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Name Andy Madeira Candidate Number Name of School ASJA Boys’ College, San Fernando Centre Number 160001 Title How do wave processes influence the development of coastal landforms at Columbus Bay?

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Name Andy Madeira

Candidate Number

Name of School ASJA Boys’ College, San Fernando

Centre Number 160001

Title How do wave processes influence the development of coastal landforms at Columbus Bay?

Table of Contents

Aim of Study

Location of Study

Methodology

Presentation of Data

Analysis of Data and Discussion

Conclusion

Bibliography

Appendices

Aim of Study

How do wave processes influence the development of coastal landforms at Columbus Bay?

Seeing as this particular topic was covered as a segment of our Geography syllabus for CSEC, it was a strong choice to partake in, containing many interesting features to assess and also many essential assessments available for my study.

Location of Study

For the Location of Study, Columbus Bay was chosen as it was a highly popular attraction in the south-west peninsula of Trinidad and featured various coastal features and landforms to find and explore. It is an area located at 10° 04, on the line of longitude, and 61° 45, on the line of latitude, surrounded by bodies of water known as the Gulf of Paria to the west and Columbus Channel to the south, these are seen in the following maps.

Methodology

On Thursday, 15th October 2015, we left for Columbus Bay located in the south-western Peninsula of Trinidad at 8:30 AM from ASJA Boys’ College in San Fernando. Throughout the journey, we travelled along the Southern Main Road passing next into La Brea, home of the famous Pitch Lake and into Grandville to Point Fortin then to Cedros tallying into a two hour total and having us arrive at our destination around 10:30 AM.

Whilst utilizing equipment such a graduated rod to measure wavelength where it was found to be 8.34 metres and 5.81 metres at Site A and Site B respectively being found as seen in the image below, stopwatches to record the duration of time between recordings, measuring tape and a clinometer which was used for measuring the angles of elevation at Site A and Site B being 1° and 5° respectively. A Beauford Scale was used to determine the wind speed and type of wind present, at Site A it was found to be a gentle breeze (1.4 ms-1 to 5.4 ms-1) and a fresh breeze (8.0 ms-1 to 10.7 ms-1) at Site B. As seen in the image below, the wave height was found by placing the graduated rod into the water and measuring from trough to crest. The measurements and findings were used as primary data and secondary data was collected from textbooks listed in the Bibliography.

Figure : Using the graduated rod to measure wave height.

Presentation of Data

Table 1: Showing data collected at Site A and at Site B.

Measurements Site A Site B

Gradient/° 1° 5°

Longshore Drift/metres 0.51 Not Present

Wave Energy/Jm-1

(Joules per Meter)49.99 139.30

Wave Frequency/wave per minute

13 21

Wave Height/metres 0.09 0.18

Wave Length/metres 8.34 5.81

Wind Description/metres per

second (ms-1)

Gentle Breeze(1.4 ms-1 to 5.4 ms-1)

Fresh Breeze(8.0 ms-1 to 10.7 ms-1)

Wind Direction South-West North-East

Table 2: Showing measurements taken at the arch.

Measurements Value

Entrance/metres 1.83

Cove Width/metres 7.5

Cove Length/metres 9.0

Table 3: Showing Measurements taken at the wave-cut platform.

Measurement Value

Length/metres 38.2

Width/metres 6.66

Notch Height/metres 1.27

0

1

2

3

4

5

6

1

5

Gradient/°

Site A Site B

0

0.1

0.2

0.3

0.4

0.5

0.6

0.51

Longshore Drift/metres

Site A Site B

0

20

40

60

80

100

120

140

160

49.99

139.3

Wave Energy/Jm-1

Site A Site B

0

2

4

6

8

10

12

14 13

2.4

Wave Frequency/waves per minute

Site A Site B

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.09

0.18

Wave Height/metres

Site A Site B

0

1

2

3

4

5

6

7

8

98.34

5.81

Wave Length/metres

Site A Site B

Analysis of Data and Discussion

Throughout the course of this expedition, the data collected showed the various characteristics of the waves which could be found at each site. At Site A the waves reached heights of 0.09 metres at frequencies of 13 waves per minute. These waves had lengths of 8.34 metres, average, with low energy levels of 49.99 Joules per meter.

The waves at Site A had properties of constructive waves which are low energy waves, the front of said waves are not too steep and the wavelength is long. A mass of foaming surf rushes up the beach breaking gently over a long distance and then flowing back again into the sea, these waves will build the shore overtime up by depositing materials onto the coast. The swash is very strong and will carry more materials than the weaker backwash as shown in the diagram below where it pushes materials onto the shore. These constructive waves would form a beach as they deposit more materials such as sand and clay onto the shore.

Figure : Movement of Constructive Waves.

However, at Site B the waves reached heights of up to 0.18 metres which was twice the height of the waves at Site A traveling at frequencies of 21 waves per minute. These waves extended to lengths of 5.81, but with high energy levels of 139.3 Joules per meter. They were denoting features of destructive waves which are high energy waves where the crest of the wave curls forward over a large air pocket and then vertically downwards. Overtime the coast will be eroded away as the backwash drags away more materials into the sea than the swash will be depositing onto the coast, as seen in the diagram below, the materials are being dragged away from the shore by the backwash back into the sea eroding away the coastline.

