The end.

That's a wrap everyone! We have now finished our time in the GWK flume. On our final day yesterday, we tested the response of our revetment with added thickness at the face to both normal and storm wave conditions. The revetment began with an initial slope of 1:4. Firstly, when exposed to 2 hours of normal waves (Hs = 0.8m, Tp = 6s), the revetment did not change much at all. We then applied storm waves (Hs = 1m, Tp = 8s), in which we observed the same behaviour as in previous tests - the revetment flattened in response to the larger waves (approaching 1:6 slope), mostly as a result of large overtopping events bringing down the crest. We then reverted back to normal wave conditions for 2 hours to rebuild the revetment crest and front face slope to roughly 1:4. 

Following these tests we ran even bigger storm waves (Hs = 1m, Tp = 9s). Surprisingly, the revetment did not flatten out in response to these larger waves - in fact, the crest of the revetment began to build upwards! In addition the revetment was translating landwards! Another test with EVEN BIGGER waves (Hs = 1.2m, Tp = 8s) still could not destroy the revetment, it did not flatten out and also managed to accrete a little bit. How dynamic is this thing?! We will have to analyse the profiles further, although one clear observation was that for these latter tests, overtopped water receded back through the core of the now thicker revetment - protecting the crest from backwash.

Figure 1 - The thickened revetment after running various wave cases. The revetment retained most of its volume during testing and the large storm waves caused the crest to accrete and the revetment to translate landward.

Today, Paul and I have been cleaning up the flume and the gear. A huge thanks to everyone that was involved in the experiment. We now get to jump into the data, make some discoveries and hopefully change the world!

Figure 2 - Deconstructing the revetment :(

Dynamic Revetment - Response to Storms!

We have now finished testing the response of our dynamic revetment to storm conditions (using various combinations of higher wave heights and longer periods). During these tests significant overtopping was observed and the revetment changed a lot. The revetment appeared to try and form a new flatter equilibrium shape in response to storm conditions. Over the course of the tests we observed the front slope of the revetment vary from the initial 1:4 to a flatter 1:6. This change was primarily driven by large overtopping events that pulled the revetment crest down the front slope. Our observations indicated that the equilibrium shape of the revetment was primarily driven by the wave period. While large overtopping events did flatten the revetment, they also carried pebbles landward and we saw a notable amount of deposition of pebbles landward of the revetment.

Figure 1 - A large overtopping event causing significant movement of pebbles.

Figure 2 - The flattened revetment after being exposed to storm conditions.

Following the storm tests that effectively flattened the revetment, we reverted to initial wave conditions for a few hours to see what would happen. Much to our delight, after only 2 hours of normal wave conditions, the revetment crest began to rebuild and the front slope reverted back to more-or-less a 1:4 slope. A dynamic revetment indeed!

Today, the flume paddle required maintenance. The three of us remaining at the flume (Paul, Gwyn, Tom) took the opportunity to RFID the tagged pebbles in the revetment, and then add an extra 4m^3 of pebbles to the revetment face so that we could test our hypothesis of whether or not a thicker revetment face could mitigate underlying sand loss (and associated revetment lowering) or change any of the behaviour observed in the tests performed to date. Tomorrow will be our last day of testing in the flume, where we plan to hit our new thicker revetment with normal and storm wave conditions!

Figure 3 - The new revetment with added thickness on the front slope!

Figure 4 - Paul taking a nap on the beach after a long day.

The sea level has stopped rising! (in the flume...)

So our sea level rise experiments have finished. This morning we finished testing the highest water level of 4.9m on our dynamic revetment and have now moved on to testing storm conditions. As described in the previous blog post, the revetment responded interestingly to sea level rise forcing - the revetment retained the majority of its pebbles and the toe remained in the same cross-shore position, but the revetment face lowered considerably due to underlying sand being lost. This lowering, with a fixed toe position, resulted in a steepening of the revetment and a thinning of the revetment face thickness. During SLR step 3 (water level 4.8m) and step 4 (water level 4.9m) we did observe pebbles beginning to 'roll-over' and build up the crest of the revetment - as we'd hoped would happen with this 'dynamic revetment'. Throughout the final test at water level 4.9m, underlying sand loss also appeared to be reducing, and the revetment was becoming relatively stable in its position and steepness. We did wonder whether or not having an initially thicker revetment face may have mitigated some of the underlying sand loss and the resulting lowering of the revetment. Fortunately we will get a chance to test this next week! We have time enough to drain the flume, add more pebbles to the revetment, and then re-run some waves.

