geography exam

sediment routing

Sediment is transferred from source to sink along trajectories. (dashed lines)

Same trajectories involve short transit times with brief periods of storage ( small cirlces on river bed)

Whereas, others involve long transit times with long periods of storage (larger circles on floodplain)

Sediment routing is the relationship between transport and storage

example of people interrupting the sediment routing cycle

sediment routing reading

erosion depends strongly on climatic factors such as wind, temperature and rain exogenic (plus tectonic activity, endogenic)

sediment is transformed, phase-shifted and lagged by the internal dynamics of the routing system

local processes: sediment accumulation is controlled by local hydraulic variables, the range of sediment available and the details of the local topography of the channel, bars, banks and flood plain.

longterm= subsidence and tectonic activity

Mountains disturb atmospheric circulation that can influence climate such as some areas getting more rain than others. Changes in the amount of precipitation can influence erosion.

erosion occurring over an active tectonic plate that occurs within the crust and ends up changing the earth’s surface can cause a flow of rocks towards the surface of the basin.

tectonic folds are expanding and being eroded (then can cause earthquakes).

sediment budget

20 billion tonnes of particulate sediment is delivered to the ocean every year

diagram to draw

magnitude

the intensity of different events

high magnitude events tend to be low frequency

frequency

how often something occurs

magnitude and frequency

can be used to predict natural hazards such as storms and floods

need a long duration of records to predict accurately- better freq and mag relationships

if we didn’t know the data historically, may think that the big floods that have happened recently have been the biggest flood with the highest magnitude. not accounting for bigger floods that could have occurred in the past. - will change the output of data

need to account for climate change

Intermediate magnitude-frequency events generally dominate fluvial sediment transport- more work done

only using the max- could be a smaller flood in the future that is larger than the previous maximum

hillslope

Sides of valleys and the margins of eroding uplands

varying degrees of slopes and angles

material is loosened by weathering and then transported down slope to a river channel via exogenic processes and gravity

controls on slope instability

Determined by the balance of shear stress ( driving force of failure, gravity)

And shear strength 9resisting force, friction holding material on hillslope)

factor of safety: >1 no fail,

driver of instability: Relief

Higher elevation is more potential energy of force for something to move down the hill

angle of repose: Steepest angle, relative to the horizontal plane at which material can pile up without falling

Can change with material type

driver of instability: grain size

For dry material the angle of repose increases with grain size, (30-37 deg)

Fine sand: lower angle as less friction between

Angular pebbles: Material is ore spaced out and can stack ontop

driver of instability: water content

water increases cohesion of soil grains via surface tension. Thin film of water that covers sand grains and enables them to stick together= Makes slopes more stable



If the sand gets too wet it can flow like a fluid, water also adds weight to slopes so water will fill the gaps in the soil and push the air out. High rainfall events= trigger slope failure

Dry unconsolidated, slightly wet and saturated material

dry unconsolidated: Form a pile with the slope angle determined by the angle of repose, there is grain to grain frictional contact

Slightly wet: high angle of repose, surface tension holds the grains in place, good cohesion

saturated: Low angle of repose, flows like a fluid. Water between the grains removed grain to grain frictional contact

driver of instability: Vegetation

Roots will stabilize the soil so hold hillslopes in place and will intercept raindrop erosion

The excess weight of the soil and trees and added wind force

windthrow- Trees on hillslope when strong winds, roots connected to the soil so will dislodge soil up with the tree as it falls on its side

people removing vegetation promotes slope instability- Material (slash) gets pushed down into rivers which can cause issues for farmers etc.

driver of instability: fire

Fire can cause hydrophobic soils ( waxy oil layer above the soil) ash and organic material that has been burnt, and doesn’t allow water to go below the soil layer. Slopes fail as water cant infiltrate into the ground

driver of instability: geology

Weaker rocks or soils, such as loose sands, clays, or weathered materials, are more prone to slope failure than stronger rocks

