Aims of the Experiment

  • Aims in 3 bullet points ----------------------------------------. Page 3

Introduction – Diagrams, Pictures and Photos

  • Picture of our residence --------------------------------------- Page 3
  • Diagram of waves’ energies ------------------------------------ Page 4
  • Constructive waves diagram ----------------------------------- Page 5
  • Destructive waves diagram ------------------------------------ Page 5
  • Erosion – Corrosion/Abrasion diagram ------------------------ Page 6
  • Erosion - Scouring diagram ------------------------------------ Page 7
  • Erosion - Hydraulic Action diagram --------------------------- Page 7
  • Erosion - Solution diagram ------------------------------------. Page 8
  • Erosion – Attrition diagram -----------------------------------. Page 8
  • Longshore Drift diagram --------------------------------------. Page 9
  • Porlock Bay map ------------------------------------------------ Page 11
  • Porlock Bay sketch --------------------------------------------- Page 12
  • Porlock Bay formation ----------------------------------------- Page 13
  • Picture of Porlock Bay overview ------------------------------ Page 14
  • Waves formation diagram ------------------------------------- Page 14
  • Photo of Porlock Bay overview -------------------------------- Page 15
  • Solutions – Offshore submerging breakwater diagram -----. Page 17
  • Solutions – Rip-rap diagram ----------------------------------- Page 18
  • Tabulated effectiveness of solutions ------------------------ Page 18
  • Porlock Bay idea map ------------------------------------------ Page 20

Introduction – Information, Reasoning’s and Analysis’

  • Coast definition ------------------------------------------------ Page 3
  • Wave definition ------------------------------------------------ Page 4
  • Wave factors --------------------------------------------------. Page 4
  • Constructive Wave information ------------------------------- Page 5
  • Destructive Wave information -------------------------------- Page 5
  • Erosion – Corrosion/Abrasion information -------------------- Page 6
  • Erosion – Scouring information -------------------------------- Page 6
  • Erosion – Hydraulic Action information ----------------------- Page 7
  • Erosion – Solution information -------------------------------- Page 7
  • Erosion – Attrition information ------------------------------- Page 8
  • Longshore Drift information ----------------------------- Pages 8 & 9
  • Longshore Drift & Its Properties ----------------------- Pages 9 & 10
  • Porlock Bay formation information ---------------------------. Page 13
  • Porlock Bay story and situation ------------------------. Pages 14 & 15
  • Solutions – Beach Nourishment information ----------- Pages 15 & 16
  • Solutions – Groynes information ------------------------------ Page 16
  • Solutions – Submerging breakwaters information ----. Pages 16 & 17
  • Solutions – Rip-rap information ------------------------ Pages 17 & 18
  • Tabulated solutions analysis ----------------------------. Page 18 & 19

Hypothesis

  • Hypothesis according to aims --------------------------------- Page 21

Method

  • Method in evidence for Longshore Drift --------------------- Page 21
  • Method used for beach profile information ------------ Page 21 & 22
  • Beach Profile method ---------------------------------- Pages 21 to 27
  • Random Numbers table ---------------------------------------. Page 23
  • Powers Index sheet ------------------------------------------- Page 24
  • Beach Profile graph -------------------------------------------. Page 25
  • Beach Profile graph analysis ---------------------------------- Page 25
  • Beach Profile results ------------------------------------------ Page 26
  • Beach Profile results analysis --------------------------------. Page 26
  • Photo of Gore Point facets -----------------------------------. Page 26
  • Pebble Size & Shape method -------------------------. Pages 27 to 33
  • Photo of Gore Point headlands -------------------------------. Page 27
  • Porlock Bay defence map -------------------------------------. Page 28
  • Groups results arrangements --------------------------------- Page 29
  • Beach layout diagram -----------------------------------------. Page 29
  • Photo of working groups --------------------------------------. Page 29
  • Pebble length results -----------------------------------------. Page 30
  • Pebble length results analysis -------------------------------- Page 30
  • Pebble shape results ------------------------------------------ Page 30
  • Pebble shape results analysis --------------------------------- Page 30
  • Results graph -------------------------------------------------- Page 31
  • Average results sheet ----------------------------------------. Page 32
  • Photo of pebble sample ---------------------------------------. Page 33
  • Possible Minehead solutions --------------------------. Pages 34 to 36
  • Solutions – Recurved sea wall information ------------ Pages 34 & 35
  • Solutions – Rock armour information ------------------------- Page 35
  • Solutions – Beach nourishment information ------------------ Page 36
  • Minehead methods --------------------------------------------. Page 36
  • Building use sheet --------------------------------------------- Page 37
  • Pedestrians number map -------------------------------------- Page 38
  • Number of Pedestrians in Minehead ------------------------- Page 39
  • Land use type sheet ------------------------------------------. Page 40
  • Car registration origin sheet --------------------------------- Page 41

