Thursday, 28 June 2012

First overwash run

Today we finished first overwash run D1 (0.8 m high and 4 second waves) with the new instrument set-up. Bit of a slow start because the beach kept adjusting to the increasing water level by building up the nearshore bar. Finally with water level at 4.2 m overwash occurred. A deep channel rapidly developed at the back of the barrier which compromised the measurements somewhat. After brief discussion, it was decided to fill in the channel by hand to prepare for the next overwash run. After a solid 1 hour of digging, involving the entire team and two wheel barrows the beach is now ready for the next overwash run with 5 second waves.

Top view of back-barrier overwash channel being filled in through manual labour: bootcamp BARDEX! Video below shows activities at ground level. Commentary by Jack Puleo and sand kicking activities by Aart Kroon.

Wednesday, 27 June 2012

Ready for overwash

Today a massive effort of the team. We rebuild the scaffold frame (some 2.5 m poles were practically covered and other were practically exposed); moved 15 bed-level sensors from the bottom of the beach to the top and back of the barrier; took out all Vectrino II and sheetflow probes; moved the three swash rigs to the back of the barrier and morphed them into 4 overwash rigs; moved back the video trolley and installed all the video ground control points; reconfigured the 2 vertical pressure sensor arrays into a cross-barrier pressure sensor array; and surveyed all new instrument positions in. The Deltaflume team had the wave paddle repaired very conveniently while we were adjusting our rigs. Bring on the overwash!

Tuesday, 26 June 2012

Arrival of the Portugese

BARDEX II has now been taken over by the Portugese (Ana, Barbara, Pedro and Rita) and the French (Bruno, Benjamin and Florent) in preparation for the overwash runs. Series A, B and C are now all successfully completed, and the tidal run provided a taster for what overwash will look like.

Thursday, 21 June 2012

All the way to New Zealand!

#Update: added even more heroic pictures

Heroic scenes today in the wave flume, as the University of New South Wales (Australia) boys, with aid from the other teams, dug a massive hole in the beach to retrieve their groundwater kit. After about 3 hours, the kit was retrieved, the holes were filled and the beach profile was restored to its original state.
Afterwards, test series B1 was run with waves of Hs=0.8 m and Tp = 8s (the same as series A1) in order to rebuild the bar. Based on the beach profile at the end of the day, it seems like we managed to create a (modest) bar indeed.

Wednesday, 20 June 2012

Groundwater effects!

Run A7 has given some problems. The accretionary swashes have really build up the beachface, but the combination of a very steep beach and high lagoon level has resulted in the development of groundwater drainage channels around the rig that have sufficient flow power to move sediment.

Thijs kneeling in the drainage channel trying to adjust sensor elevation.

Comparison of beach profile before the experiment and after test A7 - note that the nearshore bar that developed during tests A1-A5 is now completely gone and that the newly-formed berm represents almost 1 m of accretion.

Monday, 18 June 2012

Sediment volumetric change in the swash zone

It is nice to look at beach profile development, but easy to lose the oversight because there are so many profiles to look at! A convenient way to get insight into the profile development so far and place it in the context of all the tests conducted so far is to plot the time series of the change in upper beach sediment volume. The plot below shows exactly this and illustrates: (i) progressive loss of upper beach volume during tests A1, A2 and A3; (ii) some recovery during A5 when the beach was subjected to several sequences of monochromatic wave action; (iii) stabilisation during run A4 (erosive waves, but low lagoon level); and (iv) very rapid upper beach accretion during the first accretionary test A6. Interesting question will be how the trend of beach accretion continues under high (A7) and low (A8) lagoon level conditions.

More berm building

As test series A6 was finished today, the beach is now showing a significant berm. Two offshore bars were found in the beach profile, but it seems like the outer one has almost disappeared. Monochromatic and bichromatic waves at the end of the day do alter the profile somewhat, but the effect from these two conditions is mostly canceling each other out.
The mobile Argus station, courtesy of Utrecht University.

Utrecht University's surf zone rig.

Hachem (University of Southampton) inspects the ripple profiler data in the logging hut.

Sunday, 17 June 2012

Morphological update

At present we have a nice beach profile with bar and berm. The berm is likely to grow over the next few days (A6, A7 and A8), but the bar may disappear as sediment is moved onshore by powerful plunging breakers and swashes. We shall see - the entire BARDEX II team has not been particularly successful in predicting morphological response!

Comparison between profile at the start of BARDEX II and the profile measured halfway during test series A6. Green, blue and red circles represent positions of offshore, surf zone and swash zone rigs, respectively. 

Saturday, 16 June 2012

Accretionary wave conditions

We have now completed tests A1-A5. The wave forcing for these tests was supposed to have been accretionary (H = 0.8 and T = 8 s), but they turned out to be erosive and caused bar formation. To ensure that the next set of tests (A6-A8) will be accretionary it was decided to reduce the wave height to 0.6 m and lengthen the wave period to 12 s. Friday 15 June the beach was forced with 2.5 hours of these accretionary wave conditions, and the strong and long swashes resulted in more than 0.15 m deposition in the upper swash zone and hence the development of a berm. In the offshore region all was well too, and nice onshore migrating wave ripples were recorded with the Sand Ripple Profilers (Southampton). Some repairs were required to the surf zone rigs (Utrecht), but all is ready for the second half of series A6 on Monday 18 June.

