EQ3-coastal recession and flooding Flashcards
physical factors
geological factors
-Lithology - soft rock type, weak cohesive bonds, porous rocks
-Geological structure - well jointed rocks, rocks with seaward dipping beds, heavily faulted rocks
phsyical factors
marine factors
-long wave fetch promoting large, destructive waves
-strong LSD that quickly removes collapsed sediment allowing erosion to restart
human activity
dams
-affects operation of sediment cell
-dams trap river sediment behind dam wall
-this starves coast of sediment source
-EG Aswan high dam on river Nile 1964: reduced sediment volume from 130 mill tonnes to 15mill tonnes per yr
-erosion jumped from 20-25m per year to over 200m per year as delta was starved of sediment
human activity
dredging
-This is the removal of sediment from a beach, sea or river.
-Sands or gravels scooped/sucked up for use by construction industry
-Dredging of river mouths and estuaries often to maintain navegable channel for ship transport
subaerial processes work together to influence rates of CR
-weathering weakens rocks above high tide mark, making mass movement easier by reducing internal cohesion of rock
-repeat MM leads to rapid CR
-EG north norfolk: hard engineering coastal defences protect cliff foot from marine erosion, by hydrating weathering+repeat slumping continues rapid CR
-wave cut notch will produce cliff collapse faster=^recession
-coastal slopes experinece small scale fluvial erosion as rainwater forms rills eroding gullies in slope face, particularty in unconsolidated material
temporal (time) variations in CR
wind directions+fetch
-Wd change daily as diff weather systems pass across/near uk
-rates of recession=^when wind blowing onshore, offshore winds=calm conditions
-dominant wind=direction of strongest wind
-prevailing wind=direction of most common wind
-when wind blows from PWD strong winds=large destructive waves+rapid CR
-where wind blows from large fetch, even small winds can = destructive waves+^CR
-dominant WD coincides w direction of largest fetch=large expanse of unobstructed open water allows wind to gain strength
-EG N norfolk rare dominant wind from N w 1600km fetch across Norweign +N seas=recession of up to 8m pa
temporal variatiosn in cr
tide
-rates of CR=more rapid at high tide when deep water in foreshore zone allows waves to maintain ^energy when reach backshore
-greater energy of impact on back shore^erosion+Cr
-high tides=2 a day, 12hrs apart
-2each lunar month when gravitational pull of sun+moon=aligned=high spring rides occur
-^SL=deep water near backshore+^CR
-ipcc estimates 1cm rise in SL=1m horizontal erosion
-global warming=^SL by 18-59cm by 2100
temporal variations in CR
storms
-Storm events=deep (v low pressure) depressions
- produce large, ^ energy destructive waves + fast rates CR
-Global warming is predicted to ^ intensity of atmospheric circulation - more frequent storm events - ^ intensity of storm events - ^ rates of recession
temporal variations in Cr
seasons
-winter=storms events w ^tides+long fetch bc contrast in temp+pressure between tropical+polar air masses=greatest
-Uk: Holderness winter 2-6m of erosion when storms+spring tides=^ erosion
-amount/intensity of storms in uk vary each winter
-weaker storms during el nino events(2-7yrs)+during phases of low solar output in 11yr cycle
temporal variations in cr
weather systems
-UK at polar front between boundary of warm tropical air of Ferrel cell + cold polar air of the Polar cell
-warm and cold = high air pressure anticyclone + low air pressure depression weather systems
-Anticyclones make gentle winds and small waves - low rates CR
-Depressions - areas of rising air (low surface air pressure)
-= produce strong winds - rapid CR
-Depressions form in the N Atlantic + take days to pass across UK from SW to NE.
-As they pass the spiralling inflow air produces changes in wind direction
Local Factors that Increase Coastal Flood Risk
SLR affect uneven ppl bc
-lowlying coasts r densely populated as beach/sea attract tourists
-lowlying deltas=fertile+ideal for agriculture
-deltas=ideal for trade w good navigable access inland up rivers
-delatas support megacities:
-e.g. Shanghai, Yangtze Delta China - 24 million people
-Dhaka, Bangladesh, Ganges-Brahmaputra delta - 14 million people
-Karachi, Pakistan Indus delta - 23.5 million people
ipcc predicts by 2060…
12% of the world’s population will be living in coastal regions less than 10 m above sea level
local factors
height
-lowlying=1-2m above sea level
-temporary flood risk from storm surges+permanent from SLR
-eg maldives archipelago indian ocean =pop 340,000 over 1,200 islands
highest point=2.3m above sl
-male (capital) protected by 3m seawall
-Bangladesh. 60% =less than 3m aboive SL
local factors
subsidence
(sinks)
- lowlying areas in estuaries,deltas or outbuilding zones=subject to natural subsidence via settling+compaction of recently deposisted sediment
- but, its outpaced by fresh deposition+bioaccretion of organic matter
- deltas=periodic isostatic subsidence when weight of delta sediment reaches max suffecient = cause crust to depress=marine transgression+flood
- volcanic islands+coral atolls-seafloor spreading away from hotspot/mid ocean ridge
- isostatic readjustment after icesheet retreat (s england)
marine transgression
-a geologic event where SL^ relative to land + shoreline moves toward ^ ground, which = flooding
-can be caused by land sinking or oceans basins filling w water/decreasing in capacity