Weak spots- faults, joints, fractures and cracks which can weaken the material

* water can get into the cracks and start to weaken the material

bedding slope

least stable- bedding of slope is parallel to the slope= unstable if stuff was moving down it it will shear off big chunks

driver of instability: earthquakes

seismic movements triggers mass movement such as landslides

this can create landslide dams, had seismic shaking, destabilising material on hillslope moved from a source area down the slope and accumulated in a river channel and blocked off the river and creates a lake. - risk that water can overspill

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Mass movement: falls

Material detaches from a steep slope and free falls through the air

Fast movement which occurs of steep hillslopes/cliffs

Is triggered by earthquakes or erosional processes

Type of material= rock

Glacier retreating= increase in rockfall, not there any longer to support the walls back, as ice melts and ice creeps backwards the wall relax= rockfall

Mass movement: falls diagram

mechanical weathering

Water collects in a crack in a rock

Water will freeze and then expand, causing the crack to widen

Ice thaws then water contracts are gets deeper into the cracks

Repeated expansion and contraction causes further cracks till the rock splits

Moderate precipitation in cold environments, with seasonal variability

Mass movement: slides

Zone of weakness separates the material from the stable underlying material (moves as blocks), movement is parallel to slope, variable speeds

 

Slide: translational, will move along a planar surface

 

Slump: rotational, surface of rupture is curved concavely upward

Mass movement: slides and slumps diagram

Mass movement: flows

Moves downslope as a fluid (mud, debris, or earth), due to being saturated (high water content) and usually a mix of grain sizes

Rapid rate of movement , hazardous

Follow river channels and occur after heavy rain, common after fires

Mix of material, rocks, trees, sand, mud, debris

Mass movement: flows diagram

Mass movement: soil creep

Slow downward progression of material on low-grade slopes

common in humid and temperate climates. (seasonal changes in soil temp and moisture)

Due to the upward movement of an underlying soil layer due to the wetting and drying cycles, filling of cracks from upslope.

form terracettes

Tree trunks bend as the material moves from underneath it

Mass movement: soil creep diagram

Mass movement: solifluction

Gradual movement f water-saturated soil over frozen ground (permafrost) that acts as a sliding plane, downslope



It occurs in the summer in a periglacial environment

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Mass movement: solifluction diagram

Lahars

Violent mud/debris flow composed of a slurry of pyroclastic material, rocky debris and water

Material flows down from a volcano typically along a river valley

Destructive, mix grain size

Water picks up material and moves it off the slopes of the volcano

Hot: requires volcanic eruption, Snow/ice melted by volcano, Heavy precipitation during eruptions

Cold: no elevated temp, due to heavy precipitation or a snow melt event that mobilize loose volcanic deposits.

flood hydrographs

How drainage basin responds to rainfall

Flood planning (predicting time/magnitude)

Show the river discharge that occurs as a result of precipitation from a storm

Eventually the river discharge will return to its normal level or base flow

flood hydrographs terms

Peak rainfall= time of the highest rainfall level

Peak discharge= time of the highest river discharge

Lag time= difference in time between the peak rainfall and peak discharge

Rising limb= increase in river discharge

Falling limb= fall in river discharge

factors that affect the shape of the hydrograph

Watershed hillslope gradient: steeper generally gets water to the river faster

Drainage density: how many streams flow into a river at a certain point

Surface storage e.g. dams, lakes, reservoirs, flatten the hydrograph

Temporal and spatial distribution of rain fall, where it falls in the catchment

weather, climate,

gentle and flashy hydrograph

Flashy: river discharge increases rapidly over a short period of time

Rainwater reaches river quickly- high tendency to flood

Occur in urban areas, rivers with low rock/catchment permeability and on steep catchments, small basin

* Water cant go through the concrete and asphalt (less infiltration) running off the surface quickly,(infiltration excess runoff),Lack

of vegetation

Gentle: Gentle limbs, low peak discharge and a long lag time, areas with low relief and permeable soils, where water infiltration and runoff occur at a slower rate.

airflow over foredunes

Wind accelerates up the hill, the flow will accelerate when it has been compressed

