(e.g., north and western regions of the sound) are the most promising locations for sustainable coastal marsh restoration, at least under the committee’s projected sea-level rise for 2030 and 2050. Under the highest sea-level projections for 2100, a high sediment supply and uplift may not be enough for restoration to succeed, and additional steps will have to be taken (e.g., filling previously subsided areas).

FIGURE 6.22 Annual sediment load of major rivers draining into Puget Sound measured at or near the river mouth. The size of the arrow is scaled to the annual sediment load. SOURCE: Czuba et al. (2011).

Linking restoration plans in these areas with land use and watershed management plans would improve the sustainability of coastal habitats. Land use plans could include, for example, conservation easements or limits on construction to accommodate the lateral migration of coastal marshes as sea level rises. Watershed management plans could include changes in dam operations to increase the amount of sediment that reaches Puget Sound deltas.

Efforts to restore eelgrass in some areas of the sound have had only limited success (Thom, 1990; Carlisle, 2004; Mumford, 2007). Stamey (2004) found an overall success rate of 13–80 percent, concluding that eelgrass transplantation cannot yet be used reliably for mitigation in Puget Sound. Eelgrass restoration costs are high, between $100,000 and $1 million per acre (Fonseca et al., 1998). However, if appropriate substrate and water quality conditions can be established and maintained, the effects of sea-level rise on eelgrass is likely minimal.

Potential for Wave Attenuation

Eelgrass beds play an important role in nearshore ecosystems. The plant blades slow water currents and dampen waves, thereby trapping sediments, detritus,