Posted by Joe | Projekt Alsterälven

After being battered and bruised by a preliminary thunderstorm last Monday, the migration trap was eventually overwhelmed by a second knock out blow on wedsnesday night when yet another thunderstorm tore across Karlstad. 

Readings taken from Alsterskraftverk show that there was an increase of 40cm from the day before which stripped the trap down to 4 pieces and then dispersed them across the river. 

If you look carefully you can actually see how the yellow water pipe has been stripped away and washed across the river. The silver collection tube was also screwed down to wood on the trap but this made no difference. Fortunately, all the various components that make up the trap could be salvaged, and after a re-think, the trap has now been slightly modified.

 The photo below shows the impact of the flash flood.

 

 

 

 

 

 

 

 

 

 

New design for the collection trap is shown below:

The wooden guidance barriers are now horizontal, and contain small holes which have been drilled into the wood and then covered with netting to prevent any small fish passing through. The theory is that this will enable a more regular, and potentially higher volume/velocity of water to pass over the trap surface, therefore perhaps a higher temptation for eel elvers to commute up the trap. The top end of the trap is also far more secure with the new design, and thus any elvers which do move upwards, should almost certainly enter the collection tube down into the storage bin.

Latest figures for the traps that sit above the power station are also increasing. 56 fish caught in the last 6 days compared to 75 for the month of May. Quite a remarkable increase, largely due to high catches of mört, gös and small gädda.                                                                                  

Catches of eel however have fallen, however – there has been 4 in the last 2 days which could indicate there may be more to come…

//JOE

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