Assessment of coastal erosion problems in the outer ...

ASSESSMENT OF COASTAL EROSION PROBLEMS IN THE OUTER ATOLL ISLANDS OF POHNPEI, CHUUK AND YAP STATES, FEDERATED STATES OF MICRONESIA

Russell J. Maharaj SOPAC Secretariat, Suva, Fiji

SOPAC Technical Report 268 Prepared by the South Pacific Applied Geoscience Commission (SOPAC) SOPAC Secretariat, Suva, Fiji December 1998

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TABLE OF CONTENTS Page Number

VOLUME I: EXECUTIVE SUMMARY ..................................................................................................................... 5 ACKNOWLEDGEMENTS................................................................................................................... 4 1.0

INTRODUCTION........................................................................................................................ 9

2.0

SCOPE OF WORK AND THE REPORT.............................................................................10

3.0

METHODOLOGY.....................................................................................................................10

4.0

RESULTS.......................................................................................................................................11

5.0

DISCUSSION...............................................................................................................................14

6.0

MECHANICS OF EROSION ..................................................................................................19

7.0

PERFORMANCE AND RELIABILITY OF SEAWALLS AND GROYNES...............21

8.0

CONCLUSIONS..........................................................................................................................23

9.0

RECOMMENDATIONS...........................................................................................................24

10.0 REFERENCES.............................................................................................................................26

SOPAC Technical Report 268, Maharaj, 1998

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LIST OF TABLES Table

Page

1.1

Travel itinerary, atoll islands visited and sites surveyed in Pohnpei, Chuuk and Yap States .............................27

4.1

Sites visited and coastal problems in Pingelap, Pohnpei State ................................................................................28

4.2

Sites visited and coastal problems in Mwoakilloa, Pohnpei State...........................................................................29

4.3

Sites visited and coastal problems in Sapwuafik, Pohnpei State .............................................................................30

4.4

Sites visited and coastal problems in Nukuoro, Pohnpei State...............................................................................31

4.5

Sites visited and coastal problems in Satawan, Chuuk State....................................................................................32

4.6

Sites visited and coastal problems in Losap, Chuuk State........................................................................................33

4.7

Sites visited and coastal problems in Pollap, Chuuk State .......................................................................................34

4.8.1 Sites visited and coastal problems in Polowat, Chuuk State....................................................................................35 4.8.2 Sites visited and coastal problems in Alet, Chuuk State...........................................................................................36 4.9

Sites visited and coastal problems in Lamotrek, Yap State......................................................................................37

4.10

Sites visited and coastal problems in Elato, Yap State..............................................................................................38

4.11.1 Sites visited and coastal problems in Fecahulap, Yap State.....................................................................................39 4.11.2 Sites visited and coastal problems in Fecahulap, Yap State.....................................................................................40 4.12

Sites visited and coastal problems in Ifalik, Yap State..............................................................................................41

4.13.1 Sites visited and coastal problems in Woleai, Yap State...........................................................................................42 4.13.2 Sites visited and coastal problems in Tagaulap, Yap State.......................................................................................43 4.13.3 Sites visited and coastal problems in Falalis, Yap State............................................................................................44 4.13.4 Sites visited and coastal problems in Utagal, Yap State............................................................................................45 4.13.5 Sites visited and coastal problems in Saliap, Yap State.............................................................................................46 4.14

Sites visited and coastal problems in Eauripik, Yap State........................................................................................47

4.15

Sites visited and coastal problems in Ulithi, Yap State .............................................................................................48

4.16.1 Types of rubble sea walls constructed, failure types and reasons for failure on islands surveyed....................49 4.16.2 Types of masonry sea walls constructed, failure types and reasons for failure on islands surveyed ................50 4.16.3 Types of concrete sea walls constructed, failure types and reasons for failure on islands surveyed ................51 6.1

Reasons for coastline erosion and shoreline degradation ........................................................................................52

7.1

Recommendations for reducing coastal erosion........................................................................................................53

7.2

Recommendations for reducing coastal erosion in Pohnpei, Chuuk and Yap States .........................................54


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VOLUME II LIST OF PLATES Plate

Page #

1

Coral rubble sea wall along the east coast of Nukuoro island........................................................................................................55

2

Utilization of coastal area. Construction of an outhouse in the surf zone along the east coast of Nukuoro island ...........55

3

Coastal land loss and erosion along the southwest coast of Sapwuafik island ...........................................................................56

4

Coastal land loss and exposure of mahogany tree roots along the east coast of Sapwuafik island ........................................56

5

Coral rubble seawall along the east coast of Sapwuafik island.......................................................................................................57

6

Coastal land loss and exposure of coconut palm roots along the west coast of Pingelap island ............................................57

7

Beach and accretion south of the airstrip, along the west coast of Pingelap island...................................................................58

8

View looking south, of the accretionary area south of the Pingelap airstrip...............................................................................58

9

Erosion of the upper beach along the southeast coast of Elato island ........................................................................................59

10

Coastal land loss and erosion of upper beach area along the southwest coast of Elato island ...............................................59

11

Accretion of sand at the southwest corner of Polowat island........................................................................................................60

12

Eroded upper beach along the north-northeast coast of Polap island.........................................................................................60

13

Masonry sea wall along the northeast coast of Polap island...........................................................................................................61

14

Scouring and toe erosion of the masonry sea wall along the northeast coast of Polap island.................................................61

15

Coastal land loss and shoreline embayment due to erosion along the south coast of Losap island ......................................62

16

Eroded upper beach, with a 75 cm scarp, along the east coast of Satawan island.....................................................................62

17

Old masonry sea wall along the east coast of Satawan island ........................................................................................................63

18

Masonry sea wall along the seaward aspect of the airstrip, northeast coast, Woleai island......................................................63

19

Flanking downdrift of the seawall at the airstrip, Woleai island ....................................................................................................64

20

Shoreline erosion and collapse of large mahogany trees along the southwest coast of Woleai island...................................64

21

Summer accretion of beach sands along the southwest coast of Woleai island .........................................................................65

22

Accretion of coral gravels and sands along the NE and NNW part of an island (un-named) in the Faraulep atoll .........65

23

Part of the accretionary area (previous plate) in the Faraulep atoll. Note the extent of the deposit......................................66

24

Erosion scarps 60 cm high on the upper beach along the northwest coast of the un-named island in Faraulep atoll ......66

25

Exposed tabular slabs beach rock along southwest to west-northwest coast of an un-named island, Faraulep atoll ........67

26

Eroded upper beach and coastal land loss along the west coast of Faraulep island..................................................................67

27

Eroded upper beach and coastal land loss along the west coast of Faraulep island..................................................................68

28

Beach rock along the south coast of Mogmog island, Ulithi, exposed at low tide ....................................................................68

29

Beach rock along the south coast of Mogmog island, Ulithi, exposed at low tide ....................................................................69

30

Gravelly beach along the southwest coast of Mogmog island, Ulithi...........................................................................................69

31

Coral rubble groyne construction on the southwest coast of Eauripik........................................................................................70

32

Sand and gravel accretion at the southwest tip of Utagal island....................................................................................................70

33

Eroded scarp 60 cm high on upper beach, Utagal island................................................................................................................71

APPENDICES I Grain size scale of sediment particles.............................................................................................................72 II Wind data for Pohnpei Island..........................................................................................................................73 III Wind data for Chuuk Island.............................................................................................................................74 IV Wind data for Yap Island..................................................................................................................................75 V The Beaufort Wind Scale ..................................................................................................................................76


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ACKNOWLEDGEMENTS This project was supported by the Commonwealth Secretariat, under the Commonwealth Fund for Technical Cooperation (CFTC). The Commonwealth Secretariat/CFTC also funded the author. Logistic and other financial support, from SOPAC, prior to commencement of the survey and for the preparation of this technical report, is gratefully acknowledged. The Government of the Federated States of Micronesia (FSM) provided logistic support during the survey, including the provision of a survey vessel, supplies and a crew. The co-ordination and scheduling of arrivals and departures at each island were ably done by Captain Matthias Mangmog, Department of Transport, Government of the Federated States of Micronesia. The survey was conducted with the assistance of personnel from the Government of the Federated States of Micronesia (FSM). The co-ordination of activities before and during the conduct of this survey by Mr Francis Itimai, Fisheries Officer, Department of Economic Affairs, Government of the FSM, is gratefully acknowledged. Discussions with Mr Moses Nelson, Department of Economic Affairs, Government of FSM, and Mr Asher Edward, College of Micronesia, Pohnpei, are gratefully acknowledged. Personnel from the Departments of Marine Resources and the Environmental Protection Agency, of the State Governments of the FSM, participated in the survey. Two attendees from each of the Pohnpei, Chuuk and Yap State Governments were involved in the respective legs of the survey. The South Pacific Applied Geoscience Commission (SOPAC) supported Mr Phillip Woodward who participated in the survey. Mr Robert E. Mullane of Seagrant College, Maui, Hawaii, also participated in part of the survey, from Chuuk to Yap. Assistance was provided by the local people on the various islands visited, with field surveys and provision of historical information about the local coastlines. Their co-operation and interest in the survey are gratefully acknowledged.


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EXECUTIVE SUMMARY The Government of the Federated States of Micronesia requested the South Pacific Applied Geoscience Commission (SOPAC) to undertake a study of coastal erosion problems in several of the outer atoll islands of the FSM territory. Residents on many of the outlying atoll islands of the FSM indicate that the coastlines are being aggressively eroded and their land area becoming smaller. Consequently, a request was made by the local islanders, through their State governments, to the FSM Congress to conduct an assessment of the erosion and shoreline processes on these islands. The FSM Government subsequently made a formal request to SOPAC, and the proposal was accepted by SOPAC. The islands surveyed form part of the outer atoll islands of the Pohnpei, Chuuk and Yap states of FSM. Twenty-one islands were surveyed. Four were surveyed in Pohnpei. These are Pingelap, Mokil, Sapwuafik and Nukuoro. Five were surveyed in Chuuk State. These are Satawan, Losap, Pollap, Polowat and Alet. Twelve were surveyed in Yap State. These are Lamotrek, Elato, Fechaulap, un-named island, Ifalik, Woleai, Tagaulap, Falalis, Utagal, Saliap, Eauripik and Mogmog. The study was conducted from 20 July 1998 to 12 August 1998. The islands were visited by sea, travelling on-board an FSM patrol vessel, the FSS Constitution. More than 3000 nautical miles was traversed, over a period of three weeks at sea. The survey vessel was anchored close to shore and access to shore was gained using a small powered boat. Approximately 2-12 daylight hours were spent on each island. Initial discussions were held with the local residents on each island, highlighting the purpose and scope of the survey. In addition, discussions were also initiated to obtain information about shoreline changes in recent times. Inquiries were also made as to the effects of storms and typhoons on the local beaches and lagoon areas. During the survey, representative sections of beaches and coastline were examined. On several islands, due to their small size and the available time, it was possible to traverse the entire beach area. Beach sediments were described in the field following accepted international guidelines. Beach slopes, erosion scarps, scouring and shoreline retreat was also measured and evaluated. Aggregate extraction and construction activities along the coastline were also documented. This includes land reclamation, airstrip construction, and seawall and groyne construction. Waste disposal and nearshore/surf-zone circulation was also noted (as it relates to reef health, carbonate sand production and beach sediment dynamics). Photographs were taken of representative sites, erosion problems and failures of various constructed facilities along the coastline for each island. Based on the information collected and analysed, there are several factors which are responsible for erosion and shoreline retreat in the study area. These can be summarised under two main headings: 1. Natural Processes and 2. Man-made Processes


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Natural processes account for significant and continuous erosion on all the islands surveyed. These include waves generated by Northeast trades, westerlies, storms and typhoons. Storms and typhoons are the main agents of erosion. Although these are infrequent extreme events, they are the major factors influencing the coastal morphology of these island states. Man-made processes, in particular construction activities, are the main factors affecting the rates and severity of local erosion. Removal of aggregate from the coastal zone has been identified as the single main human factor and key “erosion” process. The extraction of aggregate resources in the coastal zone needs to be carefully monitored and controlled. While these resources are renewable, they are not renewable at rates equivalent to their removal. The inappropriate use and construction of seawalls and groynes is also a major problem. The perception that these structures will prevent or reduce erosion needs to be re-examined. In the contex of the local erosion problems, these structures serve only to exacerbate the erosion problem and do not reduce nor stop erosion. Construction activities also result in death of coastal reef species, due to either reclamation, sediment smothering or pollution. These aspects need to be considered, if future similar construction activities are planned. The importance of reef biota to the beach and nearshore sediment supply needs to be emphasised. Several recommendations can be formulated for reducing coastal erosion and improving shoreline management. Many of the recommendations emphasise preservation of the natural ecosystem and non-interference with sediment transport and movement along and across the coast. For small atoll islands like those surveyed, non-interference with natural sediment processes cannot be over emphasised. Interference with longshore transport, such as by the construction of sea walls, can cause considerable erosion and should be discouraged. In relation to coastal protection and construction, an assessment of the reliability and performance of coastal structures should be made with respect to their relevance to low-lying atoll islands. This assessment will benefit not only FSM, but also other similar south Pacific islands within the SOPAC region. Seawall construction has caused several meters of land loss in several of the islands surveyed. Several meters of land loss is large, when one compares it to the size of some of these islands, which can be 150-200 m wide, e.g. Losap or Euarapik. For this reason also, buildings should be setback from the coastline, well into the interior of the island. This will reduce the risk of exposure, vulnerability and possible damage from extreme oceanographic events. Communities should also try to re-vegetate coastal areas which have been affected by previous storms or which have been cut or burnt. These serve as wind breaks and stabilise soils and beach sediments, reducing their erosion by up-rush and backwash. The planting of common locally available coastal species is encouraged. These include mangroves, seaside mahogany, pandanus and coconut trees. Larger species like mahogany and mangroves are recommended, as these stabilise a larger area of soil and are more sturdy species.


