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TABLE OF CONTENTS

Page

SUMMARY...... 5

ACKNOWLEDGEMENTS...... 6

INTRODUCTION...... 7

STUDY METHODS ...... 11

OUTLINE OF FLAT AND ...... 11

COASTAL EROSION...... 12

Southwest ...... 12

Northwest Coast...... 18

Northeast Coast ...... 21

Southeast Coast...... 23

Lagoon Coast...... 25

DISCUSSION...... 25

CONCLUSIONS ...... 29

RECOMMENDATIONS ...... 29

REFERENCES ...... 30

ANNEX 1 Photographs taken during field survey

ANNEX 2 Beach profile locations and profiling data

ENCLOSURE Coastal Geology Map of - 1:10 000 (SOPAC Coastal Series Map 9)

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LIST OF FIGURES

1. of Tuvalu, showing location of Vaitupu.

2. Airphoto of Vaitupu taken on 8 August 1984 (the main figure) and airphoto of south corner of Vaitupu was taken on 19 August 1984. Note accumulation near the small boat navigation on the reef flat in front of Asau-Tumaseu village.

3. Coastal stability and geographical division of Vaitupu.

4. Cyclone tracks of "Kina" and "Nina" (Nippon Tetrapod Co., Ltd., 1995).

5. Beach profile TU96006-1, showing two erosion scarps. The upper scarp with exposure was formed during the 1993 cyclones, when some beach gravel was eroded away. The lower scarp with sand exposure was formed after sand once deposited on the original gravel beach. Northwest end of the southwest coast. See location on Figure 6.

6. Locations of the field photos (refer Annex 1); and beach profiles (refer Annex 2).

7. The shoreline change since 1972 at BS5 (for location refer Figure 6), northwest of the Fisheries Harbour.

8. Layout of Vaitupu Fisheries Harbour before the 1993 cyclones (Nippon Tetrapod Co., Ltd., 1995).

9. Sand distribution on the reef flat near the Vaitupu Fisheries Harbour.

10. The present sand beach south of the south of Vaitupu Fisheries Harbour.

11. Beach profile TU96004, middle section of northwest coast. A rubble beach berm occurs between the ocean beach face and the sand beach. Breccia beachrock occurs in the middle and lower of the ocean beach face. See location on Figure 6.

12. Beach profile TU96039, showing an erosion scarp, narrow sand beach and sandstone beachrock occurring on the middle and lower beach face. See location on Figure 6.

13. Beach profile TU96016, gravel on the upper beach face with erosion scarp and breccia beachrock on the middle and lower beach face. See location on Figure 6.

14. Beach profile TU96058 with a bush zone and young coconut trees zone developed on the berm indicating a prograding coast. Compare with Figure 15. See location on Figure 6.

15. Shoreline change west of VT Z 4 (east of Patamo Point) since 1971.

16. A comparison of two harbour types on the ocean coast. A: An excavated channel and anchorage with two on both sides extending from the ; B: An excavated channel and anchorage with two groynes separated from the shoreline and a pier between wharf and shore.

17. A comparison of four harbour types on lagoon coast. A: An excavated channel on lagoon reef flat; B: An excavated channel on lagoon reef flat with a jetty at the landward end; C: An excavated channel on lagoon reef flat with a pier at the landward end; D: A pier extending from shore to reef edge.

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SUMMARY

Field investigation on Vaitupu,Tuvalu was undertaken from 25 March to 18 April 1996, on the ocean coast and in selected locations in the two .

The principal conclusions are as follows.

· The reef flat is relatively simple and divided into three continuous zones (spur and groove, pavement and beach) and two discontinuous zones (rubble or rubble and pavement, and beachrock). There is no obvious reef crest.

· Both southwest and northeast have well-developed sand . The southeast coast has alternating gravel and sand beaches. The northwest coast has only gravel beach.

· Erosion has occurred on most parts of the ocean coasts.

· The 1993 cyclones caused the erosion on the southwest coast. Mining and the damaged Fisheries Harbour caused further erosion or delayed recovery of the sand beach.

· The 1993 cyclones, rubble and gravel mining caused the erosion of the south section of the northwest coast.

· Erosion is associated with progradation on the northeast coast. The erosion on both of the Alia Opeti Passage is related to mining.

· On the southeast coast, the stable or prograding coast alternates with erosional coast, the latter is mainly caused by mining.

· The two groynes of the Fisheries Harbour extending to the shore block longshore transport. Some sediment is transported into the channel and then out to the ocean.

It is recommended as follows: · The groynes of the Fisheries Harbour should be separated from the shore and a pier built to connect the two parts, permitting uninterrupted longshore sediment transport.

· Prohibit mining on the beach and reef flat. The sand and gravel dug from pits are good alternative sources of aggregate.

