The first tests with waves are currently underway. We are testing the paddle with a series of 50cm waves, then 80cm, then 1m. We are then sending 2000 waves of JONSWAP spectrum Hs=1, Tm=3.75 (Tp=4.5) with eta=2.5m (SWL condition). The waves will be 'turned off' after set numbers of waves for barrier re-profiling and instrument position sets
Yesterday the tests were water levels only. The Delft technicians worked on their pumping routine in order to keep the water levels steady simultaneously on both the lagoon and ocean side. After looking at the data last night there were a few issues with their instrument conventions and set up which we have spent the morning resolving with them. So far, we are all happy and things are going well.
Ian T leaves in about 10 minutes, so Ian - keep watcdhing this space for updates!!
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BARDEX (Barrier Dynamics Experiment), European laboratory research project investigating gravel barrier stability, overwash, sediment transport and groundwater dynamics. The project is hosted by Deltares and takes place in the Deltaflume in the Netherlands between 21 June and 1st August 2008. The principal investigator is Dr Jon J Williams, collaborating with researchers at the universities of Plymouth, Algarve, Birmingham, New South Wales (australia), Hamburg, and Southampton
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2008
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June
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- Gerd attacked by swarm of bees
- Typical wave run followed by rig adjustments
- BARDEX LOGBOOK 26/06/08 - 27/06/08
- your blogger host, with glorious beard!
- Not very interesting, but ... video snippet from t...
- BARDEX LOGBOOK 20/06/08 - 25/06/08
- the wiener melange
- The Lady of Vollenhove
- gerd, ian and paul look on as the first few waves ...
- orthorectified view from the gantry
- Vla Flip - the perfect Dutch dessert
- thats the way to move gravel!
- this project is all about the pumps - this photo i...
- The super swash rig
- Meet the team (well, as of 23rd June -it changes a...
- The first set of waves, as viewed from the overhea...
- All the benefits of the laboratory, at the scale o...
- first tests
- Desert Island Discs
- Barrier Dynamics Experiment
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June
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2 comments:
Successful first wave run (run2). The waves have just been turned off! After a test series of 20mins 0.5m Hs, 5mins 0.8m Hs, and 5 mins 1m Hs, we carried out several runs of Hs=1m of varying lengths (5mins at the start, increasing to 15mins at the end) over several hours. In between each run the barrier was reprofiled. Instruments were adjusted after each run to be in constant height above the bed. A nice berm formed almost immediately. The waves were clean and more 2D than I anticipated. The wave steering signal was good, and the 3 probe array for statistics on reflection seemed to do its job correctly (well, untilm we have a look at the data). Tonight we need to think carefully about the likely beach response to various wave conditions, now we have seen the flume in action. It may mean we carry on our groundwater tests tomorrow. Gerd did a sterling job on the pump controlling software making sure the water levels remained constant (they have a tendency to fluctuate - see below)
To recap, yesterday (24/06 - run1) we did groundwater test 1 (high sea level, low lagoon level). We logged the pump discharges, pressures seawards and landwards of the barrier,, as well as the phreatic surface within the barrier. We ironed out some early issues with large fluctuations in the stationary water levels, but some issues with that still remain. We found that the hydrualic profile was a departure from linear - it was convex. This can probably be explained thus: the cross sectional area of the barrier thins landwards becayuse the landwards slope is 1:4 (as opposed to 1:8 on the seawards side). Darcys law is Q=Ak(dh/dl). (dh/dl) will therefore increase towards the lagoon and the transmissivity of the barrier will increase, raising the water table and resulting in a convex phreatic surface.
We did a rough calculation of the hydraulic conductivity of the barrier using this information - the first of its kind anywhere in the world!!
We will have a look at the data tonight and decide what to do next. There is a distinct possibility that the second groundwater test will go ahead tomorrow (low sea level and high lagoon)
Ian T left today on his way back to Australia (via England, Austria, Switzerland, France and Germany!) Good luck Ian - pleasure to work with you over the last few months, and let's keep those plans we made for the future alive!! Ian has been replaced by the ever-smiling and all round good guy Andre - welcome to Bardex, Andre!!
The convexity of the phreatic surface is inevitable, and nothing to do with the slope of the gravel.
Darcy's law gives a direct relationship between velocity and head gradient. Because the surface has to go down as it goes through the barrier the flow must be travelling faster, and hence the gradient must get steadily steeper downstream. a linear surface (i.e. constant gradient) is impossible.
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