Coastal Characteristics and energy in coasts - Owen Shepherd

Coast is an example of a?

System

Types of coast

Drift aligned

Swash aligned

Drift aligned coast

Waves hit the coast at an offset angle to the direct backwash downslope

Means that LSD is dominant

Spits, bars, tombolos,

Spurn Head!

Swash aligned beaches

Waves do not hit at an oblique angle

No dominant wind or wave direction at angle to beach

So sediment is not transported only moved up and down beach

Limited LSD

Usually in bays after wave refraction

Why is it a system

Inputs, outputs, stores, flow component

Wind caused by?

Uneven heating of surface
High and low pressure
Fight for equilibrium

Wave energy determined by

Fetch (distance effected)
Wind Strength
Direction of wind (90 or not?)

Wave form in order of

Capillary wave
Wave sea
Swells
Wave train

Why do waves break?

Bottom is affected by friction
Slows down
The top of the wave passes over the bottom
Causes it to curl over

Constructive vs destructive depend on?

Wave energy

Constructive wave

Strong Swash
Weak backwash
Leads to depostion
Gentle sloped beach
Accretion of material

Destructive wave

High energy
Weak Swash
Strong Backwash
Steep sloped beach
Loss of material

Wave refraction

Sea Floor Raises more out of headland
So wave slows down in line with it
Around the edge = faster
Cruel round and refract around headland

Tides - two types

Spring and Neap

Spring tide

Moon and Sun opposite the earth
Leads to huge bulging either side as gravity of both and acceleration oppose

Spring tide leads to

Highest tidal variation

Neap tide

When sun and Moon at relative 90 degrees
Bulges on opposite sides cancel each other out
7 days after spring tide

Currents

Lowest effecting energy
Rip current = dangerous
Fast moving water

Where current usually flow?

Between a natural gap in landforms
Drags sediment out

Current strongest near?

Shallow surface of water

High energy coasts have?

Erosion landforms
Destructive waves
Wind and wave dominated

Low energy coasts have?

Depostional landforms
Dominated by tide or wind
Deposition exceeds erosion

How is it both open and closed

Depends on scale:
Entire Coastline: Open: Inputs and outputs from outside coastal boundary
Sediment Cell: Somewhat Closed: Hard for sediment to get in / out, and sediment is the only input / output

Example of positive feedback - think timescale!

Wave cut notch (long term)
Erode
Collapse
Ammunition
Erode
leads to overall retreat

Landform

Specific morphological feature as a result of processes in the area - shaping of the land

Landscape

The overall layout of the land as a result of many landforms

Sediment cell

a largely self-contained stretch of coastline where the movement of sediment is almost entirely contained

Sediment cells often located

Between two headlands or estuaries

How many sediment cells in the UK?

11

Sediment cells managed by?

Sediment management plan

pros and cons of sediment management plan

Pros: managed in their own cells so effects monitored correctly as cells span over many councils
Cons: Councils do not often agree on sediment management plans leading to conflict

Inputs into sediment cells

Where sediment is brought into the system

Sea level rise as an input

Pick up sediment during flooding

Outputs

Rare - often sediment cell is a closed system - but some sediment does get past each end or washed out to sea

Flows / Transfers - huge!

Sediment is moved around the cell / system

Sinks - stores within the sediment cell

Any large storage of sediment - depostional

Sinks examples

Beach, spit, tombolo, dunes

What maintains the cell?

Dynamic Equilibrium

Why are these examples good?

Example of the differences in a positive / negative feedback over time-scale - dynamic environment

Energy in a sediment cell - high to low

Waves, tide, current, wind

Wave formation

Wind friction leads to capillary wave, turn into train of many waves, gain energy, meet shoreline

Wave power determined by

Fetch, strength of wind, direction of wind (Prevailing perpendicular = more)

Fetch

the distance of open water over which the wind blows the wave, in a single, uninterrupted direction.

Waves crash over the top due to

Frictional forces turn circular motion into elliptical - crest lifted too high and collapse

Tide

Rise and fall of sea level due to gravitational effect of moon and sun, and centrifugal force of their orbit and the rotation of the earth.

2 types of tide

Spring, Neap

Strongest tide?

Spring - highest variation in tidal range, when moon and sun are opposite to earth, 2 x a month

Weakest tide?

Neap, when moon and sun are at a relative 90 degrees to each other, happens 7 days after - effects relatively cancel out, lowest tidal variation

Why this way?

Gravity leads to bulge on close side - centrifugal leads to bulge on far side.

Spring = Amplified, Neap = Nullified

Wind - Aeolian

Pressure gradient - as a result of uneven heating leads to imbalance = movement of air

Current

Flow of water due to changes in temperature and salinity - leads to transport of material

Examples of high energy coastline erosional landforms

Wave cut platform, Cliff, Headlands and bays, Caves, arch, stack, stump

Depositional landform examples

Reef, island, beach, spit, Slat marsh, mudflat

Sediment budget

Balance of sediment in / out of the cell
Determines accretion and subsequent extension
Removal and retreat

Positive budget

In > out, leads to accretion of sediment and then Shore Extension

Negative budget

Out > in, leads to removal of sediment and then Shore Retreat

Headland

Sticks out into the sea, eroded slower, leads to wave refraction

Wave refraction

Wave bend around headland to attack headland perpendicular to the coastline, leads to a reduction in energy of the wave too

Landforms as a result of wave refraction

Crack, Cave, Arch, Stack, Stump

Types of coast

Concordant
Discordant

Concordant coast

lithilogy aligned with the direction of coast
Parallel to coast layers of rock
Erode at same rate
Until one ‘broken through’ forms a cove where inside then eroded slower

Discordant coast

Layers of soft and hard rock are perpendicular to the coast
Hard erodes slower
Soft erodes faster
Forms bays and headlands, where eroded at different rates

Deposiotion happens when

Sediment load exceeds waters ability to carry it

Energy decrease due to

Increase in friction - Shallow water etc
Turbulent flow - obstacles slow the flow down

Mudlfow

Heavily saturated - typically over unconsolidated material - flows down the slope - steep ish - no vegetation to support

Wave refraction

Waves come into shallower water around a headland first
Get bent around the headland and attack at angles
Dissipates wave energy