Blow outs expand because the wind funneled through the blowout maintaining a vegetation free zone

Due to compression there is a higher wind speed near the top, create conditions for sand to get blown out

which maximises erosion

Threshold velocity wont get the particle to move

* Based on a single grain on a flat surface and is perfectly spherical
* The sand grain on the beach sits inside of the other sand grains, only part of the grain is exposed ( part of grain is always hidden)
* Need an excess of the threshold velocity for it to move

vegetation is crucial for

dune stability

Starting conditions for sand dunes

* Either a river or coast (no vegetation, delivery of sand)
* Location with a coastline that’s prograding, gets lots of separated beach ridges, wet sand won’t move as it’s held in position due to cohesion- From material blown onto the beach

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If you hold the beach in position for a long time, dune builds up

Beach eroding- scarps form

blowout shapes

Dune edge breaches wash out during storm or high tide- Don’t create dunes inland

Airflow funnels into a gap and the dune extends- Propels sand inland

dunes and wind

Dunes align along the net vector direction of the wind flow

Only the stronger winds will move a lot more sediment

A=Shows direction wind is coming from, Direction of wind towards to NW

B=Wind drift potential, A lot of sand will go to the NW

Storm hits the coast with a given amount of energy, no dunes, and then the energy goes to roads and buildings. The sand acts as a buffer

sub-areial dunes depend on

depends on whether there is sand available to move or not

vegetation cover

Can the wind directly access the sand

linear dunes

Dunes of sand starvation

* Not much sand in the landscape
* Wind organises the sand in linear ridges
* Wind circulations between edges= any sand that ends on flat areas between gets blown back onto the ridges

Fixed in position, Bimodal winds

Little vegetation- cant stop formation of dunes

* Have more vegetation than surrounding country, but the wind can still get to the sand

deserts

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Why do linear dunes elongate but don’t change position

Linear dunes are often asymmetric due to the differences in the strength of the 2 wind fields’

wind direction from S in winter and NW in summer= get a net vector of direction. Dominant wind from, more of a push from the NW side,

Inside the dune, the zone on top that’s active, crest will lean in the direction of the net wind and will move seasonally.

Trace linear dune back to the source



Temp rivers, get flushes of sediment, from the edges of the rivers, the dunes are developed

parabolic dunes

can see Blow outs, generate new bog parabolic dunes, Some at the coastline but are v small

Unlimited sand available, hard for wind to get the sand, as there is forest cover

Depends on an erosional gap of blow out which the wind can exploit

 Erosional gap in the middle of the dune, and the middle of the dune has winds which pushes through and leaves a trail, one side larger than the other (aligned with the wind)

carlo sandblow- rainbow beach

W- see diagonal lines, wind catches sand near the coast, pushes the sand through, and the diagonal lines show the migration of the dune through the countryside

E- Harder, material, development of soil, exposed to light and heat, bakes into a chemical rock

 Current blowout is eroding through fast dues

Heavily vegetated landscape, buries trees as it goes across

transverse dunes

Inside of a parabolic blowout

4 blow outs that have been migrated and have joined, have no choice but to migrate through the dense forest

 Supply limitation= duenes aligned down the wind

Lots of supply, dunes turn around, so once in an open area they are at right angles to the direction of the wind

 Each sand wave is a transfer dune

analysis of this picture

transverse: Sharp ridge going across= parabolic migrated off this coast and it migrated across the whole island, blow outs migrate rapidly inland

NW: Remnants of dunes, time series, dunes at modern beach= recent, dunes near 6000yrs old, parabolic= 180,000yrs, Green= 350,000 yrs- 1000000

front middle: White= parabolic- hook shapes on the end of them, migrating through a forested area

Older= less formed, angle of repose= highest angle at which the material will support itselfs,

Dune at 10 deg the sand wont migrate

Steeped up the angle of repose

coastal dunes in France

No strongly developed parabolic form

 

Area covered in forest

 

Wind will "freeze" in place

 

Each line represents a coastal potion that has been filled up with sand and then abandoned and move on

 