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ACKNOWLEDGEMENTS

Funds for this project were contributed by the Government of the People's Republic of China.

The work was carried out in collaboration with the Tuvalu Government. Particular assistance was received from the Land and Survey Department, the Ministry of Natural Resources and the Council of Vaitupu. Appreciations extended to Mr S. Solomon for the useful comments on the drafts of the report.

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INTRODUCTION

Vaitupu (7º 29'S; 178º 41' E), the largest (land area of 5.29 km2) is located 130 km north of the capital (Figure 1). It is elongate northwest-southeast and narrows to northwest. It is 5.1 km long and is a maximum 2 km wide at the southeast (Figure 2). It has geomorphological characteristics of both an and a reef island. It has two shallow lagoons with passages opening to the east coast; a smaller lagoon to the northwest, and larger one in the central southeast. Elevations are commonly less than 5 m, and there are seven small along the northeast coast (McClean et al., 1991). Most people live in the U-shaped double village of Temaseu and Asau on the southwest coast (Figure 3).

The coast can be divided clockwise from the northeast into four parts (Figure 3). The northeast coast is from Teakenga Point (in the north) to Motuosina Point in the south and this is subdivided into three sections: the north, middle and south sections. The middle section is near the passages of the larger lagoon where the widest reef flat occurs. The southeast coast extends west from Mutuosina Point to Patamo Point. The southwest coast is from Patamo Point to the turning point of the shoreline a little northwest of VT Z 19 trigonometric point. The northwest coast extends from this turning point, north to the entrance into the smaller lagoon.

Figure 1. Atolls of Tuvalu, showing location of Vaitupu.

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Figure 2. Airphoto of Vaitupu taken on 8 August 1994 (the main figure) and airphoto of south corner of Vaitupu was taken on 19 August 1984. Note sand accumulation near the small boat navigation channel on the reef flat in front of Asau-Tumaseu village.

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Figure 3. Coastal stability and geographical division of Vaitupu.

McLean et al. (1991) divided the land into nine geomorphological units: northern , western ridge complex, eastern ridge complex, southern ridge complex, inter-depression and flat, lagoon margin, lagoon entrance ridges, saline flat, and pulaka pit - spoil bank complex. They also measured some cross sections. Nippon Tetrapod Co., Ltd. (1995)

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conducted continual observation for 15 consecutive days using a tide gauge. During this period the mean-tide range was 1.16 m, and the spring-tide range was 1.86 m.

Vaitupu Fisheries Harbour was built in 1992 by the Japanese. It was seriously damaged soon after completion in the 1992-1993 cyclone season by waves attributed to two large cyclones "Kina" and "Nina". At the time of the survey the Fisheries Harbour was being reconstructed by Japan at the request of the Tuvalu Government.

Cyclone Nina was a small system originating in the Sea of Arafura to the north of Australia, and which headed east and reached a point about 500 km SSW of Vaitupu on January 3, 1993. Cyclone Kina originated about 1000 km southwest of Vaitupu on December 27, 1992 and passed through and to the south of the Kingdom of . This cyclone was large and remained powerful as it proceeded in a southeastern direction from a point 1000 km distant from Vaitupu (Figure 4). Both cyclones advanced to the southeast between 1-4 January, 1993 generating strong WNW winds and waves, which propagated to Vaitupu as swell waves (Nippon Tetrapod Co., Ltd., 1995). These swell waves resulted in erosion on the southwest coast.

The field survey for this report was conducted from 25 March to 18 April 1996. Work was concentrated around the coast and in selected locations in the two lagoons.

Figure 4. Cyclone tracks of “Kina” and “Nina” (Nippon Tetrapod Co., Ltd. 1995).

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STUDY METHODS

The reef flat and beach were digitised to produce a computer drawn base map from the topographic map (1:10000), which was based on 1971 air photographs taken by the Department of Lands, Mines and Survey of Fiji. This map was published in 1974, by the Directorate of Overseas Survey, Ministry of Overseas Development, British Government. Beach profiles were measured using a level (SOKKIA model C3E), staff, and tape measure. The base stations were each given a relative elevation of 0 m. Observations were also made of coastal processes at the time of the survey.

Interviews with residents on the island were an important source of information on the timing of human activities.

The map of coastal geology of Vaitupu produced during this survey is included as an Enclosure (inside the back cover) and is available separately as “Coastal Geology Map of Tuvalu - Vaitupu 1:10 000”, (Xue, 1996: SOPAC Coastal Series Map 9).

OUTLINE OF REEF FLAT AND BEACH

The ocean reef flat of Vaitupu is comparatively narrow; about 200 m wide on the northwest, southwest and southeast coasts, and 400 m wide on the northeast coast with the exception that in the middle section it is 800 m wide. The reef flat is composed of three continuous zones; spur and groove, pavement, and beach. Two discontinuous zones; rubble or rubble and pavement, and beachrock are also recognised.

