6 test campaigns with live fishes have been carried out to demonstrate the fish-friendliness of the VLH and its very low impact upon the mortality of downstream migrating species crossing the turbine in operation, in April 2007 (smolts), December 2007-January 2008 (eels), February 2008 (smolts) October 2010 (eels) May 2013 (Big and small trouts) June 2013 (Big and small Carps)

Tests with live eels

October 2010 Live eels passage test in the Frouard HPP on the Moselle river

After a first series of tests with live eels carried out in 2008, outstanding results were obtained but some improvement of the VLH design were identified and should bring even better results. A second test was performed in 2010 on a VLH of 3rd generation in order to assess its final impact on eel migration.

The Frouard hydroelectric power plant is located on the Moselle river. This project has been disclosed in our previous Newsletter n°9.

The power plant comprises a 400-kW DN 4500 VLH under a 2.5-m head.

This latest-generation VLH is provided with a discharge ring having a spherical shape at the transition between the inlet cone and the actual discharge ring.

As in the first Millau tests, a first series of tests intended to try the equipment and the scientific protocol has been carried out in June 2010.

Once the equipment has been tested, the official tests were carried out in October.

The system of injection at several points and the recovery device are very similar to those used in the first 2008 tests in Millau on the Troussy VLH. After each specimen has been measured and inspected, the eels were distributed in batches and were directly introduced into the VLH immediately upstream of the guide vanes through a Ø 200 PVC tube.

The injection point could be displaced along the distributor spoke. 4 different points have been used in Frouard.

The recovery device was identical to that in Millau.

This 2nd test is the result of an international cooperation. A scientific committee has been formed, comprised of the best French specialists of hydroelectric turbine crossing, from the ONEMA, and of German and Belgian scientists. Further, a team of Polish specialists and members of the Commission internationale de protection de la Meuse et de la Sarre (CIPMS) have also attended the tests.

244 eels have been fished in Germany and transported to the Frouard site where they have been housed, with a water supply from the Moselle. The storage water parameters, such as temperature and dissolved oxygen rate, have been controlled.

The eels have been introduced by hand into the injection system.

They have then been recovered in the fish box installed in the floating pontoon connected to the outlet of the recovery net.

The recovered specimens have then been examined and placed back in their housing to remain under observation for 48h.

Outcome of the tests: After the tests and 48h of observation, no direct mortality has been observed for the 200 injected eels.

The survival rate is 100%

The VLH thus gives the proof that hydroelectricity is not incompatible with the protection of fishery species.

May and June 2013 Salmonids and Cyprinids Live passage test in the La Glacière HPP on the Tarn River.

In order to simulate the downstream migration of Salmonids (Salmons, Sea Trouts, Rainbow Trouts) in their adult or juvenile stage (smolts for the salmons) we have used a sample of 700 Trouts which size is ranging from 20 cm up to more than 75 cm for the biggest. The test was performed on the latest commissioned VLH installed in Millau on the Tarn River in the south of France. The test protocol is similar to the one used before for eels and smolts. It consists of 3 different injection points on the turbine radius (Outer medium and inner).

  • Outer and medium injection points
    Outer and medium injection points
  • Recovery net downstream of the turbine
    Recovery net downstream of the turbine
  • Recovery platform at the end of the recovery net
    Recovery platform at the end of the recovery net

For these particular tests 3 different opening positions of the blades were tested for each of the 3 injection points; 50%, 75 % and 100 % opening position.

Synthesis of the results of the tests (for a detailed test report go to …

The mortality ratio of the tested fishes of the VLH DN5000 with spherical stay ring and spherical hub installed on the River Tarn at the La Glacière HPP are the following:

  • From 1.1% to 4.4%, according to the blade opening position for the big rainbow of sizes and weight comparable to adult Salmons in downstream migration stage
  • 0% at all opening position and all injection points for the smaller rainbow trouts of size and weight comparable to smolts in downstream migration
  • 0% at all opening position and all injection points for the big carps
  • From 0% to 1.1%, according to the blade opening position for smaller carps


  • Big Trout
    Big Trout
  • Big Carp
    Big Carp

On the base of these unique and outstanding results, the VLH will be the hydroelectric turbine qualified as fish friendly by the French administration.

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