Through idealized, numerical models this work investigates flows on a reef geometry which has received significant attention in the literature; a shallow, fringing reef with deeper, shore-ward pools or lagoons. This paper shows that reef roughness (and thus reef health) plays a significant role in determining circulation patterns and residence times. A rougher, healthier reef has a shorter residence time and more circulation than a less rough, unhealthy reef. Thus, loss of reef roughness could have implications for transport and mixing of nutrients and water masses, as well as larval dispersal.

Reefs are incredibly diverse in terms of biology, ecology, physical environment, and geometry. We set up numerical models of two typical types of reef geometries, barrier reefs and fringing reefs, and investigated how the forcing and flow on the reefs varied with tides and incident wave heights. Depending on forcing, the reefs behaved more open channel-like ('open reefs') or beach-like ('closed reefs'), and open reefs had stronger flow and water renewal than closed reefs. The figure above is from our paper, where we summarize characteristics of the two dynamical regimes.  The paper is inspired by observations from Ofu, American Samoa, a reef that seems to transition between open and closed depending on wave and tidal conditions, making it particularly interesting. 

We are combining 3D reef models from Structure-from-Motion with observations from acoustic Doppler current profilers (ADCPs) to understand the spatial homogeneity of reef boundary layers. Field work is always limited by time and resources, so how representative are our measurements? If our instruments were displaced slightly on the reef, would we get the same results? Results from a reef in the Chagos archipelago show surprising agreement between different types of instruments distributed over the reef, see the video above. Here the velocity measurements from three instruments are superimposed on the reef bathymetry, and all instruments are capturing the same overall flow structure in the water column. This is encouraging news for scientists working in the field! Read our paper here, a press release here, and watch a short video here.

Combining estimates of flow and turbulence with biogeochemical measurements, our colleagues at Stanford Earth System Science can estimate reef metabolism rates and take the pulse of the world's reefs. The photo shows a setup in Chagos, where we deployed these systems on three different reefs in 2019. In collaboration with colleagues from the Zoological Society of London we are carrying out an interdisciplinary study combining results from physical oceanography, chemistry, and genomics to understand the influence of environmental conditions on benthic communities and coral recruitment across the three reefs.

As part of a larger project lead by USGS and University of Western Australia, we deployed using a large array of pressure sensors monitoring waves over a three month period in 2018 in Moloka'i, Hawaii (above). Using techniques originating from seismology, we are able to identify along-shore propagating edge waves, and correlate them to a number of hurricanes and storms passing through the region during the period. While edge waves are typically longer, lower amplitude waves than swell waves, they can be important for transport of sediments and nutrients and coastal morphology.

As part of my masters degree I worked with numerical modelling of estuaries. Together with the Technical University of Denmark and Deltares, I used Delft3D to study stratified circulation in the Rio Magdalena in Colombia (above), and later as a research assistant at Berkeley I studied the influence of upstream wetland sediment deposition on the Pescadero estuary in California.