The outer shallow spur and groove zone is poorly understood, since the survey only reached the inner boundary of this zone.

The pavement zone occupies most of the reef flat and is scattered with rubble. It extends from the spur and groove zone to the base of the beach on half of the southwest coast and some parts of the northeast coast. Patch rubble areas (or rubble and pavement) are mainly distributed in three areas: north of Motuosina Point and north of Teakenga Point on the southeast coast and northwest of the Fisheries Harbour on the southwest coast (Plate 1 and Enclosure). The beachrock zone mostly consists of breccia. Continuous breccia beachrock occurs on the northwest coast, and as several long narrow reef flat ridges with some gravel cover extending from the shore towards the ocean on the reef flat of the middle

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section of the northeast coast (Figure 2, Plates 2 and 3). Continuous sandstone beachrock with a sharp surface also occurs on the reef flat of the middle and south sections of the southwest coast (Figure 2 and Plate 4). In addition, limited patches of sand are distributed on the reef flat close to the base of beach.

The beach zone is composed of sand beach and gravel or rubble beach. Well-developed sand beaches are found on most of the southwest coast and the northeast coast . All of the beach on the northwest coast is gravel. Alternating sand beach and gravel beach (with scattered rubble beach) are distributed along the remaining coastline.

COASTAL EROSION

Erosion has occurred on most parts of the ocean coastline.

Southwest Coast

The southwest coast is straight with well-developed sand beaches along the central portion and gravel beaches to the north and south. Sandstone beachrock occurs on the reef flat of the middle and south sections, and breccia beachrock occurs on both ends. Limited areas of rubble and pavement occur in front of the sandstone beachrock. The pavement occupies most of the reef flat, with spur and groove at the reef edge.

Erosion of the southwest coast has been caused recently by cyclones "Kina" and "Nina", and human activities. In the northwest a gravel beach extends for about 260 m. A clear erosion scarp with exposed gravel is present. This scarp was formed during the 1993 cyclones. After the cyclones, sand accumulated over the original gravel beach. This sand has since been eroded away, leaving a lower erosion scarp. This double scarp is characterised by different : the upper scarp with exposed gravel and a lower scarp with exposed sand or sand overlying gravel. The height of both scarps is 0.8-1.3 m and they extend for 156 m (Figures 5 and 6, Plate 5). Further south two erosion scarps, both with exposed sand, extend for another 46 m. To the southeast, the lower erosion scarp disappears and reappears south of the Fisheries Harbour (Figure 6).

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Figure 5. Beach profile 6, showing two erosion scarps. The upper scarp with gravel exposure was formed during the 1993 cyclones, when some beach gravel was eroded away. The lower scarp with sand exposure was formed after sand once deposited on the original gravel beach. Northwest end of the southwest coast. See location on Figure 6.

Figure 6. Locations of the field photos (refer Annex 1); and beach profiles (refer Annex 2).

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During the 1993 cyclones, a portion of beach sand was transported landward to the beach berm and in some places the sand covered the coastal road (local resident provided information). An erosion scarp was formed along all of the southwest shoreline and even now, the scarp is still clear in most places, although the sand scarp collapses easily (Annex 2, Figure 7, Plates 6 and 7 and Table 1). Some of the sand may have been transported onto the reef flat and also possibly beyond the reef. The coconut trees living on the protrusive remainders of the former surface indicate the shoreline retreated at least 2-4 m. Local residents indicated that the 1972 shoreline was very close to the present beach berm crest (Figure7). The distances between the 1993 erosion scarp and new beach berm crest commonly are 6-10 m. So it is estimated that the shoreline retreated about 5-6 m during the 1993 cyclones.

Figure 7. The shoreline change since 1972 at BS5 (for location refer Figure 6), northwest of the Fisheries Harbour.

After the cyclones the sand beach gradually recovered. However, the present crests of the beach berm are commonly 0.5-0.8 m lower than the top of the old scarp and the sand beaches have still not recovered to their original states (Plate 7). This is primarily a result of three factors: sand loss during the cyclones, construction of the Fisheries Harbour, and sand mining.

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Table 1. Relationship between the erosion scarp formed during 1993 cyclones and the recent beach berm crest (for locations see Figure 6).