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The disposal of waste in mangroves and cutting of these species should be discouraged, as they are important coastal stabilising vegetation, in addition to contributing to the productivity of coastal ecosystems, like fisheries and corals (which contribute beach and nearshore sediments). As for aggregates, these may be obtained from summer sandbanks, preferably from adjacent, uninhabited islands or from mainland areas, providing surplus quantities are available. However, even if this activity is pursued, extraction can only be minimal. Large volumes for housing and airstrip construction are neither feasible nor sustainable. Their extraction locally should be reduced and eventually stopped. This point cannot be over-emphasised, as their continued removal from these small islands contributes to increased exposure to waves and storms, increasing their vulnerability to oceanographic hazards and erosion. This eventually leads to erosion of land area, causing further reduction in size of these already small islands. From the surveys conducted, aggregate extraction from nearshore areas was found to be a major factor contributing to high rates of erosion. Technical investigations and environmental impact assessment (EIAs) should precede major construction or development activities, such as airstrip construction, reef channel cutting or aggregate mining. These studies will identify the best environmentally sound options for pursuing the desired activities. As population increases on these atoll islands and societal needs for natural resources increase, such as for aggregate, housing material, infrastructure and land area, efforts must be made to address these needs. This is particularly important if these natural resources are to sustain the existing population and future generations. If the same finite volume of resources is tapped, at an increasing rate with time, then these resources can easily dwindle. Therefore, resources must be carefully managed and should not impair the capacity to benefit future generations; users should, therefore, consider the total and cumulative effect of their actions. An important issue, which therefore must be addressed by these small island developing states (SIDS), is the capacity of these small islands to sustain the existing and future demands and needs for aggregate, land area, housing material and living resources in the coastal zone. In addition, changing trends of lifestyle and customs and socio-economic pressure cause changes in societal needs. Particular cases are the departures from traditional thatched housing to concrete buildings and infrastructure/facilities, the need for airstrips to improve efficiency of inter-island communication and seawalls and groynes to protect seafront buildings. These changing needs cause a demand for building material and land area, which leads to aggregate mining, nearshore reclamation and coastal construction. These activities cause deleterious impacts in the coastal zone, causing death of reef biota, loss of carbonate-sand-producing organisms, and loss of natural wave breakwaters (coral heads and coral reef rubble). This reduces the natural protection of coastal areas, increasing their vulnerability to extreme oceanographic events, causing exacerbation of local erosion and decrease in land area. Since many of these islands are very small (less than 2-3 km2) and are already affected by high rates of natural erosion, any alteration of natural coastal systems will cause negative impacts along the coastline, ultimately leading to erosion and decrease in land area. If such erosion continues,


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one option, which may require some consideration within the short term and in the long term, is re-location of the local population. Further to discussions with residents on the islands surveyed, it became apparent that most of the population were unaware of the dynamic relationships which exist between beach processes, erosion, sediment transport, pollution, coastal vegetation and reef dynamics (both biological and physical). The perception that beach activities only affect beach erosion and deposition is widespread. To effectively implement and pursue coastal management guidelines and strategies, this misconception must be clarified. Public awareness of the oceans, the values they represent and the risk they face, must be emphasised. The more aware people become of nearshore processes and coastal systems, the easier it is to use available resources with respect and intelligent care, safeguarding them for future generations. Public awareness and participation in ocean governance and management is also a pre-requisite for the implementation of successful coastal management strategies. It is therefore recommended that a public education/awareness programme be implemented, for the island residents, on the use and management of coastal resources and ocean space. In addition, local technical personnel should be trained in coastal zone management to effectively address local issues affecting the islands of FSM.


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1.0 INTRODUCTION 1.1 Background The Government of the Federated States of Micronesia requested the South Pacific Applied Geoscience Commission (SOPAC) to undertake a study of coastal erosion problems in several of the outer atoll islands of the FSM territory. Residents on many of the outlying atoll islands of the FSM indicate that the coastlines are being aggressively eroded and their land area becoming smaller. Consequently, a request was made by the local islanders, through their State governments, to the FSM Congress to conduct an assessment of the erosion and shoreline processes on these islands. The FSM Government subsequently made a formal request to SOPAC, and the proposal was accepted by SOPAC. This document is a report of this assessment and investigation. The report presents the problem, the methods of evaluation, the results and conclusions of the study. Recommendations are also presented to complement the findings. 1.2 The Study Area The study area is located in the North Pacific Ocean, between latitudes 2 to 12o north and longitudes 138 to 165o east (Figure 1.1). The islands surveyed form part of the outer atoll islands of the Pohnpei, Chuuk and Yap states of FSM. Table 1.1 presents a list of all the islands visited and the atoll groups to which they belong. Twenty-one islands were surveyed. Four were surveyed in Pohnpei. These are Pingelap, Mokil, Sapwuafik and Nukuoro. Five were surveyed in Chuuk State: Satawan, Losap, Pollap, Polowat and Alet. Twelve were surveyed in Yap State: Lamotrek, Elato, Fechaulap, an un-named island, Ifalik, Woleai, Tagaulap, Falalis, Utagal, Saliap, Eauripik and Mogmog. 1.3 Period of the Study The study was conducted from 20 July 1998 to 12 August 1998. The travel itinerary, with ETAs and ETDs are presented in Table 1.1, while the geographical coverage of the cruise is shown in Figure 1.1. The survey period corresponds to the Northern Hemisphere mid-latitude summer and the lowlatitude dry season. Strong Northeast trades and low rainfall and a general absence of typhoons or northerly swells generally characterise this period.


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2.0 SCOPE OF WORK AND THE REPORT This report presents the results of field geological and environmental surveys and analysis of field geological information on the erosion and stability of coastlines on the outer atoll islands (Table 1.1) of FSM. The study is the first study of its kind in this part of the FSM area and in the outer atoll islands visited. At this time, the information and analysis presented document the problems and state of the coastlines on each of these islands. The geological information collected for each island is tabulated for ease of reference and clarity. Each individual problem which exists along each coastal segment surveyed is also presented separately, for comparative purposes within the island and between islands. There is one table for each island. While many of the coastal problems on each of the islands surveyed are similar, it is necessary to present the data for each island separately. This will assist in the formulation of recommendations and management strategies, which are specific to each island and the local environment. Representative glossy colour photographs of natural and built coastlines, and of eroding and accreting areas, are presented as plates at the back of this report. Information on seawalls (which are common for shoreline protection on these islands) is also presented in tabular form. The different types of seawall used, their characteristics and performance are highlighted. Reasons for failures are also discussed. A summary of the factors contributing to coastal erosion is presented. Recommendations for reducing coastal erosion and shoreline management are also discussed. 3.0 METHODOLOGY The islands were visited by sea, travelling on-board an FSM patrol vessel, the FSS Constitution. More than 3000 nautical miles was traversed, over a period of three weeks at sea. The survey vessel was anchored closed to shore and access to shore was gained using a small powered boat. Approximately 2-12 daylight hours were spent on each island. This includes arrival and departure times, survey time and discussions with the local residents. Initial discussions were held with the local residents on each island, highlighting the purpose and scope of the survey. A tour guide was subsequently assigned to the survey team, to show area of concern and the more problematic sites affected by erosion and coastal land loss. In addition, discussions were also held, to obtain information about shoreline changes in recent times. Inquiries were also made as to the effects of storms and typhoons on the local beaches and lagoon areas. During the survey, representative sections of beaches and coastline were examined. On several islands, due to their small size and the available time, it was possible to traverse the entire beach area.


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Beach sediments were described in the field following accepted international guidelines described by vanRijn (1989; Appendix I). Beach slope, erosion scarps, scouring and shoreline retreat was also measured and evaluated according to standard practice described in Herbich (1991). Aggregate extraction and construction activities along the coastline were also documented. This included land reclamation, airstrip construction, and seawall and groyne construction. Waste disposal and nearshore/surf zone circulation was also noted (as it relates to reef health, carbonate sand production and beach sediment dynamics). Photographs were taken of representative sites, erosion problems and failures of various constructed facilities along the coastline for each island. 4.0 RESULTS 4.1 Shoreline Characteristics Many of the islands have similar beaches and coastlines. Consequently, to avoid repetition, separate discussions of beaches on each atoll will not be presented here. However, a discussion of the general characteristics will be presented, highlighting examples from the various atoll islands. Plates 1-33 present some representative sections of natural and built coastlines surveyed from the various FSM atoll islands. 4.1.1 The East/Windward Coast The east coasts (including the northeast and southeast) of the atoll islands are well exposed to strong trade winds and swells. The coastlines are extremely eroded (Plates 3, 4 and 6), with narrow beaches composed of coarse, abraded sands, gravels, cobbles and boulders (Plates 16 and 30). These sediments are angular to sub-angular (Plate 6). Sediments are typically coral reef rock debris (Plate 12), Mollusca spp shell fragments, with some Halimeda spp, Rodophyta spp and foraminifera tests (Plate 11). Beaches vary from 5 to 7 m wide, averaging 6 m (Plate 29). Beach slopes vary from 10 to 20o, averaging 15o, and are slightly concave in profile. Erosion scarps are typically well exposed and are found at the vegetation line (Plate 33). These vary from 1 to 2.5 m high. Creeping vines and small shrubs usually overhang at eroded scarps. They scarps are usually vertical and are maintained by wave runup and erosion (Plate 27). Numerous toppled trees, including coconut, pandanus and mahogany, breadfruit and other species are found along the east coasts of the atoll islands (Plate 26) .


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4.1.2 The West Coast The west coast of the islands surveyed are generally more sheltered, with wider, more sandy beaches. Beaches vary from 4-15 m wide, with 8-10o slope (Plate 6). Sediments are dominantly coarse to medium sands, typically of coral reef rock debris, Halimeda spp, Rodophyta spp, and foraminifera tests. Sands are less angular than those on the east coast, with less gravels and cobbles. On the atoll islands surveyed, especially those in Pohnpei and Yap States, the western shore is generally narrow, less than 5 m wide. This is due to the presence of relatively deep nearshore lagoons, with steep beach slopes, estimated at greater than 12o. These lagoons occupy a part of the western/backreef coast and vary from 8-29 fathoms deep. Lagoon depths range from 15-29 fathoms in Pingelap; 16-22 in Mokil; less than 3 in Nagtik; 1022 in Nukuoro; less than 5 in Satawan; 5-8 in Pulap; 3-7 in Puluwat; 10-18 in Lamotrek; 6-8 in Elato; 4-10 in Woleai; 4-6 in Tagaulap; 4-8 in Falalis; 5-8 in Utagal; and Saliap; less than 5 fathoms in Eauripik and 5-8 fathoms in Mogmog. Lagoons cause large waves to approach the beach, causing scouring of the lower beach. Since these lagoons have steep offshore gradients, backwash results in significant sediment removal by gravity flow, from the beach to deep lagoon areas. Backwash on beaches fronting these deeper lagoons causes significant cross-shore sand transport, directing much sediment to the deep areas of the adjacent lagoons. Analysis of navigational charts for the Yap and Pohnpei islands show significant sediment gravity flows, on nearshore beach-lagoon slopes, towards deeper lagoon areas. This supports the hypothesis that beach sand removal by erosion results in a nett loss of sediment from the nearshore sand budget, to the deep lagoon areas. Beaches on the western coastline are composed of thicker sand deposits, usually greater than 20 cm (Plates 8, 21 and 22). While they are also subject to erosion (Plate 21), the more sheltered nature of the western coastal areas contributes to sediment accretion (Plates 8 and 22). A classic example of sediment accretion was observed on one of the islands in Faraulep atoll (Plates 22 and 23). This sediment accretion area, or more appropriately a typhoon bank, was almost equivalent in size to the island around which it has accreted, being produced by storm/typhoon events over several years during the past decade (information from the island residents). It is at least 2 m thick along the crest of the main lobe deposit (Plate 22), being more than 600 m long and 500 m wide. The sediments are typically coarse sands, gravels and cobbles, more than 70 % of which are corals. The deposits have since been colonised by various coastal shrubs, suggesting that these areas have been relatively stable in recent years. Typhoon banks are found in all the atoll islands visited. Deposits usually accumulate on the western coast (including the northwest and southwest), since it is from this direction that typhoons originate. Deposits usually accrete in backreef and lagoon areas, such as on Faraulep. Deposits may accrete also on land, such as on west Polap, west Polowat, southern Lamotrek, southeast Elato, southwest Mogmog, south Faraulep, western Woleai and northeast and southwest Falalis. These on-land deposits can be up to 8 m high and more than 30 m wide, with slopes up to 30o, and consist largely of gravels and cobbles. Deposits also accrete between atoll islands such as in Ifalik, western Utagal, western Saliap and western Eauripik. These deposits are usually finer, consisting of sands and gravels.


