2014/07/16 Council Agenda Packet

are rising due to the subduction of the Juan de Fuca oceanic plate beneath the North American continental plate, while the Puget Sound basin is subsiding due to these same forces. Local vertical land movement is an important factor in local sea level rise as it can enhance or reduce relative sea level rise in any particular area. 3) Atmospheric dynamics play a lesser role than the first two components of local sea level rise. The combination of a northward wind along the coast and the rotation of the earth drive oceanic tides towards land, which affects sea level. The potential future impact of atmospheric dynamics was determined through evaluating numerous global climate models and determining an appropriate estimate. The sea level rise estimates for the Puget Sound are: 2050: Low — 3"; Medium — 6"; High — 22" 2100: Low — 6"; Medium — 13"; High — 50" Storm Surge Scenarios Decisions with long term effects and low risk tolerance, such as infrastructure development, should take into account high risk scenarios (Mote et al. 2008). Storm surge is an important component to include in the analysis of high risk scenarios. According to the National Oceanic and Atmospheric Administration (NOAA), "storm surge results from severe storms... as strong winds combined with low pressure drive water onshore." Impacts from sea level rise will be evident in the long-term ascent of the ordinary sea level coupled with episodic events such as high tides and extreme storms. Included in the series of maps for Seattle are storm surge scenarios; storm surge data were not available for the other areas at the time of this report. The storm surge height for Seattle is 12.14ft8 above NAVD88 zero9. This height was applied to each of the sea level rise scenarios to create a more robust picture of how sea level rise coupled with an extreme storm event would impact the area. Puget Sound Region Mapped Scenarios The mapped scenarios take into account the accuracy of our Light Detection and Ranging (LiDAR) data and the published sea level rise estimates. Only the medium and high sea level rise scenarios were mapped due to the accuracy of the LiDAR data. The LiDAR data has a vertical accuracy on the order of one foot, although the accuracy may be significantly less in highly sloped areas and along piers, seawalls and other structures on the shoreline. At this time, the elevation uncertainty is not depicted on these maps. Future sea level rise studies in the region might choose to do so10. The mapped scenarios were determined with guidance from the Washington State Department of Ecology. The depositional areas of the Puget Sound will be exposed to sea level rise due to their low-lying nature. The Seattle, Tacoma, and Everett ports are all located in river deltas and therefore face possible inundation due to long-term sea level rise and episodic storm surge. The scenarios are mapped for the Seattle, Tacoma and Bremerton port areas. The Everett port area was not mapped due to technical issues with the data that were not resolved in time for the publication of this report. This area may be addressed in the future. Bremerton 2050: Medium Sea Level Rise Scenario, High Sea Level Rise Scenario Bremerton 2100: Medium Sea Level Rise Scenario, High Sea Level Rise Scenario Seattle 2050: Medium Sea Level Rise Scenario, High Sea Level Rise Scenario Seattle 2050: Medium Sea Level Rise Scenario and Storm Surge Seattle 2050: High Sea Level Rise Scenario and Storm Surge Seattle 2100: Medium Sea Level Rise Scenario, High Sea Level Rise Scenario Seattle 2100: Medium Sea Level Rise Scenario and Storm Surge Seattle 2100: High Sea Level Rise Scenario and Storm Surge 6 This is the highest recorded water level at the Seattle NOAA monitoring gauge in over 100 years, so it serves as a proxy for the height of an extreme event storm surge. Monitoring station website: http://tidesandcurrents. noaa.gov/station_info.shtml?stn=9447130+SEATTLE,+PUGET+SOUND,+WA 9 NAVD88 is the geodetic vertical datum to which the elevation data is referenced. 10 For an example method. see Gesch, D.B., 2009 Analysis of lidar elevation data for improved identification and delineation of lands vulnerable to sea -level rise. Journal of Coastal Research, SI(53), 49-58. L-16 Appendix L: Climate Change Background