AIM OF STUDY

The aim of the study is to describe and explain the impact of coastal processes on a section of

The Palisadoes, Kingston and Hector’s River, Portland, Jamaica.

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Location of Study Areas

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Methodology

Primary Data was collected on Thursday the 4th of October, 2012 between the hours of 8:30 AM

and 6:00 PM during a field exercise by students and teachers of Wolmer’s Boys’ School. The

areas chosen for field study along the eastern coast of Jamaica were the Palisadoes, the Yallhas

Ponds and Hector’s River. At each location data was collected on wave patterns. The wave type

was recorded by observing how the waves broke on the shore. The frequency of the waves was

determined by examining the average of three recordings of the amount of breaking waves per

minute for each stop. The frequency was taken through an experiment. An approximation was

made of the wave height at each stop. Pictures were taken of the coastal features and diagrams

illustrating coastal processes were sketched.

Secondary Data was collected from maps and aerial photographs to identify larger features. The

internet and text books were consulted to explain the coastal processes and maps and pictures

helped to demonstrate the observations made and present information on the location of the

stops. Notes were taken of information provided by the teachers explaining coastal processes.

The Palisadoes is a part of the parish of Kingston and is south of the capital Kingston and the

Down Town area. The Palisadoes is a tombolo that begins at the southern wing of Harbour View

and terminates in the Caribbean Sea 3 km away from the other end of the harbour. It connects

Port Royal to Harbour View and separates Kingston Harbour from the Caribbean sea. The point

along the Palisadoes at which we stopped is commonly referred to as Plumb Point. Plumb Point

is adjacent to Norman Manley International Airport and is 6.4 km into the tombolo from the

roundabout at Harbour View. The second stop was Hector’s River which is located in the parish

of Portland nearby the border of Portland and St. Thomas along the coast. The Hector’s River in 6

Portland. Hector’s River is approximately 27.4km south of the capital Port Antonio. Hector’s

River is east of a main road in Portland and two communities, White Lane and Hordley. Hector’s

River is not actually a river but a series of headlands and bays, coves and inlets (See Appendix

1).

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Presentation, Analysis and Discussion of Data

Stop1- The Palisadoes

The Palisadoes is a strip of land, some 14 km long, that almost completely encloses the Kingston

Harbour (See Figure 1). The Palisadoes tombolo connects the island of Port Royal to Harbour

View. The study area commonly known as Plum Point was adjacent to the Norman Manley

International Airport and was situated 7 km from the Harbour View roundabout. The tombolo

which is exposed to wave actions also had mangroves growing atop secure sediments that were

characterized by dune vegetation on the southern windward side and mangrove thickets on the

northern leeward side. The coastal features identified at the Palisadoes include beaches (storm

beaches), sand dunes, berms, bays and a tombolo (Defined in Appendix 1).

Figure 1- The Palisadoes Tombolo

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Wave Action

The dominant waves approaching the Palisadoes came from the south east resulting in

longshore drift current which moves sediments gradually westward along the shore. The waves

at The Palisadoes were observed to break at the crest of the wave resulting in turbulence

spilling down the face of the wave and a mass of foaming surf rushing up the beach. Based on

this observation the type of waves at the Palisadoes were determined to be “spilling” breaker

waves. The wave height was also estimated to be about 3 feet high.

Table 1- Wave Frequency at the Palisadoes

Trial Number Time(s) Number of waves1 60 72 60 83 60 9Average wave frequency 8 waves per minute

When waves break at a rate of ten or less a minute, each breaking wave is able to run its course

without interference from the wave behind it. These waves are called constructive waves. (See

Table 1 above and Appendix)

The waves that were observed had a strong swash and a less powerful backwash therefore

material is always deposited and transported up the beach. This leads to the formation of

predominantly depositional features.

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Coastal Formations

Tombolo

Scientists have called The Palisadoes both a spit and a tombolo. Records show that Port Royal

was once an island totally cut off from Jamaica. Sand and shingle along with alluvium from

rivers have been transported down the coast by long shore drift (See Appendix 1) until the

coast suddenly deviated resulting in sedimentation. The deposits eventually formed a spit

through accretion, which continued to grow until island and cays were connected to the main

land. The spit then became the Palisadoes Tombolo because it linked an island to the mainland.

If the Palisadoes were not replenished by sediment, it would become detached from the

mainland getting smaller and smaller through progressive loss of its eastern end, and eventually

cease to exist. The Hope and Cane Rivers and possibly other sources further east, bring sand

and gravel down to the coast, where it is added to the beach system and is gradually moved

west to the Palisadoes.

