Reef Hydrodynamics and Sediment Processes

Science Center Objects

We are conducting geophysical and geochemical research to address questions about coastal groundwater-to-reef flow and coral reef health, with the goal of informing management decisions related to planning and implementing activities in priority watershed-coral reef systems.

Underwater photograph of a shallow, partially sandy reef environment with a 3-legged metal frame holding instruments.

Tripod deployed on the reef flat off Jurabi, Ningaloo World Heritage Site, Western Australia, with instrumentation designed to measure tides, waves, currents, and sediment being transported across the reef. Photo credit: Curt Storlazzi, USGS

The Problem

Over the past decade, we have primarily focused on fine-grained terrestrial sediment dynamics on reefs, due to its role as the greatest stressor to high-island fringing reefs throughout the U.S. and U.S.-Affiliated Pacific Islands, such as Hawaii, Guam, American Samoa, and large Office of Insular Affairs islands. However, recently we have expanded our focus to include carbonate sediment, as approximately 80-90% of coral reefs are constructed of lithified carbonate sediment (carbonate sand and rubble adhered together by calcareous algae, not intact coral growth). Because this carbonate sediment is a critical component of beach sediment supply, it represents an important resource for recreation and coastal storm protection. Although a key factor in the vertical growth of reefs and their ability to keep up with rising sea levels, carbonate reef sediment dynamics are poorly understood and this knowledge gap was recently determined to be a critical area of research for investigating climate-change impacts to coral reef-lined coasts.

Four illustrations in a panel show a group of islands and lines to show predictions of coral larvae dispersal patterns.

Numerically simulated Lagrangian coral larval dispersal patterns from the Olowalu reef on west Maui, Hawaiʻi, for four different coral larval spawning events. Such modeling demonstrates the potential for a given reef to seed different islands and their respective reefs over relatively short timescales.

Our Approach

The overall objective of this research is to better understand how hydrodynamics and sediment processes influence the development of coral reefs and their adjacent shorelines. Specifically, we are:

  1. Evaluating the role of coral-reef morphology on waves and wave-driven water levels over coral reefs and their resulting influence on coastal flooding.
  2. Elucidating the patterns of flow over coral reefs that result from different forcing mechanisms such as waves, currents, surface tides, internal tides, and subtidal motions.
  3. Determining the sources, pathways, and retention times of sediment, nutrients, and contaminants over complex coral reef morphologies.
  4. Identifying the circulation pathways that link separate reefs through larval or pollutant transport, and determine the spatial and temporal scales at which these pathways occur. 
  5. Evaluating how these processes and linkages will be affected by projected changes in climate such as sea-level rise and changes in the frequency and intensity of storms.

The overall objective of this research effort is to better understand how circulation and sediment processes impact coral reefs and their adjacent coastlines.

Caption for large photo at top of page: Photograph of large (6-meter-/20-foot-high) waves resuspending terrestrial flood sediment on the coral reefs off Puʻukoholā Heiau National Historic Site and Kawaihae Harbor, Hawaiʻi.