Precise Levelling in the Sultanate of Oman


In 1985 I was contracted by Cansult Limited, a Canadian civil engineering firm, with a branch office in Muscat, Oman, and with whom I had been employed previously, to carry out a precise levelling survey for the Public Authority of Water Resources of the Sultanate of Oman.

This was to be done to first order specifications along 130 km of the highway along the Batinah Coast in the North of the country. Its purpose was to provide a basic network of bench marks, which could be utilised in their monitoring program of water levels in the various wells in that area. Topographically the route presented no problems, the area was flat, and there was a wide median between the two carriageways of the divided highway which could be used as the levelling route, as well as for transportation by pick-up truck between set-ups. However, climatically we were presented with a significant problem. By contract we were forced to do the survey during the hot season, and the Batinah Coast is a very hot and uncomfortable place indeed during that part of the year.

Daytime temperatures were always in the 45 degree Celsius range, and, as this was close to the sea, this was combined with near 100%  humidity. We soon found out we could not  work after 10:00 hours in the morning, observations just became impossible. Working hours were re-scheduled then to between midnight and 09:00 hours, so we could take advantage of cooler temperatures, and without observations being hindered by heat shimmer. Of course, the levelling staves had to be illuminated.

Note keeping at night was not a problem, though. For the sake of speed and efficiency I had already decided to keep notes on electronic media, and the screen of the RADIOSHACK Model 100 laptop computer could be illuminated internally. These were very much the early days of computers. At the time the Model 100 with its 64Kbyte RAM (upgraded from 8 Kb) was cutting edge of technology. I had written a BASIC program to store the readings and pre-process them to check for agreement with the stipulated tolerances prior to proceeding to the next set-up. After having returned to camp at the end of the working day (night), data were dumped, finally processed and printed out. Even with 64 Kb of RAM this sometimes was not enough to hold one full field day's worth of data. So, most days, the data had to be dumped onto cassette tape in the field, before carrying on. All in all, the system worked extremely well, it speeded up operations significantly as the notekeeper was spared the task of checking the readings, since the machine did it for him, emitting different beeps for check or no check. Also for several days, when we were short of staff, I could eliminate the notekeeper altogether.

We soon learned not to carry our equipment, especially the Model 100, in the air-conditioned cab of our truck, when we went out to work. As the cold equipment was suddenly exposed to the heat and humidity, condensation took place. It took me a little while to find out why my computer worked in camp but initially not out on the road, two circuits on the board had been bridged by a drop of condesation.

Having the wide median available, permitted us to use our vehicle to advantage. The pick-up truck was used to move the back levelling staff and the instrument forward quickly, with a trailing rope to ensure equal sight distances. While setting up, the truck reversed back from forward staff to back staff. The whole procedure was a little unconventional, but it saved walking for everybody, and we were able to cover more ground more quickly.When everything was said and done, we were able to stay well below our fixed price budget.

It was a demanding job for sure, a time for experimentation and learning, but ultimately rewarding as we succeeded. It was always a special moment in the morning, just before sunrise, when the muezzins in the surrounding villages called the believers to prayer.