BARDEX LOGBOOK 17/07 - 18/07

Thursday 17/07/08

Series D2 – low lagoon level run first because not enough water in the system for a high lagoon run. Will need to be pumped in tonight.

Began approx 10:30. Sea level 1.75—3.25m over 90 mins, lagoon level 1.5m

Some issues in the morning stabilising water level in the lagoon, but eventually stabilised to a satisfactory +/- 2cm. Some concerns over the stability of the lagoon at 1.5m at high tide (sea level = 3.25m) because of the head difference, but decided to continue and see what would happen at high tide – because the earlier tests were done with 1.5m, it is desirable to keep this lagoon level for comparative purposes.

Offshore rig data downloaded. Subsurface PTs reset. Offshore EMs adjusted. Swash rigs and bed level sensors logged as usual. Sediment photos at end. No problems with video.

File split into D2 and D22 because the wave machine was switched on and off by mistake, causing problems in the wave paddle, and new run file was set up for the rest of the experiment.

File D222 is the run logged overnight (again logging the seepage, and groundwater response back to equilibrium)



Friday 18/07/08

Another D-Day in the Deltagoot. The water required for today’s run (D3 – high lagoon plus tide) was pumped in over night.

Major concerns today over first the level of the buffer, then the rates at which we can achieve pumping out of the sea (so concerns over first the time it takes to achieve a low sea level to start the run, and then the length of the ebb tide later on the experiment). The pump which pumps water from the buffer to sea was working against the pump which pumps the water from the sea to buffer (because the buffer was so high the head above the pump was prohibitively high), so the ramp down to low tide was very long, and concerns that the system was at stretching point for the ebb tide to happen within the desired 90 minutes. An option was to lower the level of the lagoon, or to increase the length of either the whole tidal curve to keep it symmetric but within the limits of the pumping system, or to have an asymmetrical tide. It was decided that none of these options was desirable, because it would mean re-runs of at least yesterday’s test (and possibly more). Thus we asked for another solution to be found – the pump from buffer to sea was disabled, which helped the sea level drop, but still it was not fast enough for our ebb tide rate. Other options were considered including opening the release gate at the end of the flume to drain water out on the ebbing tide, thus aiding the speed at which we could achieve the ebb, using smaller pumps. It was felt that these pumps were not strong enough to make a noticeable difference.

By this point, there were fears over the stability of the front of the barrier because of a long delay in the start of the experiment, with high lagoon levels and low sea levels. So it was decided to start the run (pumping issue not a problem on the flood tide), and in the meantime wait for the pumping company to bring an extra submersible pump, to aid the ebb tide. At some point on the flood tide the pump would have to be reactivated in order to achieve a smooth flood tide, and we hope that the extra pump on the ebb would make the difference.

Pump reactivated on flood tide, and it worked well to keep the sea level stable.

Did first half of D3 (until high tide, until which point the problems with pumping out fast enough would not be realised), then installed 2 new pumps, ready for the ebb tide on Monday morning. In consequence, overwash rigs would have to be reconfigured on Mon afternoon, in order to record the swash on the remainder of D3.

Jon and Saul still trying to clear data from the srp using dos commands, problem is there are permissions set – no-one at the moment knows how to remove the directories, and Jon is awaiting response from Marine Electronics. Discovered that files can be accessed and deleted through internet explorer (ftp to there rather than through windows explorer or DOS, as before) – all instruments reprogrammed to sample from tues morning at 9am.