Beach

The constructive wave action along this coast resulted in the deposition of pebbles, shingle and

sand. There is a long stretch of unconsolidated beach all along the seaward side of the

Palisadoes. The beach materials identified at the Palisadoes were small black rounded pebbles,

shingle, trash and shingle from dumping and predominantly grey sand (See Plate 1). The grey

sand and black pebbles are assumed to be alluvium originating from the two rivers that both

cut through a black marl quarry and Cement Company’s marl quarry(as shown on Map 2) and

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alluviate at the base of the tombolo. The shingle and trash are dumped up on the back shore of

the beaches by man, while sand and boulders are moved to the backshore by storm surges. The

dark colour of the beach can also be attributed to the absence of coral which would normally

make the beach lighter coloured.

Plate 1- Beach Material at Palisadoes

The beach at Plumb Point was determined to be a storm beach as sand and shingle were found

to be far beyond the level reached by waves at high tide forming a berm with many sand dunes

(See Appendix 1). Mankind’s soft engineering has also affected the formation of the berm as

ample shingle was added to the ridge of sand over the years. (See Plates 2 and 3)

Plate 2 and 3 - Back and front of the berm at the Palisadoes

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The appearance of the beach suggests that many processes such as abrasion, hydraulic action

and attrition were at work in its formation. Long shore drift was observed to carry sediments

westward along the tombolo which are deposited along the coast and cause the formation of a

beach. Some other observations that indicated coastal processes were:

The pebbles at the shore of the beach were small and round suggesting that abrasion is

occurring as beach material is hurled at the beach by the waves and causes the surface

of the rocks to be grinded down.

The presence of attrition is evident as pebbles become rounded through comminution.

Hydraulic action and wave pounding were also observed and can hasten the rate of

erosion of sediments.

Figure 2- Slope of the beach at Palisadoes and the sediments found on it

The stones have an obvious grading of pebbles as seen in figure 2, from large to small, with the

larger diameter stones arrayed at the highest beach elevations at The Palisodoes.

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Bay

The bay at the Palisadoes occurs as a result of beach depletion and particularly because of

sediment transportation and not as a result of erosion. In more recent years, the rivers that

supplied sediments to the tombolo became barren, therefore reducing the supply of material.

However, longshore drift continues and as a result the sediments transported from the base of

the tombolo are not replenished resulting in the formation of a bay.

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Stop 2- Hector’s River

Hector’s River is an area of rocky coast that is now a series of headlands, bays and inlets along

the eastern coast of Jamaica that are exposed to wave action. Hector’s River is close to Wharf

Road and is the site of the Water Lane community (See Figure 3). Hector’s River is located 3.9

km south of Manchioneal along the main road. Hector’s River is also composed of a type of rock

called honey comb coral. In addition to cliffs and bays there are many other features such as

coves, inlets, caves, arches, stacks, stumps, wave cut platform and notch, headlands, bay head

beaches, blow holes (Defined in Appendix 1).

Figure 3- Hector's River

Wave Action

The waves were observed to collide with the cliff and were launched violently upward at the

headlands interfering with the observation of wave type. Despite this, the waves were observed

to be swell waves at the headlands and “surging” waves at the bay head beaches. At the bays

the waves would break like a “plunging” breaker trapping a pocket of air and creating

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turbulence as it touched the underlying surface of water before reaching the coast. The

turbulence then formed a wall of foaming surf surging up to the coast. The wave height was

estimated to be 3 feet.

Table 2- Wave Frequency at Hector's River

Trial Number Time(s) Number of Waves1 60 102 60 123 60 10

The average wave frequency was 11 waves per minute. This wave frequency would make the

waves at Hector’s River destructive. (See table 2)

The waves that were observed broke frequently and the backwash of the wave ran into the

swash of the wave behind it. The force of the swash was reduced in comparison to the back

wash resulting in waves having a strong backwash or undertow and a weak swash causing

material to be eroded. The Coastal Features found at Hector’s River are predominantly

erosional.

Headlands, Bays and Coves

The headlands at Hector’s River were formed through the continual build up of a fringing reef

along the coast line which left deposits of limestone forming a limestone pavement. The type of

coral that formed much of Hector’s River is called honey comb coral. A large flat topped

platform with many cusps was observed.

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The headlands at Hector’s River were observed to alternate with the bays and coves along the

coast. This suggests that there are alternating beds of hard and soft rocks. Harder rocks are

more resistant to wave erosion and eventually stand out as a headland while the softer rocks

are easily eroded, by hydraulic action and corrosion, to form a curved indentation called a bay.