Figure 1 - The revetment after the sea level rise experiments.

Figure 2 - Here I am looking professional in the flume.

For now, we have begun testing 'storm waves'. The water level has been fixed at 4.9m (the highest applied SLR scenario), and Hs has increased by 10cm to 0.9m (Tp = 6s). We are observing very high rates of overtopping in these tests and pebbles are moving around quite a lot on the revetment but we will have to wait until we collect more profile data to determine if the revetment is responding 'dynamically' to these storm conditions. 

Figure 3 - Overtopping waves during storm conditions.

Dynamic Revetment - Response to Sea Level Rise!

Hello everyone! We have a new team here with a lot of expertise and the experiment is running on schedule! We are on the second phase of the DynaRev experiment - testing the response of a 'dynamic revetment' to both sea level rise and storm conditions.

Figure 1 - The new team!

To refresh: the revetment is composed of 9m^3 of pebbles, placed directly on top of the sandy profile in the wave flume. Initial thickness varied from 30 cm (at the toe and crest) to 15cm in between toe and crest and landward of the crest. The revetment is called 'dynamic' because it is meant to respond to storm or sea-level rise forcing by 'rolling' landward. Within the revetment 97 pebbles with embedded RFID tags were placed, with focus on the revetment toe and crest. The location of these pebbles is measured after each sea level rise implementation to observe how the revetment is moving.

Figure 2 - The initial revetment.

The water level in the flume started at 4.5m. We have raised the water level in 4 steps of 0.1m to a final level of 4.9m. For the first 2 steps, little change was observed of the revetment and there was minimal overtopping.

Figure 3 - Revetment toe after SLR step 2.

During step 3 (water level 4.8m) the revetment began to be affected. Pebbles were lost seaward from the revetment, but not a significant amount. The revetment toe mostly stayed in the same location as where it was first constructed, however the toe and front face of the revetment has lowered significantly (e.g. a lowering of 0.4m has occurred at the toe). This is most likely due to underlying sand being lost through the porous pebble revetment. The result is a revetment face that is steeper, longer and thinner. RFID surveys of the tagged pebbles revealed that there has been mostly movement of pebbles seaward.  Overtopping was also occurring at this step 3 water level (4.8m) at approximately 30 overtopping waves per hour. We are now currently testing the final water level of 4.9m. The revetment continues to change with the same trend (toe staying fixed but revetment face lowering) and overtopping rates are significant at about 300 overtopping waves per hour. About 95% of the pebbles remain part of the revetment but they have moved around a lot. We have now begun to see noticeable movement of pebbles landward, i.e. waves pushing pebbles up the revetment to or beyond the crest. While this has resulted in the revetment crest increasing in thickness, it has not increased in elevation due to underlying sand loss. It remains unclear whether or not the lowering of the revetment due to underling sand loss will continue, if it does, the revetment will continue to thin and potentially fail. We wonder if we had made the revetment thicker initially whether or not sand loss through it could have been minimised. On the other hand, it could be that to mimic the natural version of these 'dynamic revetments' (that have evolved over thousands of years) we need a well mixed composite profile of sand and pebbles (as evident in nature) on which to place our protective structure.

After this final sea level rise test, we move on to testing storm waves. Bring on the destruction!

Figure 4 - Revetment after step 3.

Figure 5 - Revetment after step 4. Clusters of rock are only just visible in the pools of water seaward of the revetment toe.

The Dynamic Revetment is here!

