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Appendices to Twenty-eighth Annual Report 



The intake of the pass from the stream above is sluiced, but as the 

 volume of water is not great, no severe pressure is exerted. Moreover, the 

 sluice is either fully opened or fully closed according as the pass or the 

 waterfall is supplied with water. 



Unfortunately, a good deal of silt is carried into the pass from an 

 accumulation of sand and gravel which forms at the intake owing to the 

 presence of the weir. This bank is annually dug out and shovelled over 

 the weir or into the sand trap of the weir. Many of the pools of the pass 

 have to be cleared at the same time. The difficulty might, I think, be in 

 great part overcome if the intake were moved — as it could be without 

 much trouble or expense — to the upper part of the pool, and the bank at 

 the new intake protected against scouring. 



The Kingairloch Pass. — In this structure the pools have a rather special 

 formation. I have already described them as excavated in the floor of the 

 pass. I have now further to describe them as having a slope of floor 

 against the direction of the water, or, in other words, being deeper at the 

 " head " than at the " tail." Farther, they are pools in which the sill is 

 overflowed by the water, which, descending gently into the head of the 

 pool, strikes against the bottom and then has to flow up an inclined plane. 

 The steeper the incline the stronger the check. The uniform gradient is 

 represented by the succeeding sills. 



There are 23 pools in continuous succession, each having the upward 

 slope of the floor. A row of cement blocks, similar to the stones used in 

 the pool-less passes of uniform gradient already described, is placed just 

 above the sill of each pool. At this point, in all ordinary levels of water, 

 the current is so easy that the blocks seem to me superfluous. In flooded 

 conditions they may be more serviceable ; but then the admirable flood 

 overflow comes into play. 



The arrangement of the floor of each pool will be readily understood 

 from the accompanying section plan. It does not show a plan of the 

 particular pass now under review, but is simply intended to show the 

 admirable arrangement. It is an imaginary case of a pass with a gradient 

 of 1 in 24, having two pools with a short run between them, as might be 

 adopted in certain localities. In the section the vertical scale is twice the 

 horizontal for the purpose of emphasising the formation. 



The steep slope of the upper end of each pool must have at one point a 

 good deep V or U cut into it to save the necessity of ascending fish leaping 

 when leaving the pool. In the channel the breaks of upright stones are 

 advisable. If pools follow one another in quick succession, the V or U 

 cuts should alternate so as to be first at one side of the pass, then at the 

 other. This gives a certain amount of cross water. With pools 25 to 30 

 feet long, in all ordinary water levels, the water becomes very easy, and 

 aeration practically disappears. In high water the pass is much easier than 

 if no pools were present, and valuable rests are afforded to ascending fish. 

 An objection to allowing fish to rest in pools of this kind is that they are 

 more open to the attacks of poachers. This may be so, but the objection 

 is, in my opinion, not sufficient to counterbalance the advantage of the 

 pools. The pass must be watched or otherwise protected if there is any 

 fear of poaching. If the water is really heavy, fish may lie the greater 

 part of a day in such pools, and only complete the ascent at night. 



If a pool be constructed of such length that the drop into it is two feet 

 or so, a valuable assistance to fish leaving the pool may be provided by a 

 " break " projecting from the side of the pass a short distance below the V 

 or U, which break may conveniently be propped by strong supports from 

 the bottom or side of the pool. The action of such a break is to form a 

 water-cushion by piling up the water which spouts from the U, and so 

 raising the level between the U and the break. The difference made by a 

 simple contrivance of this kind is most marked. If pools are at all shallow 



