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.
Monday 21/07/08
Because some water had to be drained from the flume in order for the pump installation on Friday, and because the technicians forgot to refill, the first part of Monday morning was spent reintroducing the lost water to the flume, before the rest of D3 could begin. Then delay when wave paddle overheated. In meantime, we put the offshore rig back in. Started run at 10:45 approx (series D33)
Computer in control room was not switched on for timings file (seq) for series D33 – clocks reset, and new run started – ‘Series D333’ approx 13:15. At the start of D333, there’s 2 mins of ‘accidental waves’ at the start, and camera not in position. Afterwards, no problems to the end of the run.
Response of the profile was to cut back from the beachface and accretion offshore. The elevated groundwater table made a significant difference to the dynamics of the beachface.
Meanwhile, offshore rig moved – landward side rotated off the wall – will have to be replaced.
In the afternoon, the swash rigs were reconfigured. The two suspect EMs (red cyclinder) were removed. The remaining 4 EMs were configured on their own at 4 different locations from barrier crest to lagoon mid-slope, each with a PT. The central logger was turned around and moved ~2m landwards. The two EM cyclinders were moved to over the break in slope at the lagoon side. None of the bed level sensors were touched. All instruments were cleaned and surveyed in using a total station. The offshore PT was moved ~3m landwards, and the 3 infiltration/exfiltration PTs were moved landwards to the crest. The atmospheric PT was repositioned higher, on the top of the flume wall. The remote control was also strapped higher to avoid submersion.
The video camera was tilted downwards, and the profiler carriage was moved to a new position for the runs, some 10m or so back, in order to catch the back of the barrier. This video camera now has a field of view stretching from the lagoon water line at 2.5m, to the barrier crest. The second video camera will be logging for the shorelines, and activity seawards.
Torsten from Hamburg installed 2 high frequency (1kHz) pressure transducers near the likely breakpoint, mounted on a scaffold pole which could be easily moved between wave runs if necessary to catch the plunging face of the wave
Tuesday 22/07/03
Series E1 – varying sea level (2.5 to 3.625 in increments of 0.125m). Hs=1m, Tp=4.5s
The response of the beach was cutback of the crest face, and accretion of the crest of the barrier. The barrier is now thinner than at any point previously. A decision was taken not to reset the barrier because it would be impossible by hand, and long period waves would now only serve to overwash the barrier. Crestal accretion was achieved through infiltration-enhanced runup limit, but overwash sensu-stricto was not achieved.
Series E2 – constant sea (3m) and lagoon level (2.5m), varying wave height (1.05 in 0.05 to 1.2 m). The run was stopped when waves breaking off the paddle, and therefore dissipating energy before they arrived at the beach. Afterwards it was realised that probably the maximum wave height acheived was 1.15 +/- 5cm.
Sediment photos taken at end.
Still gaps in the video record during runs because the video camera keeps going onto ‘demo mode’ and i haven’t figured out how to turn that off. I can’t be there to tend to the video camera all the time, so asked the profile technicians to keep an eye on it for me, but still not perfect
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