Coastal Erosion on Majuro Atoll : Marshall Islands with Special Regard to Sea-Level Rise

Abstract

The Republic of the Marshall Islands is nation consisting of small coral atolls located in Pacific Ocean. It is a nation currently listed as a developing country according to the Organization for Economic Co-operation and Development. The Marshall Islands have through history been colonized by Spain, Germany and Japan, and was later during the World War II claimed by the United States. The current population on Marshall Islands are 60 000 and about half of the population is residing on Majuro, the capital island. Majuro is also the most developed atoll in the Marshall Islands.
Development and increasing population growth on Majuro has brought attention to the coastal problems Majuro is currently facing. Coastal erosion and sea-level rise have become a real and visible threat. Sandy beaches on Majuro are no longer common on the island and seawalls are being built more frequently.

In the IPCC (the Intergovernmental Panel on Climate Change) Fourth Assessment report 2007, small islands are mentioned as particularly sensitive to the effects of climate change, sea-level rise and extreme events. The characteristics of small islands, such as physical size, proneness to natural disasters and low adaptive capacity, make them especially vulnerable to climate change.

To calculate the coastal erosion on Majuro, the first step was to identify and understand different coastal processes. Two types of sediment transport have been analyzed in the thesis, longshore sediment transport and cross-shore sediment transport (dune/berm impact). The longshore sediment transport calculation is based on a wave climate in the lagoon developed from wind data taken from Majuro Sea Level Station. Waves from the ocean side have also been included in the calculations. The results for waves in the lagoon show a sediment transport direction going from east to west, with exception for the most western point on the island. The sediment transport for waves in the lagoon is in the range of -6 000 to 36 500 m3/year (negative means transport from east to west) along the south and west coastline. For ocean side waves the sediment transport range from -66 000 to 105 000 m3/year along affected coastline stretches. Waves from the ocean side reach only some parts of the coastline but show a large impact on the sediment transport along those stretches. A detailed future scenario for the longshore sediment transport was not investigated due to the complexity of the calculations and high uncertainties regarding future wind conditions. However, 10% increase in wind speed yielded 25% increase in sediment transport, which shows the potential impact of a climate change.
The rate of erosion from dune/berm impact was calculated using beach profile measurements performed by SOPAC (Pacific Islands Applied Geoscience Commission) and Professor Yokoki and his collegues between 1997 and 2009, and the wave climate in the lagoon. The dune/berm impact is also dependent on sea level, which is simulated by using three different sea-level rise scenarios, 0.25m, 0.44m and 0.76m by the year 2100. The third scenario, however, is assumed to have an exponential sea-level rise while the first two are assumed to be linear. The results shows that an estimated 32m (32m is chosen due to limitations in the profile measurements) of erosion inland will occur within 70-80 years for the first scenario and 50-60 years for both the second and the third scenario. In the latter half of the simulation period between 2050-2100, the erosion for the third scenario becomes extremely large because of the exponential increase in sea-level rise.

The risk of overtopping in the Majuro city center in the eastern part of the island has also been investigated in combination with a possible sea-level rise. Statistical analysis based on current wave conditions show that for an increase of 0.2 m in sea level the risk of overtopping will increase 3.5 times. For a 0.4 m sea level rise the risk will increase by 8.5 and for 0.6m the risk increases 15 times.

Climate change and sea-level rise is a multilateral threat for the coastal areas of Majuro. Though coastal management and awareness programs are present on the island it is hard to ignore the fact that Majuro is facing an uncertain future.

• author: Huang, Tai and Rapp, Henrik
• supervisor: Magnus Larson
• organization: Division of Water Resources Engineering
• course: VVR820 20091
• year: 2010
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Coastal Erosion, Majuro Atoll, Marshall Islands
• publication/series: TVVR10/5014
• report number: 10/5014
• ISSN: 1011-9824
• language: English
• additional info: Examiner: Hans Hanson
• id: 1670491
• date added to LUP: 2010-09-16 15:52:35
• date last changed: 2019-03-27 11:48:13