CHANGES IN BARRIER ISLAND ENVIRONMENTS DURING SEA-LEVEL RISE James C. Gibeaut Bureau of Economic Geology Jackson School of Geosciences The University of Texas at Austin Funding From: Galveston Bay Estuary Program, NOAA through the Texas Coastal Coordination Council, Texas General Land Office, Army Research Office, NASA Texas A&M Sigma Xi Symposium, March 30, 2006 Talk notes: Talk about fault Map the upland boundary and see how much vertical change from 1950’s to 2002 – compare to SL rise Show tide curve at time of lidar survey to illustrate the “elevation classification problem this could present. Talk about bay shoreline erosion – we don’t have the bay shoreline data do we? Look at areas that are within the range of elevation for marsh but are not marsh – figure out why this is – what are the other factors besides elevation that makes a marsh a marsh.
Texas Coast Brief overview of shoreline types, bays vs. Gulf. Shoreline monitoring is challenging because of the length of shoreline and variety of shoreline types.
Regressive Barrier Island ( a ) b B A Y R I E S L G U F O M X C y m r g i n d e s w l o v t f - u c h q V p k Z Q 3 1 7 P N Regressive Barrier Island Transgressive Barrier Island
Transgressive (Matagorda Peninsula)
Regressive (Galveston Island)
Color IR Mosaic Gulf of Mexico
Barrier Island Environments
University of Texas Airborne Topographic Lidar System (Optech model ALTM1225)
1 – Meter Lidar Digital Elevation Model Shaded relief image of digital elevation model of the study area. Banding in open-water areas is oriented parallel to the acquisition flight lines and is the result of about 0.05 m vertical error across the data swaths. The banding is only apparent on the very smooth water surface.
Habitat Classification Map From Color IR Photography Data from White et al., 2002
Average Heights and Standard Deviations of Barrier Island Habitats
Change Induced by Rising Sea Level From Brinson, Christian, and Blum, 1995
Relative Sea-Level Change Pier 21 - Galveston y = 0.652x - 1145.6 R 2 = 0.9436 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 Year Average water level (cm) 4.36 + 2.16 = 6.52 mm/yr Local land subsidence Global ocean-level rise
Land Subsidence Relative to Pier 21, 1958 – 1978, mm/yr Pier 21 tide gauge
Vertical Accretion Function Maximum rate = 0.0064 m/yr Vertical Accretion Function Evidence for decreasing rate and max rate from Callaway et al., 1997
Shoreline Change
Tide Gauge Record Change Rate = 0.0064 m/yr ) m ( l e v e l e d i t h 2.5 Tide Gauge Record Annual Averages of MHHW at Pier 21, Galveston ) 2 m ( l e v e Change Rate = 0.0064 m/yr l e d i t h g i H 1.5 H i s t o r i c a l l e v e l L i n e a r f i t P r o j e c t e d l e v e l 3 - y r m o v i n g a v e r a g e 1 1900 1920 1940 1960 1980 2000 2020 2040 2060 2080 2100 Y e a r
Model Flow 1-year loop DEM Yes (original) No Future date reached? Classify elevation by environment types Environment grid Yes No Adjusted DEM Apply vertical accretion adjustment Output habitat grid 1-year loop Shoreline change data Retreat shoreline Apply sea level adjustment Apply local subsidence adjustment Compute statistics of habitat status Maps Statistics Graphs
Eight Analysis Areas
All Areas
All Areas
Eight Analysis Areas
Follets
Follets
Eight Analysis Areas
West Galveston
West Galveston
Eight Analysis Areas
Bolivar
Bolivar