Today's the day, what we've all been waiting for, the dynamic revetment!
We no longer need to stop and start all the instruments, therefore completing the profiles in-between each run goes a lot faster! So fast, that we are ahead of schedule again, completing all of DR1.
This meant we also had time to attempt the first trial of using the antenna to locate the pebbles in the revetment.
For those of you who are unaware, I shall quickly explain how this part of the experiment works.
The dynamic revetment consists of 9 m^3 pebbles, 5 m long shore and 7 m cross-shore (fig.1). This is meant to act as a defence from storms along the coast. The reason why it is called 'dynamic' is because (hopefully) the waves are meant to crash onto the revetment causing the pebbles to roll back landwards. Therefore the revetment is self maintained, causing it to be a cheaper alternative sea defence in the future. We have 97 seperate pebbles which have been painted either green (layer 1), orange (layer 2) or pink (layer 3). These pebbles have been implemented into the cross-shore center line of the revetment, depending on which layer they are in (either 1, 2 or 3). Each of these pebbles have a transponder located inside (so we can use the antenna to detect and locate them). These pebbles will then represent each layer of the dynamic revetment (dynarev), and hopefully we will be able to track where they move. This process will be done at the end of each test e.g. DR1, DR2 etc.

Fig.1 - The dynamic revetment in all its glory (yellow line indicating the crest of the revetment). You can just about see the green pebbles dotted around in the middle cross-shore section. 

Fig.2 - The green pebbles with transponders located inside.

Fig.3 - After a few hours of waves- loosing quite a few pebbles to the flume!

Fig.4 - Paul fixing the reader for the transponders,
 after he managed to drop it...not to worry everyone, it still works!

Fig. 5 - Paul attempting to locate the pebbles, the long pole is proving difficult to control.

Fig. 6 - Jens came up with the brilliant idea of attaching some rope to the end of the antenna and hold it the other side of the flume to support the pole, preventing it from wobbling around - worked a treat!

Deconstruction of rigs/Construction of revetment

Today was a sad day...We had to pack all of our equipment away. It has been a long 5 weeks and it certainly felt strange not turning on any of the laptops or instruments!
So, we had two groups of people, one working in the flume dismantling the rigs whilst the others were building the revetment at the top of the beach. All exciting stuff!
By the end of the day, everything was packed in boxes, and the revetment was up and running ready for waves tomorrow. Hopefully we have packed everything correctly and not left anything behind...! (Peter don't worry we definitely do have everything packed cleaned, dried and bubble wrapped! Aaron made sure of that) - if anything happens blame the shipping!
Anyway, everything is done...it is beer o'clock!

Before the destruction began!

All instruments and cables all dismantled,
 ready to be cleaned and packed.

Emily and Jak removing the final instrument, 3D sonar scanner.

And that's it, everything has been packed!

The revetment is in!

Even at home the work continues...Did someone say Matlab?

DR0 - completed!

Today the final set of tests for rig 1 and 2 were completed (DR0 - 20 hours), and the instruments logged for the final time. 

Half way through the test the vectrinos were buried, and we jumped into the freezing flume (for the last time-Yay!). We rotated the clamps up, rising the entire rig. All the equipment actually worked, apart from the final 3 hour run, our ABS would not respond...obviously something had to fail. On a positive note, the profiles came out looking pretty good (fig.1). When comparing test SB0_14 to DR0_14 (fig.3), which is the final profile of the tests, they should be identical (in theory) due to it being the same test being repeated. In general the profile is very similar, and only significantly differs ~235 m where SB0 has bedforms and DR0 has an inner sand bar.

So, apart from that me and Emily are done and dusted for our part of the experiment. We were joined by two more people from Plymouth Uni, Jak and Aaron, to help dismantle and pack everything from rig 1 and 2, ready to be shipped back to the UK. 

Fig 1 - Me and Paul braving the water for the final time!

Fig.2 - Cross-shore profile of test DR01 to 14. An increase in erosion is occurring on the beach-face, moving the sediment offshore, increasing the size of the sand bar. 

Fig.3 - Cross-shore profile of SB0_14, DR0_14 and the original profile of SB0. These two profiles have had the same time length of waves (20 hours), so in theory they should be the same.