AimThe purpose of this is to investigate and explain the influence of wave action on the wave

action on the coastline at Las Cuevas Bay, along the North Coast of Trinidad.

Location of Field Study The field study was conducted at Las Cuevas Bay along the North Coast of Trinidad.

Methodology Where:The field study was conducted at Las Cuevas bay, along the north coast of Trinidad.

When:The field study was done on Thursday 22nd October, 2015 between the hours of 10:00am and 2:00pm.

How:1. Sketch of study area: a sketch map was done of the area under study based on

observations made of features seen on the bay at the time.

2. Wave count and observation of wave action: each group conducted a wave count on

separate areas of the bay. Within each group was responsible for setting the timer while

the other person was responsible for counting the wave, this was done at one minute

intervals with a one minute rest between them. After each minute of counting was

complete the number was recorded on the instruction sheet.

3. Long shore drift: a football was thrown into the water. The direction that the ball drifted

in the water was observed and recorded.

4. Beach profile: a meter rule was placed upright on the sand from the backshore a

measuring tape was then placed on top of the meter rule and pulled from the rule until the

water mark (sea level). At one metre intervals from the backshore to the water mark the

difference in height from the measuring tape and the ground was measured and recorded.

Presentation and Analysis of Data

Las Cuevas which is located at the north coast of Trinidad which is approximately two

hours from Port of Spain. This bay can be described as a famous tourist attraction in Trinidad. As

for this SBA all the information presented was obtained from Las Cuevas bay. This study was

done on coasts. According to Rahil (2010) a coast is a zone or strip of land. This feature is

formed by wave action. Wave action is the movement of the waves. A wave count was done to

identify the types of waves present. According to Rahil (2010) a wave is an oscillatory

movement, up and down from side to side.

There are two types of wave’s constructive and destructive waves. Constructive Wave are

waves break at a rate of ten or less per minute each wave is able to run up the beach and drain

back again before the next wave arrives. The swash is more powerful than the backwash so

deposition can occur. Destructive Wave Is waves break at a rate of more than ten per minute

each wave is able to run up the beach but unable to drain back again before the next wave

arrives. Thus the backwash of the previous wave interferes with the swash, reducing its

efficiency. Such waves remove material from a beach and are destructive.

Table 1: Comparison between constructive and destructive waves.

Constructive waves Destructive waves

Spilling breakers Plunging breakers

Have depositional properties and help build the beach

Have erosional properties and erode/wear away the beach

Swash carries more material than that removed by the backwash

Backwash drags away more materials than the swash carries up

Waves of minimal force which deposit sediment Powerful waves which aid in erosion

Moderate short profile/height Generally steep profile/ height

High/low wave length Short wave length

Low wave frequency:- 6 to 8 waves per minute Greater wave frequency:- 10 to 14 waves per minute

Wave Frequency Count

A study was done on wave count and the actions of the waves were observed. The table

below shows the number of waves which occurred at one minute intervals on the day the data

was collected.

Table 1: showing wave frequency

Time NUMER OF WAVES

Western Eastern

1st minute 6 9

3rd minute 5 8

5th minute 6 8

7th minute 5 6

9th minute 5 8

From the table above you can see that on the depositional side of the bay there were

waves of 6 and less but can be still described as constructive waves. Constructive waves can be

defined as waves that approach the shore at a rate of about seven per minute. Waves on the

erosional side of the beach can also be seen as a constructive zone. Constructive waves are low

energy waves deposit materials upon the shore. The constructive waves show that the beach was

created by materials such as sand and shingle, onto the shore and depositing them there. Erosion

has slowed over the years with a slowed backwash with allowed the sediments to be deposited

over the years to form the beach. A beach is a pebbly or sandy shore, especially by the sea

between high- and low-water marks.

Conclusions that can be drawn however, is that there is conflict within this study

due to the fact that erosional features were observed along Las Cuevas Bay. According to Darsan

(2005) the seen are old features and were formed many years ago when the sea levels were seen

to be a lot higher.

. 1st minute 3rd

minute 5th

minute 7th

minute9th

minute

0

1

2

3

4

5

6

7

8

9

western eastern

Figure1: Bar Graph Showing Comparisons for Wave Frequency

Wave CharacteristicsWave Height Constructive waves were seen to be the most prevalent waves at the bay. The wave height of the beach was observed to be (0.5m) 50cm.

