Intro to coasts and wave types and tides

The point where the land meets the sea. It is constantly changing due to the effect of land, marine and air processes.

Coasts are regarded as a system because they have inputs of energy which drive key processes which result in outputs.

These inputs lead to erosion depositions and transportation which result in outputs such as 

beaches, sandunes,bars, headlands and bays , cliffs , wave-cut notch,  wave-cut platforms , caves , arches , stacks , stumps.

Marine inputs
waves
saltspray
tides

Atmospheric inputs-
wind speed direction
precipitation
air pressure 
sun

Human in puts
pollution
settlements
defenses

How are waves created- by the wind blowing over the surface of the sea, the friction between the wind and the waves gives waves a circular motion.

Key terms-
Crest is the highest point of the wave
trough is the lowest point
wave frequency is th number of waves per minute
wave period is the tie taken for a wave to travel to one wave length
wave energy- LH2 L- length and H is the height
wave steepness- The ratio of wave height to wave length cannot be steeper that 1:7 as this is when the wave breaks.

Why do waves break ?
There are 2 types of breaking waves constructive and destructive.

Constructive waves - have a long wave length(100m) and a low height. They have a low frequency of 6-8 per minute.  The are known for depositing material up the beach as the wave breaks the swash loses volume and energy as water percolates through the sand. This gives them a weak backwash which means there is no force to pull sediment off the beach leading to deposition.

Destructive waves- High waves steep waves of high frequency (10-14 per minute). As they approach the beach they steepen and when breaking the plunge down. Creating a  powerful backwash this causes the material to be moved away.

Destructive wave

constructive wave

Wave refraction- As waves approach the coast line, they leave deep water and enter shallow water. This causes the wave to be affected by the friction, drag due to contact with the sea bed so waves slow down. This changes the direction of the waves causes them to become more parallel to the coast.The wave energy concentration is on the headlands causing erosion. The low energy waves diverge in the bays causing deposition if sediment due to slowing down of waves. Wave refraction occurs due to the shape of the coast line.

Wave refraction

What is fetch? Is the maximum distance of the sea the wind has blown over in creating the waves.

Tides are periodic rise and fall in the level of the sea. They are caused by the gravitational pull of the sun and the moon. The moon has greater influence as it is closer to us it pulls water towards it creating high tide this causes a budge on the opposite end of earth. areas between the two bulges have low tide.(neap tide)

A spring tide is when there is greatest distance between high tide and low tide. 2 times a month the sun and the moon are positioned to 90* to each other this gives the lower monthly tidal range eg low tide. Which is the spring tide.

neap and sprig tides

Tidal range is the difference between high and low tide.

Storm Surge- is when spring high tide can produce a high water level than high tide.(1953) North sea is affected by SS and leads too erosional landform formation.

Reasons -
high spring tide 
Low pressure
High winds which increases friction.

Consequences-
Water levels exceeded the mean and was 5.6 meters above.
1836 deaths
Properties damage.

Erosion types
Hydraulic action - air compressed into crack the force of water applies pressure causing sediment to fall off over time.
Abrasion or corrasion- rocks or eroded material hitting the cliff causing further erosion.
Solution- dissolving of rocks chemically
Attrition- stones hitting each other

Transportation
Solution -dissolved in water
Saltaion- bounce along the river bed
Suspension-fine particles transported by turbulence
Traction- rolling materials along the river bed

The hjulstrom curve shows the link between velocity and particle size eg the larger the particle the more chance of deposition.

Fluvial erosion landforms-

Waterfalls form where there are alternating layers of hard rock and soft rock. The soft is eroded faster than soft rock resulting on a step eg (knick point)  The water flowing over the step speeds up due to lack of friction. Speed increases means more erosive power causing further erosion resulting in the undercutting on hard rock.

Under cut hard rock collapsed a deep plunge pool in carved from the rock due to abrasion occurring as the collapsed rock is swirled around by turbulence. over time this process reoccurs and leads to the waterfall retreating leaving behind a steep sided gorge.

Potholes- small hollows in river bed due to heavy material that has been deposited the bounder is too heavy to be transported by traction so eddie currents cause it become abrasive and erode a pothole in the river bed.


Rapids- Steep sections due to alternating resistant and less resistant rock

  in a river that cause turbulent flow.

Water cycle and soil moisture budget

Drainage basin the area surrounding the river.

Water shed is the boundary of the basin.

The hydro-logical cycle is the cycle by which the of water circulates between the earths atmosphere land and oceans.

inputs include all moisture eg hail rain snow.

outputs include evapotranspiration

storage includes- 

interception- precipitation lands on vegetation or impermeable rock type it is only temporary as it is evaporated soon after.

vegetation storage is water that had been taken up by plants.

surface storage includes puddles lakes and ponds etc.

groundwater storage is the storage of water under the water table by permeable rock type with is porous. (aquifers)

Channel storage- water held n stream or a river.

Flows and processes -

Surface run off- (overland flow) is when water is unable to infiltrated due to impermeable rock type of hard baked soil or prolonged rainfall. 

Through fall- is the movement of water from leaf to leaf or through other parts of a plant.(stem flow is waters flow through a trees stem)

Through flow- is the downhill movement of water through the soil.

Infiltration- is water soaking into soil.

Percolation - is the movement of water through rocks past soil into the water table

ground water flow is the movement of water below the water table through permeable rock.

Baseflow- is ground water flow that feeds into river through river banks.

Soil Moisture Budget-

Water surplus occurs when evaporation/transpiration is low and precipitation is high ground stores fill and there higher runoff increasing river discharge.

In drier seasons precipitation is lower ground stores are depleted and theirs is deficit so the moisture is recharged when it rains again.

How to calculate hydraulic radius

Hydraulic radius is the measure of the river channel efficiency to flow.

How meanders are formed (Alevel)

Meanders

Meanders are an erosion and depositional land form.

Meanders for where there are alternating pools(deep water) and riffles (Shallow) develop at equal spaced intervals across a stretch of a river. (Distance between pools is 5x the distance of the river bed)

Due to the channel being deeper in pools the river has more erosive power, whereas a river looses energy at a riffle due to friction between the water and the river bed.

The distance between pools and riffles causes the rivers flow to become uneven and its concentrated on one side.

Turbulence increases around pools as the river has more energy which forms a corkscrew like movement called helicoidal flow- this helicoidal flow deepens pools and causes deposition occur inside the bend where the river looses energy.

Also meanders have an asymmetrical cross section 

Depositional land forms (deltas)

Delta is a fluvial depositional land form - When a river meets the sea or lake (mouth) the rivers energy is absorbed by the slower moving water on the sea. This causes a river to deposit its load. This deposit builds up on the sea bed until the alluvium (deposited sediment) rises above sea level partially blacking the mouth of the river. The river has to braid into several tributaries, in order to meet the sea forming a delta.

An example is the Birds foot delta in Mississippi-

River Rejuvenation( incised meanders)

What is river rejuvenation - an increase in the energy of the river due to a fall in its base, or  an uplift of the land.

2 factors that cause this is a fall in sea level relative to the land, or and rise in land relative to the sea.

What is a incised meander?

A meander that is becoming rejuvenated or deepened due to the energy of the river this caused deep valley with steep sides. The river is far below the former flood plain.

The river Colorado