Projections of Future Transitions in Tidal Wetlands under Sea Level Rise within the Port Gamble S’Klallam Traditional Use Areas Mary F. Ramirez and Charles A. Simenstad School of Aquatic and Fishery Sciences, University of Washington January, 2018 i Table of Contents Background ................................................................................................................................................... 1 Approach ....................................................................................................................................................... 2 Projected Sea Level Rise .......................................................................................................................... 4 Methods ........................................................................................................................................................ 4 Elevation ................................................................................................................................................... 5 Wetland ..................................................................................................................................................... 6 Land Cover................................................................................................................................................ 7 Levee ......................................................................................................................................................... 7 Analysis .................................................................................................................................................... 7 Results ........................................................................................................................................................... 9 Point Gamble S’Klallam Tribe Primary Traditional Use Area ................................................................. 9 Major River Deltas .................................................................................................................................. 12 Kilisut Harbor and Port Gamble Bay ...................................................................................................... 22 Discussion ................................................................................................................................................... 28 Conclusions ................................................................................................................................................. 30 Acknowledgements ..................................................................................................................................... 30 References ................................................................................................................................................... 31 Figures Figure 1. Generalized schematic of estuarine wetland types along the tidal inundation gradient (top). Transgressive migration is the process by which tidal wetlands migrate landward in response to new tide range elevations (middle). Where natural or artificial barriers prevent transgressive migration, the acceleration of sea level rise puts tidal wetlands at risk of submergence (bottom). .............................................................................................................. 3 Figure 2. Port Gamble S’Klallam Tribe Traditional Use Area. ................................................................ 5 Figure 3. Representative Puget Sound estuarine wetland types................................................................ 7 Figure 4. Proportional composition of tidal and non-tidal wetland categories within the Tribe traditional use area (PGSK) and major river deltas under the initial condition and by year 2100 relative to three scenarios of sea level rise. .......................................................................................... 10 Figure 5. Area (hectares) of wetland categories and corresponding wetland classes at time steps between 2004 (initial condition) and 2100 under three scenarios of sea level rise (SLR). ..... 10 Figure 6. Scaled bubble plot of the area (hectares) of transgressive migration by PSNERP process unit (PU) and proportional loss of tidal wetlands relative to the initial area by PU under 1.4 m ii SLR. Increase in bubble size corresponds with more migration of tidal wetlands landward (green) and a greater proportion of tidal wetland loss (blue). ................................................. 16 Figure 7. Area (hectares) of tidal and non-tidal wetlands within major river deltas under initial condition (year 2004) and projected under three scenarios of sea level rise by 2100. ............ 17 Figure 8. Projected tidal wetland outcomes in the five major river deltas within the Tribe’s interest area by year 2100 under 1.4 meters sea level rise. .......................................................................... 18 Figure 9. Initial condition (top row) and SLAMM modeled change by 2100 under three sea level rise scenarios around the Dungeness River delta. Red inset boxes show zoomed areas (right column). ................................................................................................................................... 19 Figure 10. Initial (2004) wetland and land cover in the Kilisut Harbor (left) and Port Gamble Bay (right) areas………………………………………………………………………………………… 23 Figure 11. Example of a barrier lagoon with an adjacent barrier estuary at the mouth of Mystery Bay in the Kilisut Harbor area (left) and Point Julia barrier lagoon at the entrance to Port Gamble Bay (right). Washington State Department of Ecology Shoreline Photos (2006). .................. 24 Figure 12. Projected tidal wetland outcomes in Kilisut Harbor by year 2100 under 1.4 meters sea level rise. Inset maps detail projections in two areas along Marrowstone Island. ........................... 26 Figure 13. Projected tidal wetland outcomes in Port Gamble Bay by year 2100 under 1.4 meters sea level rise. Inset map detail projections around Point Julia barrier lagoon. .............................. 27 Tables Table 1. Input parameters to SLAMM. ....................................................................................................... 6 Table 2. Source wetland and land cover data for SLAMM classification. ................................................. 8 Table 3. Initial (2004) area (hectares) of individual SLAMM land cover classes and projected area and percent change in area from initial condition by 2100 under three sea level rise scenarios. ...... 11 Table 4. Transition matrices comparing initial area (hectares; rows) to year 2100 area (columns) under A) 0.6, B) 1.4, and C) 2.0 meters sea level rise. Highlighted cells show the area that did not change land cover class (persistence). Open water classes were compiled into a single category as were low tidal classes other than tidal flat.............................................................................. 13 Table 5. Area and percent change in land cover classes under three scenarios of sea level rise within each of the five major river deltas (A-E) located in the study area. .................................................... 20 Table 6. Area and percent change in land cover classes under three scenarios of sea level rise within A. Kilisut Harbor, and B. Port Gamble Bay. ................................................................................... 25 Table 7. Summary of sea level rise (SLR) outcome probabilities under 2 emissions scenarios by 2100 and 2150 (based on updated projections (unpublished) from CIG for the Washington Coastal Resilience Project). ..................................................................................................................... 28 iii Background Although the global projections of relative sea level (RSL) rise suggest a net trend of 0.3-0.8 m of eustatic RSL by 2100 (Church et al. 2013), regional variability in sea level changes deviate substantially from that global mean (Carson et al. 2016). Sources for this variability range from large-scale, dynamic ocean and atmospheric processes as well as finer scale isostatic and tectonic adjustments. Planning for sea level rise, and other related climate changes, at the regional scale often embodies equally uncertain variability, suggesting that coastal zone management would benefit from more strategic analysis of the scope, scale and direction of RSL. This is particularly the case for tidal wetlands, which through biophysical feedback processes have the potential to build vertically commensurate with sea level rise, even under accelerating RSL conditions (Kirwan et al. 2016). The Pacific Northwest coast of North America is one of those regions with variable sea level rise (NRC 2012), and is identified to have less sea level rise, as much as 0.1 m lower than the global average (both Intergovernmental Panel on Climate Change (IPCC) RCP 4.5 and RCP 8.5 scenario models; Carson et al. 2016). Furthermore, factors affecting both projected RSL and climate change-associated sediment delivery, sedimentation and accommodation area for transgressive development of tidal wetlands in newly inundated shorelines are spatially variable even within the Salish Sea/Puget Sound (Mauger et al. 2015). It is well established that global warming is happening and impacts are already being observed in the Pacific Northwest (Glick et al. 2007, Mauger et al. 2015).