Initial environmental evaluation for beach replenishment at Kadhdhoo Airport VIP Area, Laamu Atoll

Abstract

This report addresses the environmental concerns of the proposed beach nourishment at the VIP Area at the southern end of Kadhdhoo Domestic Airport in L. Kadhdhoo. The area is devoid of beach due to the flow of current in the channel. In addition, there are deepened areas just next to the beach which act as a sink for sediments moving longshore. Therefore, it is proposed to place sand in these deepened areas to reduce depth so that erosion is minimized and the safety of swimmers is enhanced. The borrow sites for the proposed beach nourishment will be in the eastern side reef flat. However, the appropriateness of this location as a borrow site has not been studied so far. It is expected that an area of about 20,000m2 would have to be excavated to a depth of about 3m below MSL. This would be adequate to fill the dredged locations in the VIP area and to nourish the approximately 470m long stretch of beach to about 10m from the current high tide line. It would be necessary to sieve the sand before it is placed on the beach to match natural beach conditions preferred by clients. Without structural protection, it may not be possible to keep the beach intact after nourishment. Therefore, regular beach nourishment would be required in the absence of structural protection. Hence, it is proposed to undertake regular beach nourishment by borrowing sand from the southeastern lagoon from the same location as the proposed borrow area or by moving further south and southwest of the proposed borrow area. Since the borrow area is on the rim reefward side of the lagoon, currents are never expected to take the sediment towards the reef on this side. The reef on the western side is at quite a considerable distance that sedimentation of the reef would be unlikely. Therefore, there are no major impacts due to the proposed beach nourishment activity as anthropogenic impacts currently present in the area have greater impact. Deepening the rim reefward end of the channel may affect flow in a positive way as it is expected to dampen the currents flowing in the channel by absorbing part of the energy. Sand pumping from nearshore locations has the potential to aggravate erosion as the borrow pits can become sediment sinks over a considerable period of time. If borrow areas are too close to the shore, the impact on the island shoreline and the erosion of the nourished beaches would be quite rapid. Therefore, it is recommended to keep the borrow areas as far as possible from the beach. In the case of the proposed area, the movement of beach material into the dredged area would be minimal given that there would be a net westerly current most of the time. Yet, it is suggested to keep the borrow area at least 40m from the beach line. The other possible impact would be the hindrance to growth of patch corals within the lagoon. However, there are no significant coral patches within the lagoon which may be affected by the proposed beach nourishment activity. Given that biological resources are not directly affected, aesthetic concerns are of importance in the proposed project. Therefore, in order to maintain the aesthetic value of the beach and enhance the socio-economic benefits of the proposed project, it is important beach nourishment is undertaken in such a way that beach nourishment frequency does not exceed twice a year. The most important mitigation measure in the case of the proposed project aimed at providing closely simulated natural beach condition would be to sieve the borrow material to remove coral rubble to match natural beach conditions to the greatest possible extent. The remaining coarse material after sieving shall be placed away from the local beach areas on the western side so that they rarely get washed on to the shore. Regular monitoring of the coastal area is essential to ensure that the sediment movement patterns are clearly understood so that future mitigation measures will be more useful and meaningful. It would also help to alter beach nourishment profiles so as to minimize the frequency of beach nourishment. Long term monitoring would also help to design sustainable structural protection for long term protection. Therefore, monitoring the beaches before, during and after the initial beach nourishment is recommended. It is recommended to monitor beach profiles and currents in the channel as regularly as possible preferably every two months for the first two years. It is also recommended to undertake regular beach nourishment at no more than twice a year. Given that the project has minimal impact on the environment or ecological resources but high socio-economic benefits, it is recommended to allow the project to proceed. However, the Proponent shall be required to follow the proposed mitigation measures of placing only sieved sand on the beaches and regular monitoring of shorelines, beach profiles and currents in the channel.