Location Height of 1993 Distance between 1993 Height difference between (m) scarp (m) scarp and recent berm 1993 scarp and recent berm crest (m) 9606-1 0.60 3.7 0.75 BS1 0.44 7.8 0.53 BS2 0.56 5.5 0.47 BS3 0.41 7.2 1.36 BS4 not clear 9.7 0.75 BS5 not clear 5.7 0.42 BS6 not clear 12.9 0.82

Before the Vaitupu Fisheries Harbour was built in 1992, there was a very narrow and shallow channel for small fishing boats in the same position as the present channel. Undoubtedly, this small channel trapped sand and its inner part filled quickly with sand due to the blocking of sediment transport paths by piled reef rocks on the reef flat excavated from the narrow channel. Sand can be seen to be accumulating on the reef flat near the inner part of the channel in front of Asau-Tumaseu village on the 1984 airphoto (Figure 2). This small channel also caused coastal erosion, however, since its inner part was filled and the channel was very narrow, the erosion induced was probably small and there are no records of it.

Vaitupu Fisheries Harbour was completed in 1992. It is composed of several parts: an excavated channel with expanded anchorage; a narrow, shallow passage for small fishing boats; a slipway for launching small boats; and two groynes with a wharf on the north groyne (Figure 8 and Plate 8). The groyne construction consisted of a sand core covered with sand bags and mats to retain the sand and this was topped with stones of about 500 kg. Both groynes were totally destroyed by the 1993 cyclones. Both the sand fill and sand bags flowed out and were scattered, as were the lightweight reef stones. A few bigger reef stones of 1 tonne or more remained in their original positions. The concrete apron at the back of the wharf was destroyed but the wharf suffered no damage (Plate 8) because it was made of massive concrete (Nippon Tetrapod Co., Ltd., 1995). While the completed harbour only existed for a short period, the remains continue to affect coastal processes.

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Figure 8. Layout of Vaitupu Fisheries Harbour before the 1993 cyclones (Nippon Tretrapod Co.,Ltd.,) 1995.

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The north groyne blocks the southeast longshore sediment transport. Sand has been deposited on the reef flat, on the updrift (north) side of the groyne (Figure 9). A zone of pavement separates the sand with seagrass area from the groyne because of backwash water flow (Plate 9). The longshore currents and backwash can further transport sand into the channel, bypassing the groyne during northwest and westerly storms. As the remains of the north groyne are much lower than the original structures, the currents carrying suspended sand can cross over it and go into the channel. Moreover, after swells pass the edge of reef flat, wave set-up occurs on either side of the channel, forming a higher water level. This induces rip currents within the channel, resulting in sand transport out into deep water. There is no weather record available for Vaitupu, but the Funafuti weather data can be used for reference. During December through March stronger west and northwest winds appear in Funafuti (Carter, 1986). Strong westerly winds did not occur during the survey period, so the processes were probably not as active as they would be during December through March, although the water in the channel was more turbid than water outside during the survey period.

The processes to the south of the groyne are similar to those discussed above but occur during periods of southerly waves. As result, small amounts of sand accumulate on the south side of the south groyne (Plates 10 and 11). Because the sand supply on the coast southeast of the harbour is much less than on the northwest (the sand beach coastline southeast of the harbour is much shorter), the influence of the harbour on this shore is more obvious, and severe erosion is shown by four observations. First, there is an erosion scarp 0.3-0.4 m high on the new crest of the new beach berm extending for 212 m from 103.5-315.5 m south of the south groyne (Figures 5, 6 and 10), which indicates recent erosion (Plate 12). Second, the distances between the old erosion scarp top and the new crest of the beach berm are more than 11 m with one exception of only 6.5 m because of its proximity to a man-made rubble beach face reef rock revetment (Figure 10 and Plate 13). These distances are much greater than those northwest of the harbour (Table 1). Third, the height differences between the top of the old scarp and recent berm crest are more than those northwest of the harbour (Figure 10, Plate 13, Table 1). Fourth, there is white beachrock in front of the present sand beach, indicating that it has been recently exposed after beach sand was eroded away. The above four observations indicate that the beaches north of the harbour have recovered more than those to the south following the 1993 cyclones. Erosion occurred because sand has been transported into the channel. Both coastal segments north and south of the harbour have eroded because of sand loss. However, the sand loss was just distributed over a much greater length of the beach to north, where the effect is not very clear.

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Beach sand mining is another cause of erosion. During the surveying period, people were observed transporting beach sand with a tractor.

Northwest Coast

The coast is curved and subdivided into three sections; west, middle and east (Figures 2 and 3). The middle section which corresponds to the northernmost part of Vaitupu, has a narrow rubble berm and connects the sand beach of the small lagoon to the ocean beach to the northwest. Gravel commonly occurs only at the upper part of the beach face. Almost continuous breccia beachrock occupies most parts of the middle and lower beach face (Figure 11). Patches of rubble or rubble and pavement were only seen on the reef flat of the east section. However, there used to be big reef rocks on the reef flat on the west section, but they were removed and used to build the Fisheries Harbour.