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The formation of typhoon banks results in the mobilisation and transport of large volumes of reef and backreef sediments into shallower nearshore and land areas. This causes sediment depletion from deeper areas and a corresponding increase in water depths due to sediment loss. In addition, the natural removal and re-distribution of reef rubble and sediments by typhoons causes some removal of natural shore protection, allowing larger waves to approach the beaches in the future. 4.1.3 Beach Rock On all the islands, beach rock is exposed in the surf along the east and west coasts. These deposits vary between 5 and 50 m wide. They are of late Holocene age, are generally tabular and are well cemented, e.g. Plates 25, 28 and 29. Sediment constituents of the beach rock vary from fine sand (Plate 25) to coarse gravel (Plate 29) and represent a polymictic assemblage. Sand particles are angular, while the coarse gravels and abraded are sub-rounded. The surface slope on these deposits is generally the same on all the islands on which they are exposed. This varies between 12 and 18o, e. g. Plate 25. In addition, the surface of these deposits, on the lower beach, are scoured and abraded to produce a pothole appearance, as in bedrock fluvial systems, e.g. on Mogmog island. Beaches backing these deposits are usually highly scoured and eroded, with erosion scarps (Plate 25). This is due to runup and local turbulence at high tide. Turbulence develops due to interactions between breakers, variable seabed slope and hardness and backwash from shore. This results in significant sediment scouring and removal from the beach, e.g. Plate 25. 4.2 Coastal Erosion Problems Tables 4.1-4.15 present detailed summaries of the various coastal erosion problems which currently exist on each of the islands surveyed. The information and observations for each coastal segment, on each island, have been tabulated separately. Most of these coastal erosion problems are common, whether they are natural or man-made. Plates 1-33 present representative sections of coastlines surveyed from the various FSM islands visited. Plates 3, 4, 6, 12, 15, 20 and 26 show examples of coastal erosion, land loss and undermining of coastal vegetation. This includes fallen trees (Plates 20 and 26), scouring and embayments around coconut trees (all other Plates) and exposure of large tree roots (Plates 3, 4 and 20). These suggest shoreline instability and recent shoreline retreat. Plates 10, 16, 24, 30 and 33 show examples of summer erosion scarps on sandy and gravel beaches. This includes replacement of beach sands with coarser gravels and cobbles. Beach slope and sediment characteristics are also seen. Plates 25, 28 and 29 show examples of exposed beach rock along several coastlines. These deposits are typical of beach rock in the outer FSM islands and are generally tabular (Plate 25)


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and wide. Beaches backing these deposits are usually highly scoured and eroded, with erosion scarps (Plate 25). Plates 7, 8, 9, 11, 21, 22, 23 and 32 show typical examples of preferential shoreline accretion along some of the shorelines surveyed. They include summer sand bar deposits (Plates 11, 21 and 32), sand impoundment updrift of an airtsrip (Plates 7 and 8) as well as extensive storm deposit accumulation (Plates 22 and 23). These suggest that sediments are generally available to the natural coastal system for seasonal re-cycling. Tables 4.16.1-4.16.3 present a summary of the types of seawall used their designs and failure characteristics. Three main types of wall are common throughout the study area. These are interlocking rubble, rubble masonry and re-inforced concrete. However, the design criteria used on each island are similar. Consequently, when they fail, the reasons for failure are also similar. Tables 4.16.1-4.16.3 give details of failures and the reasons for failure. The various types of seawall used on each island are mentioned in the island summaries, Tables 4.1-4.15. Plates 1, 2, 5, 13, 14, 17, 18, 19, 27 and 31 show representative examples of coastal seawalls and groynes. Masonry walls are shown in Plates 13, 14, 17 and 18, and interlocking rubble walls in Plates 1, 2 and 5. Groynes are shown in Plates 27 and 31. Flanking is seen in Plate 19. A high, inclined seawall is seen in Plate 18. Failure types (Plates 14 and 17), sediment impoundment (Plate 31) and erosion characteristics adjacent to seawalls are also seen. Beach sediments adjacent to seawalls are also seen. 5.0 DISCUSSIONS: FACTORS AFFECTING SHORE INSTABILITY 5.1 Weather Several general comments can be made regarding coastal erosion and instability, applicable to all the islands visited. Analysis of the geological information shows that many of the islands have experienced similar erosion problems in the past. They are all affected by high rates of natural erosion and coastal land loss during storms and typhoons, e.g. in Falalis and Satawan. Typhoons are common during the local rainy season or during the Northern Hemisphere late summer, fall and early winter seasons. These weather events usually originate in the mid-west Pacific Ocean (U.S. Navy, 1996) and are have disastrous effects along the south and west coasts of these islands. They travel westwards across to the Philippines, but usually turn northwest and then east to northeast along the eastern Pacific Ocean (U.S. Navy, 1996). Data presented by Van Loon (1989) and U.S. Navy (1996), show that July to November are the most typhoon prone months, with 2-7 events per month and with an average of 28 events per year, for this part of the Pacific Ocean. Storms and typhoons cause significant erosion and coastal land loss in many islands. In addition, they cause significant onshore transport of coarse marine carbonate sediments from the reef crest and back-reef areas, to the south and west coastal areas, where they are deposited as storm/typhoon banks, e.g. on Fechaulap. The removal of shallow-water carbonates from back-


15

reef areas, by storms, causes alterations in bathymetry and a general increase in water depths in nearshore areas. These facilitate the propagation of larger, potentially more destructive waves during subsequent events, and in the short term, increasing the erosion susceptibility of adjacent coastlines. Strong westerly winds also affect the FSM area, from July to September, especially in Chuuk and Yap (Appendices II and III), and cause upset wave conditions to develop along the west coast of this island. These cause wave run-up, overtopping of coastlines and shoreline erosion during swash and backwash, e.g. in Eauripik. The northeast trades are also a major element influencing wave climate and wave approach in this region (see Appendices I, II and III). These produce significant northeasterly approaching waves, with southerly-directed longshore transport, causing considerable erosion of easterly shorelines. For all the islands surveyed, the eastern/windward shorelines are the most aggressively eroded, the most rocky, with negligible fine sediment close to shore, especially in the surf zone, e.g. in Polowat. Eroded scarps are usually the highest, sometimes close to 2 m, and usually clear of vegetation, e.g. in Sapwuafik. 5.2 Geology and Geomorphology Geologically, all of the islands surveyed are composed of Quaternary sediments, in particular, Holocene reef carbonates. These sediments which are the building block of these islands are generally coarse sands and gravels with some cobbles. They are angular, platy to flat, with high void ratios, due to their porous nature. They contain very little fines and are generally cohesionless or can be considered frictional material. Moving water, especially during turbulence associated with breaking waves and storm and typhoon wind-waves, easily dislodges these types of material. In addition, since these materials are porous, with high void ratios, they can become easily entrained in swash and backwash and be transported out of the beach and nearshore area to deeper water. The porous nature of these sands also causes their settling velocities to be less than those for solid, less porous grains. Consequently, sediment erosion and removal can be very rapid on beaches composed of these types of sand. In should also be noted that the effective friction angle of these carbonate sands is generally less than 10o, when saturated. Such low friction is generally not sufficient to resist scouring and erosion during swash and backwash. The low island elevation, usually less than 3 m above mean sea level, also renders the land areas susceptible to run-up and overtopping during high-water spring tides, storms and typhoons. This causes much erosion of coastal land and removal of beach sediments to deeper water. 5.3 Beach Water Table The near-surface beach water table is another important factor contributing to beach sediment saturation, sediment mobility and beach instability. Seepage is common on mid-beach areas during a low spring tide on several of the islands surveyed, e.g. Saliap. In addition, sand on the lower beach is usually quick, even at low tide,


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rendering it highly susceptible to re-suspension in the water column and erosion by breaking waves. Short-period waves also keep the beach saturated, as drainage of the beach sediments is never complete before the arrival of the subsequent wave and swash. These processes cause the beach sediments on the mid beach and lower beach areas to be saturated. Sediment saturation causes instability and buoyancy, leading to sediment entrainment in swash and backwash and transportation out of the surf zone. This repeated process leads to beach erosion and shoreline retreat. 5.4 Dynamic Wave Loading and Liquefaction During storms and typhoons, waves approaching the shoreline usually break as plunging breakers. These waves are also larger than normal, usually more than 1 m high. Such large breaking waves cause liquefaction of saturated beach and surf-zone sediments. Liquefaction of these sediments is possible due to dynamic wave loading on the porous, low-density, saturated beach sands. Repeated and short-cycle wave loading associated with short-period plunging breakers can cause significant liquefaction of surf-zone sediments. This will cause suspension of beach sediments and their entrainment in the water column and surf, resulting in their removal from the beach area. This type of erosion can account for significant sediment erosion and removal from the surf zone during typhoons and storms. 5.5 Wave Climate From field observations, wave and breaker heights in all of the islands vary between 0.1 and 0.30 m on the lagoon and west coastal areas and between 0.25 and 1.50 m on the windward, east coast. Wave periods were between 6 and 10 s for both the windward, lagoon and west coasts. Breakers on the east/windward coast were usually plunging, while on the west and lagoon coastline were sometimes surging and spilling. Hindcast or field wave data are generally unavailable for the FSM area. Wind speed estimated (Beaufort Scale) in the field was generally less than 1 m/s. However, data from Van Loon (1984) show that wind direction can vary from northeast to southeast for most of the year, except from July to October, when westerly and south-westerly winds are common in Yap and Chuuk States. Data from Van Loon (1984) show that wind speeds vary from 1.4 to 4.9 m/s, with higher speeds of 2.1-4.9 m/s from October to June, during which time the North East Trades are prevalent (Appendices 1, II and III). Wind speeds associated with typhoons and extratropical depressions are usually greater than of 25 m/s (Van Loon, 1989 and U.S. Navy, 1996). These wave parameters will change during storms and typhoons, during which time it can be expected that waves will be largely plunging or surging breakers, with short periods of less than 10 s, and with larger heights, generally in excess of 1.5 m, rendering them more destructive.


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In addition, long-period swells are to be expected during the Northern Hemisphere winter, travelling south, into the FSM area. These tend to be greater than 2.0 m high (Captain M. Mangmog, personal communication). These waves are generally destructive, transforming to plunging breakers in the surf zone. Whilst many of the islands are protected by reefs and sheltered by lagoons, waves approaching the coast usually have short periods and therefore, frequently impact on the coast. Short-period waves and swells, transforming into plunging and surging breakers, impart considerable stress to beaches rendering them unstable. Dis-equilibrium conditions also develop in response to these waves. On the trade wind/east coast, larger plunging and surging breakers and shorter-period waves are common, as they are during storms and typhoons. These tend to be quite erosive and destructive (as discussed previously). The outer atoll islands of the FSM are also located within the pathways/tracks of typhoons, storms and extratropical depressions, which originate in the mid-west Pacific Ocean. Many of these events usually originate between 5 and 25o N, travelling along the east Pacific Ocean coast, northwards. In addition, much of this storm and typhoon activity is concentrated between 110 and 145oW, well within the FSM territorial waters and in the outer atoll islands ocean space (Van Loon, 1984 and U.S. Navy, 1996). The frequent occurrence of these extreme weather phenomena causes significant change in wave climate and upset conditions in nearshore areas. The most significant change is the formation of large, short-period plunging and surging breakers. These have disastrous erosion effects along beaches on the low atoll islands of FSM, causing the removal of large volumes of beach sediments and runup and coastal flooding on land. Since typhoons, storms and depressions occur on an annual basis in the study area, these events lead to continuous erosion of the shorelines and coastal land loss. 5.6 Shoreline Construction: Airstrips, Seawalls, Groynes, Houses and Public Buildings Construction within the coastal zone is a main factor responsible for aggressive and exacerbated shoreline erosion. This includes the construction of airstrips, seawalls, groynes, shorefront houses and buildings, e.g. in Pingelap, Mokil, Sapwuafik and Eauripik. These facilities interfere with longshore and cross-shore sediment transport, causing sediment impoundment on the updrift side and sediment erosion and flanking on the downdrift side. Sediment starvation, due to impoundment in updrift areas, is the main reason for flanking and erosion, e.g. at the seawall fronting the Woleai airstrip, Woleai island. In response to sediment starvation, longshore currents and waves will tend to erode downdrift coastlines to recover the loss of sediment from the longshore sediment budget, causing aggressive downdrift erosion. This was best seen in Euarapik, which had the most “engineered” coastline of all the islands surveyed. Erosion in these downdrift areas is aggressive, because the length of coastline from which this sediment recovery has to take place is usually much shorter than the length and coastal area from which sediment was naturally supplied. This causes significant coastal land loss and coastline recession.


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With regards to seawalls or groynes, these do not stop nor reduce erosion along the shoreline. While they may appear to do so, temporarily, they cause erosion spots to migrate downdrift, causing beach erosion of much greater severity and land loss at downdrift sites (as discussed above). Airstrip construction on several of the islands was a major reason for coastal aggregate extraction, e.g. Pingelap and Mokil. The volume of aggregate extracted for an airstrip, 300 m long, 30 m wide and 2 m high, was usually greater than 20 000 m3, e.g. Pingelap and Mokil. This represents a significant volume of available nearshore carbonate sediments. The removal of this aggregate causes an increase in nearshore water depths and removes natural coral breakwaters, thereby reducing the amount of natural protection and wave dissipation afforded to beaches and coastal land. This renders the coastline more vulnerable to erosion. The construction of concrete houses, sea walls, groynes, water tanks and pathways also increases the demand for carbonate aggregate, e.g. in Woleai. While these individual volumes are usually smaller than for an airstrip, their cumulative and continued extraction causes significant sediment starvation from nearshore areas, resulting in shoreline instability and erosion. Aggregate extraction also causes deepening of nearshore areas, causing larger waves to be propagated from offshore, onto the beach, e.g. in Satawan. This leads to erosion and shoreline instability, e.g. in Woleai. Sediment extraction within the coastal zone also causes increase in water turbidity, and sedimentation covering live coral and other reef biota, e.g. in Eauripik. The removal of rubble also results in the removal of live coral heads and other benthic organisms, essential to a healthy reef ecosystem and carbonate sand production, e.g. in Eauripik. In addition, structures such as airstrips interfere with nearshore circulation, causing stagnation and death of nearshore reef dwellers, e.g. in Mokil. These all decrease carbonate sediment productivity and the volume of available sediments in the coastal zone. It is noteworthy to mention that while aggregate for construction can be easily extracted within months or even a few years, replacement of this material in natural carbonate systems (like the ones which exist in the study area) will take hundreds to thousands of years. Therefore, the use of this resource must be considered from the viewpoint of sustainability and renewal. This is particularly important, especially since aggregate demand for housing and other construction activities increase, with increases in population and changes in cultural practice and societal needs. Coastal reclamation, such as for airstrip construction, e.g. at Sapwuafik, or for housing, e.g. at Eauripik or Mokil, causes death of marine reef biota. Effects include direct covering of live organisms and smothering of carbonate producing biota by sediment plumes during reclamation. These activities kill carbonate-sand-producing organisms, especially corals, and decrease the availability of their skeletal remains to produce sediments in the nearshore area. This results in a reduced nearshore sediment budget, beach sediment starvation, eventually causing erosion. Consequently, construction on live coral reef areas, whether backreef or lagoonal, should also be discouraged. It must be borne in mind that shoreline construction activities not only decrease the long-term and available carbonate sediment supply, but also reduce the available and potential fisheries resources and other biota in the environment. Man’s interference with the natural reef ecosystem, whether biological or physical, causes upset in the natural balance of these biosystems. This creates dis-equilibrium in the ecosystem, usually with disastrous effects. Therefore,


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the utilisation of coastal/ocean space and resources must be rational and with the view to sustain existing and future generations. 5.7 Scale and Geographical Disposition In open-ocean, geologically young islands like those surveyed, erosion is inevitable. This is particularly true for these types of island composed of soft, low-density, cohesionless sands, like in FSM area. When one compares the size of these islands to that of the surrounding Pacific Ocean and landocean-atmospheric processes which affect them, it is not difficult to reason that they will continue to be stressed and battered by erosion processes. Many of the extreme oceanographic events, like storms and typhoons, occur at scales much larger than the size of any of the islands surveyed. Individual typhoons with gale winds can cover an area of about 100 km2, while extratropical depressions can cover a much larger geographical area (Van Loon, 1989). Consequently, entire islands are usually engulfed and stressed by these extreme events, causing significant alterations to the natural bio-physical environment, including coastal erosion. It is noteworthy to mention that the geographical location of many of the islands surveyed, especially those in Yap State, renders them susceptible to annual typhoons and storms. These events usually originate in the territorial waters of the FSM (Van Loon, 1984) and are also the primary agents responsible for coastal erosion. Consequently, the outer islands of FSM, especially those in Yap and Chuuk States, will continue to be affected by storm and typhoon induced coastal erosion and land loss. 6.0 MECHANICS OF EROSION 6.1 Introduction Fluid flow around submerged particles in seawater exerts shear stresses, and results in incipient particle dislodgement and motion. However, to initiate incipient motion in coarse carbonate sands, like those surveyed in FSM, the shear stresses must exceed the resisting forces due to intergranular friction, submerged particle unit weight and apparent cohesion/suction. Threshold particle motion occurs when the hydrodynamic moment of forces acting on the sediment surface balances the resisting moment forces. The sediments are then said to be at incipient motion. 6.2 Sediment Properties For the coarse carbonate sands and gravels which are present on the atoll islands of FSM, several factors influence their erosion mechanics. The carbonate sediments, which are deposited along shorelines of the FSM outer atoll islands, are similar in composition, texture and hydraulic properties. They are Holocene/present-day sediments and are composed largely of abraded coral sands and gravels. In addition, Halimeda algae fragments, Rhodophyta algae and benthic macro-foraminifera are significant constituents of beach sediments on all the atoll islands.


