Underwater PE 100 pipeline for potable water

Pipeline on the ground of the Traunsee lake

The municipality Gmunden (Austria) discovered a potable water resource of considerable quality and quantity at the nearby mountain Traunstein - at the Eastern lakeside. Due to the continually worsening supply quality studies about the possibility of an integration of this potable water resource into the water supply of the city Gmunden were conducted.

A conventional trench installation was no option because of geographical and traffic reasons. It would have been very expensive, affected the traffic tremendously and been a disturbance of the local population. After many considerations the option of a 8.6 km long potable water pipeline between the newly built waterworks Traunstein-West and the existing high zone pump station close to the hydro power plant Gmunden was chosen.

Pipe material selection and design

Due to the high strength and durability required for this project called “Lake pipeline Traunsee” a polyethylene (PE) pipe material of the classification PE 100 was chosen. According to the technical requirements the 8.6 km long potable water pipeline was designed and specified the following:

• 4.6 km potable water pipeline of the dimension OD 315 mm SDR 9 for 20 bars (red line in draft)
• 4.0 km potable water pipeline of the dimension OD 315 mm SDR 11 for 16 bars (blue line in draft)

Pipe production

In order to reduce the number of pipe connections, i. e. welded connections and to be within a reasonable installation schedule and budget the pipe was produced on-site by means of mobile extrusion machinery (including the necessary periphery) at the Western lakeside of the Traunsee between Altmünster and Traunkirchen.

Machinery data as well as geometric measurements were permanently recorded by ultra sonic wall thickness measurement. The production of the entire PE 100 potable water pipeline was realised within a period of about four weeks.

Quality assurance

Besides the quality assurance measures on-site by an automatic recording of the machine parameters and a continuous ultra sonic wall thickness measurement the quality capability of the pipe manufacturer was of uttermost importance for this kind of project.

Pipe installation

The PE 100 pipeline sections were positioned across the lake at good weather conditions. Afterwards the pipe connections - via stub flanges and backing rings - were situated on workboats (pontoons) and finally the entire potable water pipeline was continuously equipped with ballast weights made of ferro-concrete. The pipeline was filled with air to position it along the planned route by satellite navigation and lowered slowly to the bottom of the lake (up to 150 m depth) via water filling and air back pressure.
The potable water pipeline rises continually until the lake’s outlet in the area of the bridge of Gmunden. Later on course the pipeline installation in the river called Traun - in the water storage area of the power plant Gmunden - was completed. After the installation of the pipeline the connections on land were realised - the waterworks Traunsee-West as well as the high zone pump station of the town Gmunden. Then an overall pressure test including the entire pipeline was carried out successfully.

Operation and total costs

In autumn 1998 the test operation of the PE 100 potable water pipeline began. In March 1999 the pipeline’s all-out operation started with a maximum capacity of 75 l/s. Since then more than 50 % of Gmunden’s potable water originates from the new potable water resource at the Traunstein.

The overall costs of the project “Lake pipeline Traunsee” were about Euro 2.6 million. A rough estimation of the construction on land added up to Euro 5.8 million.Therefore more than 50 % of the costs could be saved compared to the common solution. Since the beginning of operation in the year 1999 the loss of water of the new pipeline was 0.