The USGS is working to provide a better understanding of how spatially-varying atoll morphology and coral cover interact with changes in water level to affect the propagation of waves of different heights and wavelengths across atoll reefs.
Overview

Roi-Namur is the northernmost and second largest island on Kwajalein Atoll, the largest coral atoll in the world. The atoll is in the Republic of the Marshall Islands, which is a self-governed and freely associated republic with the United States. The atoll lies near the equator about 3,900 km (2,100 mi) southwest of Hawaiʻi, and is comprised of 97 islands and islets. Originally two smaller islands, Roi on the west, and Namur on the east, the two were joined with fill during World War II. The single island now encompasses a total area of about 2.5 sq km (about 1 sq mi). Roi-Namur is known locally as “Roi.” Roi and several other islands on the atoll (including Kwajalein Island), are leased by the United States as part of the U.S. Army Kwajalein Atoll, part of the Ronald Reagan Ballistic Missile Defense Test Site formerly known as the Kwajalein Missile Range.
Motivation
Observations show that sea level is rising globally at a rate almost double the Intergovernmental Panel for Climate Change’s 2007 report, and up to half and order of magnitude greater in the central and western Pacific Ocean. Recent estimates suggest sea level will exceed 1.0 m, and may reach 2.0 m, above 2000 levels by the end of the 21st century. Sea-level rise is particularly critical for unconsolidated low-lying coral atoll islands, many of which have maximum elevations of less than 4 m above present sea level, such as Roi-Namur. These islands support 2000+ year-old cultures, yet the amount of land and water available for human habitation, water and food sources, and ecosystems is limited and extremely vulnerable to marine inundation from sea-level rise. Vertical coral reef flat accretion rates for coral reefs exposed to open-ocean storm waves (1 to 4 mm/yr) are up to an order of magnitude smaller than the rates of sea-level rise projected for the years 2000–2100 (8 to 16 mm/yr), therefore projected sea-level rise will outstrip potential new reef flat accretion, resulting in a net increase in water depth over exposed coral reef flats on the order of 0.4 to 1.5 m during the 21st century. The extreme vulnerability of these communities to changing oceanic and atmospheric conditions represents a serious threat through impacts on food and water security, public safety, and environmental health.
The USGS is working with Deltares, NOAA, and the U.S. Department of Defense to provide a better understanding of how spatially-varying atoll morphology and coral cover interact with changes in water level to affect the propagation of waves of different heights and wavelengths across atoll reefs. Such information is necessary to model how predicted sea-level rise and climate change may alter wave-driven inundation, and thus impacts to infrastructure, agriculture, and natural habitats, on low-lying atoll islands.
For additional information, visit the site, "The Impact of Sea-Level Rise and Climate Change on Pacific Ocean Atolls."
Learn more about coral reef and atoll studies at the USGS.
Low-lying areas of tropical Pacific islands
The Impact of Sea-Level Rise and Climate Change on Pacific Ocean Atolls
Coral Reef Project: Kwajalein Island
Below are data releases associated with this project.
Model parameter input files to compare the influence of channels in fringing coral reefs on alongshore variations in wave-driven runup along the shoreline
Model parameter input files to compare locations of coral reef restoration on different reef profiles to reduce coastal flooding
Cross-reef wave and water level data from coral reef environments
Database to model three-dimensional flow over coral reef spur-and-groove morphology
Coral reef profiles for wave-runup prediction
Model parameter input files to compare wave-averaged versus wave-resolving XBeach coastal flooding models for coral reef-lined coasts
Physics-based numerical model simulations of wave propagation over and around theoretical atoll and island morphologies for sea-level rise scenarios
Below are publications associated with this project.
A numerical study of geomorphic and oceanographic controls on wave-driven runup on fringing reefs with shore-normal channels
Spectral wave-driven bedload transport across a coral reef flat/lagoon complex
Modeling three-dimensional flow over spur-and-groove morphology
Sea‐level rise will drive divergent sediment transport patterns on fore reefs and reef flats, potentially causing erosion on atoll islands
The importance of explicitly modelling sea-swell waves for runup on reef-lined coasts
In situ observations of wave transformation and infragravity bore development across reef flats of varying geomorphology
Hydro-morphological characterization of coral reefs for wave runup prediction
Steps to develop early warning systems and future scenarios of wave-driven flooding along coral reef-lined coasts
Assessing morphologic controls on atoll island alongshore sediment transport gradients due to future sea-level rise
HyCReWW: A hybrid coral reef wave and water level metamodel
Tropical cyclone projections: Changing climate threats for Pacific Island defense installations
Most atolls will be uninhabitable by the mid-21st century because of sea-level rise exacerbating wave-driven flooding
Below are news stories associated with this project.
Below are partners associated with this project.
