BARDEX LOGBOOK 30/06/08

Monday 30/06/08

Arrived at flume and the water levels were too low in flume and lagoon because of a minor fault in the pumping system. Took an hour to pump the water levels to the required level for today’s series run (high lagoon 4m max, MSL, Hs=.8m Tp=4.5s) – C2. Start-up problems:
· Scouring at the front of the barrier; therefore, lagoon level set to 3.5
· The EMCM at +10 and 14 are now set to +3 and +7, because the lower EMCM pair is not working
· Matlab does not want to initialise on the SRP laptop; Dan is trying to use other laptop. We are now logging every individual segment as an .avi. using open source capture software as an emergency measure. Not great because it drops frames with alarming regularity, it doesn’t time stamp, big files, etc. Played around with sample frequencies – settled on 25 f/s to try to counter the problem of dropped frames, but effectively couldn’t achieve 4Hz as desired. Will have to decompoile and sync with the wave trace record (until fixed). This problem was unresolved by the end of the series, but is imperative to fix this problem this evening.

· Johan pointed out a problem in our methodology of estimating the seepage through the barrier: there is leakage from the buffer to lagoon through the gate, and this leakage is unrecorded. Back-of-the envelope calculations suggest that the seepage through the gate may be up to 10% of the seepage through the barrier.

· [5,5,5,5,10,10,15,15,20 mins] plus 5mins regular waves. Profile after each run, and rig adjustments. The response of the bed was to become very steep at the landwards runup extent, then a shallow slope to the breakpoint

From the 2nd 10 minute run (run 6 or F), the wave reflection compensator (ARC) was turned on because of an estimated 15cm (30s period) standing long wave, calculated from linear wave theory. Initially there was a worry that the use of the compensator would compromise on the efficacy of the pumpos and wave steering mechanism, but by the end of series C2 it was apparent that these fears had not been realised.

· Sediment photos taken at end
· Problems downloading the data from SRPs. Charlie and Andre investigating
· Offshore rig frame lifted by crane to the top of the barrier, ready for instrumentation

Summary
Series C2 (high lagoon) did not make the beach as unstable as expected. Deltares PTs worked fine except 7 and 12 (as usual). 9 looked a bit noisy. The bottom UoP EMs still don’t appear to be working but the others are fine, and the PTs are all fine. The bed level sensors are holding up, although a couple on the crest (sensors 14 and 15) are beyond their minimum range (30cm,) so are currently not sending back useful information. Its a priority to get the video sorted out. The SRP is logging, and working, and we are able to program it. However, we cannot talk to the SRP computer to retrieve data etc in windows explorer. We can do it in DOS, so working on brushing up our DOS knowledge to extract all the files from the ftp site on the srp logger, rather than one at a time. Later, we found that the command ‘mget’ does the job nicely. Also working on either changing the default settings in the configuration file to retrieve data as ASCII rather than binary, or write matlab scripts to read the binary files in

The wave reflection is small on the monochromatic wave runs (5mins at end of program, in order for the ensemble swash statistics) from observation. Managed to get rid of the long period standing wave using the wave reflection compensator, which works really well – eliminated the standing wave completely without compromising the wave steering or pumping system. Lawrence will check the wave statistics of the 2nd 10 mins segments from the series BB1 (Friday) and C2 (today) to see how they compare. If they are very different we will have to think about getting a new wave steering signal generated which takes into account the compensator

Tomorrow we will aim to resolve problems with video and srp, and start mounting instruments on the frame. Someone needs to continually check the pumps – boring job but necessary. Johan knows the mechanics of the pumping system so any problems ask him.