Plate1: Showing Wave Height

Wave Height

Wave TypeOn the day that the study was done the wave type was observed. The type of wave that

was dominant was that of constructive waves. It was also seen that the swash was greater than

the backwash. The swash is the transporter of sediments from the sea onto the shore and deposits

it onto the bay. The backwash is pulled back into the sea by a force of gravity.

And as there is a stronger swash at the beach the swash is deemed to be strongest on the

beach it results in spilling breakers. The spilling breakers are the waves that break slowly as they

approach the shore resulting in the flat gentle gradient of the beach.

Diagram1.Showing wave type

Wave processes (Long shore Drift)When waves break on to a beach at an angle, material is pushed up the beach at an angle

by the swash, but pulled back down the beach by the backwash at ninety degrees to the coast. In consequence, material is slowly moved along the coast, in the direction of the waves. Waves deposit materials such as sand and pebbles on the beach. The materials by the swash of the waves. Long shore drift was conducted along Las Cuevas Bay, by the process as explained in the methodology (page4). It was observed that the waves moved in a westerly direction as it is influenced by the northeast trade winds.

Diagram2. Showing long shore drift

Erosional and Depositional FeaturesThe following are the erosional and depositional features that were located along Las Cuevas Bay at the time of the study.

Erosional features The proceeding is a list of each erosional feature found at Las Cuevas at the

time of the study also there formations will be discussed. The features found at the bay were headlands, bays, cave, arch, stacks and cliffs.

Headlands: Areas of harder rocks tend to resist the erosive powers of the sea. The resulting area of land, jutting out into the sea, is a headland. Bays are to be found between headlands.

Plate.1

Headlands Formation

Las Cuevas Pt. Abercromby Pt.

Headlands are formed where the coast of alternating bands of hard and soft rocks offer a greater degree of resistance to erosion. As the softer rocks are eroded, the bands of more resistant rocks stand out from the coast as headlands with steep cliffs projecting into the sea.

Bays: A bay is a broad and curved inlet with headlands on either side

Bays Formation

Bays are formed as a result of differential erosion in a similar way to headlands. In this case, softer rocks are easily eroded by wave action and retreat inland. In due course a curved indentation is formed in the coast. This called a bay. Bays are separate by headlands and enclose part of the sea on three sides

Diagram1: Showing the Formation of Headlands and Bays

Cliffs: A steep, and usually high, rock face found at the edge of the land where it meets the sea. Cliffs can be formed from most rocks, height generally increasing with hardness of rock.

Diagram2: Showing the Formation of Sea Cliffs

Sea cliffs Formation Sea cliffs are formed when waves strike vigorously against a steep coast

Both corrosion and hydraulic action assist in the formation of cliffs. Erosion is confined to the area between high and low tide levels and is influenced by the rock strata and joints, and the strength of the waves. Existing cliffs are undercut by wave action, causing them to collapse and to recede inland.

Landslips can occur when the rocks dip seawards; overhanging cliffs are formed when the rocks dip land wards.

P late3

Cliff Vegetation on cliff

Blowhole: A blowhole is a hole in a sea cliff or coastal terrace through which columns of spray are jetted upward.

Plate.1

Blowhole Formation A blow hole is formed when a joint between a sea cave and the land surface above the cave becomes enlarged and air can pass through it. As water flows into the cave, air is expelled through the pipe like joint, sometimes producing an impressive blast of air or spray which appears to emanate from the ground.

Cave: A weakness, such as a joint, is enlarged by wave action, finally creating a cylindrical tunnel which follows the line of weakness. Caves developing back to back may give rise to arches and stacks.

Plate.4

Cave Formation Caves are formed when line of weakness and soft rocks .Lines of weakness and soft rocks are attacked through the processes of abrasion and hydraulic action. This occurs on both side of a headland. Fissures and joints in coastal rocks can gradually be enlarged and eventually develop into sea caves. Refer to diagram 4 on page16.

CaveEntrance- Height 12.2mInside-Height 9.2mWidth 14.6m

Cave entrance

Length 20.6m

Arch: When caves, which have developed on either side of a headland, join together they form a natural arch.

