Surf Science & Surfbreak Protection

Surfbreak protection is an ever-increasing trend. In the last decade we have seen the inauguration of world surfing reserves and changes to policy that stand to protect these valuable resources.  However, the development of unprotected sections of coastline will continue. How will we know if a protected surfbreak is undergoing changes?  How will we know if the changes are the result of natural variations or influenced by mans actions?

In order to answer these questions, a protected surfbreak requires consistent monitoring. Initiating monitoring when a surfbreak is at risk or when change is already apparent is simply not sufficient.  The monitoring of a protected surfbreak is required from the moment that it is designated. Without reliable data all opinions are speculative, which can easily lead to disagreements that are difficult, if not impossible, to settle.

A terrestrial National Park is not designated and then ignored.  Commonly, educated Park Rangers are employed to help preserve the environment.  They ensure that equilibrium is maintained by observing and monitoring indicator species for changes and ensuring that the natural resource is not compromised.

If there is a requirement for a “Park Ranger” element to surfbreak management, the next question is what can be monitored?

In the marine environment many surfers consistently assess the “indicator species” integral to a surfbreak’s health. Surfers discuss the swell direction, height and period e.g. “the swell has too much south in it for the points……” They talk about how the sandbanks have changed and the shape of the waves.  Long time locals of surfbreaks often start to notice seasonal patterns beyond just swell height.  However, anecdotal evidence that a surfbreak no longer produces the type of waves that it used to, no matter how compelling, is insufficient.

Google Earth image of a well-known Peruvian point break. Annotations show an average peel angle through that section 40° – great for high performance surfing.

Fortunately, scientists have identified the physical components that comprise surfbreaks and have developed methods of quantifying them.  In New Zealand, a formal definition of a surfbreak has been included in the country’s most recent coastal policy statement which formally protects 17 nationally significant surfing breaks.  The definition includes and describes some of the components integral to a surfbreak.  This statement is a great source of reference, from it we can take that a surfbreak does not start and end with the seabed immediately below the breaking part of the wave.  On the contrary, the shape of the seabed (morphology) and the waves and currents (hydrodynamics) of the ocean, from the swell source to the final shoreline, influence the way a wave breaks.

The offshore region, through which swell travels from its source in order to reach a surfbreak is the surfbreaks ‘swell corridor’.  As waves make their way landward within the swell corridor water depth will generally start to decrease. Interactions between surface waves and the seabed can begin at large distances from a surfbreak e.g. at the edge of the continental shelf for waves with periods of 16 seconds or greater. The interactions will continue all the way until the depth is sufficient to cause the waves to break.  The extent to which waves change is due to the seabed morphology, with certain features within the swell corridor modifying the swells characteristics. For example, some features may cause a localised area of increased wave height and a focussing of wave energy.

The seabed morphology closest to a surfbreak has the most influence over a wave’s final performance, or surfability.  The morphology determines wave shape, length of ride and how fast it breaks along its length.  These are all things surfers consider before getting in the water, during and after surfing. Is the wave barrelling? Or is it fat? Can you do any number of turns or just one before the ride is over? Is the wave a close-out or does it peel perfectly down the line?  Scientific investigations have determined what seabed configurations are conducive to certain wave types.  Of course some seabeds do not stay the same. Sandy beaches or river mouths undergo changes on sub-daily to multi-decadal timescales, and the changes will be manifested in the characteristics of the breaking waves.

It is evident that the physical process and components that comprise a particular surfbreak operate on a range of spatial and temporal scales.  The next question is how do we define or monitor all these processes?

One method developed for defining a swell corridor uses a computer based wave simulation model. The model simulates wave propagation from offshore to nearshore locations accounting for interactions with the seabed morphology.  The offshore wave conditions comprising waves from all possible wave conditions are simulated, however only the swell source locations that significantly influence wave height at the surfbreak are considered. The final result is a geographically established area that is integral to the existence of a surfbreak.

Profile photo of a breaking wave annotated to show the fundamentals of wave shape

Seabed morphology plays a huge part in the processes so far described.  Because of the fundamental relationship between morphology and wave breaking, the seabed provides an excellent proxy for “surfbreak health”.  The seabed can be monitored by conducting bathymetric surveys (finding the depth of the seabed over a certain area), often in conjunction with beach profiles.  A comparison of repeat surveys gives an indication to the extent of change to the seabed during the time between surveys.  The more frequent surveys are the more information can be gathered regarding the fluctuations in seabed levels, and/or the stability of certain seabed features.  Just as importantly, the longer that repeat surveys continue for the better understanding there will be of seasonal, annual, multi-annual, decadal and even multi-decadal patterns of morphological change.  An important point to note about the establishment of a long-term bathymetric dataset is that it provides the foundation for the differentiation between natural and anthropogenic change.

