Shoreline Mapping & Erosion Patterns Along the Massachusetts Coast Julia Knisel Julia Knisel Coastal Shoreline & Floodplain Manager
CZM Shoreline Change Project Timeline 1989: produced coast wide maps with shorelines from mid 1800 s to 1982 1997: completed analysisof shoreline change rates every 40 meters alongshore 2001: added 1994 shoreline & updated rates with assistance from USGS & Woods Hole Sea Grant 2006: contracted t dapplied dcoastal lto delineate 2001 shoreline for South Shore 2010: USGS derived a 2000 shoreline 2013: released 2007 2009 shoreline mapped & analyzed by USGS at 50 meters alongshore
1989 Shoreline Change Maps
2001 Shoreline Change Browser
Shoreline Change in MORIS
Analyzing Shoreline Change Comparison of high water lines over time Data sets: historic topographic surveys aerial photographs orthophotos LIDAR(high resolution topographic) surveys Rate calculation l at individual d shore perpendicular transects Account tfor uncertainty tit in each shoreline position: survey methods digitizing interpretation
Shoreline Sources & Uncertainties 1844 1897: topographic sheets (~ 38 ) 1909 1938: 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 )
Shoreline Position? Mean high h water elevation High tide line seaward of storm debris wrack line: tonal changebetween 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 & water
Computing Change Rate Statistics USGS Digital Shoreline Analysis System manual, 2009
2013 Update USGS delineated spring 2007, 2008 & 2009 shorelines ~ 26,000 transects along 1,100 miles Updated rates from 1800s to 2009 USGS 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 (68%) 53 (5%) 146 (13%) 160 (14%) USGS Open-File Report, 2013
Trends Unidirectional Change Osterville
Trends Unidirectional Change Nantucket
Trends Unidirectional Change Rockport
Scituate Trends Unidirectional Change
Trends Fluctuating Shoreline Salisbury
Brewster Trends Fluctuating Shoreline
Trends Structure Impacts Oak Bluffs
Trends Structure Impacts Sandwich
Trends Structure Impacts Winthrop
Average Shoreline Change Rates Long term ~ 150 years State average = 0.62 ± 0.066 ft/yr Short term ~ 30 years State average = 0.95 ±0.23 ft/yr Popponesset Bay, Mashpee erosion ( ) accretion (+)
Highest Average Erosion Rates Communities
Highest Avg. Erosion Rates Public Beaches Long term
Highest Avg. Erosion Rates Public Beaches Short termterm
Coastal Structures Region Shoreline Length (miles) Private Structure Length (miles) Public Structure Length (miles) Percent Protected North Shore Boston Harbor South Shore Cape Cod & Islands 160 50 24 46% 57 12 21 58% 129 28 29 44% 615 66 11 13% South Coastal 154 49 7 36% TOTAL 1,115 205 92 27%
Seawalls
Revetments
Consider all available information Long term & short term shoreline change data Seasonal trends & storms Rate uncertainty (+/ ) Management history: coastal structures & nourishment ih Other site conditions: dry beach width & vegetation Recent changes in shoreline uses: development Other alterations ti to natural shoreline processes
Long Term Maximum Erosion Rates Region Maximum erosion rate (ft/yr) North Shore 4.3 ± 3.9 Greater Boston 4.9 ± 0.46 South thshore 8.5 85 ± 32 3.2 Cape Cod Bay 11 ± 4.9 Outer Cape Cod 25 ± 12 Cape Cod South 14 ± 5.5 Buzzards Bay 3.2 ± 1.5 Elizabeth Islands 3.3 ± 2.3 Martha s Vineyard 12 ± 0.43 Nantucket 22 ± 4.9
Short Term Maximum Erosion Rates Region Maximum erosion rate (ft/yr) North Shore 53 ± 0.62 Greater Boston 25 ± 2.0 South Shore 19 ± 15 Cape Cod Bay 30 ± 1.3 Outer Cape Cod 36 ± 9.5 Cape Cod dsouth 8.5 85 ± 92* 9.2* Buzzards Bay 18 ± 26* Elizabeth Islands 3.6 ± 0.26 Martha s Vineyard 19 ± 12 Nantucket 38 ± 35
Long Term Trends Sector 1A 1B 2 3 4 5 6 7 8 9 10 Max. Erosion (ft/yr) Max. Accretion (ft/yr) 4.8 0 2.7 8.5 23 23 13 9.2 0 1.6 7.9 11 7.1 7.2 2.1 0.95 14 5.2 3.8 4.3 0 9.9
Long Term Trends Long term erosional trend at red transects