lb' 



Appendices to Twenty -eighth Annual Report 



bye- wash. The arrangement is an expensive adjunct, but, in my opinion, 

 it provides most satisfactorily the sort of regulative operation necessary to 

 overcome the drawback of having more than one inlet to a single pass. It 

 is apparently an adaptation to the needs of a loch fish pass of a system of 

 outlet employed in reservoirs. I have not seen it employed in any other 

 fishing loch for the purpose of regulating the pass. If used in a loch of 

 any size it would necessarily have to be of considerable dimensions, but 

 that it is a valuable addition I have no doubt. I shall refer to the pass at 

 Kingairloch when dealing with the subject of pools. For the present I 

 seek to emphasise the advantage, as it seems to me, of doing away with a 

 sluiced pass-inlet even in a loch, and of securing a direct and single pass. 



Pool Passes. 



The pass which has as a radical part of its structure a series of pools 

 seems to me to present, in the main, the most satisfactory results. In the 

 natural channel of a river of steep gradient, if there are no pools, the 

 current is swift and troubled. When pools occur, the aeration disappears, 

 and the water pauses in its hurry. As a consequence, short intervals 

 become more steep, but, within limits, the ascent is easier for fish. A 

 quick effort enables them to swim from pool to pool, and in the pools they 

 can rest. In my opinion, a long pass should provide the same conditions, 

 and pools can be so formed as to provide a maximun of resistance to 

 descending water and yet enable fish easily to swim from pool to pool. I 

 do not think pools should be constructed, or need be constructed, 

 which require fish to leap. A fish never leaps if it can swim. I had 

 rather, therefore, provide a pooled pass of this nature with an open 

 unrestricted inlet and allow of flooding, than accept the disadvantages I 

 have tried to indicate as inseparable from an unpooled pass of a uniform 

 incline with breaks at intervals, if it is necessary to cut off" water to 

 preserve its tranquility. In the upper part of the Invermoriston new 

 pass, it was found that the gradient was faulty, and that an abrupt drop 

 occurred at the intake. The proper gradient was restored by forming 

 pools in this upper portion. Battens were placed across the pass where 

 the rows of stones previously occurred, and a depth of four feet was secured. 

 This, with the alteration of the intake already referred to, resulted in a 

 great improvement. 



At Loch Doon outlet, there are two separate passes of good gradient 

 which are formed in tunnels through a rocky barrier over which a road 

 crosses. Below the tunnels, a considerable section of the cutting is open. 

 They are adjusted to suit high and low levels of the loch, and they answer 

 their purpose well. They were first formed about a hundred years ago, 

 but were much altered in 1885.* The low-level pass is seldom used, and is 

 made without pools. The passes are each about 155 feet in length, and 

 the gradient of the one chiefly employed is about 1 in 20. The water has 

 considerable depth, owing to the presence of wooden barriers placed across 

 the pass at intervals so as to form pools. Fish ascend over the wooden 

 barriers, as in the upper part of the Invermoriston Pass. The 

 number of fish which may be seen at times leaping at the difficult fall 

 which occurs away above Loch Doon, sufficiently indicate how well salmon 

 are able to ascend the pass in question. The water in the Doon pass pools 

 is " black," because of the gentle gradient plus the depth of the water in 

 each pool. Two other arrangements of pool formation have to be noted, 

 however. In the one case — that of the Torrbol pass on the Carnach, a 

 tributary of the Fleet in Sutherland — the walls of the pools are built so 

 high that the water cannot overflow them and has to circulate in the pools 

 before it is able to find an exit. In the other case — that of the Glen - 



* A plan of this Pass was given in the Annual Report for 1887, Part II., Appendix IV. 