- Overview
The USGS is working to provide a better understanding of how spatially-varying atoll morphology and coral cover interact with changes in water level to affect the propagation of waves of different heights and wavelengths across atoll reefs.
Overview
Sources/Usage: Public Domain. Visit Media to see details.Defense Department facilities are visible in this satellite image of Roi-Namur Island. Credit: DigitalGlobe, Inc., Creative Commons Attribution 4.0 International Public License Roi-Namur is the northernmost and second largest island on Kwajalein Atoll, the largest coral atoll in the world. The atoll is in the Republic of the Marshall Islands, which is a self-governed and freely associated republic with the United States. The atoll lies near the equator about 3,900 km (2,100 mi) southwest of Hawaiʻi, and is comprised of 97 islands and islets. Originally two smaller islands, Roi on the west, and Namur on the east, the two were joined with fill during World War II. The single island now encompasses a total area of about 2.5 sq km (about 1 sq mi). Roi-Namur is known locally as “Roi.” Roi and several other islands on the atoll (including Kwajalein Island), are leased by the United States as part of the U.S. Army Kwajalein Atoll, part of the Ronald Reagan Ballistic Missile Defense Test Site formerly known as the Kwajalein Missile Range.
Motivation
Wave-driven flooding and overwash on Roi-Namur Island. Observations show that sea level is rising globally at a rate almost double the Intergovernmental Panel for Climate Change’s 2007 report, and up to half and order of magnitude greater in the central and western Pacific Ocean. Recent estimates suggest sea level will exceed 1.0 m, and may reach 2.0 m, above 2000 levels by the end of the 21st century. Sea-level rise is particularly critical for unconsolidated low-lying coral atoll islands, many of which have maximum elevations of less than 4 m above present sea level, such as Roi-Namur. These islands support 2000+ year-old cultures, yet the amount of land and water available for human habitation, water and food sources, and ecosystems is limited and extremely vulnerable to marine inundation from sea-level rise. Vertical coral reef flat accretion rates for coral reefs exposed to open-ocean storm waves (1 to 4 mm/yr) are up to an order of magnitude smaller than the rates of sea-level rise projected for the years 2000–2100 (8 to 16 mm/yr), therefore projected sea-level rise will outstrip potential new reef flat accretion, resulting in a net increase in water depth over exposed coral reef flats on the order of 0.4 to 1.5 m during the 21st century. The extreme vulnerability of these communities to changing oceanic and atmospheric conditions represents a serious threat through impacts on food and water security, public safety, and environmental health.
USGS researcher drills an instrument mount into a reef flat on Roi-Namur Island, Kwajalein Atoll, Republic of the Marshall Islands, in the Pacific Ocean. Photo by USGS. The USGS is working with Deltares, NOAA, and the U.S. Department of Defense to provide a better understanding of how spatially-varying atoll morphology and coral cover interact with changes in water level to affect the propagation of waves of different heights and wavelengths across atoll reefs. Such information is necessary to model how predicted sea-level rise and climate change may alter wave-driven inundation, and thus impacts to infrastructure, agriculture, and natural habitats, on low-lying atoll islands.
For additional information, visit the site, "The Impact of Sea-Level Rise and Climate Change on Pacific Ocean Atolls."
- Science
Learn more about coral reef and atoll studies at the USGS.
Low-lying areas of tropical Pacific islands
Sea level is rising faster than projected in the western Pacific, so understanding how wave-driven coastal flooding will affect inhabited, low-lying islands—most notably, the familiar ring-shaped atolls—as well as the low-elevation areas of high islands in the Pacific Ocean, is critical for decision-makers in protecting infrastructure or relocating resources and people.The Impact of Sea-Level Rise and Climate Change on Pacific Ocean Atolls
Providing basic understanding and specific information on storm-wave inundation of atoll islands that house Department of Defense installations, and assessing the resulting impact of sea-level rise and storm-wave inundation on infrastructure and freshwater availability under a variety of sea-level rise and climatic scenarios.Coral Reef Project: Kwajalein Island
The USGS is working to provide a better understanding of how spatially-varying atoll morphology and coral cover interact with changes in water level to affect the propagation of waves of different heights and wavelengths across atoll reefs. - Data
Below are data releases associated with this project.