When the rock has a fault or crack the waves attack the weakness in that rock and eventually

breaches it to form an inlet. When this inlet is eroded further it forms a circular bay with a

narrow entrance like the one at Hector’s River that we identified.

There were also some beaches identified at the head of the bays (See Plate 4). The waves were

observed to travel into the bay slowly, after crashing into the headlands, depositing sand and

other materials.

Plate 4- Bay head beach

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Cliff, Wavecut Platform and Notch

We observed several cliffs along the coast as

seen in Figure 2. The cliff was formed from

honey comb coral a very resistant form of limestone (See Plate 3). We can conclude from

observation that these cliffs were formed by the destructive waves attacking the headlands.

Over time the headland becomes undercut by erosion and a notch and cliff develop. In some

areas we also noticed a terrace at the base of the cliff. This terrace is called a wave cut platform

(See Appendix 1).

The main erosional process at Hector’s River is hydraulic action as the cliff is undercut, though it

is also affected by corrosion, abrasion and attrition.

Cave, Arch, Stack and Stump

The caves and arches at the Hector’s River were located at the side of headlands where as

stumps and stacks were found isolated in front of the headlands.

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Plate 5 - A cliff at Hector's River

Plate 6 - A Stack at Hector's River

This is because headlands contain fissures and cracks that can be widened by hydraulic action,

abrasion and corrosion to form caves. The caves develop on either side of a cliff along the same

line of weakness and are eventually eroded until they meet forming a natural arch. The roof of

the arch connecting the headland to the other column of land eventually collapses leaving an

isolated sea stack (See Plate 5 above). The stack can also be further eroded to form a stump.

Evidence of a blow hole was observed at one of the cliffs at Hector’s River where a deep inlet

was located. It is beleave that this was the remains of a collapsed blow hole , which formed

when a cave forms along a line of weakness at the base of the cliff. The cliff develops into a

cavern and eventually the cavern is eroded upward until the ceiling collapses leaving a hole.

The hydraulic action compressing air in the joints is the cause of the collapse. Each time a wave

surged through the cave, spray shot up to considerable heights through the opening, known as

the blowhole.

The main point of comparison between the two areas of study is that the types of waves found

at each site are different. The waves at the Palisadoes are constructive while the waves at

Hector’s River are destructive. The features at the Palisades are created from the deposition of

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materials along the coast giving rise to features such as a storm beach, berm, and Tombolo. The

features at Hector’s River on the other hand are as a result of erosion and form features like a

cliff, wavecut platform and notch, headland and cove, inlet, cave, arch, stack, stump, bay head

beach, blow hole.

The angles at which the waves interact with the shores are also different. At the Palisadoes the

waves break obliquely to the shore and cause long shore drift. At Hector’s River the waves are

refracted toward the headlands and cliffs and are diffracted on entering the coves and bays.

This results in the undercutting of cliffs and the deposition of material at bay heads.

The structure of the rocks at both stops was drastically different. At the Hector’s River stop the

rocks were a form of coral limestone called honey comb coral that is very resistant to erosion in

the form of hydraulic action and corrasive action but weak against corrosive action. The rocks at

this stop were homogenous and displayed horizontal stratification. The rocks at the Palisadoes

were eroded into shingle, sand, alluvium and pebbles.

Some of the processes at the Palisadoes and Hector’s River were similar in nature, such as bays

and beaches. The colour of the beaches differed depending on the material that comprises

them. The colour of the beach at the Palisadoes is considered black due to the river and gully

deposits composed mostly of alluvium and marl that form it. Some of the beaches at Hector’s

River are white in contrast because the beaches are formed from coral formations being

eroded.

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Conclusion

At The Palisadoes constructive waves give rise to predominantly depositional features.

Whereas, at Hector’s River destructive waves result in mainly erosional features. The features

at both areas of study were impacted by coastal processes such as hydraulic action, attrition,

abrasion. However, the coast at The Palisadoes is comprised essentially of sediments and as a

result of the processes of, alluviation, sediment transportation and longshore drift and to a

lesser extent mankind’s interference, we were able to observe the creation of wide beaches,

berms and bays comprised mainly of sand shingle and pebbles. At Hector’s River we noted

that processes such as corrosion, wave pounding and wave refraction impacted on the rocky

limestone coast to form features such as headlands, caves, stacks, stumps which were not

present at the Palisadoes.

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