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Beach sediments are generally angular to sub-angular, especially the coral, Halimeda and Rhodophyta constituents. Foraminiferal constituents are generally sub-rounded, due to their initial oblate to disc shape. Most particles are irregular, with larger particles being lenticular. The algae and foraminiferal particles have large surface area to volume ratios, with high aspect ratios, rendering them buoyant. Coral and algal fragments are of high porosity, also rendering them buoyant. Beach sediments of these particles have estimated peak friction angles of 30-32o, with residual friction less than 15o. Further, they are cohesionless, with only apparent cohesion or pseudocohesion at point contacts. Beach deposits of these sediments have low relative densities, and are soft and highly permeable. These types of sediment are of low specific gravity, generally less than 2.50 (vanRijn, 1989) and therefore of low unit weight. When these types of carbonate sand are agitated and become suspended in the surf zone, due to their low specific gravity and buoyancy, their fall velocity is usually low. Computation of the fall velocities for medium to coarse carbonate sands (1.00-2.00 mm in diameter; the common sediment texture on FSM beaches), at 20oC, in still water, indicate that their fall velocities are about 60% of that for quartz sand of the same texture. For 2 mm carbonate sands, settling velocities are 0.166 m/s, compared to 0.283 m/s for quartz. For 1 mm size carbonate sands, settling velocities are 0.114 m/s, compared to 0.160 m/s for quartz (Julie, 1995). In the surf zone, where there is significant wave agitation and turbulence, and for higher seawater temperature and lower density like in FSM, the fall velocities of these carbonate sands can be expected to be even lower. Settling velocities can be expected to be less than 50 % of that for quartz of the same size and under similar hydraulic conditions. This is due to turbulence and eddies resulting from wave action and the high density of seawater. These movements sustain the sediment particles in suspension, reducing their settling rates. As a result, these sands can remain in the water column for long periods, before settling to the sediment surface or accumulating on adjacent beaches. Carbonate sands are porous and permeable, with high intra-granular porosity, producing beach deposits of high void ratio and low relative density. Their high intra-granular porosity also causes trapping of air, rendering them buoyant. This facilitates their easy suspension in the surf zone. The high inter-granular and intra-granular porosities of carbonate sediments cause them to have high hydraulic conductivity. 6.3 Wave Erosion When a wave approaches the shoreline and breaks, it causes dynamic loading on the saturated sediment surface. This transmits cyclic shear stresses within the saturated sediment, causing the generation of positive pore-water pressure within the sediment. The generation of positive porewater pressure results in particle instability and the development of neutral stresses within the media, causing strength loss and incipient particle mobility.


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Strength loss is caused by a combination of wave-induced liquefaction and particle motion due to inter-particle stresses. The buoyant nature of carbonate sands also causes their easy dislodgement in response to positive porewater pressure. Breaking waves also cause sea-bed instability due to swash and backwash, which produce significant bed shear stresses along the sediment surface. These forces, acting simultaneously with cyclic wave loading, cause disturbance of the sediment surface and sea-bed instability. This instability results in particle dislodgement in the surf and on the beach, causing suspension of beach sediments in the surf zone. For carbonate sands, with properties described above (Section 6.2), particle dislodgement is facilitated by the low specific gravity, low relative density, high porosity, no cohesion and the buoyant nature of these sediments. In addition, the low fall velocities of carbonate sands also facilitate sediment removal by backwash from the beach. This causes the transport of these sands away from the beach into deeper lagoon and offshore areas. In the FSM area, wave climate is an important factor influencing erosion mechanics. For normal wave conditions (no storms, typhoons or swell) such as during the survey, waves periods averaged 8 s. Using Soulsby (1998) wave equations of motion, for 8 s waves, the threshold orbital velocities required to move carbonate sediments between 1 and 2 mm in diameter, vary between 0.20 and 0.30 m/s. Using computational methods described by Soulsby (1998), this corresponds to wave heights of less than 1.0 m. For extreme erosion events like storms, typhoons or swells, waves are much larger than 1.0 m, with more plunging and surging breakers approaching the shoreline. While these wave parameters change during extreme events, sediment properties do not. Consequently, the threshold particle stress required to cause motion is easily exceeded, causing significant beach sediment removal and shoreline erosion. Since these extreme events occur on an annual basis and are the main natural erosion forces in the study area, then it can be expected that the FSM atoll islands will continue to experience erosion in the future from extreme events. 7.0 PERFORMANCE AND RELIABILITY OF SEAWALLS AND GROYNES Seawalls and groynes are common on almost all the atoll islands surveyed. Tables 4.1-4.15 indicate the presence of these structures on the various islands, while Tables 4.16.1-4.16.3 gives details of wall types, performance and failure characteristics. Seawalls and groynes are the preferred choice of coastal stabilisation structures on almost all the FSM islands. However, these structures are usually not planned or designed and are poorly constructed. They are constructed by the local residents and usually without sound technical basis for their siting, dimension, construction details and maintenance. In all cases, for the sites surveyed, construction is usually labour intensive and expensive, with several deleterious impacts to the natural environment. Several of these have already been discussed in Section 5.6 and will not be repeated here. For example, on Satawan’s east coast, masonry seawalls along part of this coast incurred in excess of USD$700,000 in labour and material. This is a high capital expenditure, for a single activity, for a small island developing state.


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There are several factors which affect the reliability and performance of seawalls and groynes in FSM. These can be summarised as follow: q

First, many of these structures are not appropriate for the small segments of coast they front.

q

These structures cannot be justified, based on technical soundness, cost, availability of construction material, environmental impacts and alteration of bio-physical processes.

q

In addition, these structures cannot protect the shoreline from extreme oceanographic and weather events, which are usually more erosive and damaging than normal weather and wave processes.

q

These structures temporarily protect only the segment of coastline behind the structure.

q

They cause sediment starvation downdrift of the structure.

q

They cause aggravated erosion downdrift of walls, causing significant erosion embayments.

q

Seawalls cause flanking of the structure since wing walls are not designed or constructed.

q

Seawalls and groynes cause significant reflection of wave energy, onto the beach and into the surf due to their vertical seaward faces.

q

Wave reflection causes aggravated beach scouring and nearshore sediment removal.

q

Scouring causes undermining, leading to foundation failure and toppling of the structure.

q

Walls and groynes are usually founded on brittle beach rock and/or soft, low-bearingcapacity, frictional carbonate sands. These materials deform easily under the structural load, causing foundation settlement and failure of the wall by toppling and collapse.

q

Most seawalls are not backfilled, usually leading to scouring and washout by runup and overtopping typhoon waves, and ultimately collapse.

q

The carbonate reef rock, which is normally used for seawall and groyne construction, is of low specific gravity and is highly porous, with high water absorption. These rock properties do not render them suitable for coastal engineering structures (CIRIA, 1991 and Thorne et al., 1995).

q

Recent carbonate reef rock is of low impact strength to breaking waves (CIRIA, 1991 and Thorne et al., 1995), and consequently can easily fracture on impact by storm and typhoon breaking wa.ves.

q

Walls constructed of these types of aggregate are usually of low strength and are easily dislodged and toppled by waves.

q

Carbonate reef rocks are also of low abrasion resistance to surf-zone processes (CIRIA, 1991, Latham, 1988 and Thorne et al., 1995) and are easily abraded in the surf, leading to strength loss and failure.

q

Several walls are plastered with ASTM Type I, Portland cement/sand mixture and are of mortar. These usually deteriorate due to sulphate reactions of seawater with cement (Neville, 1981), causing strength loss, brittleness and ultimately, collapse of the wall.

q

Where concrete walls are built, ASTM Type I cement is used, also with similar chemical attack and strength loss.

q

Aggregate used for concrete walls is of a varied grain size, from coarse gravel to silt, causing the resultant mixture to have a pitted outer surface, rendering it porous to seawater. This leads to salt water intrusion and chemical decay of the concrete and wave abrasion of the outer pitted surface.


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q

Sand and gravel for concrete seawalls are also of a marine origin, containing chloride and sulphate ions. These seawater ions lead to alteration of the concrete pH and chemistry by chemical attack and decay, leading to cracking of the structure.

q

Concrete walls are usually reinforced with 0.5 in steel bars (re-bars). These are usually placed near or at the outer surface of the structure. Re-bars usually suffer from corrosion and expansion due to salt water and air ingress, causing cracking of the low-tensile-strength concrete. Re-bar corrosion results from chloride ion attack, which causes the breakdown of the passivity of the steel members, leading to corrosion. This chemical decay is well documented in the literature on concrete (Neville, 1981).

q

In addition, expansion and tensile failure of the concrete leads to further salt water ingress and sulphate ions/cement reactions, leading to ettringite formation, expansion of the concrete, strength loss and further cracking (Neville, 1981).

q

Seawalls and groynes usually cause smothering of reef species, destruction of nearshore habitats, development of localised higher energy and turbulent conditions, siltation of nearshore areas, increase in beach erosion and loss of nearshore sediments. These all contribute to deterioration of the reef ecosystem and reduction in carbonate sediment production, beach erosion and loss of nearshore carbonate sediments.

Based on the foregoing data and analysis, one can summarise that seawalls and groynes in the FSM outer atolls are not suitable for the areas where they are placed. They are also poorly designed and constructed considering the local hydrodynamic, geological and environmental conditions, especially extreme events. Further, these structures are not suitable for these low, sandy, small atoll islands, as they usually lead to exacerbated erosion and ultimately coastal land loss. 8.0 CONCLUSIONS Based on the information collected and analysed so far, there are several factors which are responsible for erosion and shoreline retreat in the study area. These can be summarised under two main headings. They are: 1. Natural Processes and 2. Man-made Processes (Table 6.1) q

Natural processes account for significant and continuous erosion on all the islands surveyed. These include waves generated by northeast trades, westerlies, storms and typhoons.

q

Storms and typhoons are the main agents of erosion. Although these are infrequent extreme events, they are the major factors influencing the coastal morphology of these island states.

q

Man-made processes, in particular construction activities, are the main factors affecting the rates and severity of local erosion.

q

Removal of aggregate from the coastal zone has been identified as the single main human factor and key “erosion” process.

q

The inappropriate use of mineral aggregate resources in the coastal zone needs to be carefully monitored and controlled. While these resources are renewable, they are not at the rates equivalent to their removal.

q

The inappropriate use and construction of seawalls and groynes is also a major problem.


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q

The perception that these coastal structures will prevent or reduce erosion should be reexamined.

q

In the context of the local erosion problems, seawalls and groynes serve only to exacerbate the erosion problem and do not reduce nor stop erosion.

q

Construction activities result in death of coastal reef species, either due to reclamation, sediment smothering or pollution. These aspects need to be considered, if future similar construction activities are planned.

q

The importance of a healthy reef biota to the beach and nearshore areas and their importance to contributions of sediments should be emphasised.

9.0 RECOMMENDATIONS FOR SHORELINE MANAGEMENT Based on the fore-going data and discussions, several recommendations can be formulated for reducing coastal erosion and improving shoreline management. These are summarised in Table 7.1. Many of the recommendations emphasise preservation of the natural ecosystem and noninterference with sediment transport and movement along and across the coast. For small atoll islands like those surveyed, non-interference with natural sediment processes cannot be over emphasised. Interference with longshore transport, such as by the construction of sea walls, can cause considerable erosion and should be discouraged. Seawall construction has caused several meters of land loss in several of the islands surveyed. Several meters of land loss is large, when one compares it to the size of some of these islands, which can only be 150-200 m wide, e.g. Losap or Euarapik. For this reason also, buildings should be set back from the coastline, well into the interior of the island. This will reduce the risk of exposure, vulnerability and possible damage from extreme oceanographic events. Communities should also try to re-vegetate coastal areas which have been affected by previous storms or which have been cut or burnt. The vegetation serves as wind breaks and stabilises soils and beach sediments, reducing their erosion by up-rush and backwash. The planting of common locally available coastal species is encouraged. These include mangroves, seaside mahogany, pandanus and coconut trees. Larger species like mahogany and mangroves are particularly encouraged, as these stabilise a larger area of soil and are more sturdy species. The disposal of waste in mangroves and cutting of these species should be discouraged, as they are important coastal stabilising vegetation, in addition to contributing to the productivity of coastal ecosystems, like fisheries and corals (which contribute beach and nearshore sediments). As for aggregates, these may be obtained from summer sandbanks, preferably from adjacent, uninhabited islands or from mainland areas, providing surplus quantities are available. However, even if this activity is pursued, extraction can only be minimal. Large volumes for housing and airstrip construction are neither feasible nor sustainable. Their extraction locally should be reduced and eventually stopped. This point cannot be over-emphasised, as continued removal of material from these small islands contributes to increased exposure to waves and storms,