Model parameter input files to compare the influence of channels in fringing coral reefs on alongshore variations in wave-driven runup along the shoreline
An extensive set of physics-based XBeach Non-hydrostatic hydrodynamic model simulations (with input files here included) were used to evaluate the influence of shore-normal reef channels on flooding along fringing reef-lined coasts, specifically during extreme wave conditions when the risk for coastal flooding and the resulting impact to coastal communities is greatest. These input files accompanyModel parameter input files to compare locations of coral reef restoration on different reef profiles to reduce coastal flooding
This dataset consists of physics-based XBeach Non-hydrostatic hydrodynamic models input files used to study how coral reef restoration affects waves and wave-driven water levels over coral reefs, and the resulting wave-driven runup on the adjacent shoreline. Coral reefs are effective natural coastal flood barriers that protect adjacent communities. Coral degradation compromises the coastal protectCross-reef wave and water level data from coral reef environments
Coral reefs provide important protection for tropical coastlines against the impact of large waves and storm damage by energy dissipation through wave breaking and bottom friction. However, climate change and sea level rise have led to growing concern for how the hydrodynamics across these reefs will evolve and whether these changes will leave tropical coastlines more vulnerable to large wave evenDatabase to model three-dimensional flow over coral reef spur-and-groove morphology
This data set consists of physics-based Delft3D-FLOW and SWAN hydrodynamic models input files used to study the wave-induced 3D flow over spur-and-groove (SAG) formations. SAG are a common and impressive characteristic of coral reefs. They are composed of a series of submerged shore-normal coral ridges (spurs) separated by shore-normal patches of sediment (grooves) on the fore reef of coral reef eCoral reef profiles for wave-runup prediction
This data release includes representative cluster profiles (RCPs) from a large (>24,000) selection of coral reef topobathymetric cross-shore profiles (Scott and others, 2020). We used statistics, machine learning, and numerical modelling to develop the set of RCPs, which can be used to accurately represent the shoreline hydrodynamics of a large variety of coral reef-lined coasts around the globe.Model parameter input files to compare wave-averaged versus wave-resolving XBeach coastal flooding models for coral reef-lined coasts
This data release includes the XBeach input data files used to evaluate the importance of explicitly modeling sea-swell waves for runup. This was examined using a 2D XBeach short wave-averaged (surfbeat, XB-SB) and a wave-resolving (non-hydrostatic, XB-NH) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Results show that explicitly modelling the sea-swell componenPhysics-based numerical model simulations of wave propagation over and around theoretical atoll and island morphologies for sea-level rise scenarios
Schematic atoll models with varying theoretical morphologies were used to evaluate the relative control of individual morphological parameters on alongshore transport gradients. Here we present physics-based numerical SWAN model results of incident wave transformations for a range of atoll and island morphologies and sea-level rise scenarios. Model results are presented in NetCDF format, accompani - Publications
Below are publications associated with this project.
Filter Total Items: 31A numerical study of geomorphic and oceanographic controls on wave-driven runup on fringing reefs with shore-normal channels
Many populated, tropical coastlines fronted by fringing coral reefs are exposed to wave-driven marine flooding that is exacerbated by sea-level rise. Most fringing coral reef are not alongshore uniform, but bisected by shore-normal channels; however, little is known about the influence of such channels on alongshore variations on runup and flooding of the adjacent coastline. We con-ducted a parameAuthorsCurt D. Storlazzi, Annouk Rey, Ap van DongerenSpectral wave-driven bedload transport across a coral reef flat/lagoon complex
Coral reefs are an important source of sediment for reef-lined coasts by helping to maintain beaches while also providing protection in the form of wave energy dissipation. Understanding the mechanisms by which sediment is delivered to the coast as well as better constraining the total volumes generated are critical for projecting future coastal change. A month-long hydrodynamics and sediment tranAuthorsKurt J. Rosenberger, Curt D. Storlazzi, Olivia Cheriton, Andrew Pomeroy, Jeff E. Hansen, Ryan Lowe, Mark BuckleyModeling three-dimensional flow over spur-and-groove morphology
Spur-and-groove (SAG) morphology characterizes the fore reef of many coral reefs worldwide. Although the existence and geometrical properties of SAG have been well documented, an understanding of the hydrodynamics over them is limited. Here, the three-dimensional flow patterns over SAG formations, and a sensitivity of those patterns to waves, currents, and SAG geometry were characterized using theAuthorsRenan da Silva, Curt D. Storlazzi, Justin S. Rogers, Johan Reyns, Robert T. McCallSea‐level rise will drive divergent sediment transport patterns on fore reefs and reef flats, potentially causing erosion on atoll islands