Analysis

  • Longshore Drift evidence analysis --------------------------- Page 42
  • Longshore Drift effect on pebble length -------------------- Page 42
  • Longshore Drift effect on pebble shape --------------------. Page 42
  • Porlock Bay defence analysis --------------------------------- Page 43
  • Minehead defence analysis ---------------------------- Pages 43 & 44
  • Photo of Minehead’s headlands ------------------------------- Page 44

Conclusion

  • Conclusion of Somerset’s situations -----------------. Pages 44 & 45

Limitations

  • 5 good points of experiment --------------------------------- Page 45
  • 5 bad points of experiment ---------------------------------- Page 46
  • Photo of Minehead’s groynes --------------------------------. Page 46
  • Improvements in experiment --------------------------------. Page 46

Glossary

  • Glossary of key words --------------------------------- Pages 46 to 49

Bibliography

  • Sources of information -------------------------------- Pages 49 & 50

Coastal Processes - Coursework

Aims Of Investigation

  1. To investigate the evidence of Longshore Drift in Porlock Bay, Somerset.
  2. Consider the alternative ways for protecting the land behind Porlock Bay from being flooded by the sea.
  3. To look at the effectiveness of the Minehead sea defence scheme completed in 1999 at a cost of £12.7million.

Introduction

During Thursday 10th June – Saturday 12th June 2004, our geography group went on a field trip to Somerset. We went to Porlock Bay and Minehead, Somerset’s main attractions. Our stay was for 2 nights and 3 days. This was based on the learning of Longshore Drift and how coasts may be protected. The weather during our stay was very warm and dry (temperature 27 °c.)

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A coast is where the land meets the seas. Coastal areas are in a state of constant change. The relentless force of the impact of waves and daily tides wear down features of the coast, therefore igniting the movement of sediment and development of depositional features. Often, changes such as these remain unnoticeable but extreme weather conditions are able to cause rapid changes to a coastline.

Waves are formed by wind blowing on the surface of the sea. This exerts drag or friction on the water, creating a swell in the water. The wind and its energy cause water particles to rotate as the wind passes over. The wave carries on moving but the water particle returns to its original position. Three factors affect the strength of the wave:

  • The strength of the wind. The stronger the wind, the bigger the wave.

  • The time of the winds blowing. If the wind happened to be blowing for a prolonged time, this would mean the wind energy becomes transferred into the wave.

  • The size of the fetch. If the fetch is long, the wave is likely to be bigger.

Waves, depending on the force, are able to erode the coast according to the coasts geological features.

        

  Gravitational Potential Energy (GPE)                        Potential Energy

    Beach                                Kinetic Energy                     Sea

The diagram above shows how waves are formed at every stage, showing its potential, kinetic and gravitational potential energy. The diagram overleaf describes the two different waves and their effects.

  • Constructive waves build beaches. Each wave is low. As the wave breaks it carries material up the beach in its swash. The beach material will then be deposited as the backwash soaks into the sand or slowly drains away. These waves are most common in summer

  • Destructive waves destroy beaches. The waves are usually very high and very frequent. The backwash has less time to soak into the sand. As waves continue to hit the beach there is more running water to transport the material out to sea. These waves are most common in winter.

The geological structures can help shape the coastline. The geology shows the rocks are aligned west to east and that the rocks have a different resistance to erosion. A discordant coastline is where the rocks outcrop at right angles to the sea and where there is a series of headlands and bays. In the South where rocks are parallel to the sea, there is a concordant, with cliffs formed by the resistant band of limestone.  

        Waves crashing into the coast exert considerable force. Researchers estimate pressures upwards of 30 tonnes per square metre can occur. This figure will vary with location and the shape of the coast. The main cause of erosion to the coast is the impact and force generated by the vicious waves. Waves have five different ways in which to attack the coast. Often we believe, for example, attrition is the main reason why seas erode coasts, but not only is attrition at work, it is mainly a combination of different methods to erode. Attrition however is doing most of the damage.

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  1. Corrosion/Abrasion – The breaking waves scoop up stones and fragments of scattered rock and hurl these at the cliffs. This has the effect of chipping away at the rock, which leads to them eventually falling off.

  1. Scouring – Wave which break at the base of a cliff and swirl and remove loose rock with the strong current.

  1. Hydraulic Action – The pressure exerted by breaking waves traps and compresses air in cracks. The intense pressure forces open the cracks further so weakening the rock.

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