Another very cost-effective method for looking at long term change is using photographic imagery. Images from a fixed camera are geo-rectified, or transformed to a birds view with a spatial reference.  Data is collected as time-lapsed images of the surf-zone. From the images investigators can examine wave breaking patterns, beach width, rip currents, intertidal morphology, wave period and direction, and determine volumetric changes of the shoreline.

Some of the advantages of imaging systems are that: it is a form of remote sensing (i.e. it’s non-intrusive); it’s almost continuous which can capture the short term spatial variability of nearshore hydro and morphodynamics; and the system can be fully automated once the equipment has been setup, which is relatively inexpensive.

Whilst the above monitoring and research methods provide data concerning morphological change and designation of areas of interest, both of which are extremely important factors in learning about a surfbreaks environment, they are only indicative to a surfbreaks current state of health.  Regarding waves for surfing there are two fundamental parameters that determine the class in terms of difficulty and performance. One is wave shape, and the other is rate at which a wave breaks along its length. The latter is proportional to what is called the peel angle.  

Schematisation of peel angle

The peel angle is the angle between the unbroken wave crest and the path of the break point as it moves shoreward.  Wave shape can be described in terms of a vortex ratio. A wave vortex is a scientist’s way of describing what surfers call the barrel – the space left open between a wave crest and the wave face as the crest projects forward during breaking.  The vortex ratio is a comparison of the vortex’s length and width.  Neglecting the quality of surfing waves and all its associated subjective arguments, these two parameters provide a quantifiable profile, comparable to finger prints, except vortex ratio and peel angle can be somewhat variable (depending on swell, tide, wind etc).  Many surfers intuitively understand the vortex ratio, evident by their ability to name well-known surfbreaks from just photographs of the barrel.

Both of these parameters can be measured directly in the field, or numerically modelled. In the field both vortex ratios and peel angles are measured through photographic image analysis. Simple wave propagation (phase averaged) numerical models that include depth induced breaking can be used to predict wave vortex ratios and peel angles.  Better still is the use of more complex and computationally demanding models where individual wave propagation is predicted (phase resolving).  Both methods need a detailed digital terrain model of the seabed to propagate the waves over, which may require the collection of bathymetric data in the field.  For confidence in the models to accurately predict these wave breaking characteristics, a calibration of the model is required. This would also involve the fieldwork methods described previously.

The advantage of numerical models is that once a model is calibrated it can be used to predict any number of results for a range of conditions within the bounds of the calibration.  A good example of this on a larger scale are the wave forecast sites that many surfers utilise – these are numerical models using predicted parameters to forecast the surfing conditions for the coming week.  At a local scale, model calibration doesn’t just apply to the prediction of wave breaking characteristics but also morphological change.  A calibrated morphological model is capable of investigating changes on a whole range of time scales. It can be used to examine singular events, such as storms or beach replenishment or predict shoreline response over the next decade.  If used properly, a numerical model can become a premium tool for coastal resource management.

The fact that there is a range of practices for monitoring and defining a surfbreak is of a great benefit because each surfbreak, and any associated monitoring or research budget, will require a tailored monitoring programme.  Some locations may require complex, in-depth studies, others a simple, cost effective monitoring campaign.  While not everyone is able to conduct bathymetric surveys, install remote cameras and operate numerical models, there are some aspects of surfbreak monitoring that everyone can contribute to.  For example, taking photographs each time you go to the beach. This will document changes, especially when taken from the same location, whether photos are of the beach or the waves.  Some groups could conduct basic beach profiles.  Taking photos and filming from in and out of the water of people surfing, and the waves that are breaking, also helps to build up the picture of a surfbreak.  One exercise that could not have been done a decade ago, but is now readily available is logging the length of a surfers ride on a wave using a waterproofed GPS.  Ride length is regarded by some as one of the most desirable aspects of a wave for surfing.  If a dataset of ride lengths can be established, it can also be used an indicator of surfbreak health.

It is now well established that high quality surfbreaks increase tourism potential; and tourism can often encourage development.  In some cases coastal management practice has compromised surfbreaks. This is partially down to a lack of education and awareness regarding a surfbreaks amenity value, and knowledge with respect to what actually ‘makes’ the surfing break.  The future is encouraging for surfbreak protection, evident by the conceptualisation of surfing reserves and active changes to policy.  However it is imperative that a protected surfbreak or reserve be monitored. By establishing a comprehensive monitoring campaign a surfbreak can be sustainably managed through an adaptive approach that has its foundations in our understanding of the local system, not through a process of trial and error.

The details in this article have been provided by eCoast Ltd, a group of marine researchers and consultants.  For more information about eCoast, the groups work or any of the details within or related to this article please feel free to email e.atkin@ecoast.co.nz or visit the website www.ecoast.co.nz