Gravel mining also occurred at the time of building the Fisheries Harbour and may still be occurring since the road for transporting gravel is clearly visible. Though erosion may principally have occurred during the 1993 cyclones, mining has undoubtedly promoted coastal erosion. Erosion scarps 0.4 - 0.8 m high occur almost continuously along the shoreline of the west section; the middle section is stable; an eroding coastline dominates the west part of the east section, and a prograding and stable coastline dominates the east part (with maximum progradation of 24 m) at the entrance to the lagoon.

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Figure 9. Sand distribution on the reef flat near the Vaitupu Fisheries Harbour

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Figure 10. The present sand beach south of the south groin of Vaitupu Fisheries Harbour.

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Figure 11. Beach profile TU96004, middle section of northwest coast. A rubble beach berm occurs between the ocean beach face and the lagoon sand beach. The breccia beachrock occurs in the middle and lower of the ocean beach face. See location on Figure 6.

Northeast Coast

The reef flat of the northeast coast is commonly 400 m wide on the northwest and southeast sections and increases to 800 m along the middle section. Beachrock (breccia) is discontinuously distributed on the reef flat, in front of the base of beach, and on the beach face associated in some cases with a narrow gravel beach. A series of narrow, long, reef flat ridges (made up mainly of breccia beachrock and some rubble on the surface) are present on the wide reef flat of the middle section (Figure 2). Limited rubble areas occur on the southeast end of the coast. Sand beaches are more developed than gravel beaches, and areas of erosion generally alternate with areas of progradation.

On the north section of the coast, erosion is mainly observed at the north end. Some surviving trees indicate that the shoreline has retreated 2.4-3.3 m (Plates 14 and 15). Erosion has also occurred on the small northwest of Motutanifa . Progradation is mainly seen on the south part of the north section (Figure 3 and Enclosure). Based on the distribution of young coconut trees, the shoreline northwest of Motutanifa Islet has prograded 1.5 - 5 m (Plate 16). And the shoreline west of Motutanifa Islet has prograded a maximum of 13 m (Plate 17), which might be due to protection by the islet. It is possible, that in recent years more northerly storm waves have affected the coast, which has resulted in erosion to the north and accumulation to the south.

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The northwest shore of the middle section is eroding and has retreated at least 1.9-2.5 m (Plate 18). The NW -SE extending shore in the northwest of Tefuta Passage is semi- enclosed and comprises two small narrow bays which are protected from north and east waves and therefore this coast has been prograding. A mud flat more than 50 m wide has accumulated in front of the undeveloped muddy sand beach and even reaches the shoreline without a definite sand beach in places (Plate 19, and Enclosure). The northwest coast of Tefuta Passage and part of the southeast shore (on Tafia Islet) are eroded. Storm waves and flood-tide currents have caused the erosion of these areas. The erosion on both sides of the Alia Opeti Passage is more severe. The outer section of the southeast coast has retreated 4.9-7.2 m (Plate 20) and is one of most severely eroded locations on Vaitupu. The outer section of the northwest coast of the passage (south Tafia Islet) has retreated at least 3 m (Plate 21), and the surface grass on southeast Tafia Islet has been washed away (Plate 22). The funnel-shaped passage may help to amplify storm wave heights. Mining is another cause of erosion. In order to build the Fisheries Harbour, 17-20 trailers of gravel were removed from the beach of the outer section of the southwest coast of Tafia (information from Tafia Islet residents) and this resulted in erosion. Before Motufoua High School was built, the Vaitupu Secondary School was located on the southeast shore of Alia Opeti Passage. For building houses, some sand and gravel must have been removed from the nearby coast and this likely caused erosion.

On the south section of the northeast coast, the erosional and stable or prograding coasts alternate. The erosional coasts occur mainly along the north side of the . West of the Masana Islets, sand beaches with an erosion scarp are very narrow (4.7 m) and sandstone beachrock occupies most of the beach face (Figure 12). The shoreline west of the Lusamotu Islets has prograded a maximum of 12 m (Plate 23). The shapes of rubble ridges near Te Motu Olepa Islet are N -S and result from of northerly storm wave events.

Figure 12. Beach profile TU96039, showing an erosion scarp, narrow sand beach and sandstone beachrock occurring on the middle and lower beach face. See location on Figure 6.

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Southeast Coast

The reef flat along the southeast coast is relatively narrow, 100-240 m wide. There are patch rubble areas and breccia beachrock on the reef flat. Gravel and sand beaches alternate along the coast. Gravel beaches are mainly on the protruding coasts. Sand beaches are on the curved or straight coasts. The stable or prograding coasts also alternate with erosional coasts (Figure 4 and Enclosure). Erosion scarps are common (Plate 24) with loose sediment only developed on the upper beach face and a breccia beachrock in the middle and lower beach face (Figure 13). The erosion of the protruding coasts, where waves are reflected concentrate more energy, is partly controlled by natural forces. However, the erosion on the southeast coast is closely related to sand and gravel/rubble mining activity. Beside the road, stockpiles of rubble collected from the beach and reef flat were present during the surveys.