Coast- long term house will be safe as the sand is moving into the sea

not all dunes point in the same way

Form with a nose into the wind, and the trail being down wind of what the wind direction is

model of dune change

Dunes forming parabolic, get position where they join together, will get an area where you will get transverse dunes

Increase in sand availability through increasing wind strength or drought stress ( decrease vege)

 

White= no change, but ready to go if a disruption



Reduce wind speeds or allow vegetation to form, transition from transverse to parabolic

podsol development

Soils developed on dunes is dominated by podzolization, soil increases in thickness with age

Initially become more nutrient-rich

But as soils continue to deepen, nutrient status declines

Layer on top= of organic litter, producing acids that wash into the sand

End up with pure white sand,

 

Can be bright orange yellow soils

 

erosion of dunes

Go from youth to old age

Then something comes and lifts it up again and the cycle restarts

non-tectonic settings dunes

Away from nz

Gradual landscape lowering

 

Soil diffusivity = weathering process going on in top soil and have a zone before underlying rock where you have broken up rock and soil,.

 

Loose material at top of hill, will go down by soil diffusion processes

 

Steeper slope faster the diffusion down the slope

once dunes are emplaced, how do they evolve?

There are records of what the dunes look like at different time periods

Typical shape of dunes: Convex then concave with flat in the middle

Gradually reduce convexity of one end of slop and concavity over time

Through time curvature evens out



Curvature can help work out the age

* Younger= steep dunes with high curvature, have small scale landslides occurring, Fire will disrupt the slope and sediment slips down the slope
* Older= gentle and lower curvature



Pretty good match for 1st 3 major peaks with changing sea levels

 Disruption at the beach when dunes forming, dunes at the back at the beach more inclined to be over run by storm events, moving them

what records can we obtain from dunes?

fire records

There was one big fire that burnt half the island and caused lots of damage

 2 phases

* layers of charcoal
* Layer above it with continuous charcoal

 

Can measure individual fires going through 

* material becomes buried in Lakes and ponds
* Use buried dune records to reconstruct fires

what forces act on a grain of sand

impelling force: Power relationship, ability to move sand grains increases exponentially as the wind speed increases

resisting stress: Much easier for things to move in water, as it is denser as has more mass, and more force

also shear and resisting stress

entrance processes of IOCES

Intermittently open/closed estuaries

Periodically close by the formation of a berm/bar across the mouth

Influenced by rivers and tides but mostly wave dominated

Competing energies (Onshore sand transport by waves vs ebb tidal currents (outgoing tide and river flow)

* Open: high river discharge and strong ebb tidal currents

Low wave energy which causes net offshore sediment transport

* Closed: low river discharge, weak ebb tidal currents

High wave energy which causes net onshore sediment transport

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entrance processes of IOCES: tidal and ebb tidal prism

Tidal prism= the volume of water exchanged over a tidal cycle

Ebb-tidal prism= tidal prism and outgoing river flow

global distribution of IOCES

More common in micro-tidal estuaries

Need

Relatively consistent high-wave energy

* Berm building
* Swell-dominated coasts with bigger waves

Small tidal range

* Weak tidal currents at the entrance (allows sand to stabilize the mouth)
* Micro and meso coasts with a tidal range from 0.5 to 2.5m
* variability seasonally and interannually, sometime it will be low river flow, easier for waves to win, high rainfall all the time= hard for waves to bring sand onshore
* Rivers with low mean annual and specific discharge
* Smaller rivers and catchments
* Common on rivers with variable flow regimes

NZ distribution of IOCES

East coast of the South Island and Northland

why?

