Waves in Shallow Water (WASH)

EPSRC-funded research into breaking and broken ocean waves.

First WASH Publication

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Congratulations to PhD student, Kevin Martins for leading the first peer-reviewed journal publication from the WASH project.

Martins, K., Blenkinsopp, C.E., Almar, R. & Zang, J. 2017. The influence of swash-based reflection on surf zone hydrodynamics: a wave-by-wave approach. Coastal Engineering, 122, pp. 27-43.

An accepted proof of the paper can be downloaded at:

http://people.bath.ac.uk/km661/Martins_et_al_Swash_Based_Reflection.pdf

 

 

Chile!

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The second WASH experiment was successfully completed in Quintero, Chile between November 21-28, 2016.  The main part of the project team consisted of Dr Chris Blenkinsopp, Erwin Bergsma and Kévin Martins (Bath), José Beya (Universidad de Valparaiso, Chile), Hannah Power (University of Newcastle, Australia) and Roberto Agredano Martín (Pontificia Universidad Católica de Chile).  We were also ably supported at times by Anne Quaas, Francisca Quijada  and Harold Diaz - students from Universidad de Valparaíso and Universidad Técnica Federico Santa María.

Fig1

The study site at Quintero was quite a contrast to Saltburn as it is home to a wide range of heavy industry.  The beach is exposed to consistent large swells from the Pacific and it was the opportunity to measure consistent, large breaking waves that led us to choose this site.  To mount the Lidar instruments for our experiment, we were very kindly granted access to utilise the 750 m long loading jetty of Oxiquim S.A.

Fig2

Wave conditions during the experiment were very consistent throughout the experiment, with wave breaking height around 2m.  The wind was generally light every morning making this the ideal time to focus our efforts and hence necessitating some early rises.

Fig3

The experimental setup was similar to that at Saltburn, with 3 Lidar instruments deployed at 30 m intervals along the jetty, approximately 7 m above the mid tide water level.  A monitoring camera was installed on the hill behind the beach to monitor run-up processes, beach changes and potentially provide the opportunity to estimate nearshore bathymetry using a depth-inversion type approach.  Additionally, two ADCPs were deployed in 18 m water depth – one owned by Oxiquim which recorded spectral parameters and another installed with the help of the Chilean Navy specifically for the project which recorded time-series data.  GPS beach surveys were completed every low tide, along with wading total station surveys to get surf zone profiles, backed up by rope soundings from the jetty itself.

Fig4

The installation of in-situ instrumentation on the beach was limited by the fact that the tidal range at the site is only 1.8 m and thus to install surf zone instruments would require a boat which was not possible in the wave conditions.  A swash zone ADV and pressure transducer were deployed on a scaffold frame every low tide with the aim of obtaining measurements during high tide.

Fig5

Overall, the experiment was a great success, bringing together scientists from 3 continents to obtain some truly unique measurements.  We were aided by significantly warmer weather than for our Saltburn experiment and consistently good wave conditions with light winds.  As well as providing our project with great data, we were very lucky to get the opportunity to visit Chile, eat too many avocados and attempt some very poor Spanish.

Huge thanks must go to Erwin, who was thrown straight into organising most of the instrumentation and logistics from Bath.  Our hosts, Oxiquim were fantastically helpful throughout the experiment, in particular Marcelo Gomez who went out of his way to assist us with support from boats, divers and welders.  Most of all thanks go to Jose Beya whose help with translating, organising logistics and also arranging a very well attended post-experiment seminar made the whole experiment possible.

 

First Waves

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It has been a while since the experiment in Saltburn, with much of the team's time taken up with preparations for the second experiment in Quintero, Chile later this month.  However as a taste of things to come we have produced a short animation of the surface elevation data for a series of waves captured by the Lidar array around high tide at Saltburn.

By capturing the water surface about every 10cm over almost 100m, 25 times per second we are effectively able to take a cross-section out through 1.5 m high breaking and broken waves!

At high tide, large waves were reflected by a steep gravel slope on the upper beach and the Lidar data captures the collision of these reflected waves with the incoming waves.  The level of detail captured by the data is fantastic and the ability to capture highly-localised and short duration processes is very promising for our future work.  A short communication paper detailing the experiment, processing methodology and some initial results is currently in preparation.

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Saltburn Experiment

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Less than 2 months after the start of the WASH project our team have successfully completed the first of the two major field experiments at Saltburn-by-the-Sea, Yorkshire, UK between April 4-14th, 2016.  Our international experiment team (Figure 1) consisted of Dr Chris Blenkinsopp and Kevin Martins (Bath), Dr Hannah Power (Newcastle, Aus) and Drs Jack Puleo, Brittany Bruder and Aline Pieterse (Delaware, USA).

