Norwegian invention is key to water resources development in Nepal

By Svein Tønseth
Photo: Haakon Støle and Jens Søraa

The problem: In many parts of the world, rivers carry large quantities of sediments. This is the River Tinau in Nepal, photographed during the monsoon season.

In the heart of this Himalayan kingdom, the Jhimruk hydropower plant is under construction. Technology from SINTEF and NTH will safeguard the power plant from the huge amounts of sediment carried by the river Jhimruk Khola on its way to the Ganges during the monsoon season. The new sediment technology from Norway can improve the performance of many hydropower plants throughout the world by reduced investments and increased energy production.

The sediment loads of most rivers in Asia, Africa and America make the use of the water-resources for development purposes more difficult and expensive. But the sedimentation problem has also been encountered in Europe.

The 12 MW power station on Jhimruk Khola will start generating electricity in mid 1994. With the patented system that is being installed there, SINTEF NHL (Norwegian Hydrotechnical Laboratory) and NTH´s Division of Hydraulic Engineering have broken new ground in the field of water resources development in river basins with severe sediment loads.

Statkraft (Norwegian Energy Corporation) has licensed the technology, and is currently launching it on the international hydropower market under the name of the Serpent Sediment Sluicing System.

Mountain rivers carry sediment of all sizes from clay particles to boulders. If the water is to be used for energy production, irrigation or general water supply, the major sediment load must be removed from the withdrawn water and returned to the river downstream of the intake.

The Serpent Sediment Sluicing System removes the sediment load from the water while it is flowing continuously to the plant. This offers both considerable gains in energy production as well as reduced investments and operation costs. Existing technologies cause irregular production during periods of high sediment loads, as well as high operation and maintenance costs.

Haakon Støle, a scientist at SINTEF NHL (Norwegian Hydrotechnical Laboratory), has developed the "Serpent Sediment Sluicing System".

Overseas business areas

"The system is something completely new in this field, and Statkraft intends to exploit it commercially. With the sluicing system as a leading product, we will now look into the possibility of establishing sediment handling as a new international business area for Statkraft," says Øyvind Ulfsby, who is in charge of StatkraftΔs growing overseas activities.

The solution: In the Jhimruk Valley in Nepal, a new hydropower plant is being built; technology developed by NTH/SINTEF helps to protect it against river sediments. The "Serpent Sediment Sluicing System" will remove the sediments that will settle in the basins in the foreground.

Sluicing system

In order to maintain the sediment trapping ability of a settling basin, the settled sediments must be removed from the basin. The Serpent Sediment Sluicing System is an innovative approach to this requirement.

Haakon Støle, a research engineer at SINTEF NHL, invented and developed the system. Dr. Støle has lived for several years in Nepal, where he studied sedimentology with Professor Dagfinn K. Lysne of NTH.

"The need for new technology in the field of sediment handling techniques was obvious. Most existing systems for removal of sediments from settling basins under operation work only on the drawing board," says Støle who has covered this area in his thesis for Doctor of Engineering degree.

Continuous energy generation

The main criterion for the development of a new sediment removal system was the need for undisturbed power generation during the sediment removal process. During periods of heavy sediment transport, the basins must be cleaned several times a day.

In many hydropower plants, energy production has to be reduced or stopped during flushing of the settling basins because the basins must be de-watered in order to flush out the sediments. The need for continuous and regular power generation overrules the need for sediment removal. The result of this, however, is that the trapping ability of the basins is reduced and the turbines are damaged.

"Existing methods for sediment removal from basins in operation suffer from technical drawbacks, such as high consumption of flushing water. This gives a higher water transit velocity in the basin and thus a lower sediment trapping efficiency. It is always difficult to monitor the performance of a settling basin due to the silty water. If the quality of the water released for power generation is poor, the turbines will suffer again," says Støle.

"With the Serpent Sediment Sluicing System we have eliminated these drawbacks. The system uses less water than any other known flushing system, and it is so simple that the operator can easily monitor the performance of the basin and the flushing process. The low flushing water consumption allows our system to be operated as often as required," explains Haakon Støle.

Svartisen

The system has also been tested by Statkraft in a pilot project at Svartisen hydropower project in northern Norway. The pilot project in the glacier fed river Beiarelv has now been in operation for two years.