Appendices to Twenty -eighth Annual Report 



become somewhat reduced. There would be advantage, therefore, in making 

 the main line of advance, the direct inlet, at a distance below the summit 

 of the dam to be fixed by the amount of water necessarily run off to com- 

 plete the artificial flood on the river. This requires a somewhat nice 

 calculation of the volume of water shown to be available after a careful 

 survey of the land surface to be flooded by raising the loch. 



In the Loch Vennacher pass there are two inlets at different levels, but 

 these are parallel, and are both direct inlets from the loch. They unite at 

 an angle or turn of the pass, after which the channel is single. This in 

 my opinion is preferable to the arrangement at, Loch More, but unfortu- 

 nately the sluices at Loch Vennacher outlet are opened by being lowered 

 rather than raised, hence if a fish ascends the pass when — as commonly 

 may be the case — one or other sluice is only partially opened, it is met by 

 a perpendicular iron sluice gate, over which it has to leap if it can manage 

 to do so. 



The same drawback exists at the Loch Katrine outlet and pass, the 

 reason, no doubt, being that the Glasgow Water Trust engineers sought to 

 conserve the water supply held up in these lochs in the best possible way, 

 so that accurate measurements could be obtained at the gauges. In cases 

 such as these, where water is required for most important economic and 

 domestic purposes, the interests of the salmon must necessarily occupy a 

 secondary place, yet I think modifications might have been so arranged as 

 to secure a more hopeful result for the ascent of salmon. But it is 

 extremely difficult to adjust passes at proper levels when other purposes 

 have first to be fulfilled. 



Sluices at Waterfalls. — I now desire to say a word or two about sluices 

 at natural obstructions in rivers. As at dam dykes, pass-makers have 

 generally adopted sluiced inlets at waterfalls in order to prevent flooding. 

 The erection of a sluice is perhaps the most natural expedient thought of, 

 such a structure being commonly used with satisfactory results at the 

 intakes of lades and water channels. We have to think of salmon ascent 

 as well as water-flow, however, and I confess I have become very sceptical of 

 the benefits of sluices. A pass at a waterfall being adjusted to the most 

 suitable level of the river, when a rise of water-level takes place, a 

 considerable pressure soon is exerted on the sluice. This not only often 

 jams the sluice, but causes a violent up-boiling at the back of it as the 

 water rises towards its own level. If a little experiment be made by 

 operating a sluice where a sufficiently strong power can be exerted, it will 

 be seen that as the water is cut off from the pass the inrush gradually takes 

 the form of a rectangular douch of increasing pressure and velocity, and 

 that, conversely, as the sluice is opened the pressure is relieved, till the 

 water assumes the appearance of a deep but natural current. Now it may 

 be admitted that by lessening the actual amount of water in the pass 

 flooding is avoided, and the entrance or lower end is kept from possibly 

 becoming too rapid and aerated ; but by lessening the amount of water the 

 intake receives such pressure that a new obstacle to the ascent of fish is 

 created. I am convinced that in the case of most sluiced inlets of any 

 size which I have studied, the partial closing of the sluice or sluices results 

 in such force of water that no fish entering the pass can readily get out 

 of it. 



Another objection to the partially-closed sluice — and especially of a fixed 

 and restricted opening of any kind — is that the natural rise of river is not 

 communicated to the pass, the result being that the water at the " entrance " 

 tends to be thrown out of proper relation to the river. A pass-entrance, 

 to be attractive to fish, to make its presence felt in the fall-pool, must 

 necessarily be supplied with a good amount of water. When the river is 

 in running order and the pass is working at its best, the allowance of 

 water in the pass should be sufficient to provide the best conditions. When, 



