ESPL lecture 2
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- Created on: 29-05-22 16:57
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- ESPL - Aeolian block lecture 2
- coastal aeolian systems
- dunes microscale controls
- –Wind regime –Grain size –Beach width –Beach slope
- Controls on q (sand transport) Controls between grains - largest 1m scale Can make predictions but they are often quite flawed due to the everchanging nature and complexity of the interactions
- Sarre (1989)
- Braunton Burrows, SW
England
- Transport prediction equation Driving force related to V*
- based on sarre the actual and measured movement were compared
- Highest predictions for winter Highest actual rates in summer (sand condition and moisture)
- predictions almost always higher then the observed
- important variables
- •Beach watertable (groundwater) •Tidal effects •Fetch (length of beach wind sees) •Evaporation + precipitation •Grain size
- 1.Changes
in the water table
2.Rainfall
intensity
3.Amount
of precipitation
- 4.Temperatures These factors impact susceptibility to erosion – although the wind is higher in winter the other conditions impact how susceptible the sand is to transport ?
- Empirical
equation is very site specific i.e.
can apply to
Braunton
Burrows
only
- Corrected q = better agreement between predicted and actual, but still a lot of variance
- influence of beach width on sediment transport
- 1)Together
with wind direction, beach width determines sand source extent
- 2)Together with thickness of sediment above beach water table, it determines total volume of sand available
- 3)Indirectly influences sediment transport through effect of beach form and slope
- 2)Together with thickness of sediment above beach water table, it determines total volume of sand available
- BEACH WIDTH Width and wind direction determine source of sand Source as an Area X Depth = volume available to move
- 1)Together
with wind direction, beach width determines sand source extent
- carrying capacity and transport
- Once threshold is reached the speed reached has its own threshold of sand it is capable to moving It becomes a saturated flux
- – it cannot pick up any more sand Faster speeds of winds have greater ability to transport sand
- Once threshold is reached the speed reached has its own threshold of sand it is capable to moving It becomes a saturated flux
- MACRO SCALE interactions
- relate types of coastal dune systems to
beach types, and long-term sediment budgets
- beach type
- 1.Dissipative
beach:
strong wave energy, but energy dissipated in surf zone, some distance from
beach face
Used and lost in surf zone – crashing
waves
Surf zone is a far distance away from the
beach zone – there is little beach wave interaction
- finer
as the limited energy on the beach leads to finer sediment settling
- After due initiation the dunes are likely to progress due to the stable nature of the beach
- finer
as the limited energy on the beach leads to finer sediment settling
- 2.Reflective
beach:
wave energy dissipated on the beach
Smaller width of beach meaning there is
more interaction of the waves with the beach
- the
larger energy means that coarser sediment can be brought on shore further up
the beach.
- Variability in shear stress, sediment texture, surface roughness from wave energy – less stable to less likely for the dunes to progress and become mature
- the
larger energy means that coarser sediment can be brought on shore further up
the beach.
- 1.Dissipative
beach:
strong wave energy, but energy dissipated in surf zone, some distance from
beach face
Used and lost in surf zone – crashing
waves
Surf zone is a far distance away from the
beach zone – there is little beach wave interaction
- beach type
- relate types of coastal dune systems to
beach types, and long-term sediment budgets
- dunes microscale controls
- beach system
- FRONTAL DUNE
- BEACH
- out put to frontal dune from beach = 1 landward aeolian transport
- input to beach = alongshore sand supply
- out put from beach = alongshore sand loss
- input = onshore sand supply
- output = offshore sand loss
- out puts to beach from dune = 1 wave erosion 2 seaward aeolian transport
- out put to land = 1 inland aeolian transport
- BEACH
- Inputs (***) Outputs (ASL) These processes and their balance lead to aggradation or degradation
- On-shore inputs (OSS) marine inputs Off-shore outputs (OSL) marine outputs
- Fluxes between landforms
- Erosional (WE) from dune to beach Erosional/depositional (LAT) from beach to dunes Erosional (SAT) from dune to beach Erosional (IAT) from dunes in land
- Mablethorpe Lincolnshire
- Use of the processes and landforms
Manipulation of processes to promote
deposition or prevent erosion
Flux
- sizes and interaction levels These change the form of the dune and beach
- Range of interactions control form and change Can look at micro, meso and macro-scales
- Use of the processes and landforms
Manipulation of processes to promote
deposition or prevent erosion
Flux
- FRONTAL DUNE
- coastal aeolian systems
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