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Figure 1 - The project team

Saltburn was chosen as it is home to a beautiful Victorian pier (Figure 2) which enabled us to suspend a network of Lidar instruments approximately 6-7m above breaking and broken waves.  We also chose Saltburn as it has one of the most consistent wave climates in the UK at beaches with existing piers, as well as a large tidal range which enabled us to install instrumentation on the beach in the dry at low tide and then wait for the tide to come in.

Figure 2. Saltburn Pier at low tide.

Figure 2. Saltburn Pier at low tide.

Over the first two days our major tasks were to complete a topographic survey and begin installing our instrumentation.  On the pier we installed three SICK LMS511 2D Lidar which were suspended on scaffold frames 2m from the pier railing over the surf/swash zone (Figure 3).  These instruments use a scanning eye-safe laser to obtain water surface measurements, 25 times per second at 1000's of locations along an 80m line parallel to the pier.  This means that when waves are breaking under the pier between mid and high tide we were able to get fantastic data (effectively a slice through the waves for many thousands of waves up to approximately 2m in height) from the point of wave breaking to the maximum runup on the beach (examples to follow in a subsequent post).  At times a 4th Lidar was also installed to monitor some interesting sediment transport and wave reflection processes occurring on a high tide shingle ridge, this instrument captured the process of wave reflection from a steep slope fantastically well.  In addition to the Lidars, Hannah got to work setting up a camera on the pier to monitor inner surf and swash processes with the aim of adding surface velocity data to the information from the Lidar (Figure 4).

Figure 3. Lidar suspended from the pier.

Figure 3. Lidar suspended from the pier.

Dr Hannah Power setting up the swash camera.  Image from www.davecharnleyphotography.com.

Figure 4. Dr Hannah Power setting up the swash camera. Image from www.davecharnleyphotography.com.

To measure in-situ hydrodynamic and sediment transport properties, 3 instrument frames (Figure 5) were installed on the beach below the pier but offset from the Lidar scan.  On each frame we installed an acoustic Doppler velocimeter (ADV) to measure horizontal and vertical flow velocities, a pressure transucer (PT) to measure flow depths and an optical backscatter sensor (OBS) to estimate the concentrations of sediment suspended in the water.  These data will be used to supplement the Lidar data and provide a link between wave shape and sediment transport parameters, hopefully enabling better predictions of sand movement on beaches.  In addition to the beach frames, PTs were also installed along the pier legs to measure waves in deeper water, offshore of the Lidar array.

Figure 4. Beach instrument frame.

Figure 5. Beach instrument frame.

We were lucky enough to get excellent wave conditions throughout the experiment, varying from small, short period waves to larger (1.5m) longer period waves, generally with light or offshore winds providing ideal measurement conditions (Figure 6).  Over the period from Thursday to Monday however it also provided ideal conditions for the region's surf community to be out in force (much to the jealousy of many of our team). Discussions were held with the local surfers to ensure that the instrument frames did not provide a safety hazard and the local surf businesses and websites assisted us by helping to inform all surfers about our experiment.  Thanks to all who assisted and in particular Stephen Bulmer.

Figure 5. Surf and sun!

Figure 6. Surf and sun!

We are pleased to report that the experiment was a real success, we were incredibly lucky with the wave conditions and the Lidar instrument worked fantastically well, capturing what we believe to be the most detailed measurements of breaking and broken waves in the field ever obtained - watch this space from some preliminary Lidar data.  While we were lucky with the wave conditions, the North East treated us to some pretty chilly weather which was particularly a challenge for our colleagues from warmer climes and got through all 6 layers after 14 hours on the beach.  Nonetheless the sun did make some appearances and those on the late shift were treated to some spectacular sunsets.

Purple Sunset
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Figure 7. Sunsets.

Saltburn is a beautiful, and as we discovered, very busy beach - over the course of the week we talked to hundreds of people all of whom were interested and supportive of our work.  I think our team were all pretty blown away by the friendliness of the local people and businesses who made our time there a pleasure.  Particular thanks goes to the Saltburn Cliff Lift staff for sharing their lunch space and giving free lifts up to cliff to tired legs, and Perveen Mian at Redcar and Cleveland Borough Council who made the experiment possible!

Victorian scientists.

Victorian scientists.

Kevin Martins hard at work (www.davecharnleyphotography.com)

Kevin Martins hard at work (www.davecharnleyphotography.com)

Jack Puleo

Jack Puleo installing PTs

Best seat in Saltburn.  Chris and Hannah looking chilly.

Best seat in Saltburn. Chris and Hannah looking chilly.

Brittany Bruder, camera shy.

Brittany Bruder breaking free

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Pier in the sun.

Saltburn looking fine.

Saltburn looking fine.