25

increasing their vulnerability to oceanographic hazards and erosion. This eventually leads to erosion of land area, causing further reduction in size of these already small islands. From the surveys conducted, aggregate extraction from nearshore areas was found to be a major factor contributing to high rates of erosion. Technical investigations and environmental impact assessment (EIAs) should precede major construction activities such as airstrips, reef channel cutting or aggregate mining. These studies will identify the best options for pursuing the desired activities in an environmentally sound manner. As population increases on these atoll islands and societal needs for natural resources increase, such as for aggregate, housing material and land area, efforts must be made to address these needs. This is particularly important if these natural resources are to sustain the existing population and future generations. If the same finite volume of resources is tapped, at a rate increasing with time, then these resources can easily dwindle. Therefore, resource use must be carefully managed and should not impair their capacity to benefit future generations; users should, therefore, consider the total and cumulative effect of their actions. An important issue, which therefore must be addressed by these small island developing states, is the capacity of these small islands to sustain the existing and future demands and needs for aggregate, land area, housing material and living resources in the coastal zone. In addition, changing trends of lifestyle and customs and socio-economic pressure cause changes in societal needs. Particular examples are the departures from traditional thatched housing to concrete buildings and infrastructure/facilities and the need for airstrips to improve efficiency of interisland communication and seawalls and groynes to protect seafront buildings. These changing needs cause a demand for building material and land area, which leads to aggregate mining, nearshore reclamation and coastal construction. These activities cause deleterious impacts in the coastal zone, causing death of reef biota, loss of carbonate-sand-producing organisms, and loss of natural wave breakwaters (coral heads and coral reef rubble). These reduce the natural protection of coastal areas, increasing their vulnerability to extreme oceanographic events, causing exacerbation of local erosion and decrease in land area. Since many of these islands are very small (less than 2-3 km2) and are already affected by high rates of natural erosion, any alteration of natural coastal systems will cause negative impacts along the coastline, ultimately leading to erosion and decrease in land area. If such erosion continues, one option, which may require some consideration within the short term and in the long term, is re-location of the local population. Further to discussions with residents on the islands surveyed, it became apparent that most of the population were unaware of the dynamic relationships which exist between beach processes, erosion, sediment transport, pollution, coastal vegetation and reef dynamics (both biological and physical). The perception that beach activities only affect beach erosion and deposition is widespread. To effectively implement and pursue coastal management guidelines and strategies, this misconception must be clarified. Public awareness of the oceans, the values they represent and the risk they face, must be emphasised. The more aware people become of nearshore processes and coastal systems, the easier it is to use available resources with respect and intelligent care, safeguarding them for future generations. Public awareness and participation in ocean governance and management is also a pre-requisite for the implementation of successful coastal management strategies. It is therefore


26

recommended that a public education/awareness programme be implemented for the island residents, on the use and management of coastal resources and ocean space. In addition, local technical personnel should be trained in coastal zone management to effectively address local issues affecting the islands of FSM. 10.0 REFERENCES CIRIA, 1991. Manual of the Use of Rock in Coastal and Shoreline Engineering. CIRIA Special Publication 83 & CUR Report 154. A. A. Balkema, Rotterdam. Herbich, J. B. 1991. Handbook of Coastal and Ocean Engineering. Volumes 1 & 2. Gulf Publishing, New York. Julien, P.Y. 1995. Erosion and Sedimentation. Cambridge University Press. Latham, J.P. (ed.) 1998. Advances in Aggregate and Armourstone Evaluation. Geological Society, London, Engineering Geology Special Publication, 13. Neville, A. M. 1981. Properties of Concrete. Longman, London. Soulsby, R. 1998. Dynamics of Marine Sands. Thomas Telford, London. Thorne, C. R., Abt, S. R., Barends, F. B. J., Maynord, S. T. and Pilarczyk, K. Y. 1995. River, Coastal and Shoreline Protection. Erosion Control Using Riprap and Armourstone. John Wiley, New York. U.S. Navy, 1996. Global Tropical/Extratropical Cyclone Climatic Atlas. CD-ROM, Version 2.0, September 1996. U. S. Fleet Numerical Meteorology and Oceanography Detachment, National Climatic Data Centre, NOAA & U. S. Naval Meteorology and Oceanography Command. Van Loon, H. 1984. Climates of the Oceans, Volume 15. Elsevier, Amsterdam. VanRijn, L. C. 1989. Handbook of Sediment Transport by Currents and Waves. 2nd Edition. Delft Hydraulics, Netherlands.


27

Table 1.1 Travel itinerary, atoll islands visited and sites surveyed in Pohnpei, Chuuk and Yap States, Federated States of Micronesia. ATOLLS

ISLANDS

Pohnpei Pingelap

Pohnpei Pingelap

Mwoakilloa/Mokil

Mwoakilloa/Mokil

Sapwuafik/Ngatik

Sapwuafik/Ngatik

Nukuoro

Nukuoro

Satawan

Satawan

Losap

Losap

Chuuk Pollap/ Pulap Polowat/ Puluwat

SITES SURVEYED

ARRIVAL TIME

DEPARTURE TIME

1. None 1. Airstrip 2. Lagoon/west coast 3. Windward/east coast 1. Airstrip 2. Lagoon/west coast 3. Windward/east coast 1. Airstrip 2. Lagoon/west coast 3. Windward/east coast 1. Lagoon/west coast 2. Windward/east coast

20.7.98 @ 0400 hours 23.7.98 @ 0915 hours

22.7.98 @ 1839 hours 23.7.98 @ 1600 hours

24.7.98 @ 0745 hours

24.7.98 @ 1600 hours

25.7.98 @ 0725 hours

25.7.98 @ 1400 hours

26.7.98 @ 0930 hours

26.7.98 @ 1512 hours

27.7.98 @ 0645 hours

27.7.98 @ 1600 hours

28.7.98 @ 0615 hours

28.7.98 @ 0945 hours

Weno/Moen Pollap/Pulap

1. Western coast 2. Windward/east coast 1. Western coast 2. Windward/east coast None 1. Western coast

28.7.98 @ 1500 hours 31.7.98 @ 0725 hours

30.7.98 @ 1725 hours 31.7.98 @ 1600 hours

Polowat/Puluwat

2. Windward/north and east coasts 1. Western lagoon coast

31.7.98 @ 1730 hours

1.8.98 @ 1323 hours

1.8.98 @ 1445 hours

1.8.98 @ 1515 hours

1.8.98 @ 1530 hours

1.8.98 @2105 hours

2.8.98 @ 1712 hours

3.8.98 @ 1439 hours

3.8.98 @ 1530 hours

4.8.98 @ 1900 hours

4.8.98 @ 0657 hours

4.8.98 @ 1712 hours

1. Lagoon/west coast 1. Airstrip 2. Lagoon/south coast 3. West and north coasts 1. North coast 2. South coast 1. West and south coasts 2. North and east coasts 1. West coast 2. East coast

6.8.98 @ 0630 hours 6.8.98 @ 1435 hours

6.8.98 @ 1100 hours 6.8.98 @ 1725 hours

6.8.98 @ 1740 hours

6.8.98 @ 1900 hours

7.8.98 2 0733 hours

7.8.98 @ 1030 hours

7.8.98 @ 1105 hours

7.8.98 @ 1300 hours

Alet

2. South and east coasts 3. Windward/north coast 1. Lighthouse/high school site 1. Returned to main island

Polowat/ Puluwat Polowat/ Puluwat Lamotrek

Polowat/Puluwat

Elato

Elato

Fechaulap/ Faraulep

Fechaulap/Faraulep

1. Western/lagoon coast 2. Windward/east coast 1. Western/lagoon coast 2. Windward/east coast 1. South and west coasts

Fechaulap/ Faraulep Ifalik Woleai

Un-named

2. North and east coasts 1. West and east coasts

Woleai

Tagualap

Woleai

Falalis

Woleai

Utagal

Woleai

Saliap

1. South/lagoon coast

7.8.98 @ 1330 hours

7.8.98 @ 1430 hours

Woleai Eauripik

Woleai Eauripik

7.8.98 @ 1555 hours 8.8.98 @ 0718 hours

8.8.98 @ 0100 hours 8.8.98 @ 1300 hours

Ulithi

Mogmog

9.8.98 @ 1400 hours

9.8.98 @ 1850 hours

Yap

Yap

1. Returned to main island 1. South and west coasts 2. Windward north and east coasts 1. South and west coasts 2. North coast 1. End of survey/cruise

10.8.98 @ 0419 hours

12.8.98 @ 1730 hours

Lamotrek

Ifalik Woleai


28

Table 4.1 Coastal problems in Pingelap, Pohnpei State, Federated States of Micronesia. ATOLL Pingelap

ISLANDS Pingelap


SITES 1.

Airstrip

COASTAL PROBLEMS • • • • •

Built on 12 000 m2 of reclaimed shoreline. Aggregate volume of 24 000 m3. Eroded on the seaward aspect. scoured segments 25-30 m long and 5 m wide. Settlement, with cracking and warping, especially along the peripheral seaward aspect. • Some sand and gravel accretion to the north end of the airstrip. • The south/sheltered and landward side of the airstrip is stagnant. • Accretion of the south aspect with mud and some sand since construction.

2. Lagoon/west coast

• Negligible erosion. • Some accretion over the past years. • Beach sand removal for housing, pathways, seawalls, water catchments and the airstrip. • Natural erosion by high spring tides and cyclones.

3. Windward/east coast

• High-energy eroding coast. • High erosion due to trade wind waves. • Overtopping and runup during high-water tides, storms and typhoons. • Erosion is continuous and by natural processes, especially trade wind waves, storms and spring tides. • Mining of back-reef coral rubble for domestic use. • 0.5-1.0 m erosion scarps at upper beach.

29

Table 4.2 Coastal problems in Mwoakilloa, Pohnpei State, Federated States of Micronesia. ATOLL Mwoakilloa /Mokil

ISLANDS Mwoakilloa/ Mokil

SITES

COASTAL PROBLEMS

1. Airstrip

• • • • •


• Relatively deep lagoon subject to sediment accretion and storage. • Some erosion and accretion. • Shore front buildings. • Many concrete buildings. • Scouring in front of rubble and masonry sea walls • Scouring downdrift of coral rubble groynes. • Flanking at sea walls. • Beach sand removal for housing, pathways, seawalls, water catchments and the airstrip. • Natural erosion by high spring tides and cyclones. • Accelerated erosion due to mining, sea wall and housing construction.


• • • •

Built on 12 000 m2 of reclaimed shoreline. Aggregate volume of 28 000 m3. Eroded to the north and east. scoured segments 5-10 m long and 3-5 m wide. Settlement, with cracking and warping, especially along the peripheral seaward aspect. • Some sand and gravel accretion at the south/sheltered end. • Erosion by natural processes, especially storms and typhoons and trade wind waves.

• • • • • •


High-energy eroding coast. High erosion due to trade wind waves. Coastal recession of several metres. Overtopping and runup during high-water tides, storms and typhoons. Exposed tree roots at upper beach. Toppled coconut and pandanus trees. Erosion is continuous and by natural processes, especially trade wind waves during storms and high spring tides. Mining of back-reef and beaches for domestic use and for aggregate when the airstrip was built. 0.5-1.0 m erosion scarps at upper beach. Failed/toppled sea walls.

30

Table 4.3 Coastal problems in Sapwuafik, Pohnpei State, Federated States of Micronesia. ATOLL Sapwuafik/ Ngatik

ISLANDS Sapwuafik/ Ngatik


SITES

COASTAL PROBLEMS

1. Airstrip

• Being built on 12 000 m2 of reclaimed back-reef coastline. • Estimated aggregate volume of 30 000 m3 when completed. • Erosion along the seaward/east and the western/lagoon aspects of the airstrip. • Erosion by NE trades. • scoured segments 5-10 m long. • Channel formation by sediment scouring and removal along the west aspect. • Significant sand and gravel accretion to the west of the airstrip. • Formation of sand shoals to the west. • Remains of a 20-year-old airstrip foundation, west of the present structure. • Remains are two concrete walls, with a 25 m spacing 100 m long and 0.7 m wide. • These walls have caused sand accretion between them and to the lee/west side of the new airstrip site.

2. Lagoon/east coast

• Relatively deep lagoon, subject to sediment accretion and storage. • Some erosion and accretion. • 0.5-0.7 m erosion scarps. • Scouring in front and downdrift of rubble sea walls. • Flanking at sea walls. • Beach sand removal for housing, pathways, seawalls, water catchments and the airstrip. • Natural erosion by high spring tides and cyclones. • Accelerated erosion due to mining and sea wall construction.

3. Windward/west coast

• High-energy eroding coast. • Overtopping and runup during high-water tides, storms and typhoons. • Erosion is by natural processes, especially by trade wind waves and during storms and spring tides. • Mining of back-reef and beach coral rubble for domestic use, including sea walls and for aggregate for the airstrip. • 0.5-2.5 m erosion scarps. • Exposed tree roots at upper beach. • Toppled coconut and pandanus trees. • Scouring in front of rubble and masonry sea walls and downdrift of coral rubble groynes. • Flanking at sea walls. • Failed/toppled sea walls.

31

Table 4.4 Coastal problems in Nukuoro, Pohnpei State, Federated States of Micronesia. ATOLL Nukuoro

ISLANDS Nukuoro


SITES

COASTAL PROBLEMS


• • • • •


• High energy eroding coast. • High erosion due to trade wind waves. • Overtopping and runup during high water tides, storms and typhoons. • Coastal recession of several metres. • Erosion is continuous by natural processes, especially trade wind waves storms and spring tides. • Mining of back-reef and beach coral rubble for pathways, some houses, rubble sea walls. • Straightening of coastline. • 0.5-1.75 m erosion scarps to the north. • Exposed mahogany tree roots at upper beach. • Toppled coconut and pandanus trees. • Scouring in front of rubble and masonry sea walls and downdrift of coral rubble groynes. • Flanking at sea walls.

Relatively calm and deep lagoon. Lagoon sediment accretion and storage. Shore front buildings. Some erosion to the south. Flanking of rubble sea walls.