The stable coasts are mainly between Motuosina Point and Melia and southwest of Melia. A prograding coast occurs east of Patamo Point, where a 10 m wide young coconut tree belt and a bush belt (several metres wide) indicate progradation in recent years (Figure 14, Plate 25). A maximum of 20 m was measured along the east end coast as determined by a comparison of the coast (vegetation line) on the map, airphoto and present surveys (Figure 15). There was an obvious concave landward coastline on the 1974 topographical map (1:10 000, based on the 1971 airphoto), which was about 45 m south of the road. This distance had changed by about 56 m as shown by the 19 July 1984 airphoto (Figure 2) and is now 68.5 m (by tape measurement). It means that the maximum shoreline progradation is about 20 m.

Figure 13. Beach profile TU96016, gravel on the upper beach face with erosion scarp and breccia beachrock on the middle and lower beach face. See location on Figure 6.

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Figure 14. Beach profile TU96058, with a bush zone and young coconut trees zone developed on the berm indicating a prograding coast. Compare with Figure 15, See location on Figure 6.

Figure 15. Shoreline change west of VT Z 4 (east of Patamo Point) since 1971.

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Lagoon Coast

Coastal protection of the larger lagoon was discussed in a report by Reynolds (1988). The two passages into this lagoon are narrow and shallow and only limited ocean generated waves can affect the northwest and northeast lagoon coasts, where there is no coastal protection. Seawalls have been built along the west and south shores of this lagoon and a causeway has been constructed along the swamp area to the east. These seawalls were not for protection from waves, but were built to protect the pulaka pits from floods of sea water associated with spring tides and storm surges (based on interview with local residents). During storms, waves flood over the lagoon shore and into the coastal pulaka pits, resulting in the death of pulaka plants. However, these seawalls have not successfully protected the pulaka from flood seawater because they are not high enough, and they only protect the land. Extensive seawall construction has destroyed the lagoon landscape and is not good for any possible future tourism development.

DISCUSSION

Local residents remove sand, gravel and rubble from the beach and reef flat for constructing houses, (seawalls and Fisheries Harbour) and road. When this investigation was conducted, good sand was being mined from the beach for paving roads. Up to the present time, bricks for house construction are imported from overseas. If house walls are built with local material as on (Xue 1996) mining aggregate will increase. Therefore, it is very important to develop alternative sources of aggregate. Pulaka is one of the main local foods. For planting pulaka, many pits have been dug, and sand, gravel and rubble are put beside the pits. This is a good source of aggregate, and should be used in order to avoid mining the beach and reef flat of Vaitupu.

The Fisheries Harbour built in 1992 was destroyed in the 1992-1993 cyclone season and is being reconstructed following a design which is similar to the old one. The construction includes widening the anchorage and reinforcing the two groynes. From the point of coastal processes, this design is much better than the simplest harbour - an excavated channel, extending to the base of the beach without groynes, which directly traps longshore transported sediment and transports sediment oceanward. However, the groynes stop longshore transport of sediment, which is deposited on the updrift side of the groynes. From

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there the sand can be moved into the channel and transported to the ocean, although this process is much reduced compared with a channel without groynes (Figure 16A). The newly constructed harbour should stand for a long time, but it will eventually contribute coastal erosion both to the north and south.

The recommended small harbour design is shown in Figure 16B. Two groynes 100 m apart extend from the edge of the reef. A pier connects the wharf and shore, a slipway for transporting small fishing boats could be built inside of one groyne and the boats could be moved onto the land or stored on the wide groyne. About 80 m wide reef flat close to beach should be left to permit longshore sediment transport, so sand loss to the channel and ocean will be much reduced.

Harbours or passages have been built on lagoon coasts of both Funafuti and Nukufetau. The simplest harbour is an excavated channel extending from the lagoon reef edge to the base of the beach. Several channels at , and the present harbour at and are basically of this type. These channels directly trap sediment and transport it into deeper water in the lagoon (Figure 17A). These harbours are one of principal causes of erosion in Tuvalu (Radke, 1985; Xue and Malologa, 1995, Xue, 1996a, 1996b). The disused Vaiaku Wharf was reconstructed on the basis of a channel excavated in the Second World War - a dock built at the landward end of the channel (Figure 17B). A third type of harbour is an excavated channel with a pier at the landward end, for example, the Funafuti Fisheries Harbour (Figure 17C). From the point of coastal processes, both the second and third harbour types cause increased erosion similar to the first type. The fourth harbour type (Figure 17D) a pier extending from shore to the edge of the lagoon reef flat is the best. This type does not interfere with the longshore currents and should not cause erosion.

