80 THE SALMON RIVERS OF SCOTLAND 



structure of some magnitude. It is situated on the left or 

 Bonskeid side, and has been blasted out of the solid rock to a 

 depth of over 30 feet. It is 140 yards long by 10 feet wide, 

 and has a uniform gradient of 1 in 23. Forty yards are in 

 tunnel at the upper end, the tunnel being 6 feet high, and as 

 the upper end has been carried some little distance above the 

 actual falls, the height surmounted is 18 feet. Rows of upright 

 stones are placed across the pass every 14 feet to act as breaks 

 to the descending water, the individual stones having spaces 

 of about 16 inches between them. Wooden battons were at 

 first placed experimentally at the upper end for the purpose 

 of preventing a too great inrush of flood water, the effect being 

 practically that of a partially closed sluice. This has been 

 somewhat modified, and it has also been found necessary to 

 deal with an accumulation of gravel in the channel at the 

 upper end, and to construct a large concrete barrier to protect 

 this end from the strong inwash during floods. The barrier 

 constructed, for the same purpose, at the upper end of the 

 Invermoriston pass (Ness District) answers very much better, 

 in my opinion, and I think it would be better in the case of 

 the Tummel Pass to make a downstream projection at the end 

 of the barrier to pass the gravel on. At first the effort was 

 made, here, to secure a depth of water in the pass of about 17 

 inches, and even then the lower section was fairly well filled 

 with white water at times of ideal flow. The District Board 

 have more recently decided to increase the flow. 



However, a wire and wood trap like a cruive box was inserted 

 for a time at the head of the pass to ascertain how many fish 

 were going through and, as a result, the success of the pass was 

 quite well established. 



As a second line of ascent for fish, when the river is low, it 

 was wisely decided to remove a point of rock against which 

 leaping fish commonly struck themselves, so that they might 

 more readily reach the trough with the water cushion already 

 referred to. Furthermore the entrance for fish to the pass 

 was brought downstream to the foot of the pool below the fall 

 called The Pot, and since in low river fish were likely to pass 

 the mouth and swim up to the actual obstruction, this improve- 

 ment in the old line of ascent was a prudent one. 



When the river is at all high, however, fish cannot lie near 



