Tracking Marsh Elevation and Water Levels in Elkhorn Slough January 2017 1931 Charlie Endris GIS Specialist Elkhorn Slough NERR Elkhorn Slough Foundation Central Coast Wetlands Group 2015
Questions Are the marshes in Elkhorn Slough drowning?
Questions Are the marshes in Elkhorn Slough drowning? What are the tools used to observe a drowning marsh?
Questions Are the marshes in Elkhorn Slough drowning? What are the tools used to observe a drowning marsh? What does the data show?
Questions Are the marshes in Elkhorn Slough drowning? What are the tools used to observe a drowning marsh? What does the data show? What are the potential drivers?
Questions Are the marshes in Elkhorn Slough drowning? Historic evidence is well documented (Van Dyke and Wasson, 2005) 1870
Questions Are the marshes in Elkhorn Slough drowning? Historic evidence is well documented (Van Dyke and Wasson, 2005) 2000
Observation Tools What are the tools used to observe a drowning marsh? Photographs
Observation Tools What are the tools used to observe a drowning marsh? Aerial Photographs 1931
Observation Tools What are the tools used to observe a drowning marsh? Aerial Photographs 1980
Observation Tools What are the tools used to observe a drowning marsh? Aerial Photographs 2007
Observation Tools What are the tools used to observe a drowning marsh? 2007 Aerial Photographs
Observation Tools What are the tools used to observe a drowning marsh? Aerial Photographs 2007 2016
Observation Tools What are the tools used to observe a drowning marsh? Aerial Photographs 2007 2016
Observation Tools What are the tools used to observe a drowning marsh? Water level sensors, SETs, and CORS
Observation Tools What are the tools used to observe a drowning marsh? Water level sensors, SETs, and CORS www.ysi.com
Observation Tools What are the tools used to observe a drowning marsh? Water level sensors, SETs, and CORS Surface Elevation Table (SET)
Observation Tools What are the tools used to observe a drowning marsh? Water level sensors, SETs, and CORS Vertical Control Network https://www.unavco.org/
Observation Tools What are the tools used to observe a drowning marsh? GPS, Differential Leveling, TLS, and Remote Sensing Static GPS (+2 hr) Terrestrial LiDAR aka TLS (terrestrial laser scanning) Differential Leveling
Questions Are the marshes in Elkhorn Slough drowning? What are the tools used to observe a drowning marsh? What does the data show?
Data Results Remote sensing: Marsh Classification 2004-2012 High loss Moderate loss No change Moderate recovery High recovery Very high recovery
Data Results Remote sensing: Marsh Classification 1980-2003 2004-2012 High loss Moderate loss No change Moderate recovery High recovery Very high recovery
Data Results TLS and remote sensing: NDVI (normalized difference vegetation index) NDVI 2009 Marsh Transect Legend NDVI_ES_NAIP2009.tif Value High : 0.5 Low : -0.75
Data Results TLS and remote sensing: NDVI (normalized difference vegetation index) NDVI 2014 Marsh Transect Legend ES_NAIP2014_NDVI.tif Value High : 0.5 Low : -0.75
Data Results TLS and remote sensing: Elevation correlates with NDVI 0.4 0.3 Elevation vs NDVI R² = 0.5307 0.2 0.1 NDVI 0.0-0.1-0.2-0.3-0.4 1.00 1.20 1.40 1.60 1.80 2.00 2.20 2.40 Elevation
Data Results TLS and marsh transect data: marshes are low in the tidal frame Frequency distribution of salt marsh elevations MHW MHHW Frequency 120 130 140 150 160 170 180 190 200 Elevation (m NAVD88)
Data Results Benchmark Surveys: Subsidence = 2.75 mm/yr mm 10 5 0-5 -10-15 -20-25 -30-35 Elevation Change at Benchmarks (2008 to 2016) Laser Leveling
Data Results SET data: Accretion outpacing elevation; Subsidence = 2.6 mm/yr
Data Results CORS (P210) data: Vertical plate motion 20 15 P210 CORS Station Vertical Motion: Elkhorn Slough 2006-2017 10 Elevation change (mm) 5 0-5 -10 Vertical (mm) -15 12/2014 - Present -0.84 mm/yr 60 per. Mov. Avg. ( Vertical (mm)) Linear (12/2014 - Present) -20 1/1/2006 1/1/2007 1/1/2008 1/1/2009 1/1/2010 1/1/2011 1/1/2012 1/1/2013 1/1/2014 1/1/2015 1/1/2016 1/1/2017
Data Results CORS (P210) data: Vertical plate motion 20 15 P210 CORS Station Vertical Motion: Elkhorn Slough 2006-2017 10 Elevation change (mm) 5 0-5 -10-15 0.33 mm/yr Vertical (mm) 60 per. Mov. Avg. ( Vertical (mm)) -20 1/1/2006 1/1/2007 1/1/2008 1/1/2009 1/1/2010 1/1/2011 1/1/2012 1/1/2013 1/1/2014 1/1/2015 1/1/2016 1/1/2017
Data Results Water Level data: Monterey Tide Station https://tidesandcurrents.noaa.gov/
Data Results Water Level data: Monterey Tide Station Source: tidesandcurrents.noaa.gov/
Data Results Water Level data: Monterey Tide Station Source: tidesandcurrents.noaa.gov/
Summary Historical and recent data suggests Elkhorn Slough s marshes are drowning Rate of local subsidence of 3 mm/yr has been fairly consistent Rate of sea level rise has dramatically increased since 2014 With sustained high water levels, significant die-off of pickleweed in Elkhorn Slough is likely Marsh restoration efforts are imperative
Questions?