* Variable, mostly dry compared to W
* Low flow rivers and seasonal
* High ocean waves, small tidal range, rivers that have seasonally low flow

opening processes of IOCES Catchment

Periods of high rainfall and river flow

Raise the water level of the lagoon and sits inline with the sand berm and spills over top, thin flow and gradually widens the channel

elevation difference between them causes a channel to be mad

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opening processes of IOCES marine

overtopping and seepage

* Big strong waves that spill water into the lagoon, add a little bit of water for the lagoon to go over the threshold 
* Berm saturated already, sapping/seepage; big indents, water takes sediment with it
*  if it keeps happening, causes cracks and induces mechanical failure of the berm 

opening processes of IOCES mechanical (artificial)

* people open it before the natural threshold is reached 
* Dig a channel from the edge of the lagoon out to sea 


* Improves water quality stuff like algal blooms, and bad temp, goes out to sea, and leaves good stuff behind 
* Fish passage: Salmon and eels that need to get out to migrate - cultural significance as mahinga kai species 
* Flood mitigation: Water went into the lagoon and raised the level enough for it to open.
* Affects floodplains and agriculture, people and recreational sites, Getting rid of flooding, stranded communities

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standing wave sin IOCES

Standing waves working, forms under supercritical flow, water moving fast and is turbulent



Getting rid of flooding

Ecological risks associated



Bumps in water surface, antidunes that migrate upstream and then collapse

Geomorphic change

* Slow to kick off, Subcritical flow, slowly starting to increase in velocity, Mouth not being super high 
* Supercritical flow, expanding quickly, deeper and winder and increase in velocity increase in discharge 
* Water level decreases, while discharge and channel width increase further

not all follow this pattern

Measure near continuous geomorphic change at the estuary mouth and linking it to change in basin water level

opening up ICOES on a steep grade

Grade= energy gradient between estuary and the sea

Opened with steep grade so have big elevation between estuary and the tide but not much distance for that to travel across

Go through sequence of change quickly = Reach peak within a few hrs

Opening- velocity reaches it peak (within a few hrs) then tapers off quickly

Same with channel width

Hydrograph discharge= sharp

 Opened on a falling tide, grade was getting steeper

opening up ICOES on a lower grade

Lower grade, when opened took a long time to really kick off and reach its peak velocity, width, discharge

Opened on a rising tide, the grade wasn’t getting steeper, was getting more gentle

when can artificial openings fail

Big waves that bring sediment onshore to infill the channel- stormy seas

Insufficient energy to maintain offshore transport to push sand offshore, waves can deposit sand and shit the channel

Combination of above

120m long channel, grade is low, didn’t have the potential energy to move sand off shore at the mouth

how to predict wether an artificial opening will fail or succeed

Grade steeper than 1:60 ratio is needed for a successful opening and waves lower than 4.3m to avoid infilling from ocean

Low grade, high waves and on a tide that was rising so decreasing the head, so it closed off

Within grade threshold, steeper, low waves and did it at a falling tide= successful

ecological implications of opening IOCES

Open at really steep grades and track through drainage sequence quickly = bad for lagoon

 

Stratification: Freshwater sits on top of normal water, all deoxygenated water can result in fish kills.

 

Need to take note of water quality in lagoon, low dissolved oxygen not a good idea to open, see the oxygen rich layer drain off and what's left behind will suffocate the fish

**Hapua**

braided river mouth lagoons

Form on mixed sand and gravel beaches

Shore parallel barriers built by longshore drift

Build by sediments being pushed by the currents of the river

Don’t have a lot of tidal influence, due to mouth being offset, doesn’t allow for tides to come in and change the water levels

Wave dominated estuaries

**Waituna**

freshwater coastal lagoon, which is large and lake-like

Form on mixed sand and gravel beaches

Shore parallel barriers built by longshore drift

Wave dominated estuaries

Smaller rivers that flow into them, tend to have lower flows, closed for long periods of time

Water and stuff that comes in sits for a long time before it goes out to sea

Hapua and Waituna in NZ

Lots of the East coast of S Island, some on W too

Lots of mixed sand and gravel beaches

High energy coastlines

Natural river flow regimes, severely altered by high levels of water extractions (Variable river flow, push through the barrier)

Small tidal range

There isn’t many hapua in the North Island as they don’t have many braided rivers and super steep mountains

what shapes Hapua and Waituna morphology

**Tectonics and sediment**: Southern Alps that provide coarse material that is brought down from the mountains by alluvial fans and braided rivers and break it down