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Figure 16. A comparison of two harbour types on the ocean coast. A: An excavated channel and anchorage with two groynes on both sides extending from the shore. B: An excavated channel and anchorage with two groynes separated from the shoreline and a pier between wharf and shore.

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Figure 17. A comparison of four harbour types on lagoon coasts. A: An excavated channel on lagoon reef flat. B: An excavated channel on lagoon reef flat with a jetty at the landward end. C: An excavated channel on lagoon reef flat with a pier at the landward end. D: A pier extending from shore to reef edge.

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CONCLUSIONS

· The reef flat is relatively simple and divided into three continuous zones (spur and groove, pavement and beach) and two discontinuous zones (rubble or rubble and pavement, and beachrock). There is no obvious reef crest.

· Both southwest and northeast coasts have well-developed sand beaches. The southeast coast has alternating gravel and sand beaches. The northwest coast has only gravel beach.

· Erosion has occurred on most parts of the ocean coasts.

· The 1993 cyclones caused the erosion on the southwest coast. Mining and the damaged Fisheries Harbour caused further erosion or delayed recovery of the sand beach.

· The 1993 cyclones, rubble and gravel mining caused the erosion of the south section of the northwest coast.

· Erosion is associated with progradation on the northeast coast. The erosion on both shores of the Alia Opeti Passage is related to mining.

· On the southeast coast, the stable or prograding coast alternates with erosional coast, the latter is mainly caused by mining.

· The two groynes of the Fisheries Harbour extending to the shore block longshore sediment transport. Some sediment is transported into the channel and then out to the ocean.

RECOMMENDATIONS

It is recommended as follows:

· The groynes of the Fisheries Harbour should be separated from the shore and a pier built to connect the two parts, permitting uninterrupted longshore sediment transport.

· Prohibit mining on the beach and reef flat. The sand and gravel dug from pulaka pits are good alternative sources of aggregate.

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REFERENCES

Carter R., 1986. Wind and sea analysis, Funafuti Lagoon, Tuvalu. SOPAC Technical Report 58, 9 pp.

McLean R. F. Holthus P. F. Hosking P. L. and Woodroffe C. D., 1991. Vaitupu. Tuvalu Land Resources Survey Island Report No 5, 78 pp.

Nippon Tetrapod Co., Ltd., 1995. Basic Study Report on the reconstruction project of the Fisheries Harbour at Vaitupu in Tuvalu. 60 pp.

Radke B. M., 1985. Bathymetry and beach profiling, Funafuti, Tuvalu, 24 September- 19 October 1984. CCOP/SOPAC Cruise Report 106, 18 pp.

Reynolds C. 1988. Coastal erosion in Tuvalu. 30 pp.

Xue C, and Malologa F., 1995. Coastal sedimentation and of Fongafale , Funafuti Atoll, Tuvalu. SOPAC Technical Report 221, 54 pp.

Xue C., 1996a. Coastal sedimentation and coastal management of Amatuku Island , Funafuti Atoll, Tuvalu. SOPAC Technical Report 234. 34 pp.

Xue C., 1996b. Coastal sedimentation, erosion and management of Southwest Nukufetau Atoll, Tuvalu. SOPAC Technical Report 238.

[TR243 - Chunting Xue] [31]

ANNEX 1

Photographs taken during field survey

[TR243 - Chunting Xue] [32]

Plate 1. The patch rubble and pavement zone, northwest of Tumaseu Village, southwest coast. View 315º, for location refer Figure 6.

Plate 2. The reef flat ridges (breccia beachrock) extending from the northeast point of Tafia Islet, middle section of northeast coast. View to 025º, for location refer Figure 6.

[TR243 - Chunting Xue] [33]

Plate 3. “Y” shaped reef flat ridges (breccia beachrock), northwest of Tefuta Passage, middle section of northeast coast. View to 020º, for location refer Figure 6.

Plate 4. The sharp surface of sandstone beachrock on the reef flat northwest of the Fisheries Harbour. View to 160º, see location on Figure 6.

[TR243 - Chunting Xue] [34]

Plate 5. Double erosion scarp on the northwest end of southwest coast. The upper scarp formed during 1993 cyclones is composed of gravel. Then sand accumulated on the original gravel beach, and then most of the beach sand was eroded away and the top sand layer was kept, forming the lower erosion scarp. Northwest end of southwest coast. View to 115º, see location on Figure 6.

Plate 6. Erosion on northwest section of southwest coast near site of VT Z 18. Living coconut tree is at present 2.4 m in front of 0.5 m high erosion scarp formed during 1993 cyclones. VT Z 18 triangulation station has been lost. View 030º, for location see Figure 6.