Plate 5

Arch Formation If caves are formed on both sides of a narrow headland, eventually, after constant erosion from both sides a tunnel forms right through to form an arch or sea arch. As a result of erosion two caves on opposite sides of a headland unite, forming an arch refer to diagram 4 on page 16.

Diagram4: Showing the formation of caves, archs, stacks and stumps

Stump: A stack is a landform consisting of vertical column of rock in the sea formed by wave erosion.

Plate.6

Stump Formation

A stump is formed when part of a headland is eroded by hydraulic action which is force of the

sea or water crashing against the rock. The force of the water weakens cracks in the headlands

and the headlands later forms arches and eventually the arch collapses to form stacks. Reference

can be drawn to diagram four (4) on page 16.

Vegetation

Stump

Depositional features Marine depositional features can only be formed if material is first eroded and then

transported to the deposition site. One of the key ways in which eroded material is moved is

along shorelines by the action of waves. The following features were found on Las Cuevas Bay

on the day of the study. The depositional features found at Las Cuevas bay are beach and berm.

Beach:A beach is a shoreline feature of deposited materials comprising an accumulation of

materials such as boulders, pebbles, shingles, sand and mud on sloping or shelving ground.

Plate.7: Photograph

How it is formed.

The beach is formed as a result of wave action. Waves or currents may move the sand or other loose sediments of which the beach is made, as particles held in suspension. Larger materials may be moved by saltation (a bouncing movement of large particles).some of the largest beach materials may only be moved at times when the beach is subject to storms.

Berm:

A berm is a flat area at the uppermost level of the beach. A berm is a narrow shelf or

terrace of sand or shingle deposited on the beach by storm waves or very high tides.

Plate12: Picture showing berm

BERM

Beach Profile The beach profile was measured and recorded as described in the methodology (page 4).as seen below.

M CM0 1022 1184 1276 1308 13210 13112 12714 12016 11318 10620 10022 9024 8026 7428 9030 8932 9034 9236 8938 8340 8842 100

Table3: showing readings used to construct graph

Results

The beach is seen to gently sloping. Constructive dominate the beach overtime in the accumulation of sand to form a crescent shaped beach. As the wave’s beak on an average of 5 waves per minute, the swash was able to deposit materials onto the bay.

Conclusion

Las Cuevas Bay, Trinidad is the second most popular beach along Trinidad’s North Coast

and is approximately eight (8) km east of Maracus Bay. The name “Las Cuevas” is derived from

the Spanish word for caves and there are many caves on this beach. The bay is more sheltered

than Maracus and is therefore calmer which provides for exceptional swimming conditions.

Waves on the beach can be seen to be that of constructive waves and it can be seen to

have a strong swash with contributes to the construction of the bay. When the wave count was

done it was seen that the waves crash upon the beach on an average of 6 waves per minute. The

waves on the western side of the bay are seen to be much more frequent than the eastern side of

the bay because all the erosional features were found on the western section of the bay. The

strong swash indicates that there was really constructive waves present at the bay which results

in the gradient of the bay to be gently sloping.

Las Cuevas Bay also had depositional features that were recorded. The features were a

beach and a berm, which were formed the constant deposition of sand, pebbles and small rocks

and the waves playing their part to help form these features.

Erosional features were also found at Las Cuevas Bay. These features include: headlands,

bays, cliffs, caves, notch, arch and stump which were formed many, many years ago. Headlands

and bays were formed by the processes of wave refraction and the erosion of the soft (less

resistant) rocks. The other features such as: cliffs, caves, arch, stump, and notch were formed

when the waves force their way into cliffs and cracks (notches) and eventually it forms a cave.

Further erosion of a cave can form an arch and as times passes by the arch collapses to form a

stump. The blowhole is another feature that was present at the beach and is formed within a cave,

as strong waves reach within a cave and forces it way to the top of the cave and then it erupts

upward forming a shaft within the cave and eventually a blowhole.

Due to the fact that there are so many erosional features on the beach and constructive

waves are present we can refer to Junior Darsan’s theory that all these features were formed

many years ago when sea levels were relatively higher. In conclusion the aim of the study was

deemed to be a success.