IMMEDIATE SCIENCE REPORT
K193 CAPE ROBERTS TIDE GAUGE
NEW ZEALAND ANTARCTIC RESEARCH PROGRAMME 1990/91
Antarctica New Zealand November 1990
The purpose of this project was to install a permanent tide gauge at Cape Roberts. In November 1988 a tide gauge pressure transducer was installed at Cape Roberts within a steel pipe bolted to the coastal rock. This installation was subsequently lost when the coastal ice foot broke off in February 1989. The transducer site we had choosen was the best available because it had deep freely circulating water under the ice foot close to shore but it was clear that a permanent installation required greater protection. I believed this could be achieved by installing the transducer in a hole drilled at an angle through the rock to exit into free water beneath the ice foot.
Scientific Endeavours & Achievements.
The first stage of this seasons field programme was to drill a hole in the coastal rock using the "portable" Winkie diamond coring drill belonging to DSIR Antarctic. This season the ice foot (above free water) was thicker than usual (5.5m) and a large amount of ice had been pushed against the shore and incorporated into the overthickened ice foot. These unusual ice conditions prevented the use of video camera modified to work under the ice which we intended to use to establish the best site for the transducer hole. Instead five holes were drilled in the ice foot to establish the ice thickness and where free water occcurred. The site choosen for drilling was within 5m of the previous tide gauge site and required a hole to be drilled 450 from the verticle. This was accomplished succesfully in 2 days of drilling with breakthrough occurring at approximately 12.8m. Sea water with a small quantity of Calcium chloride (50kg) was used for drilling fluid and will have no lasting effect on the near shore environment. All equipment was removed after drilling leaving only the transducer cable protected in a polyethylene pipe and steel support cable anchored at the hole.page break
The transducer is located in a cage at the end of a 32mm low denisty polyethylene pipe lining the drilled hole. The transducer cable became frozen within the hole as expected within a few hours. Two days later the transducer was removed and rechecked by unfreezing the cable with about 51 of isopropal alcohol poured into the plastic liner pipe. This shows that it will be possible to remove the transducer for replacement if it becomes faulty in the future and it should also be possible to adjust the liner pipe and transducer cage at a later date by unfreezing the liner pipe with a submersible heating element.
The water level transducer in connected via a 32m suspended cable to the data logger/meteorological instrumentation on a rock promintory at the eastern end of Cape Roberts. New gell cell batteries were installed and the met. instruments replaced and checked this season. The system is currently programmed to record a 10 minute average of water depth each hour with hourly averages of wind speed and direction, air temperature and solar radiation. Memory storage has been increased so that data can be recorded for a full year.
In the 1991/92 season it will be necessary to accurately relevel, and reclibrate the water depth transducer for connection to the tidegauge bench mark and to Cape Roberts trig. Installation and operation of the tide gauge/met. instrumentation at Cape Roberts has been jointly sponsored by the Antarctic Research Centre, Victoria University of Wellington, the N.Z. Meteorological Service and the Department of Survey and Land Information (DOSLI). This seasons programme was carried out as DOSLI event # K193 and DSIR Antarctic provided logistic support, drill equipment and drilling expertise for the transducer installation.
The success of this seasons programme has shown that it is now possible to establish similar remote tide gauge systems on other parts of the Antarctic coastline. Sites would be on rocky capes or promintories where sea ice breakout occurrs regularly with deep water close to shore and rock suitable for drilling and setting up the drill rig.
The other members of this event, Garth Varcoe, Paul Woodgate and "Ben" Bensemann require special mention for their efforts in drilling the hole for the transducer installation at Cape Roberts. Also at Cape Roberts members of the survey event K192 helped with this programme. Peter Isaac provided valuable advice and encouragement from Britina Island while setting up and programming the instrumentation. John Alexander (Operations Manager) and other members of the Scott Base staff provided invaluable support. At Victoria University; Eric Broughton, Jimmy Millar and the Mechanical Workshop helped with the preparation and checking of equipment. Finally Charlie Thurgood of Scott Technical Instruments Ltd. provided an excellent service to replace a faulty transducer for the programme.