32

Table 4.5 Coastal problems in Satawan, Chuuk State, Federated States of Micronesia. ATOLL Satawan

ISLANDS

SITES

1. Satawan

1. Western coast



COASTAL PROBLEMS • Shore front buildings. • Many concrete buildings. • Mining of beach and back-reef for sand, gravel and rubble for sea walls, water catchments, housing and pathways. • Construction of steel-reinforced concrete sea walls. • Flanking of rubble, masonry and concrete sea walls. • Scouring at base of sea walls. • Failed/toppled sea walls. • Localized erosion due to coastal mining and sea wall construction. • 0.5-0.75 m erosion scarps. • Natural erosion by high spring tides and cyclones. • Accelerated erosion due to mining and sea wall construction. • Mining of beach and back-reef for sand, gravel and rubble for sea walls, water catchments, housing and pathways. • Sand pits on NE coast. • 0.5-1.5 m erosion scarps. • Overtopping and runup during high water tides, storms and typhoons. • Construction of steel-reinforced concrete sea walls, NE and E. • Flanking of rubble, masonry and concrete sea walls. • Scouring at base of sea walls. • Failed/toppled sea walls. • Localized erosion due to coastal mining and sea wall construction. • Exposed tree roots and fallen trees. • Dry season accretion at NE tip, with sand bar and shoal formation. • High erosion due to trade wind waves. • Natural erosion by high spring tides and cyclones.

33

Table 4.6 Coastal problems in Losap, Chuuk State, Federated States of Micronesia. ATOLL Losap

ISLANDS 1. Losap


SITES

COASTAL PROBLEMS

1. Western coast

• 10 m long rubble groyne as docking facility/mid west coast. • Erosion downdrift/south of groyne. • Shore front buildings. • Some concrete buildings. • Mining of beach and back-reef for sand, gravel and rubble for sea walls, water catchments, housing and pathways. • Construction of rubble and masonry sea walls to the W and NW. • Flanking sea walls. • Scouring at base of sea walls. • Failed/toppled sea walls. • Localized erosion due to coastal mining and sea wall construction. • 0.25-0.5 m erosion scarps. • Natural erosion by high spring tides and cyclones. • Accelerated erosion due to mining, housing and sea wall construction.


• Cutting of localized red mangrove trees for fuel, houses and fish pots. • Garbage disposal in mangroves. • Housing construction in mangroves. • Overtopping and runup during high water tides, storms and typhoons. • High erosion due to trade wind waves. • Construction of rubble sea walls and NE and SSW tips. • Flanking of sea walls. • Scouring at base of sea walls. • Failed/toppled sea walls. • Localized erosion due to coastal sea wall construction. • High erosion at NE tip due to inter-island channeling and turbulence. • Natural erosion by high spring tides and cyclones.

34

Table 4.7 Coastal problems in Pollap, Chuuk State, Federated States of Micronesia. ATOLL Pollap/ Pulap

ISLANDS 1. Pollap/ Pulap

SITES

COASTAL PROBLEMS

1. West coast

• • • • • • • • • • • •

Steep beaches affected by westerly winds. Wave and high tide overtopping and runup. Exposed coconut tree roots. Some fallen trees. Rubble mining in near-shore area. Construction of vertical rubble sea walls. Sea walls to the SW. All sea walls have failed. Flanking and scouring at wall base. Sediment accretion in adjacent lagoon. Natural erosion by high spring tides and cyclones. Accelerated erosion due to mining and sea wall construction.

2. Windward/ north and east coasts

• • • • • • • • • • • •

High-energy coastline. Exposed natural eroded coast. High erosion due to trade wind waves. Wave and high tide overtopping and runup. Exposed coconut tree roots. Some fallen trees. Construction of vertical rubble sea walls. Sea walls to the SE, E and N. Flanking and scouring at wall base. All sea walls have failed. Failures more than three times over the past 20 years. Sediment accretion in surf zone adjacent to rubble walls at SW tip. Poor circulation and partly stagnant conditions in this area. Concrete piled jetty to the SE. Scouring at pile base and adjacent beach. Beach sand erosion downdrift/south of jetty. Silting of nearshore lagoon area behind reef. Sedimentation of live coral heads. 0.25-0.75 m erosion scarps. Sand mining from bars and berm at SW and NNW tips. Sand pits on both bars. Mining of sand for water catchments, housing and pathways. Mining of backreef rubble for sea walls. Natural erosion by high spring tides and cyclones.

• • • • • • • • • • • •


35

Table 4.8.1 Coastal problems in Polowat, Chuuk State, Federated States of Micronesia. ATOLL Polowat/ Puluwat

ISLANDS 1. Polowat/ Puluwat

SITES

COASTAL PROBLEMS

1. West/lagoon coast

• • • • •

2. South and east coasts

• Beach sand mining for housing. • Storm, typhoon ad high tide erosion. • Coastline indentation, by erosion, to the SW and SE corners. • Erosion scarps up to 0.75 m. • Exposed coconut tree roots. • Some fallen trees. • Rubble sea wall construction. • Flanking and basal erosion at wall. • Partial failure of sea wall. • Natural erosion by spring tides and typhoons. • Accelerated erosion due to mining and sea wall construction.

3. Windward/ north coast

• • • • • • • • • • • • • • • •

Beach sand mining for housing. Accelerated erosion due to mining. Lagoon sand and silt accretion. Poor circulation and flushing. Some erosion to the NW end.

High energy coastline. High erosion due to trade wind waves. Exposed natural eroded coast. Storm and high tide overtopping and runup. Exposed tree roots. Some fallen coconut trees. Sediment accretion in surf zone adjacent to the NW tip. Sand shoals in this area. Poor flushing in this area. Silting of adjacent lagoon area to the SE. Sedimentation of live coral heads. 0.25-0.50 m erosion scarps. Sand mining from bars and shoals at NW tip. Sand pits on bar. Mining of sand for water catchments, housing and pathways. Natural erosion by high spring tides and cyclones.

continued


36

Table 4.8.2 Coastal problems in Alet, Chuuk State, Federated States of Micronesia. ATOLL Polowat/ Puluwat

ISLANDS 2. Alet


SITES 2. Lighthouse/ high school site

COASTAL PROBLEMS • • • • • • •

High energy coastline. Shore front building. Exposed natural eroded coast. Typhoon and high tide overtopping and runup. Exposed tree roots. Some fallen coconut trees. Natural erosion by high spring tides, westerlies and cyclones

37

Table 4.9 Coastal problems in Lamotrek, Yap State, Federated States of Micronesia. ATOLL Lamotrek

ISLANDS

SITES

1. Lamotrek

2. Western/ lagoon coast

• About 30 m of land loss at NNW tip since 1950’s. • Sand accretion and shoals at the SW and NW tips. • Deep lagoon with steep near-shore slope to Wcentral. • Lagoon is a sediment sink and accretion site. • Possible gravity flow of near-shore sands into the deep lagoon. • Active erosion ant the NW and SW corners. • Erosion scarps up to 0.70 m. • Exposed coconut tree roots. • Some fallen trees. • Natural erosion by spring tides, westerlies and typhoons. • Overtopping of shoreline during spring high tides and typhoons. • Sand and gravel mining of beaches from the W and SW corners. • Accelerated erosion due to mining.

3. Windward/ east coast

• • • • • • • • •


COASTAL PROBLEMS

High energy coastline. Exposed natural eroded coast. High erosion due to trade wind waves. Storm and high tide overtopping and run-up. Exposed tree roots. Some fallen coconut trees. 0.25-1.25 m erosion scarps. Sand and gravel mining from S and SW beaches. Mining of sand for water catchments, housing and pathways. • Accelerated erosion due to mining. • Natural erosion by high spring tides and cyclones.

38

Table 4.10 Coastal problems in Elato, Yap State, Federated States of Micronesia. ATOLL Elato

ISLANDS 1. Elato

SITES 1. Western/ lagoon coast

COASTAL PROBLEMS • • • • • • • • • • •



• • • • • • • • • • • •

Natural erosion and loss at NNW tip. Sand accretion and shoals at the SW tip. Deep lagoon with steep near-shore slope to W-central. Lagoon is a sediment sink and accretion site. Possible gravity flow of near-shore sands into the deep lagoon. Active erosion at the SSW and SW corners. Erosion scarps up to 0.50 m. Exposed coconut tree roots. Some fallen trees to the SW. Natural erosion by spring tides, westerlies and typhoons. Overtopping of shoreline during spring high tides and typhoons.

High energy coastline. Exposed natural eroded coast. High erosion due to trade wind waves. Storm and high tide overtopping and run-up. Shorefront buildings. Exposed tree roots. Some fallen trees. 0.30-1.50 m erosion scarps. 0.80 m scarps to the SE. More than 10 m of land loss to the SSE and SE. Sand and gravel mining from S and SW beaches. Natural erosion by high spring tides, trade wind waves and cyclones.

39

Table 4.11.1 Coastal problems in Fechaulap, Yap State, Federated States of Micronesia. ATOLL Fechaulap /Faraulep

ISLANDS Fechaulap /Faraulep


SITES

COASTAL PROBLEMS

1.

South and west coasts

• Natural erosion at NNW tip. • Sand accretion and shoals to the W and SW backreef. • Active erosion at the SSW and SW corners. • Erosion scarps up to 0.80 m. • Exposed coconut tree roots. • Fallen coconut and dead mahogany trees to the SW. • Natural erosion by spring tides, westerlies and typhoons. • Overtopping of shoreline during spring high tides and typhoons. • Sand mining at the SW and SSW. • Rubble groyne construction along the W coast. • High erosion along the west coast, downdrift of groynes. • Extremely eroded W and SW coasts, accelerated by mining and groyne construction.

1.

North and east coasts

• • • • • • • • • •

High energy coastline. Exposed natural eroded coast. High erosion due to trade wind waves. Storm and high tide overtopping and run-up. Exposed tree roots. Some fallen trees. 0.30-1.50 m erosion scarps. Several metres of land loss. Sand and gravel mining from S and SW beaches. Natural erosion by high spring tides, trade wind waves and cyclones.

40

Table 4.11.2 Coastal problems in Fechaulap, Yap State, Federated States of Micronesia. ATOLL Fechaulap /Faraulep

ISLANDS Un-named


SITES

COASTAL PROBLEMS

1. West coast

• Eroded by westerlies, typhoons and spring high tide. • 0.30-0.40 m erosion scarps. To the SW. • Up to 1.50-2.0 m scarps to the NW. • Large scarps produced during extreme events.

2. East coast

• Relatively stable, subject to considerable accretion of sand, gravel and rubble. • Recent growth of coastal shrub and other tree species. Some several years old. • The only site surveyed in FSM, which shows considerable accretion. • Accretion sites are greater than 400 m wide and 700 m long. • Elevations of accretion areas are similar to and sometimes greater than on adjacent land.

41

Table 4.12 Coastal problems in Ifalik, Yap State, Federated States of Micronesia. ATOLL Ifalik

ISLANDS 1. Ifalik

SITES 1.


Lagoon/west coast

COASTAL PROBLEMS • Groyne construction to the SW, from late 1800’s/German occupation. • Erosion to downdrift/south of groynes. • Erosion to the SW. • Erosion scarps up to 0.30 m. • Exposed coconut tree roots. • Some fallen coconut trees. • Accretion of lagoon by typhoon deposits. • Shallowing of lagoon to the SW of island. • Accretion caused inter-island sedimentation/ merging of main island with adjacent island to the south. • Island merging resulted from typhoon event. • Lagoon accretion caused smothering and death of corals. • Present lagoon circulation is poor due to accretion.

42

Table 4.13.1 Coastal problems in Woleai, Yap State, Federated States of Micronesia. ATOLL

ISLANDS

Woleai

1. Woleai

SITES

COASTAL PROBLEMS

1. Airstrip

• • • •

2. Lagoon/ south coast

• Several metres of land loss at NNW tip since 1970’s. • Sand and gravel accretion to the SW corner, with shoaling during summer months. • Erosion pockets along length of the coast. • 1.0-1.50 m erosion scarps. • Exposed tree roots and fallen coconut trees. • Deep lagoon with steep near-shore slope to S-central. • Lagoon is a sediment sink and accretion site. • Natural erosion by spring tides, westerlies and typhoons. • Sand and gravel mining of beaches from the SW corner. • Possibly accelerated erosion due to mining.

3. West and north coasts

• Natural erosion to the W and NW by westerlies, spring tides and typhoons. • Erosion scarps up to 1.75 m. • Exposed coconut and mahogany tree roots. • Fallen coconut and dead mahogany trees to the SW. • Overtopping of shoreline during spring high tides and typhoons. • Sand mining at the SW and SSW. • Rubble and masonry wall construction along the mid-W coast. • Sand and gravel mining for housing, roads and walls. • Mining of beaches and back-reef areas. • Erosion accelerated by mining activities.

Erosion along the seaward/northeast of the airstrip. Erosion by NE trade wind waves. 5-15 m long scoured segments. Concrete and masonry sea wall construction for coastal protection. • Flanking of sea wall. • Sea wall construction has caused erosion downdrift/south of the structure.

continued


43

Table 4.13.2 Coastal problems in Tagaulap, Yap State, Federated States of Micronesia. ATOLL

ISLANDS

SITES

COASTAL PROBLEMS

Woleai

2. Tagualap

1. North coast

• • • • • • • • •

High energy coastline. Exposed natural eroded coast. High erosion due to trade wind waves and swells. Storm and high tide overtopping and run-up. Exposed coconut and mahogany tree roots. Some fallen coconut and mahogany trees. 0.30-1.25 m erosion scarps. Several metres of land loss to the NW. Natural erosion by high spring tides, trade wind waves and cyclones.

2. South coast

• • • • • •

Active erosion at the SSW and SW corners. Erosion scarps up to 0.80 m. Exposed coconut tree roots. Fallen coconut and dead mahogany trees to the SE. Natural erosion by spring tides, westerlies and typhoons. Overtopping of shoreline during spring high tides and typhoons.

continued


44

Table 4.13.3 Coastal problems in Falalis, Yap State, Federated States of Micronesia. ATOLL

ISLANDS

Woleai

3. Falalis

SITES

COASTAL PROBLEMS

1. West and south coasts

• Natural erosion to the W and SW by westerlies, spring tides and typhoons. • Erosion scarps up to 2 m to the SW. • Exposed coconut tree roots. • Fallen coconut trees to the SW. • Overtopping of shoreline during spring high tides and typhoons.

2. North and east coasts

• Natural erosion by trades wind waves, spring tides and typhoons. • 0.30 m erosion scarps. • Exposed coconut tree roots. • Fallen coconut trees to the NE. • Shorefront buildings. • Overtopping of shoreline during spring high tides and typhoons. • Water ponding in depressions due to run-up.


45

Table 4.13.4 Coastal problems in Utagal, Yap State, Federated States of Micronesia. ATOLL

ISLANDS

Woleai

4. Utagal

SITES

COASTAL PROBLEMS

1. West coast

• Natural erosion to the W and SW by westerlies, spring tides and typhoons. • 0.30 m erosion scarps to the SW. • Exposed coconut tree roots. • Fallen coconut trees to the SW. • Overtopping of shoreline during spring high tides and typhoons. • Burning of shoreline mahogany trees.