**Coastal processes:** southerly waves generate a northward longshore drift current which builds shore parallel barriers of coarse sediment

Under a lot of pressure due to irrigation processes, water abstraction, catchment land use change

significance of Hapua and Waituna

Important habitats for native flora and fauna, mahinga kai and taonga species e.g. cockles, flax and eels

Fisheries= recreational

Culturally important

* Source of mana
* End of hapua are indicators of catchment ecosystem health and the state of the mauri of the river
* Carefully managed by tangata whenua for generations

hapua materials

Mix of coarse sand and pebbles

* Exceptions= Ashley and Waimalariri river as they enter the coast on sandy beaches, due to reduced wave energy from the shelter from banks peninsula

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waves hit the banks of the peninsula and then will lose a lot of energy so pegasus bay will receive the material

Exist on coasts that are chronically eroding, the rivers feeding into the hapua have high sediment loads so can eventually close

why are Hapua are eroding even though there is high sediment supply?

Sediment is making it to the coast but then  its being moved further on and not making it back

Need coarser material, to build up the barrier, silts and fine muds are wont build up

People are extracting gravel from the floodplains

 water limits being ignored

opening and closure of hapua

Wave vs fluvial processes

Close during low flow as the energy from the waves are "winning" until flow picks up and net energy dominates over waves= open mouth

Then when flood occurs the barrier is breaches by a main channel



Undergo a cycle of infill and erosion related to floods

When closed the water can seep through the barrier as there is coarse sediment

wave overwash hapua

Big waves go overtop the barrier and push into the lagoon

Can get movement of materials into the lagoon

Can cause barrier to roll backwards into lagoon, reduces its size

Reduces buffer space between houses

Can narrow the lagoon and move sediment into the lagoon

occurs during storms

High tide, big flood flow in river, water cant push out mouth, so holds back water and will flood towns, Erosion of back-cliffs

opening and closing in Waituna

Most are closed and may need to be opened artificially

Closures last typically months-years (longer than hapua)

Lake Ellesmere

Culturally significant to Ngai Tahu, ecological significance= aquatic wetland ecosystems

Suffered environmental degradation

Fed mostly by ground water with many springs in the catchment, there has been a decrease in groundwater levels

Due to an increase in people taking water out for drinking or agriculture

formation of lake ellesmere

With rising sea levels, spit began to form and was fed material moved alongshore from Rakaia

Spit closed off the Ellesmere embayment, which creates an enclosed freshwater lake

A permanent channel was established, and estuarine conditions were re-established

Lake started to close via the spit (longshore drift) as wasn’t getting the flow from the river

Water quality issues to long residence times

Hypertrophic and super saturated with P and N due to long residence times, trapping and storing nutrients

management issues with lake ellesmere

Co-governance to restore the lake

Replanting of riparian margins

Establishment of macrophyte beds

Ecan and Ngai Tahu work together to make sure it is the right conditions to artificially open the estuary e.g. timing it with fish making sure it is the right conditions

Te Wairewa

Te Wairewa is important to the Maori tribes and they use the lake to catch and harvest eels

As barrier is pushing out makes it harder for building channels to catch them and for the eels to compete their migration

are a mahinga kai species

 

 

beach profile, types of shores

Backshore

* Dry under normal conditions, storms= wet
* Above high tide limit
* Beach and berms



Foreshore

* Intertidal zone
* Low tide= dry and exposed
* Top of the berm to water line



Nearshore

* Underwater, shallow water processes
* Swash zone to deep water
* Wave breaking

diagram to draw beach profile

beach profile energy gradient across active profile

Offshore                                       

Deep water waves (lower energy, not interacting with the sea floor, fine grains

 

Breaking waves, higher energy, Waves are starting to break and release their energy, stir and move sediment on sea floor, coarse grains

 

Onshore

Aeolian processes, lower energy, Wind processes but don’t have as much energy as a wave, finer sediment

swash zone and berm

swash= onshore flow, Waves have broken, smaller. Pushing sand grains up with it

Backwash= offshore flow

berm= Flat area, limit of where waves are rushing up and down the beach face, form due to the deposition of material by waves

