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.

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!

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.





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.

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.



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.