Oct. 1998
description
Transcript of Oct. 1998
Oct. 1998
July 2009
2001
2008
Monitoring Shoreline Change Geological Survey of Canada, Atlantic (GSCA)
Bob Taylor, Dartmouth NS
Historical framework .........for examining shoreline change in the Gulf of St Lawrence
Geogr. Branch. 1959, Gosselin, 1972, LRIS, 1988
Shoreline sites Monitored by GSCA
Time frame: Shore measurements 1980-2006
Aerial video surveys: 1984-2000
(10 sites)
(12 sites)
(5 sites )
302 sites Atlantic Canada
27 sites in Southern Gulf
Objectives: repetitive survey and photographic measurements at representative shore sites
Define natural phases and duration of shoreline change, ie. erosion, stability and accretion.
Document impact of storms and shoreline resilience to these events. (flooding, landward migration).
Document human activities and impacts on shoreline stability.
Develop a baseline / index of “typical” types and rates of shoreline change ..........for future comparison.
http://gsc.nrcan.gc.ca/coast/index_e.php
Dune Building
Phase
1981-2008
High tide level
ocean
dune ridges
1981
2008
2001
Waterside Beach NS
Storm Impacts: wave runup, dune erosion (Dec. 2004)
Top Cliff Retreat 1981-2009: glacial deposits only vs on rock
Location No. of Years
Mean
Loss (m)
Max.
Loss (m)
Retreat Rate (m/yr)
Pleasant Bay
17 4.2 6.4 0.25
Caribou 28 5.0 7.1 0.19
Broad Cove
17 1.9 2.9 0.11
Cape John
15 2.4 3.6 0.17
Geogr. Branch: (1930s-1960) 0.18 to 0.4m/yr
Gosselin: (1930s-1970) 0.15 to 0.6m/yr
2009
1983
Long -Term Beach Recovery
from commercial sediment extraction
Belfry Beach,
Cape Breton Island
Field Measurements vs Remote Sensing
ocean
Shore cliff
1945 - 2003
New technology –larger areas covered but may not include
local area
suitable for rock shores
provides a rate of net change over set time intervals
Misses interim period and timing of changes
Similar mean rates of retreat 0.4 m/yr yet variable over time –max rate?
1. People often perceive shoreline erosion as much greater than it is in reality (long term)
- result of negative media and people see the worst in crisis
situations -demand remedial action immediately . - shorelines can respond and repair themselves naturally.
2. Decisions about shoreline repairs are often made at time of crisis, no time for consultation of monitoring results.
-plans should be made earlier in a proactive mode.
Thoughts for Discussion
3. News is short (days to months +anniv), Memory is longer (10-15 yrs); and Interest is cyclic (25-30 yrs).
2. There is no one agency monitoring and archiving long term shoreline changes (physical) and no long term baseline references to evaluate magnitude of shoreline responses.
1. In past - Field monitoring lasted months to ~ 3 years, (university or community) continuity often broken and information not archived nor easily accessible in time.
More Thoughts for Discussion
Photo C. Currie
4. GIS and GPS technology and satellite remote sensing will be the way of the future but need to maintain the "feel" and understanding of why shoreline changes are occurring.
-Shediac and Clyde River examples
Even More...........
3. No one agency assessing the impacts of shore protection structures which would improve future decisions and advice.
-Different attitudes to shore protection structures evolve with time, eg, groynes.
-scale of human activity at coast unanticipated.
Photo EAC
Community Strength - local knowledge & drive.
Document local conditions pertinent to their geographic area
2. Log date of storm events –flood levels and extent from rivers, waves or storm sewers.
3. Photo, mark and log:- wave run-up limits, dune and cliff retreat, washover channels cut into dunes, opening and closing of tidal channels.
4. Repetitive photos from established locations -at set interval and after storms (need same person / camera specs used).
1. Establish key locations (and maintain shoreline markers) for repetitive surveys.