2. East coast

• Natural erosion by trades wind waves, spring tides and typhoons. • 0.30-0.50 m erosion scarps. • Exposed coconut tree roots. • Fallen coconut trees to the NE. • Shorefront buildings. • Overtopping of shoreline during spring high tides and typhoons. • Water ponding in depressions due to run-up. • Burning of shoreline mahogany trees. • Some sand mining for sea wall construction, pathways and some buildings. • Steel-reinforced concrete sea walls to the SE. • Flanking of sea wall. • Scouring of beach at wall base. • Ponding of overtopped water behind sea wall. • Rubble groyne construction to the SE. • Erosion west/downdrift of groynes. • 0.50 m erosion scarps.

continued


46

Table 4.13.5 Coastal problems in Saliap, Yap State, Federated States of Micronesia. ATOLL

ISLANDS

Woleai

5. Saliap

SITES 1. South/ Lagoon coast


COASTAL PROBLEMS • Natural erosion by trades wind waves, spring tides and typhoons to the SE. • Rubble groyne construction along the mid–south coast. • Erosion west/downdrift of groynes. • 0.50-0.70 m erosion scarps. • Exposed mahogany and coconut tree roots. • Fallen coconut trees to the SE. • High beach water table. • Seepage from land at low tide. • Saturated beach sediments, easily eroded. • Near-shore/lagoon sedimentation. • Development of shoals to the W and SW. • Summer sand accretion to the W and SW and in the interisland channels. • Erosion and accretion are by natural processes.

47

Table 4.14 Coastal problems in Eauripik, Yap State, Federated States of Micronesia. ATOLL Eauripik

ISLANDS 1. Eauripik

SITES 1.

South and west coasts

COASTAL PROBLEMS • • • • • • • • • • • • • • •

2.

Windward north and east coasts

• • • • • • • • • • • • • • • • • •


Erosion to the W and SW. Sand accretion and shoals to the W and SW back-reef. Active erosion at the SE, SSW and SW corners. Erosion scarps up to 1.30 m to the SW and 0.80 m to the SE. Exposed coconut tree roots. Fallen coconut and dead mahogany trees to the SW. Natural erosion by spring tides, westerlies and typhoons. Overtopping of shoreline during spring high tides and typhoons. Sand, gravel and rubble mining on beach and back-reef. Mining for housing, sea walls, groynes and pathways. Rubble groyne construction along the S and SE coasts. Erosion west/downdrift of groynes. Seawalls along the mid-south coast. Scouring around groynes and sea walls. Extremely eroded S, W and SW coasts accelerated by mining and groyne construction. Natural erosion accelerated by mining and construction. Active erosion at the SE, SSW and SW corners. Erosion scarps up to 0.50 m. Exposed coconut tree roots. Fallen coconut trees to the NW and NE. Natural erosion by spring tides, westerlies and typhoons. Overtopping of shoreline during spring high tides, trade wind waves and typhoons. Sand, gravel and rubble mining on beach and backreef. Mining for housing, sea walls, groynes and pathways. Removal of rubble on reef crest and flat. Rubble groyne construction along the mid-north and NE coasts. Beachfront buildings. Coastal reclamation in surf zone. Reclamation by rectangular rubble walls, with sand and gravel backfill. Erosion west/downdrift of groynes, sea walls and reclaimed areas. Seawalls along the mid-south coast. Scouring around groynes and sea walls. Extremely eroded coast accelerated by mining, reclamation, sea wall and groyne construction.

48

Table 4.15 Coastal problems in Ulithi, Yap State, Federated States of Micronesia. ATOLL

ISLANDS

Ulithi

1. Mogmog

SITES

COASTAL PROBLEMS

1. South and west coasts

• Pier construction (World War II) along the mid-south coast. • Scouring around piers. • Mining of beaches for aggregate for housing, pathways and catchments. • Erosion by natural processes, accelerated by mining.

3.

• Exposed natural eroded coast. • High erosion due to trade wind waves and high spring tides. • Storm and high tide run-up. • Exposed tree roots. • Some fallen trees. • 0.30-1.50 m erosion scarps. • Several metres of land loss. • Sand and gravel mining from back-reef and beach. • Natural erosion by high spring tides, trade wind waves and cyclones.


North coast

49

Table 4.16.1 Types of rubble sea walls constructed, failure types and reasons for failure on the atoll islands surveyed, Federated State of Micronesia. TYPES OF SEA WALLS Interlocking coral reef rubble

CHARACTERISTICS

FAILURE TYPES

Usually 1.0-2.0 m high. 0.25-0.75 m wide. Vertical seaward face. No return/wing walls. Interlocking coral rubble. Porous and permeable. No backfill. Soft/beach sand foundation. No foundation improvement. No toe protection. No re-vegetation of site. Rubble between 0.15-0.30 m in diameter. • Aggregate is highly angular and porous. • Rubble and fine aggregate is light weight/low specific gravity.

• Toe erosion. • Crest failure. • Partial or total collapse. • Erosion and removal of rubble units. • Abrasion of the seaward face. • Washout of the foundation footing. • Scouring at base. • Flanking downdrift. • Settlement.

• • • • • • • • • • • •

REASONS FOR FAILURE • • • • • • • •

• • • • • •

• • • •


Spring high tide erosion. Storm erosion Typhoon erosion. Scouring and structural failure. Removal of rubble by impacting waves. Loss of strength due to abrasion. Foundation settlement. Interference with longshore transport downdrift sediment flanking and updrift impoundment. Inadequate strength to resist wave impact. Inadequate stability of rubble units. Inadequate weight of rubble units. Inadequate foundation support. Toe erosion and failure by wave reflection. Change in offshore bathymetry due to erosion on beach and accretion nearshore. Lowering of beach due to mining. Under-estimation of wave climate and environmental loading. Poor design and construction. Inappropriate design and solution to erosion problem.

50

Table 4.16.2 Types of masonry sea walls constructed, failure types and reasons for failure on the atoll islands surveyed, Federated State of Micronesia.

TYPES OF SEA WALLS Masonry using reef rubble

CHARACTERISTICS

FAILURE TYPES

• Usually 1.0-2.0 m high, sometimes up to 6m. • 0.25-0.75 m wide. • Vertical or inclined seaward face. • No return/wing walls. • Not free draining. • No backfill. • Soft and compressible beach sand and gravel foundation. • No or poor foundation improvement. • No toe protection. • No re-vegetation of site. • Rubble 0.15-0.40 m in diameter. • Mortar of medium to coarse, angular and friable coral beach sand. • Aggregate is highly angular and porous. • Rubble and fine aggregate is light weight/low specific gravity. • Cemented with mortar, Portland cement, ASTM Type I. • Outer face is plastered rough with asperities, or not plastered.

• Toe erosion. • Crest failure. • Partial or total collapse. • Erosion and removal of rubble units. • Abrasion of seaward face. • Washout of foundation footing. • Scouring at base. • Flanking downdrift. • Mortar cracking and spalling. • Settlement.

REASONS FOR FAILURE • • • • • • • •

• • • • • • •

• • • •


Spring high-tide erosion. Storm erosion Typhoon erosion. Scouring and structural failure. Removal of rubble by impacting waves. Loss of strength due to abrasion. Foundation settlement. Interference with longshore transport downdrift sediment flanking and updrift impoundment. Inadequate strength to resist wave impact. Inadequate stability of rubble units. Inadequate weight of rubble units. Inadequate foundation support. Inadequate drainage. Toe erosion and failure by wave reflection. Change in offshore bathymetry due to erosion on beach and accretion nearshore. Lowering of beach due to mining. Under-estimation of wave climate and environmental loading. Poor design and construction. Inappropriate design and solution to erosion problem.

51

Table 4.16.3 Types of concrete sea walls constructed, failure types and reasons for failure on the atoll islands surveyed, Federated State of Micronesia. TYPES OF SEA WALLS Steel-reinforced concrete

CHARACTERISTICS • • • • • • • • • • • •

• • • • • • • • • •

Usually 1.0-2.0 m high. 0.25-0.75 m wide. Vertical seaward face. No return/wing walls. Not free draining. No backfill. Soft/beach sand foundation. No or poor foundation improvement. No toe protection. No re-vegetation of site. Rubble between 0.15-0.30 m in diameter. Concrete of medium to coarse, angular and friable coral beach sand and gravel. Aggregate is highly angular and porous. Aggregate contains Cl- and SO42- ions from seawater. Rubble and fine aggregate is light weight and of low specific gravity. Cemented with mortar, Portland cement, ASTM Type I. Reinforced with 1.25cm diameter steel rods. Reinforced with steel mesh. Reinforcement at or near to plastered or concrete outer surface. Coated concrete is pitted, porous and permeable. Outer face is plastered rough, with aperities, .or not plastered. No weep holes.


FAILURE TYPES • Toe erosion. • Crest failure. • Partial or total collapse. • Erosion and removal of rubble units. • Abrasion of seaward face. • Washout of foundation footing. • Scouring at base. • Flanking downdrift. • Concrete cracking and spalling. • Mortar cracking and spalling. • Foundation and structural settlement. • Rebar corrosion and expansion. • Tensional cracking due to rebar corrosion and concrete expansion.

REASONS FOR FAILURE • • • • • • • • •

• • • • • • •

• • • •

Spring high-tide erosion. Storm erosion Typhoon erosion. Scouring and structural failure. Removal of rubble by impacting waves. Loss of strength due to abrasion. Loss of strength due to rebar corrosion. Foundation settlement. Interference with longshore transport downdrift sediment flanking and updrift impoundment. Inadequate strength to resist wave impact. Inadequate stability of rubble units. Inadequate weight of rubble units. Inadequate foundation support. Inadequate drainage. Toe erosion and failure by wave reflection. Change in offshore bathymetry due to erosion on beach and accretion nearshore. Lowering of beach due to mining. Under-estimation of wave climate and environmental loading. Poor design and construction. Inappropriate design and solution to erosion problem.

52

Table 6.1 Reasons for coastline erosion and shoreline degradation.

REASONS FOR COASTAL EROSION AND SHORELINE DEGRADATION

NATURAL PROCESSES q

NATURAL EROSION BY SPRING TIDES, TRADE WINDS, WESTERLIES, WINTER SWELLS AND TYPHOONS.

q

CORAL DAMAGE DUE TO SEDIMENT ACCRETION AND SMOTHERING .

MAN - MADE PROCESSES q

MINING/EXTRACTION OF BEACH SAND, GRAVEL AND REEF RUBBLE.

q

SHORELINE RECLAMATION - CONSTRUCTION.

q

INAPPROPRIATE SEA WALL AND GROYNE DESIGN.

q

DESTRUCTION OF SHORELINE VEGETATION.

q

COASTAL POLLUTION - DEATH OF MANGROVES AND CORALS.

q

CORAL DAMAGE DUE TO SEDIMENT ACCRETION AND SMOTHERING.


53

Table 7.1 Recommendations for reducing coastal erosion.

RECOMMENDATIONS FOR REDUCING COASTAL EROSION

q

DO NOT CONSTRUCT SEA WALLS AND GROYNES.

q

DO NOT RECLAIM BEACHES, MANGROVES AND REEF AREAS.

q

DO NOT MINE THE BEACHES, SURF ZONE OR BACK-REEF AREAS.

q

DO NOT BLAST THE REEF OR CUT REEF CHANNELS.

q

DO NOT BUILD ALONG THE BEACHFRONT.

q

BUILDINGS SHOULD BE SET BACK FROM THE SHORELINE.

q

DO NOT DESTROY SHORELINE VEGETATION.

q

RE-VEGETATE THE COASTLINE.

q

DO NOT DISPOSE OF WASTE AND GARBAGE IN MANGROVES AND REEFS.

q

OBTAIN AGGREGATE FROM ADJACENT, UNINHABITED ISLANDS OR THE MAINLAND.

q

NOURISH BEACHES WHERE POSSIBLE.

q

AIRPORT CONSTRUCTION SHOULD BE PRECEDED BY EIA’S/EIS.

q

RELOCATE/REDISTRIBUTE POPULATION IN CROWDED AREAS.

q

EDUCATE PUBLIC ON THE USE AND MANAGEMENT OF COASTAL RESOURCES.


54

Table 7.2 Recommendations for reducing coastal erosion in Pohnpei, Chuuk and Yap States, Federated States of Micronesia. ATOLLS Pingelap Mwoakilloa/Mokil Sapwuafik/Ngatik Nukuoro Satawan Losap Pollap/Pulap Polowat/Puluwat Polowat/Puluwat Lamotrek Elato Fechaulap/Faraulep Ifalik Woleai Woleai Woleai Woleai Woleai Eauripik Ulithi

RECOMMENDATIONS∗

ISLANDS Pingelap Mwoakilloa/Mokil Sapwuafik/Ngatik Nukuoro Satawan Losap Pollap/Pulap Polowat/Puluwat Alet Lamotrek Elato Fechaulap/Faraulep Ifalik Woleai Tagualap Falalis Utagal Saliap Eauripik Mogmog

1, 2, 3, 4, 5, 8, 10, 12, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 143, 14 1, 2, 3, 4, 5, 7, 8, 10, 12, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14 1, 2, 3, 4, 5, 7, 8, 10, 12, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14 1, 2, 3, 4, 5, 6, 7, 8, 10, 13, 14

∗NUMBERS IN RECOMMENDATION COLUMN ARE FOR ITEMS BELOW: 1: DO NOT CONSTRUCT SEA WALLS AND GROYNES 2: DO NOT RECLAIM BEACHES, MANGROVES AND REEF AREAS. 3: DO NOT MINE THE BEACHES, SURF ZONE OR BACK-REEF AREAS. 4: DO NOT BLAST THE REEF OR CUT REEF CHANNELS. 5: DO NOT BUILD ALONG THE BEACHFRONT. 6: BUILDINGS SHOULD BE SET BACK FROM THE SHORELINE. 7: DO NOT DESTROY SHORELINE VEGETATION. 8: RE-VEGETATE THE COASTLINE. 9: DO NOT DISPOSE OF WASTE AND GARBAGE IN MANGROVES AND REEFS. 10: OBTAIN AGGREGATE FROM ADJACENT, UNINHABITED ISLANDS OR THE MAINLAND. 11: NOURISH BEACHES WHERE POSSIBLE. 12: AIRPORT CONSTRUCTION SHOULD BE PRECEDED BY EIA’S/EIS. 13: RELOCATE/REDISTRIBUTE POPULATION IN CROWDED AREAS. 14: EDUCATE PUBLIC ON THE USE AND MANAGEMENT OF COASTAL RESOURCES.