Thursday, 14 June 2012

Group pictures!

Today some group pictures. We finished the erosive conditions with series A4 and will move onto accretive wave conditions tomorrow, with wave conditions with Hs=0.6 and Tp=10s.

Wednesday, 13 June 2012

Here's the frog

Not much happening yet in the goot - Ian and Jack's camera has been playing up, but hopefully they get it to work later in the day. Swash frog is still around and keeping his/her beedy eyes on proceedings.

Monday, 11 June 2012

Swash Frog

Today's blog post is dedicated to Swash Frog, the new Bardex-II mascot. Nobody knows how he ended up in the flume, but he can often be spotted enjoying a leisurely swim in a backwash. He surely won't starve in the big concrete tank, judging by the amount of dead bugs floating in the water.
After spending a long morning of thoroughly adjusting and maintaining the kit (lots of respect for the Utrecht University technicians and Florent for doing underwater instrument maintenance using diving goggles), test series A2 was commenced. Again, the boffins on the beach made the wrong guesses about the beach morphological response: hardly any profile change, despite a very high lagoon water level.

Sunday, 10 June 2012

Preliminary results

Not the whole weekend was for play (visiting Amsterdam), but also some serious data analysis has commenced. All teams have been huddling around their laptops over the weekend and in addition the UNSW team has been keeping an eye on the water levels in the flume (Johan kindly gave up an hour on Saturday and Sunday to chapperone - much appreciated!). Your chief blogger has been doing what he does best: plotting a beach profile! See below for the morphological development during Series A1 (H = 0.92 m; T = 8 s; sea and lagoon = 3 m). The bottom line is that we are already building a bar (and a small berm) and are loosing quite a lot of sand from the swash zone and inner surf zone. Not quite as expected ... actually, this is a bit of an understatement, because we expected the opposite response! Reasons are related to the finer than expected sediment size and the larger than expected wave heights. We might have to do some changes to the next set of wave conditions ...

Beach morphological change during test series A1. Red line is the beach profile before the test and the blue line is after 5 hours of wave action. The green circle is the Southampton rig, the blue circles are the Utrecht rigs (ridiculously well-positioned around the emerging bar feature) and the red circles are the Plymouth/Delaware swash  rigs that are well on their way to become inner surf zone rigs. 

Saturday, 9 June 2012

Weekend break

Irregular waves.
Test series A1 are now finished at the flume. Friday's workday was finished with runs of monochromatic and bichromatic waves, showing very good repeatability in the monochromatic waves. The bichromatic wave train proved to be larger than expected; it may be modified and made smaller for the future runs as to not damage any instruments. Also, the monochromatic and bichromatic waves caused beach accretion, against the trend of beach erosion during the irregular wave train runs during the rest of the day. Once again, it turns out to be very difficult to predict the morphological response of the beach. Monday morning, the swash instrument rigs will be moved landward since they are now mostly seaward of the shoreline.
Now it's time for a well-deserved weekend break for some rest, laundry and a sight-seeing trip to Amsterdam!

Short, intense rain showers on Friday afternoon.
The swash rig looks almost like the diagram in a previous blog post.

Thursday, 7 June 2012

First data!

Today was the first day of testing - nicely on target. There were some teething problems in the morning with pumps and various other issues, but by 11:30 the first proper waves were being recorded. On the whole all went well, but there are a number of issues that need addressing over the few days, ranging from cross-talk between instruments, potential strumming issues (vibration of instrument poles), three-dimensionality in the flume, challenges of keeping hydraulic gradient across the bed, and the minor detail of a bar forming rather than a berm. So all well in the goot!

Wednesday, 6 June 2012

First waves

The last kit has been installed in the flume under a torrential drizzle today. At the end of the work day, there was even time for a three minute trial wave run, to give the sensors the first sense of what Bardex waves will feel like.
We are also pleased to have a second blog on Bardex II, by Bardex II participant Berkley Sadana. Go take a look for more exciting updates on the experiment!

Tuesday, 5 June 2012

How deep is your flume?

Day 2. Most of the kit has now been deployed on the sand barrier, thanks to a rain-free day with some sunshine. Also, the flume has been filled to a water depth of almost one meter. The offshore rig, which was tested and approved by the University of Southampton team is now drowned as a result. The flume will be filled up further on Wednesday morning while the other rigs are completed and tested, and then we are ready for the first test wave runs on Wednesday afternoon!

Monday, 4 June 2012

Day 1 at the goot

Wet, but successful day at the flume today. Offshore rig installed, all computers time-synched and scaffold frame installed. Tomorrow all the instruments will be mounted, hopefully for intial testing on wednesday. Twenty people present at the campsite and all happy and healthy. Internet sketchy.

First picture of the flume with work in progress. Measurement cabin to the right of the flume, scaffolds leaning against the flume wall in preparation for rig construction and UNSW team huddling for shelter from the rain under orange tarp.