UNDERWATER - SEARCH & RECOVERY - Project PE Water Pipe

The complete drinking water pipeline that was floating ready and waiting on the lake surface was sunk into position on the bed of the Traunsee to plan in a spectacular action at the end of April 1998. Sinking procedures of this kind are always a very risky and difficult business, it is not uncommon for the pipeline to be destroyed or to sink down to a different position than the one that had been planned. Some weeks before heavy anchor stones each weighing 2 tons had been sunk at intervals of 820 feet along the established pipeline course. Our position determination for the gas pipelines was of decisive significance for the success of this task. The new water pipeline was intended to run parallel at a distance of 650 feet from the gas pipelines. Our position determination work meant that these anchor blocks in 2 tons of cast concrete could be sunk targeted from a work pontoon. Strong, floating plastic ropes were attached to the concrete blocks and floated up to the surface where buoys were attached to them to mark the position of the anchor stones. These ropes were used later for the controlled pipeline sinking procedure. A number of pictures follow of the sinking procedure for the newly completed water pipeline:

Following completion of the sinking procedure we were commissioned to film its entire length and to provide full documentation of the new water pipeline on the bed of the lake. It was only by this means that sure proof could be provided that the pipeline really did lie along its whole course on the mud bed of the lake – a proof that our client had to provide for the general contractor. According to our GPS and echo depth-sounder recordings an operational depth of around 525 feet was to be expected along a pipeline length of 6,500 m. Documentation of this kind – above all when it has to be thoroughly seamless – is no easy task, a fact we were well aware of from the start. Our first attempts to provide a seamless tracing of the pipeline using our towed video system were a sobering experience. A truly seamless tracing of the pipeline sections appeared to be practically impossible, even with the best wind and weather conditions. And above all it was as the depth increased that the equipment we had in use at the time proved unsuitable for the task. A left and right turning were all the maneuverability we had at our command with the drive motor of the towed video system, there was not backwards or forwards movement. This meant we were completely dependent on the course followed by the skipper at the surface. It was clear to us at once that a continuous and seamless tracing of the pipeline sections – above all at such extreme depths and using the drive and equipment that was available to us at the time – would have been a “job for life”.

Faced with this situation we at once began to reconsider our video camera as we were using it at the time from A to Z and came up with the idea of providing a main video camera drive that would enable efficient forward movement. This new drive was independent of the two motors for left and right turns. It was installed in its own pressure discharge casing placed above the video camera housing. The development of this drive, however, did not have a satisfactory development. The towed video system became heavy in the extreme due to the massive housing and the large drive motor. The pulling force required was not only an enormous stress on the video camera cable, but also on the video cameraman. He had to constantly hold the entire weight through the tensed cable and constantly adjust the cable length to the depth. Time was pressing, we had a deadline with our contractor for submission of the guide documentation that was required. We stopped work on all development activities for the additional main drive unit. In order to be ale to complete all the work on schedule we hired a massive free floating ROV from a French colleague. We had to accept that a free floating system had clear advantages over our equipment for a task of this kind. The ROV was relatively simple, but with its weight of 60 kg had a very massive structure. It was fitted with three exceptionally powerful motors. These permitted a completely free motion over the bottom of the lake independent of the workboat in conjunction with the cable that was weightless when underwater. The essential requirement here was good cooperation and communication between the ROV pilot (video cameraman), an own cable guide (operating the cable) and the workboat skipper.


The ROV in the stern of our workboat. The drum with the underwater weightless cable can be recognized to the left.		The control unit was stored protected in a compact case. To the left the monitor with integrated tape recording device.		This image of the ROV shows the vertical motion - thruster. Two additio-nal motors serves for the horizontal movement above the lake bed.

We carried out the seamless filming of the entire water pipeline on only two consecutive days. The weather was good and relatively stable. The team was in relatively good form after a three hour training session. Starting in the shallow waters to the north we continued to film the entire pipeline, covering the 7 km at walking pace. The tracing work was significantly easier in the shallows – and this was as good as an additional training session for us all. The increasing depth as we moved south, however, demanded ever greater concentration and coordination from all the team members. By the evening of our first operational day we had successfully filmed 11,000 feet of pipeline in depths of up to 450 feet and had done so absolutely seamlessly. We were very proud of this success.


The 130 lb heavy ROV is placed in the water at the operational point by two team members.		Following its “splashdown” in the water the ROV with its rigid orange floating body.		The ROV pilot during the trainings sessions. The search boat skipper sits next to him.

By the second day we were continuing with the work as though it were a regular routine. We nevertheless had to face absolutely critical situations twice at depths of 460 feet. The ROV became entangled in the floating cables that were still attached to the pipeline and to the anchor stones. Both times, however, the ROV pilot managed to pull free himself through incredibly skilled maneuvering. Entanglements of this kind represented an extreme risk for our entire project. The cables that floated up from the bed of the lake were 30 mm (!) thick. There was no question of being able to pull free by force. If the worst had come to the worst we would have had to employ deep water divers to help us, although there were scarcely any available at this time and the costs would in any case have been enormous.

The depth slowly sank further to 525 feet. The travel speed we were making slowed down as a result, but we were nevertheless making continuous progress. After 18,700 feet of pipeline the water rapidly became shallower. We had reached the steep shoreline where the depth shelves down rapidly, and we were glad to regain shallow water. By late afternoon we had reached the shore, the drinking water pipeline had been successfully filmed and documented in its entirety and without gaps over a length of some 20,700 feet. The GPS and echo depth-sounder logs that had kept constant time with the whole task had established and recorded the position and depth of the entire pipeline course in a cycle of seconds. Following evaluation of this data it could be seen that the course of the new water pipeline was beautifully parallel to the gas pipeline.


	This survey map shows the perfect positioning of the sunken and successfully filmed water pipeline with the blue travel lanes. The red travel lanes document the position of the gas pipelines.		An excerpt from the log data. Two independent GPS systems and echo depth-sounder recorded each movement of the workboat together with the current depth.

The evaluation of the data also showed the highly interesting profile of the water pipeline on the lake bed. A total of 20,700 feet of pipeline were filmed at a depth of up to 528 feet. Following on from this depth maximum the depth line rose rapidly and documented the extremely steep fall close to the shore.

This project reached a successful conclusion for us with the delivery of the film and documentation material. The contractor asked us to treat all video recordings of the new drinking water pipeline in strict confidentiality, a condition we are of course pleased to accept. This is the reason why none of the ROV screenshots are published here. Should you have a special interest in this issue we would ask you to contact us.