53

Volume 2: FIGURE & PLATES


Figure 1.1. Location map of the study area.

54


55

Plate1: Coral rubble sea wall construction along the east coast of Nukuoro island. The sea wall is about 2 m high and 0.5 m wide, with a vertical seaward face. The wall is free draining, without backfill and is about 1m deep. It is founded on beach gravel and rubble. The beach fronting the wall is 5 m wide, with a 5–8 0 slope. Photo looking south.

Plate 2: Utilization of coastal area. Construction of an outhouse in the surf zone along the east coast of Nukuoro island. These are typical along the east and west coasts. Coral rubble, extracted from the adjacent beaches, is used for construction. The structure is about 2 m above the water line. The structure also acts like a groyne and causes some sand accretion on the updrift/north aspect. Photo looking north.


56

Plate 3: Coastal land loss and erosion along the southwest coast of Sapwuafik island. Note exposed pandanus and coconut palm roots. Scouring and sediment removal is aggressive around tree roots during high tides. Many trees have fallen into the surf zone in this area. Photo looking south.

Plate 4: Coastal land loss and exposure of mahogany tree roots along the east coast of Sapwuafik island. These trees are more than 70 years old. Their exposure at the edge of the shore suggests continuous erosion and shoreline retreat. The beach is 10 m wide, with an 8-10 o slope. The beach is composed largely of medium to coarse, coral and foraminiferal sands, with coral gravel. Note the high-water, coarse sediment deposit at the vegetation line. It is coarse gravels and cobbles. Photo looking north. SOPAC Technical Report 268, Maharaj, 1998

57

Plate 5: Coral rubble seawall along the east coast of Sapwuafik island. These walls are being built with cobbles and small sub-rounded to elongate boulders. The wall is built on the upper beach deposits, while the land edge is trimmed and cleared. The seaward front of the structure is protected by large coral boulder rip-rap, averaging 40cm in diameter. Photo looking west.

Plate 6: Coastal land loss and exposure of coconut palm roots along the west coast of Pingelap island. Note some small, partly collapsed palms in the background and exposed tree roots. The beach is 12 m wide, with a 12 0 slope. It is composed largely of medium to coarse, coral and foraminiferal sands, with medium coral gravel. Photo looking south.


58

Plate 7: Beach and accretion south of the airstrip, along the west coast of Pingelap island. The accretion has produced a well-defined sand berm 1.5 m high,. This has also resulted in stabilization of the adjacent landward areas and backshore. The construction of the airstrip along the west coast has interfered with longshore transport, causing sand impoundment on the updrift side and severe erosion downdrift, to the north and west of the airstrip. Photo looking north.

Plate 8: View looking south of the accretion area south of the Pingelap airstrip. Several lobes of sand and gravel have accreted in this area. Coconut palms, coastal grasses and creeping vines now colonize some of these areas. Accretion has caused shallowing of the surf zone area, immediately south of the airstrip. Photo looking southwest.


59

Plate 9: Erosion of the upper beach along the southeast coast of Elato island. The erosion scarps are 75 cm high, at the vegetation line, with erosion at high tides. Note the exposed tree roots in the left of the photo and the accumulation of subrounded coral rubble in the foreground. The beach slopes at 10–12 o and is 6m wide, consisting largely of medium to coarse coral and foraminiferal sands and fine coral gravel. Photo looking northeast.

Plate 10: Coastal land loss and erosion of upper beach area along the southwest coast of Elato island. Residents reported severalmetresoflandlosshereduringtyphoons.Thebeachis5-7 m wide,withao slope 6 and consists largely of medium sand, with cobbles on the lower beach. Erosion embayments between coconut trees are 4–5 m wide, with 2–3 m embayments. Note exposed tree roots. Photo looking southeast. SOPAC Technical Report 268, Maharaj, 1998

60

Plate11: Accretion of sand at the southwest corner of Polowat island. The sand accretion is seasonal, summer accumulation, and extends from on-land to offshore. The sand is medium to coarse, angular coral and foraminiferal sand. Photo looking southeast.

Plate12: Eroded upper beach along the north-northeast coast of Polap island. The erosion scarp is 1.0 –1.25 m high. Note exposed roots at the vegetation line. The beach consists largely of sub-rounded coral boulders, with medium to coarse sands on the upper beach. The beach is 7 m wide, with a 10 0 slope. Photo looking northeast.


61

Plate13: Masonry sea wall along the northeast coast of Polap island. The seawall is built of Portland cement and coral rubble, with a 30 o seaward slope. It is 1.5m high and about 0.75 m wide. It is shallow, built on beach sand. The wall is fronted by a 7 0, 6 m wide, composed of rounded coral cobbles. Note the exposed beach rock in the foreground, rising 4060cm above the adjacent scoured beach. Photo looking southwest.

Plate14: Scouring and toe erosion of the masonry sea wall along the northeast coast of Polap island. Note the undercutting of the structure, the shallow nature of the foot of the wall and the absence of a firm foundation. The structure shows cracking in several places along its length. Photo looking north.


Plate16: Eroded upper beach, with a 75 cm scarp, along the east coast of Satawan island. The scarp is at the vegetation line. Note the fallen coconut palm, 0 , cobble to boulder which has grown in-place. The beach fronting the coast is a 12 beach 6 m wide, composed of sub-angular to sub-rounded coral rubble. Photo looking west.

Plate15: Coastal land loss and shoreline embayment due to erosion along the south coast of Losap island. The embayments are 1.5 m wide and 2 2-3 m deep. Note the exposed coconut palm roots and dead trees. The erosion scarps are 75 cm high, with 20 – 40 cm overhangs, supported by roots. Photo looking southwest.

62


63

Plate17: Old masonry sea wall along the east coast of Satawan island. The seawall is built of Portland cement and coral rubble, with a 90 o seaward slope. It is 1.5m high and about 0.5 m wide. It is shallow, built on beach sand and rubble. The wall is fronted by a 12 0, cobble to boulder beach 6m wide, composed of sub-angular to sub-rounded coral rubble. Note strand-line debris above the wall, transported by run-up and overtopping. Photo looking southwest.

Plate18: Masonry sea wall along the seaward aspect of the airstrip, northeast coast, Woleai island. The wall has a 45 o seaward slope and does not contain weep-holes. The wall is about 100 m long and about 1 m wide. The aggregate used for construction is coral rubble mined from the adjacent coastline. The beach fronting the wall is 5 m wide, and consists of sub-rounded gravels, cobbles and boulders. Photo looking northwest.


64

Plate19: Flanking downdrift of the seawall at the airstrip, Woleai island. The eroded coast was scoured 3 m inland. The beach consists of sub-rounded coral boulders and cobbles, is 8 m wide, with a 10 0 slope.

Plate 20: Shoreline erosion and collapse of large mahogany trees along the southwest coast of Woleai island. The erosion scarp is 1.0-1.5 m high, with shoreline retreat of several meters. Note exposed tree roots. The beach in the foreground shows summer accretion and consists of medium coral and foraminiferal sands with some coral gravel and cobbles. It is 6 m wide, with an 8 o slope. Photo looking west.


65

Plate 21: Summer accretion of beach sands along the southwest coast of Woleai island. However, note the difference in elevation/erosion scarp, of 1.5 m, between the level of the beach sand and the edge of the land. Photo looking east.

Plate 22: Accretion of coral gravels and sands along the NE and NNW part of an island (un-named) in the Faraulep atoll system. These deposits have accreted over an area as large as the island itself (more than 600 m long and 500 m wide). The deposits were deposited by typhoons and have since been colonized by various plants. This suggests that these areas are relatively stable. Photo taken along the crest of a lobe of gravelly deposit. Photo looking southeast. SOPAC Technical Report 268, Maharaj, 1998

66

Plate 23: Part of the accretionary area (previously plate) in the Faraulep atoll. Note the extent of the deposit. The beach to the right is sandy to gravelly, with coarse, angular sediments. The beach slope is about 10 0, with a slightly concave profile. Photo looking east.

Plate 24: Erosion scarp, 60cm high on the upper beach along the northwest coast of the un-named island in Faraulep atoll. The upper beach is eroded during high-tide, due to scouring and turbulence to landward of exposed beach rock. Erosion is at the vegetation line and is most aggressive during winter and typhoon season. Note the slab of exposed beach rock and sub-rounded boulders in the foreground. Photo looking east.


67

Plate 25: Exposed tabular slabs of beach rock along the southwest to west-northwest coast of the un-named island, Faraulep atoll. These slabs outcrop along 450 m of coastline, are 5-7 m wide, with a 6 0 surface slope, and are seen at low tide. Slabs vary from 15 to 30 cm thick. They occur within the surf zone and are usually exposed all year round. The upper beach is narrow, about 3–5 m, with an 8–10 0 slope, consisting of well-sorted, medium coral and foraminiferal sands. Note the exposed coconut palm roots along the upper beach, due to scouring at high tide. Photo looking northeast.

Plate 26: Eroded upper beach and coastal land loss along the west coast of Faraulep island. Note the fallen coconut trees in the water and exposed roots on the mid-beach area. The beach consists largely of medium-grained, angular coral and foraminiferal sands, is 4 m wide, and has an 8 o slope. Erosion scarps, to the right in the photo, are 75cm high. Photo looking east.


68

Plate 27: Eroded upper beach and coastal land loss along the west coast of Faraulep island. Note the exposed roots on the mid-beach area and dead coconut palms in the background. The beach consists largely of medium and angular coral and foraminiferal sands and coral rubble, and is 3 m wide, with a 10 o slope. Erosion scarps, to the right in the photo, are 30 cm high. Photo looking northeast.

Plate 28: Beach rock along the south coast of Mogmog island, Ulithi, exposed at low tide. The beach rock varies from 8 to 50 m wide, while the beach is about 5 m wide. The upper beach consists of sub-angular pebbles, cobbles and boulders, with a 10-12 0 slope. Note the fallen coconut palms along the beach. Photo looking northeast.


69

Plate 29: Beach rock along the south coast of Mogmog island, Ulithi, exposed at low tide. The beach rock exposure is about 25 m wide, while the beach is about 5 m wide. The upper beach consists of sub-angular gravels and cobbles, with a 10 0 slope. Note the sand bar/accretion in the background. Photo looking west.

Plate 30: Gravelly beach along the southwest coast of Mogmog island, Ulithi. Beach sediments consist largely of angular to sub-angular coral rubble with medium coral sands. The beach is 8 m wide with an 8 0 slope. The backbeach is vegetated and relatively stable. Photo looking west.


70

Plate 31: Coral rubble groyne construction on the southwest coast of Eauripik. The groyne is about 8 m long. The structure is has collapsed in the water and is partly eroded and scoured at its proximal end. Note some sand accretion in front of groyne/eastern updrift aspect. Note person for scale. Photo looking west.

Plate 32: Sand and gravel accretion at the southwest tip of Utagal island. Accretion is seasonal, usually during the summer period. This deposit is usually eroded during the winter period. Photo looking north.


71

Plate 33: Eroded scarp 60 cm high on upper beach, Utagal island. Note dead coconut palms partly covered with sand. The beach consists of medium to coarse, angular carbonates, mainly of coral sands and gravel, with abundant benthic shelf foramainifera. Photo looking east.


72

APPENDIX I Grain size scale of sediment particles. This scale is based on powers of 2 mm, which yields a linear logarithmic scale via the phi-parameter defined as :

Φ = –2 log. d, where d is in mm (after vanRijn, 1989) GRAIN SIZES

MILLIMETERS, mm

Boulders Cobbles Gravel

> 256 256 – 64 64 – 2

Very coarse sand Coarse sand Medium sand Fine sand Very fine sand

2.0 – 1.0 1.0 – 0.50 0.50 – 0.25 0.25 – 0.125 0.125 – 0.0625

Coarse silt Medium silt Fine silt Very fine silt Coarse clay Medium clay Fine clay Very fine clay Colloids


0.062 0.031 0.016 0.008

– 0.031 – 0.016 – 0.008 – 0.004

0.004 – 0.002 0.002 – 0.001 0.001 – 0.005 0.0005 – 0.00024 < 0.0024

MICROMETERS, µm

PHI VALUES, Φ < –8 –8 to –6 –6 to –1

2000 – 1000 1000 – 500 500 – 250 250 – 125 125 – 62 62 31 16 8

– 31 – 16 –8 –4

4 –2 2 –1 1 – 0.5 0.5 – 0.24 < 0.24

–1 to 0 0 to +1 +1 to +2 +2 to +3 +3 to +4 +4 +5 +6 +7

to to to to

+5 +6 +7 +8

+8 to +9 +9 to +10 +10 to +11 +11 to +12 > +12

73

APPENDIX II Wind data for Pohnpei Island (Van Loon, 1984)

MONTH

DOMINANT WIND DIRECTION

MEAN WIND SPEED (m/sec)

January February March April May June July August September October November December

NE NE NE NE NE NE E ESE S ESE NE NE

3.4 4.1 3.4 2.7 2.4 1.9 1.6 1.4 1.4 1.6 2.0 2.8

Annual Mean

NE

2.4


74

APPENDIX III Wind data for Chuuk Island (Van Loon, 1984)

MONTH



NNE NNE NNE NNE NNE NNE SE S SW S NNE NNE

4.9 4.8 4.7 4.1 3.1 2.2 1.9 1.9 1.6 2.0 2.8 4.0

Annual Mean

NNE

3.2



75

APPENDIX IV Wind data for Yap Island (Van Loon, 1984)

MONTH




NE NE NE NE NE NE SW SW SW W NE NE

4.6 4.8 4.5 3.6 3.4 2.6 2.4 2.4 2.6 2.9 3.3 4.0

Annual

NE

3.5


76

APPENDIX V The Beaufort wind scale (For an effective height of 10 m above sea level)

BEAUFORT NUMBER

DESCRIPTIVE TERM

DEEP SEA CRITERION

MEAN WIND SPEED EQUIVALENT

PROBABLE MEAN WAVE HEIGHT, METRES

KNOTS

M/SEC

–

0

Calm