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berm= storm and fair weather conditons

fair weather= waves push more sediment onshore than they erode as backwash (low waves flat beach)

Storm berm= More powerful waves, which erode more sediment offshore, backwash stronger than swash, Narrow beach and offshore bar storage

fair weather return: Low waves and then the bar moves back onto beach

seasonal changes in beach profile

Summer: low wave height, sediment moves onshore, beach is wide and flat

 

Winter: higher waves, sediment moves off shore, beach is narrow and steep

how do beach profiles form?

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1. Tidal Influence: Tides, which are caused by the gravitational pull of the moon and the sun, influence beach profiles by causing the rise and fall of sea levels. The cyclic tidal movements can result in the deposition or erosion of sediment, affecting the shape and elevation of the beach.
2. Wind and Currents: Wind and ocean currents also play a role in shaping beach profiles. Strong winds can create waves and generate currents that transport sediment along the shoreline. These processes contribute to the formation of different beach features, including dunes, spits, and cusps.
3. Geological Factors: The underlying geology of a coastal area can influence the formation of beach profiles. The composition and structure of coastal sediments, such as sand, gravel, or rock, can impact the beach's slope, texture, and overall shape. Geological processes like erosion and weathering also affect beach profile development.
4. Human Interventions: Human activities, such as coastal engineering and beach nourishment projects, can alter natural beach profiles. The construction of seawalls, groynes, or breakwaters can modify wave patterns and sediment transport, resulting in changes to beach morphology.

wave generation in the ocean

* Generated by vertical displacement of water (Blowing on surface on sea which creates a bulge of water that travels across).
* Winds acting on the ocean surface
* Extreme (sudden) events e.g. tsunami
* Ultra low-frequency  processes e.g. tides (Crest in the wave doesn’t pass very often)

The height of ocean wind waves is dependent on

* Windspeed; Higher waves as more energy transferred to sea surface
* Wind duration; More energy being transferred over a longer period of time
* Fetch distance Distance of water of the ocean where the wind is blowing in a common direction

 

wave process source to shore

Waves organise themsleves by period and travel in groups called swells

\-Energy from wind being transferred to the waves

\-Waves travel in a similar direction and propagate, waves that travel the same speeds will travel together

\-Interact with bottom of ocean form, release energy

wave motion

Water particles undergo circular orbital motion when waves pass

Occurs in the direction of the passing wave, due to friction

Orbital diameter decreases with depth

deep

* no interaction with bottom, no motion at wave base

 Intermediate

* Drag on the bottom of the sea floor, Bottom orbit slowing down top moves faster

Shallow

* Orbits are starting to drag at the bottom, top goes faster than the bit underneath the wave will break

wave shoaling

waves feel the ground and interact with sea floor

Waves moving from deep to shallower where they interact with seabed

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Waves become higher and steeper as the orbits interact with the bottom, due to the friction of the interaction the sea celerity decreases, the height increases due to friction

Steepness of wave increases which causes it to break

waves and beach profiles

Constructive waves build beaches = Fairweather and swash stronger, more sediment entering the beach

Destructive waves erode beaches= Big heights and close together, more frequent energy, Stronger backwash= erosion

The intensity and direction of wave action contribute to the formation of different beach profiles.

beach profile and Sea level rise

* Tides act as a base level for waves, an increase in base level= waves reaches further inland
* Higher tides can increase the inland extent of coastal inundation and erosion
* SLR will amplify the effects of storms and big tides

Sea level come up, beaches want to maintain eq profile, sea level comes up, keep the same form but just roll upwards in sand dunes

Rising sea levels can submerge and erode beaches

wave set up and set down

Set up: waves breaking along the shoreline and stack up ontop of each other, piles along shoreline

Set down, Undertow from setup that flows seaward beneath incoming waves

Rips

Strong offshore currents caused by 3d seaward return, high set up to low, concentrated in narrow zones of the beach