[TR243 - Chunting Xue] [35]

Plate 7. A new unstable berm crest formed 6-8 m in front of the erosion scarp caused by 1993 cyclones (hidden in shadows). In front of the graveyard, southwest coast, see location on Figure 6.

Plate 8. The present Vaitupu Fisheries Harbour; view to 250º. Note the original massive concrete wharf on middle of the right (north) groyne is basically kept although its back apron was destroyed along with the two groynes in the 1993 cyclones.

[TR243 - Chunting Xue] [36]

Plate 9. The sand with seagrass on the reef flat close to the north groyne of the Fisheries Harbour. View to 170º, see location on Figure 6.

Plate 10. Accumulated sand on the corner of the south groyne of the Fisheries Harbour. View to 355º, see location on Figure 6.

[TR243 - Chunting Xue] [37]

Plate 11. Accumulated sand on the reef flat at the outer base of south groyne of the Fisheries Harbour. View to 355º, see location on Figure 6.

Plate 12. The crest of new berm with erosion scarp in front of the old erosion scarp formed during the 1993 cyclones (behind bushes). Bushes are growing on the new beach berm (about 15 m wide) formed after the cyclones. View to 165º, see location on Figure 6.

[TR243 - Chunting Xue] [38]

Plate 13. Two surviving Pandanus trees (one is in front of the person and another is close to the beach berm crest) and recent bush growth on the beach berm formed after 1993 cyclones. The top of 1993 erosion scarp is at the boundary of the land with coconut trees, and is 0.79 m higher than the new beach berm. The arm of the person is pointing the position of remainder of the old soil, which is 0.78 m higher than the new beach berm. The distance between the 1993 formed erosion scarp and the new crest of berm is 16.4 m. View to 005º, see location on Figure 6.

Plate 14. A tree (Callophilum inophyllum) with landward extended roots indicate at least 3.3 m of shoreline retreat, southeast of Teakenga Point, north section of northeast coast. View to 150º, see location on Figure 6.

[TR243 - Chunting Xue] [39]

Plate 15. The protruding land with two coconut trees indicates at least 2.4 - 2.7 m of shoreline retreat, southeast of Teakenga Point, north section of northeast coast. View to 210º, see location on Figure 6.

Plate 16. Prograding shoreline with young coconut trees and bushes along the berm, northwest of Motutanifa Islet, north section of the northeast coast. View to 145º, see location on Figure 6.

[TR243 - Chunting Xue] [40]

Plate 17. Prograding shoreline with young coconut trees and bushes along the berm, west of Motutanifa Islet, north section of northeast coast. View to 310º, see location on Figure 6.

Plate 18. The erosion scarp with a convex-seaward remains of the old shoreline with coconut trees, indicating at least 2.5 m shoreline retreat, the northwest (NE - SW extending) shore of the middle section of the northeast coast. See location on Figure 6.

[TR243 - Chunting Xue] [41]

Plate 19. The prograding shore with muddy sand beach, in the bay northwest of Tefuta Passage, middle section of northeast coast. View to east, see location on Figure 6.

Plate 20. A surviving tree with landward extended roots indicating at least 4.9 m (east side) and 7.2 m (west side) of shoreline retreat, southeast shore of Alia Opeti Passage, middle section of northeast coast. View to 120º, see location on Figure 6.

[TR243 - Chunting Xue] [42]

Plate 21. The erosion scarp indicating 3 m retreat of shoreline on the east shore of northern Tafia Islet, middle section of northeast coast. View to 025º, see location on Figure 6.

Plate 22. Surface grass has been washed away and the coconut trees roots have been partly exposed, eastern part of southern Tafia Islet, middle section of northeast coast. View to 025º, see location on Figure 6.

[TR243 - Chunting Xue] [43]

Plate 23. The prograding shore with young coconut trees and bushes (foreground) and stable shore (background), west of the Lusamotu islets northwest of Motuosina Point, southeast end of northeast coast. View to 145º, see location on Figure 6.

Plate 24. A surviving coconut tree is 3.4 - 3.7 m in front of an erosion scarp, southwest end of southeast coast. View to 270º, see location on Figure 6.

[TR243 - Chunting Xue] [44]

Plate 25. A prograding shore west of VT Z 4, southeast coast, the young coconut trees are growing in a 10 m wide belt, a bush belt is developed in front of the young coconut trees and a new crest of berm is 3.6 m in front of the vegetation line. View to 270º, see location on Figure 6.

[TR243 - Chunting Xue] [45]

ANNEX 2

Beach profile locations and profiling data

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[TR243 - Chunting Xue] [47]

[TR243 - Chunting Xue] [48]

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[TR243 - Chunting Xue] [50]

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[TR243 - Chunting Xue]