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HomeMy WebLinkAboutShoreline Change Presentation_201401231600231749Shoreline Change Around Nantucket Julia Knisel Coastal Shoreline and Floodplain Manager MA Office of Coastal Zone Management Natural Process •Shoreline positions fluctuate (seasons & storms) •Dunes & banks erode & supply beaches with sand Issue: Coastal Property Damages •Development is susceptible to risks from winds, waves, storm surge, flooding, sea level rise & associated erosion Issue: Public Health and Safety •Erosion can expose septic systems & sewer pipes, contaminating shellfish beds & other resources Issue: Coastal Engineering Impact •Seawalls & other shoreline stabilization structures often increase erosion along adjacent properties Coastal Management Challenge •Understand & work with erosion – not against it •Site new development in a manner that accommodates shifting conditions •Modify existing development •Add sediment to beach systems Shoreline Position? •Mean high water elevation •High tide line seaward of storm debris wrack line: tonal change between wet & dry beach material, or a seaweed/debris line •Algal line on rocky outcrops: tonal change between wet surfaces that host algae & dry surfaces with no algae •Vegetation change between Spartina patens in upper marsh & Spartina alterniflora in lower marsh, or outer limits of emergent marsh vegetation •Interface between vertical seawalls/bulkheads & water 1989 Shoreline Change Maps 2001 Shoreline Change Browser Shoreline Change in MORIS Update •USGS delineated spring 2007, 2008 & 2009 •~ 26,000 transects along 1,100 miles •Updated rates from 1800s to 2009 USGS draft Open-File Report, 2013 2007-2009 Shoreline Indicators Region High Water Line (miles) LIDAR Mean High Water Line (miles) Marsh High Water Line (miles) Coastal Structures (miles) North Shore 106 0 16 48 Greater Boston 28 0 6 18 South Shore 85 0 24 22 Cape Cod Bay 86 0 31 9 Outer Cape Cod 30 53 19 1 Cape Cod South 62 0 2 17 Buzzards Bay 144 0 40 38 Elizabeth Islands 57 0 1 1 Martha’s Vineyard 83 0 4 5 Nantucket 81 0 4 1 State total 762 53 146 160 USGS draft Open-File Report, 2013 Shoreline Sources & Uncertainties •1844-1897: topographic sheets (~ 38’) •1909-1938: topographic sheets (~ 38’) •1943-1969: topographic sheets (~ 22-38’) •1970-1982: topographic sheets & aerial photos (~ 22’) •1994: aerial photos (~ 22’) •2000: LIDAR (~ 4’) •2001: orthophotos (~ 17’) •2007-2009: LIDAR & orthophotos (~ 4-20’) Sector Long-Term Trends Sector 1A 1B 2 3 4 5 6 7 8 9 10 Max. Erosion (ft/yr) -4.82 -2.69 -8.50 -22.67 -23.46 -12.63 -9.22 -1.61 -7.94 Max. Accretion (ft/yr) 11.32 7.12 7.19 2.10 0.95 14.04 5.22 3.77 4.30 9.88 Erosion Dominated •Long-term erosional trend at red transects Sector 1B Stable Sector 8 Stable Sector 6 Erosional Interpretation •Consider all available information: –long-term & short-term shoreline change data –shoreline position: seasonal trends & storms –rate uncertainty (+/-) –management history: coastal structures & nourishment –current site conditions: dry beach width & vegetation –recent changes in shoreline uses: development –other alterations to natural shoreline processes Application •Project siting & design: buildings & infrastructure •Project review: all boards •Land management: restoration & acquisition •Hazard mitigation planning: vulnerability assessments •Identification of other hazards: flooding & sea level rise For More Information www.mass.gov/czm/hazards/shoreline_change/shorelinechangeproject.htm maps.massgis.state.ma.us/map_ol/czm_shorelines.php csc.noaa.gov/digitalcoast/tools/slrviewer Scully Senior Center – 2 views Contacts •Shoreline Change Project: Julia Knisel at julia.knisel@state.ma.us or Rebecca Haney at rebecca.haney@state.ma.us •MORIS: Dan Sampson at daniel.sampson@state.ma.us •Regional Context: Steve McKenna at stephen.mckenna@state.ma.us •Other Support: Greg Berman at gberman@whoi.edu