Shoreline Erosion - started November 24th, 2011 Envir Sc...

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Unformatted text preview: started November 24th, 2011 Envir Sc 1G03: Earth & the Environment Shoreline erosion Outline 1. 2. 3. 4. Beach erosion Cliff erosion Erosion of the Scarborough Bluffs Coastal protection measures 1. Beach Erosion When are beaches most susceptible to erosion? - During Storms Storm surge - elevated water levels due to onshore winds, low air pressure Waves have exceptional erosive force Beach profiles change - dunes move landward - material between dunes and water removed Backflow of water to sea can also cause erosion - Narrow tourist beaches on narrow barrier islands most at risk May be completely overwashed in storms e.g. Texas coast, Carolinas 2. Cliff erosion Rock and sediment cliffs are vulnerable to erosion by waves - pounding by breakers - milling by debris moved by waves Cliff erosion... - Headlands are most susceptible to wave erosion Why? Fig. 18.15 WAVE REFRACTION - wave energy is concetrated on headlands, spread out in bays What does this produce? Straightened coastline Cliff erosion... Wave erosion concentrated at waterline - toe erosion Debris removed by currents - produces steep clis - wave cut platform - sea stacks Fig. 18.18 Sea stacks Sea stack cliff Wave cut platform What processes will occur on soft sediment coastlines? Cliff erosion... Mass movement processes important - slides, slumps, flows cali 3. Erosion of the Scarborough just east of toronto Bluffs Scarborough Bluffs - Average erosion rate ~ 1m/year (1980's) bluers park (marina) - 0-15 m/year range Why are erosion rates so high? - 'soft' sediments - urbanization 1980's several houses lost! Apartment building and townhouses at risk By mid -1980 - recognized need to protect bluffs How? Need to know processes ~1985 Erosion processes Toe erosion - waves remove debris at base of cli - sediment transport to west Where does this sediment end up? Toronto Islands! Erosion processes... Slumping - shallow rotational slumps - occur after periods of intense snow melt slump blocks trap water in cli - causes more slumping Erosion processes.. Slides and debris flows - common in spring, after storms Erosion processes.. PIPING - groundwater emerging on cli face - washes out sands - produces 'pipes' Causes collapse of everlying sediment Cli top retreat - Pipes enlarge at times of snow melt - Cause collapse of overlying sediment - Cli top retreat Erosion processes... Surface run o - produces gullies - ravines How can the bluffs be protected from further erosion? 4. Coastal Protection Measures Protect slope - encourage growth of vegetation - add fill - waste material?? Protection measures... Stabilize toe of slope - build groynes to trap sediment moving in longshore drift system Build marinas to trap sediment (ex. Bluers Park) What are the potential problems of doing this? Protection measures.. Protect toe of slope with armoured toe berms Toe berm protects cli from wave erosion - prevents removal of sediment Protection measures... Sensitive areas - such as storm water pipes - surround with gabions Protection measures... Restructuring creeks - contain surface water flow in pipes - reduce slopes ~ 5 million in 1980's Bellamy ravine Protection measures Large scale engineering - reduce overall slope - by terracing - cutting back slope What else would you have to add? Drainage system This has been done in Scarborough, U.K. Erosion on the Bluffs Future issues! north shore of lake erie - Toe erosion much reduced - Blus are stabilizing - Future Issues - groundwater discharge on cli face - changing lake levels ...
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This note was uploaded on 11/28/2011 for the course ENV SCI 1G03 taught by Professor Padden during the Fall '11 term at McMaster University.

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