Atoll reef islands primarily consist of unconsolidated sediment, and their ocean‐facing shorelines are maintained by sediment produced and transported across their reefs. Changes in incident waves can alter cross‐shore sediment exchange and, thus, affect the sediment budget and morphology of atoll reef islands. Here we investigate the influence of sea level rise and projected wave climate change oAuthorsJames F Bramante, Andrew D Ashton, Curt D. Storlazzi, Olivia Cheriton, Jeffrey P. DonnellyThe importance of explicitly modelling sea-swell waves for runup on reef-lined coasts
The importance of explicitly modelling sea-swell waves for runup was examined using a 2D XBeach short wave-averaged (surfbeat, “XB-SB”) and a wave-resolving (non-hydrostatic, “XB-NH”) model of Roi-Namur Island on Kwajalein Atoll in the Republic of Marshall Islands. Field observations on water levels, wave heights, and wave runup were used to drive and evaluate both models, which were subsequentlyAuthorsEllen Quataert, Curt D. Storlazzi, Ap van Dongeren, Robert T. McCallIn situ observations of wave transformation and infragravity bore development across reef flats of varying geomorphology
The character and energetics of infragravity (IG, 25 s < period < 250 s) and very-low frequency (VLF, period > 250 s) waves over coral reef flats can enhance shoreline erosion or accretion, and also govern extreme shoreline events such as runup, overwash, and flooding on coral reef-lined coasts. Here we use in situ wave measurements collected along cross-reef transects at 7 sites on Pacific islandAuthorsOlivia Cheriton, Curt D. Storlazzi, Kurt J. RosenbergerHydro-morphological characterization of coral reefs for wave runup prediction
Many coral reef-lined coasts are low-lying with elevations <4 m above mean sea level. Climate-change-driven sea-level rise, coral reef degradation, and changes in storm wave climate will lead to greater occurrence and impacts of wave-driven flooding. This poses a significant threat to their coastal communities. While greatly at risk, the complex hydrodynamics and bathymetry of reef-lined coasts maAuthorsFred Scott, Jose A. A. Antolinez, Robert T. McCall, Curt D. Storlazzi, Ad Reiners, Stuart PearsonSteps to develop early warning systems and future scenarios of wave-driven flooding along coral reef-lined coasts
Tropical coral reef-lined coasts are exposed to storm wave-driven flooding. In the future, flood events during storms are expected to occur more frequently and to be more severe due to sea-level rise, changes in wind and weather patterns, and the deterioration of coral reefs. Hence, disaster managers and coastal planners are in urgent need of decision-support tools. In the short-term, these toolsAuthorsGundula Winter, Curt D. Storlazzi, Sean Vitousek, Ap van Dongeren, Robert T. McCall, Ron Hoeke, William Skirving, John Marra, Johan Reyns, Jerome Aucan, Matthew J. Widlansky, Janet Becker, Chris Perry, Gerd Masselink, Ryan Lowe, Murray Ford, Andrew Pomeroy, Fernando J. Mendez, Ana C. Rueda, Moritz WandresAssessing morphologic controls on atoll island alongshore sediment transport gradients due to future sea-level rise
Atoll islands’ alongshore sediment transport gradients depend on how island and reef morphology affect incident wave energy. It is unclear, though, how potential atoll morphologic configurations influence shoreline erosion and/or accretion patterns, and how these relationships will respond to future sea-level rise (SLR). Schematic atoll models with varying morphologies were used to evaluate the reAuthorsJames B. Shope, Curt D. StorlazziHyCReWW: A hybrid coral reef wave and water level metamodel
Wave-induced flooding is a major coastal hazard on tropical islands fronted by coral reefs. The variability of shape, size, and physical characteristics of the reefs across the globe make it difficult to obtain a parameterization of wave run-up, which is needed for risk assessments. Therefore, we developed the HyCReWW metamodel to predict wave run-up under a wide range of reef morphometric and offAuthorsAna C. Rueda, Laura Cagigal, Stuart Pearson, Jose Antolínez, Curt D. Storlazzi, Ap van Dongeren, Paula Camus, Fernando J. MendezTropical cyclone projections: Changing climate threats for Pacific Island defense installations
Potential changing climate threats in the tropical and subtropical North Pacific Ocean were assessed, using coupled ocean-atmosphere and atmosphere-only general circulation models, to explore their response to projected increasing greenhouse gas emissions. Tropical cyclone occurrence, described by their frequency and intensity, near islands housing major U.S. defense installations was the primaryAuthorsMatthew J. Widlansky, Hariharasubramanian Annamalai, Stephen B. Gingerich, Curt D. Storlazzi, John J. Marra, Kevin I. Hodges, Barry Choy, Akio KitohMost atolls will be uninhabitable by the mid-21st century because of sea-level rise exacerbating wave-driven flooding
Sea levels are rising, with the highest rates in the tropics, where thousands of low-lying coral atoll islands are located. Most studies on the resilience of these islands to sea-level rise have projected that they will experience minimal inundation impacts until at least the end of the 21st century. However, these have not taken into account the additional hazard of wave-driven overwash or its imAuthorsCurt D. Storlazzi, Stephen B. Gingerich, Ap van Dongeren, Olivia Cheriton, Peter W. Swarzenski, Ellen Quataert, Clifford I. Voss, Donald W. Field, Hariharasubramanian Annamalai, Greg A. Piniak, Robert T. McCall - News
Below are news stories associated with this project.
- Partners
Below are partners associated with this project.