In the Strait of Juan de Fuca especially, the dominance of tall, steep bluffs and high-energy wave environments make armoring difficult or ineffective, contributing to the relatively higher functional condition of bluffs in this region.

When examining bluff types, the vast majority of mapped feeder bluffs in Puget Sound are classified as general feeder bluffs (FB), with smaller proportions of feeder bluffs exceptional (FBE), and feeder bluffs – talus (FB-T). FBs have experienced the most significant decline in function over time out of the three categories of feeder bluffs. Historically, there were 585 miles of functional feeder bluffs throughout Puget Sound, but only 363 miles of functional feeder bluffs remain based on the most recent mapping. This represents a net loss of approximately 222 miles of feeder bluff length and signals a widespread reduction in sediment supply that is available to support nearshore habitats (Figure 3). 

Figure 3. Historic and current length of functional feeder bluffs in Puget Sound by feeder bluff type.

Feeder bluff condition also varies at the scale of individual drift cells. Of the 1,322 miles of Puget Sound shoreline mapped within drift cells containing feeder bluffs (as opposed to no appreciable drift zones or drift cells without feeder bluffs), 931 miles have less than 50% of their feeder bluff length armored, while 391 miles are more heavily armored, with over 50% of feeder bluff length altered (Figure 4). This suggests that a significant number of drift cells have been substantially impaired, compromising their ability to support natural sediment transport processes within their respective drift cell.

Figure 4. Length (miles) of drift cells containing feeder bluffs in Puget Sound with less than or greater than 50% of feeder bluffs armored. Note that not all shorelines in Puget Sound are within a drift cell (i.e., they are in a zone of no appreciable drift), and some low energy drift cells do not contain feeder bluffs.

In a focused subset of drift cells where changes in feeder bluff function were assessed over time, most exhibited little to no measurable change (Figure 5). However, several discrete areas, such as Dyes Inlet in Kitsap County, West Seattle, and parts of Whidbey Island, showed notable improvements in function, often linked to restoration or removal of armor along feeder bluffs. Overall, within our focused subset area, there was a small net increase in feeder bluffs in functional condition of approximately 3,270 FT or 0.3% of this area (Figure 6).

Additionally, we assessed the physical condition of existing shoreline armor along feeder bluffs within a subset of regions with available data, including the entirety of San Juan and Island Counties, sections of Mason and Jefferson Counties, and within areas mapped by NSD for this project (Figure 7). Armor condition, classified as “OK,” “derelict,” or “functional but failing” (CGS 2018), directly affects a bluff’s ability to contribute sediment to the nearshore system. About one-third of the armored shorelines within this subset is in either derelict or failing condition, which may allow some limited sediment input despite impairment. However, the remaining two-thirds are in “OK” condition, effectively blocking sediment contribution and thereby rendering those bluffs non-functional. Future assessments of feeder bluff function could benefit from further exploring the role of armor condition on feeder bluff function and nearshore habitat impairment.

Figure 5. Improved or degraded feeder bluffs by drift cell for a subset of Puget Sound.

Figure 6. Length of degraded and improved feeder bluff function within a subset of Puget Sound.

Figure 7. Condition of armor along feeder bluffs for a subset of Puget Sound (San Juan County, Island County, areas mapped by NSD, 2025, and CGS, 2016). The condition of armor can affect the ability of feeder bluffs to provide sediment to beaches and drift cells.

Beach Strategies for Nearshore Restoration and Protection in Puget Sound

Changes in Shoreline Armoring in San Juan County, Washington, 2009-2019: Mapping, Analysis, and Regulatory Review

Island County 2023 Shoreline Armor Survey—Approach and Phase 1 Results

Department of Ecology Shoreline Mapping

Feeder Bluff Mapping of Puget Sound