[3] TABLE OF CONTENTS Page SUMMARY...................................................................................................................................5 ACKNOWLEDGEMENTS...........................................................................................................6 INTRODUCTION.........................................................................................................................7 STUDY METHODS ...................................................................................................................11 OUTLINE OF REEF FLAT AND BEACH..................................................................................11 COASTAL EROSION................................................................................................................12 Southwest Coast...................................................................................................................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 Tuvalu - Vaitupu 1:10 000 (SOPAC Coastal Series Map 9) [TR243 - Chunting Xue] [4] LIST OF FIGURES 1. Atolls 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 sand accumulation near the small boat navigation channel 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 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. 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 groyne 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 lagoon 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 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. 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. [TR243 - Chunting Xue] [5] 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 lagoons. 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 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. 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. [TR243 - Chunting Xue] [6] 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. [TR243 - Chunting Xue] [7] INTRODUCTION Vaitupu (7º 29'S; 178º 41' E), the largest island (land area of 5.29 km2) is located 130 km north of the capital Funafuti (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 atoll 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 islets 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. [TR243 - Chunting Xue] [8] 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. [TR243 - Chunting Xue] [9] Figure 3. Coastal stability and geographical division of Vaitupu. McLean et al. (1991) divided the land into nine geomorphological units: northern spit, 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) [TR243 - Chunting Xue] [10] 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