Figure : Movement of Destructive Waves.

Longshore drift, which is mainly responsible for transportation of sediments, such as sand, along a coast at an angle to the shoreline occurring in the direction of the prevailing winds obliquely at an angle of 45°. Referring to the diagram, the swash moves the materials along the beach and the backwash, under the influence of gravity, pulls the material back down the beach at right angles to the coastline. Over time this creates a total shift of the materials along the coast. This process was only present at Site A and measured to 0.51 metres.

Figure : Diagram of Longshore Drift.

By using the clinometer the gradients at each at site were recorded with the measurements being only 1° at Site A but a bit steeper at Site B were the gradients was 5°. The winds at each site had heavy influence on the waves as they induce the size of the wave according to their strength, i.e. stronger winds will result in larger waves. Site A had gentle breezes travelling south-west at 1.4 to 5.4 metres per second and Site B had fresh breezes moving north east between 8 and 10.7 metres per second.

Cliffs, which were common features, found at the coastline, was formed overtime by the combination of weathering, the breakdown of rock caused by various weather conditions, and erosion, where rock formations are worn away by the action of water. Softer rock will erode away easily to create gently sloping cliffs whereas the harder rock will be more resistant and slowly erode away forming steep cliffs. As seen below, the waves will drive into the lower rock, breaking away the base and forming a recession in the cliff, now known as a notch. A wave-cut platform is formed overtime by erosion.

Figure : Formation of a Cliff, Notch and a Wave cut Platform.

A cove could also be found at Site B being formed by erosion against layers of soft rock behind layers of more resistant rock. The resistant rock featured joints where a small opening is created from erosion and then starts to erode the softer rock behind the resistant rock forming a cove where an opening will be created. The cove below was found at Site B is the result of years of erosion.

Figure : Entrance of a Cove found at Site B.

Headlands, another feature which could be found at Site B, is formed when the sea attacks a section of the coast with alternating bands of hard and soft rocks. The bands of soft rock will give way to erosion faster than the bands of hard rock. This will leave a section of land jotting out into the sea, which is known as a headland. The area where the soft rocks have eroded away, next to the headland are called bays which could be found at Site A. The diagram below, shows the direction of the incoming waves as they target the coast, the resistant rock isn’t eroded and is left protruding into the sea but the softer rock is broken away leaving a bay and sand is deposited to form the beach.

Figure : Formation of a Headland and a Bay.

Further weathering and erosion and result in the formation of arches and as the arch collapses, a tall column is left which is called a stack. After time the stack will wear away forming a stump.Also seen at Site A were caves which occur when water forces entry into the cliff’s face. The water, containing sand and other materials grind away at the rock until the cracks widen overtime and become a cave, this process is known as abrasion or corrosion. With the aid of the diagram below, it can be seen where two caves are eroded away forming an arch, where overtime through further erosion, the arch will be broken away and a stack is left standing but if the said erosion occurs, it will be shortened into a stump.

Figure : Formation of a Stack.

Figure : The Three Sisters at Columbus Bay.

Figure : Michael Cazabon’s 1857 painting of Los Galos.

Conclusion

In conclusion to this assessment, I have learnt about the different types of waves at coasts, what influences them and how they can affect the coast and its features there. Becoming familiar with the various methods of data collection in these areas and how to go about correctly finding them. Site A was a beach with longshore drift being present and had constructive waves in its waters resulting in the deposition and transportation of materials such as sand and clay forming beaches whereas Site B was home destructive waves leading to an array of coastal features such as headlands, arches and stacks. Wave refraction, being the bending of waves when they approach an uneven coastline, as the waves approached the coastline they reach the headlands first, this focuses a lot of energy on these foregrounds and bends the waves into the bays where the energy will be expanded less.

However there were many limitations when collecting said data, such as the limited time period that was given to perform tasks and collect the data. The presence of a low tide also hinder many recordings as they were not taken during periods of its usual level. Also certain activates such as nearby boats influenced the results taken.

Bibliography

Philip's certificate atlas for the Caribbean (5th ed.). (2004). London, Great Britian: George Philip.

Wilson, M. (2012). The Caribbean environment for CSEC geography (4th ed.). Oxford: Oxford University Press.

Appendix

Formulae used to calculate wavelength:

For water greater than 2 metres deep:

Wavelength (m) = (1.6 x 3600)/(Frequency)2

For water less than 2 metres deep:

Wavelength (m) = ((3.1 x 60) x √Water depth in metres)/frequency

Formula used to calculate wave energy:

Wave energy (Joules per metre width of wave crest) = 740 x H2 x L

Where:

H = Wave height (in metres), and L = wavelength (in metres),

e.g. A wave with a height of 3m and wavelength of 40m has 266,400 joules of energy per metre width.